anchor
stringlengths 50
3.92k
| positive
stringlengths 55
6.16k
|
|---|---|
On the role of AGN feedback on the thermal and chemodynamical properties
of the hot intra-cluster medium: We present an analysis of the properties of the ICM in an extended set of
cosmological hydrodynamical simulations of galaxy clusters and groups performed
with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations,
we carried out two sets of simulations including radiative cooling, star
formation, metal enrichment and feedback from supernovae, one of which also
accounts for the effect of feedback from AGN resulting from gas accretion onto
super-massive black holes. These simulations are analysed with the aim of
studying the relative role played by SN and AGN feedback on the general
properties of the diffuse hot baryons in galaxy clusters and groups: scaling
relations, temperature, entropy and pressure radial profiles, and ICM chemical
enrichment. We find that simulations including AGN feedback produce scaling
relations that are in good agreement with X-ray observations at all mass
scales. However, our simulations are not able to account for the observed
diversity between CC and NCC clusters: unlike for observations, we find that
temperature and entropy profiles of relaxed and unrelaxed clusters are quite
similar and resemble more the observed behaviour of NCC clusters. As for the
pattern of metal enrichment, we find that an enhanced level of iron abundance
is produced by AGN feedback with respect to the case of purely SN feedback. As
a result, while simulations including AGN produce values of iron abundance in
groups in agreement with observations, they over-enrich the ICM in massive
clusters. The efficiency of AGN feedback in displacing enriched gas from halos
into the inter-galactic medium at high redshift also creates a widespread
enrichment in the outskirts of clusters and produces profiles of iron abundance
whose slope is in better agreement with observations. | Observing the molecular composition of galaxies: The recent availability of wideband receivers and high sensitivity
instruments in the mm and submm wavelengths has opened the possibility of
studying in detail the chemistry of the interstellar medium in extragalactic
objects. Within the central few hundred parsec of galaxies, we find enormous
amounts of molecular material fueling a wide variety of highly energetic events
observed in starbursts (galaxies undergoing an intense burst of star formation)
and active galactic nuclei (AGN, where activity is driven by the accretion of
material onto the nuclear black hole).
Here it is presented a brief summary of both the history and the latest
results in observational chemistry in distant galaxies. It will be shown how
the molecular emission, is a powerful tool to explore the physics of the
dust-enshrouded, buried nuclei of distant ultraluminous galaxies, which are
heavily obscured at other wavelengths. Special attention will be given to the
possibilities offered by next generationinstruments such as ALMA (Atacama Large
Millimeter Array), expected to have a vast impact on the field of Extragalactic
Chemistry. Molecular studies in the early Universe will become available at
unprecedented sensitivity and resolution. |
Optimal 1D Ly-$α$ Forest Power Spectrum Estimation I: DESI-Lite
Spectra: The 1D Ly-$\alpha$ forest flux power spectrum $P_{\mathrm{1D}}$ is sensitive
to scales smaller than a typical galaxy survey, and hence ties to the
intergalactic medium's thermal state, suppression from neutrino masses and new
dark matter models. It has emerged as a competitive framework to study new
physics, but also has come with various challenges and systematic errors in
analysis. In this work, we revisit the optimal quadratic estimator for
$P_{\mathrm{1D}}$, which is robust against the relevant problems such as pixel
masking, time evolution within spectrum and quasar continuum errors. We further
improve the estimator by introducing a fiducial power spectrum, which enables
us to extract more information by alleviating the discreteness of band powers.
We meticulously apply our method to synthetic DESI spectra and demonstrate how
the estimator overcomes each challenge. We further apply an optimisation scheme
that approximates the Fisher matrix to three elements per row and reduces
computation time by 60%. We show that we can achieve percent precision in
$P_{\mathrm{1D}}$ with 5-year DESI data in the absence of systematics and
provide forecasts for different spectral qualities. | Recovering cores and cusps in dark matter haloes using mock velocity
field observations: We present mock DensePak Integral Field Unit (IFU) velocity fields, rotation
curves, and halo fits for disc galaxies formed in spherical and triaxial cuspy
dark matter haloes, and spherical cored dark matter haloes. The simulated
galaxies are "observed" under a variety of realistic conditions to determine
how well the underlying dark matter halo can be recovered and to test the
hypothesis that cuspy haloes can be mistaken for cored haloes. We find that the
appearance of the velocity field is distinctly different depending on the
underlying halo type. We also find that we can successfully recover the
parameters of the underlying dark matter halo. Cuspy haloes appear cuspy in the
data and cored haloes appear cored. Our results suggest that the cores observed
using high-resolution velocity fields in real dark matter-dominated galaxies
are genuine and cannot be ascribed to systematic errors, halo triaxiality, or
non-circular motions. |
Radiative transfer of Lyman-$α$ photons at cosmic dawn with
realistic gas physics: The cosmic dawn 21-cm signal is enabled by Ly~$\alpha$ photons through a
process called the Wouthuysen-Field effect. An accurate model of the signal in
this epoch hinges on the accuracy of the computation of the Ly~$\alpha$
coupling, which requires one to calculate the specific intensity of UV
radiation from sources such as the first stars. Most traditional calculations
of the Ly~$\alpha$ coupling assume a delta-function scattering cross-section,
as the resonant nature of the Ly~$\alpha$ scattering makes an accurate
radiative transfer solution computationally expensive. Attempts to improve upon
this traditional approach using numerical radiative transfer have recently
emerged. However, the radiative transfer computation in these treatments
suffers from assumptions such as a uniform density of intergalactic gas, zero
gas temperature, and absence of gas bulk motion, or numerical approximations
such as core skipping. We investigate the role played by these approximations
in setting the value of the Ly~$\alpha$ coupling and the 21-cm signal at cosmic
dawn. We present results of Monte Carlo radiative transfer simulations, without
core skipping, and show that neglecting gas temperature in the radiative
transfer significantly underestimates the scattering rate and hence the
Ly~$\alpha$ coupling and the 21-cm signal. We also discuss the effect of these
processes on the 21-cm power spectrum from the cosmic dawn. This work points
the way towards higher-accuracy models to enable better inferences from future
measurements. | A thermally stable heating mechanism for the intracluster medium:
turbulence, magnetic fields and plasma instabilities: We consider the problem of self-regulated heating and cooling in galaxy
clusters and the implications for cluster magnetic fields and turbulence.
Viscous heating of a weakly collisional magnetised plasma is regulated by the
pressure anisotropy with respect to the local direction of the magnetic field.
The intracluster medium is a high-beta plasma, where pressure anisotropies
caused by the turbulent stresses and the consequent local changes in the
magnetic field will trigger very fast microscale instabilities. We argue that
the net effect of these instabilities will be to pin the pressure anisotropies
at a marginal level, controlled by the plasma beta parameter. This gives rise
to local heating rates that turn out to be comparable to the radiative cooling
rates. Furthermore, we show that a balance between this heating and
Bremsstrahlung cooling is thermally stable, unlike the often conjectured
balance between cooling and thermal conduction. Given a sufficient (and
probably self-regulating) supply of turbulent power, this provides a physical
mechanism for mitigating cooling flows and preventing cluster core collapse.
For observed density and temperature profiles, the assumed balance of viscous
heating and radiative cooling allows us to predict magnetic-field strengths,
turbulent velocities and turbulence scales as functions of distance from the
centre. Specific predictions and comparisons with observations are given for
several different clusters. Our predictions can be further tested by future
observations of cluster magnetic fields and turbulent velocities. |
CMB at small scales: Cosmology from tSZ power spectrum: Small scale CMB angular power spectrum contains not only primordial CMB
information but also many contaminants coming from secondary anisotropies. Most
of the latter depend on the cosmological model but are often marginalised over.
We propose a new analysis of the SPT data focusing on the cosmological
contribution of the thermal Sunyaev Zel'dovich (tSZ) effect. We model the tSZ
angular spectrum with the halo model and train a random forest algorithm to
speed up its computation. We show that using the cosmological information of
the tSZ on top of the primordial CMB one contained in SPT data bring more
constraints on cosmological parameters. We also combine for the first time
Planck tSZ angular power spectrum with SPT ones to put further constraints.
This proof of concept study shows how much a proper modelling of the
foregrounds in the cosmological analyses is needed. | Incorporating galaxy cluster triaxiality in stacked cluster weak lensing
analyses: Counts of galaxy clusters offer a high-precision probe of cosmology, but
control of systematic errors will determine the accuracy of this measurement.
Using Buzzard simulations, we quantify one such systematic, the triaxiality
distribution of clusters identified with the redMaPPer optical cluster finding
algorithm, which was used in the Dark Energy Survey Year-1 (DES Y1) cluster
cosmology analysis. We test whether redMaPPer selection biases the clusters'
shape and orientation and find that it only biases orientation, preferentially
selecting clusters with their major axes oriented along the line of sight.
Modeling the richness-mass relation as a log-linear relation, we find that the
log-richness amplitude $\ln(A)$ is boosted from the lowest to highest
orientation bin with a significance of $14\sigma$, while the orientation
dependence of the richness-mass slope and intrinsic scatter is minimal. We also
find that the weak lensing shear-profile ratios of cluster-associated dark
halos in different orientation bins resemble a "bottleneck" shape that can be
quantified with a Cauchy function. We test the correlation of orientation with
two other leading systematics in cluster cosmology -- miscentering and
projection -- and find a null correlation. Analytic templates for the
triaxiality bias of observed-richness and lensing profiles are mapped as
corrections to the observable of richness-binned lensing profiles for redMaPPer
clusters. The resulting mass bias confirms the DES Y1 finding that triaxiality
is a leading source of bias in cluster cosmology. However, the
richness-dependence of the bias confirms that triaxiality does not fully
resolve the tension at low-richness between DES Y1 cluster cosmology and other
probes. Our model can be used for quantifying the impact of triaxiality bias on
cosmological constraints for upcoming weak lensing surveys of galaxy clusters. |
Isotropic N-Point Basis Functions and Their Properties: Isotropic functions of positions $\hat{\bf r}_1, \hat{\bf r}_2,\ldots,
\hat{\bf r}_N$, i.e. functions invariant under simultaneous rotations of all
the coordinates, are conveniently formed using spherical harmonics and
Clebsch-Gordan coefficients. An orthonormal basis of such functions provides a
formalism suitable for analyzing isotropic distributions such as those that
arise in cosmology, for instance in the clustering of galaxies as revealed by
large-scale structure surveys. The algebraic properties of the basis functions
are conveniently expressed in terms of 6-$j$ and 9-$j$ symbols. The calculation
of relations among the basis functions is facilitated by "Yutsis" diagrams for
the addition and recoupling of angular momenta. | SDSS DR17: The Cosmic Slime Value Added Catalog: The "cosmic web", the filamentary large-scale structure in a cold dark matter
Universe, is readily apparent via galaxy tracers in spectroscopic surveys.
However, the underlying dark matter structure is as of yet unobservable and
mapping the diffuse gas permeating it lies beyond practical observational
capabilities. A recently developed technique, inspired by the growth and
movement of Physarum polycephalum "slime mold", has been used to map the cosmic
web of a low redshift sub-sample of the SDSS spectroscopic galaxy catalog. This
model, the Monte Carlo Physarum Machine (MCPM) was shown to promisingly
reconstruct the cosmic web. Here, we improve the formalism used in calibrating
the MCPM to better recreate the Bolshoi-Planck cosmological simulation's
density distributions and apply them to a significantly larger cosmological
volume than previous works using the Sloan Digital Sky Survey (SDSS, $z < 0.1$)
and the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) Luminous Red
Galaxy (LRG, $z \lesssim 0.5$) spectroscopic catalogs. We present the "Cosmic
Slime Value Added Catalog" which provides estimates for the cosmic overdensity
for the sample of galaxies probed spectroscopically by the above SDSS surveys.
In addition, we provide the fully reconstructed 3D density cubes of these
volumes. These data products were released as part of Sloan Digital Sky Survey
Data Release 17 and are publicly available. We present the input catalogs and
the methodology for constructing these data products. We also highlight
exciting potential applications to galaxy evolution, cosmology, the
intergalactic and circumgalactic medium, and transient phenomenon localization. |
Evaporating primordial black holes as varying dark energy: If light enough primordial black holes (PBH) account for dark matter, then
its density decreases with time as they lose mass via Hawking radiation. We
show that this time-dependence of the matter density can be formulated as an
equivalent $w(z)$ dark energy model and we study its implications on the
expansion history. Using our approach and comparing with the latest
cosmological data, including the supernovae type Ia, Baryon Acoustic
Oscillations, Cosmic Microwave Background and the Hubble expansion H(z) data,
we place observational constraints on the PBH model. We find that it is
statistically consistent with $\Lambda$CDM according to the AIC statistical
tool. Furthermore, we entertain the idea of having a population of ultra-light
PBHs, decaying around neutrino decoupling, on top of the dark matter fluid and
show how this offers a natural dark matter-radiation coupling altering the
expansion history of the Universe and alleviating the $H_0$ tension. | A Search for Axionic Dark Matter Using the Magnetar PSR J1745-2900: We report on a search for dark matter axion conversion photons from the
magnetosphere of the Galactic Center magnetar PSR J1745-2900 using spectra
obtained from the Karl G. Jansky Very Large Array. No significant spectral
features are detected. Using a hybrid model for PSR J1745-2900 and canonical
assumptions about the dark matter density profile, we exclude axion models with
axion-photon coupling $g_{a\gamma\gamma}$ > 6-34 x 10$^{-12}$ GeV$^{-1}$ with
95% confidence over the mass ranges 4.2-8.4, 18.6-26.9, 33.0-41.4, 53.7-62.1,
and 126.0-159.3 $\mu$eV. If there is a dark matter cusp, the limits reduce to
$g_{a\gamma\gamma}$ > 6-34 x 10$^{-14}$ GeV$^{-1}$, which overlap some axion
models for the observed mass ranges > 33 $\mu$eV. These limits may be improved
by modeling the stimulated emission that can boost the axion-photon conversion
process. |
Radiative stability and observational constraints on dark energy and
modified gravity: We investigate the radiative stability of Horndeski scalar-tensor theories
with luminally propagating gravitational waves (as extensively discussed in the
wake of GW170817) and show that in general there is a tension between obtaining
observable deviations from General Relativity (GR) in cosmology and the
requirement of radiative stability. Using this as a constraint, we discuss the
subsets of theories that are capable of evading this conclusion and yielding
observable, radiatively stable departures from GR. We find several classes of
theories that can do so, recovering known cases and identifying several
additional radiatively stable cases. Finally, we also extract the cosmological
signatures of two particularly well-motivated radiatively stable classes of
theories: shift-symmetric theories and theories with a conformal coupling
between the scalar and gravity. We find that cosmological parameter constraints
on dark energy and modified gravity parameters for both of these two classes,
which we explicitly compute using data from the Planck, SDSS/BOSS and 6dF
surveys, are significantly tightened with respect to generic Horndeski
theories. | Probing modified gravity theories with multiple measurements of
high-redshift quasars: In this paper, we quantify the ability of multiple measurements of
high-redshift quasars (QSOs) to constrain several theories of modified gravity,
including the Dvali-Gabadadze-Porrati braneworld scenario, generalized
Chaplygin gas, $f(T)$ modified gravity, and Modified Polytropic Cardassian
model. Recently released sample of 1598 quasars with X-ray and UV flux
measurements in the redshift range of $0.036\leq z \leq 5.1003$, as well as a
compilation of 120 intermediate-luminosity radio quasars covering the redshift
of $0.46 < z < 2.76$ are respectively used as standard probes at higher
redshifts. For all considered modified gravity theories, our results show that
there is still some possibility that the standard $\Lambda$CDM scenario might
not be the best cosmological model preferred by the current quasar
observations. In order to improve cosmological constraints, the quasar data are
also combined with the latest observations of baryon acoustic oscillations
(BAO), which strongly complement the constraints. Finally, we discuss the
support given by the data to modified gravity theories, applying different
information theoretic techniques like the Akaike Information Criterion (AIC),
Bayesian Information Criterion (BIC) and Jensen-Shannon divergence (JSD). |
On Synthetic Gravitational Waves from Multi-field Inflation: We revisit the possibility of producing observable tensor modes through a
continuous particle production process during inflation. Particularly, we focus
on the multi-field realization of inflation where a spectator pseudo-scalar
$\sigma$ induces a significant amplification of the ${\rm U}(1)$ gauge fields
through the coupling $\propto \sigma F_{\mu\nu}\tilde{F}^{\mu\nu}$. In this
model, both the scalar $\sigma$ and the Abelian gauge fields are
gravitationally coupled to the inflaton sector, therefore they can only affect
the primordial scalar and tensor fluctuations through their mixing with
gravitational fluctuations. Recent studies on this scenario show that the
sourced contributions to the scalar correlators can be dangerously large to
invalidate a large tensor power spectrum through the particle production
mechanism. In this paper, we re-examine these recent claims by explicitly
calculating the dominant contribution to the scalar power and bispectrum.
Particularly, we show that once the current limits from CMB data are taken into
account, it is still possible to generate a signal as large as $r \approx
10^{-3}$ and the limitations on the model building are more relaxed than what
was considered before. | Bayesian Estimation of the D(p,$γ$)$^3$He Thermonuclear Reaction
Rate: Big bang nucleosynthesis (BBN) is the standard model theory for the
production of the light nuclides during the early stages of the universe,
taking place for a period of about 20 minutes after the big bang. Deuterium
production, in particular, is highly sensitive to the primordial baryon density
and the number of neutrino species, and its abundance serves as a sensitive
test for the conditions in the early universe. The comparison of observed
deuterium abundances with predicted ones requires reliable knowledge of the
relevant thermonuclear reaction rates, and their corresponding uncertainties.
Recent observations reported the primordial deuterium abundance with percent
accuracy, but some theoretical predictions based on BBN are at tension with the
measured values because of uncertainties in the cross section of the
deuterium-burning reactions. In this work, we analyze the S-factor of the
D(p,$\gamma$)$^3$He reaction using a hierarchical Bayesian model. We take into
account the results of eleven experiments, spanning the period of 1955--2021;
more than any other study. We also present results for two different fitting
functions, a two-parameter function based on microscopic nuclear theory and a
four-parameter polynomial. Our recommended reaction rates have a 2.2\%
uncertainty at $0.8$~GK, which is the temperature most important for deuterium
BBN. Differences between our rates and previous results are discussed. |
Measuring the speed of light with updated Hubble diagram of
high-redshift standard candles: The possible time variation of the fundamental constants of nature has been
an active subject of research in modern physics. In this paper, we propose a
new method to investigate such possible time variation of the speed of light
$c$ using the updated Hubble diagram of high-redshift standard candles
including Type Ia Supernovae (SNe Ia) and high-redshift quasars (based on UV-X
relation). Our findings show that the SNe Ia Pantheon sample, combined with
currently available sample of cosmic chronometers, would produce robust
constraints on the speed of light at the level of $c/c_0=1.03\pm0.03$. For the
Hubble diagram of UV+X ray quasars acting as a new type of standard candles, we
obtain $c/c_0=1.19\pm0.07$. Therefore, our results confirm that there is no
strong evidence for the deviation from the constant speed of light up to $z\sim
2$. Moreover, we discuss how our technique might be improved at much higher
redshifts ($z\sim5$), focusing on future measurements of the acceleration
parameter $X(z)$ with gravitational waves (GWs) from binary neutron star
mergers. In particular, in the framework of the second-generation space-based
GW detector, DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO),
the speed of light is expected to be constrained with the precision of
$\Delta{c}/c=10^{-3}$. | Zooming in on accretion - I. The structure of halo gas: We study the properties of gas in and around 10^12 solar mass halos at z=2
using a suite of high-resolution cosmological hydrodynamic 'zoom' simulations.
We quantify the thermal and dynamical structure of these gaseous reservoirs in
terms of their mean radial distributions and angular variability along
different sightlines. With each halo simulated at three levels of increasing
resolution, the highest reaching a baryon mass resolution of ~10,000 solar
masses, we study the interaction of filamentary inflow and the quasi-static hot
halo atmosphere. We highlight the discrepancy between the spatial resolution
available in the halo gas as opposed to within the galaxy itself, and find that
stream morphologies become increasingly complex at higher resolution, with
large coherent flows revealing density and temperature structure at
progressively smaller scales. Moreover, multiple gas components co-exist at the
same radius within the halo, making radially averaged analyses misleading. This
is particularly true where the hot, quasi-static, high entropy halo atmosphere
interacts with cold, rapidly inflowing, low entropy accretion. We investigate
the process of gas virialization and identify different regimes for the heating
of gas as it accretes from the intergalactic medium. Haloes at this mass have a
well-defined virial shock, associated with a sharp jump in temperature and
entropy at ~1.25 r_vir. The presence, radius, and radial width of this boundary
feature, however, vary not only from halo to halo, but also as a function of
angular direction, covering roughly ~85% of the 4pi sphere. Our findings are
relevant for the proper interpretation of observations pertaining to the
circumgalactic medium, including evidence for large amounts of cold gas
surrounding massive haloes at intermediate redshifts. |
Gas Accretion is Dominated by Warm Ionized Gas in Milky Way-Mass
Galaxies at z ~ 0: We perform high-resolution hydrodynamic simulations of a Milky Way-mass
galaxy in a fully cosmological setting using the adaptive mesh refinement code,
Enzo, and study the kinematics of gas in the simulated galactic halo. We find
that the gas inflow occurs mostly along filamentary structures in the halo. The
warm-hot (10^5 K < T < 10^6 K) and hot (T > 10^6 K) ionized gases are found to
dominate the overall mass accretion in the system (with dM/dt = 3-5 M_solar/yr)
over a large range of distances, extending from the virial radius to the
vicinity of the disk. Most of the inflowing gas (by mass) does not cool, and
the small fraction that manages to cool does so primarily close to the galaxy
(R <~ 20 kpc), perhaps comprising the neutral gas that may be detectable as,
e.g., high-velocity clouds. The neutral clouds are embedded within larger,
accreting filamentary flows, and represent only a small fraction of the total
mass inflow rate. The inflowing gas has relatively low metallicity (Z/Z_solar <
0.2). The outer layers of the filamentary inflows are heated due to compression
as they approach the disk. In addition to the inflow, we find high-velocity,
metal-enriched outflows of hot gas driven by supernova feedback. Our results
are consistent with observations of halo gas at low z. | Mergers of primordial black holes in extreme clusters and the $H_0$
tension: We consider a cosmological model with dark matter in the form of
$\sim10^{-12}M_\odot$ primordial black holes in dense weakly relativistic
clusters with masses $18-560M_\odot$. It is shown that during the multiple
collisions of the black holes the $\sim10$\% of the initial cluster mass can be
transformed into gravitational waves in the time interval from recombination to
the redshifts $z\geq 10$. At the recombination epoch, the density of matter was
larger by $\sim10$\% and, accordingly, the universe expansion rate was higher.
This leads to a shortening of the sound horizon scale, as is necessary to solve
the "$H_0$ tension" problem. |
Constraining the interacting dark energy models from weak gravity
conjecture and recent observations: We examine the effectiveness of the weak gravity conjecture in constraining
the dark energy by comparing with observations. For general dark energy models
with plausible phenomenological interactions between dark sectors, we find that
although the weak gravity conjecture can constrain the dark energy, the
constraint is looser than that from the observations. | What collisional debris can tell us about galaxies: I review what tidal tails in particular, collisional debris in general, might
tell us about galaxies (their structure, current content and past mass
assembly) about mergers in the nearby and distant Universe (major vs minor, wet
vs dry, number evolution) and finally about the laws of gravity. |
Comparing different realizations of modified Newtonian dynamics: virial
theorem and elliptical shells: There exists several modified gravity theories designed to reproduce the
empirical Milgrom's formula (MOND). Here we derive analytical results in the
context of the static weak-field limit of two of them (BIMOND, leading for a
given set of parameters to QUMOND, and TeVeS). In this limit, these theories
are constructed to give the same force field for spherical symmetry, but their
predictions generally differ out of it. However, for certain realizations of
these theories (characterized by specific choices for their free functions),
the binding potential-energy of a system is increased, compared to its
Newtonian counterpart, by a constant amount independent of the shape and size
of the system. In that case, the virial theorem is exactly the same in these
two theories, for the whole gravity regime and even outside of spherical
symmetry, although the exact force fields are different. We explicitly show
this for the force field generated by the two theories inside an elliptical
shell. For more general free functions, the virial theorems are however not
identical in these two theories. We finally explore the consequences of these
analytical results for the two-body force. | Pseudoscalar sterile neutrino self-interactions in light of Planck, SPT
and ACT data: We reassess the viability of a cosmological model including a fourth
additional sterile neutrino species that self-interacts through a new
pseudoscalar degree of freedom. We perform a series of extensive analyses
fitting various combinations of cosmic microwave background (CMB) data from
Planck, the Atacama Cosmology Telescope (ACT) and the South Pole Telescope
(SPT), both alone and in combination with Baryon Acoustic Oscillation (BAO) and
Supernova Ia (SnIa) observations. We show that the scenario under study,
although capable to resolve the Hubble tension without worsening the so-called
$S_8$ tension about the growth of cosmic structures, is severely constrained by
high-multipole polarization data from both Planck and SPT. Intriguingly, when
trading Planck TE-EE data for those from ACT, we find a $\gtrsim 3 \sigma$
preference for a non-zero sterile neutrino mass, $m_s=3.6^{+1.1}_{-0.6}$ eV (68
% C.L.), compatible with the range suggested by longstanding short-baseline
(SBL) anomalies in neutrino oscillation experiments. The pseudoscalar model
provides indeed a better fit to ACT data compared to $\Lambda$CDM
($\Delta\chi^2 \simeq -5$, $\Delta \rm{AIC}=-1.3$), although in a combined
analysis with Planck the $\Lambda$CDM model is still favoured, as the
preference for a non-zero sterile neutrino mass is mostly driven by ACT
favouring a higher value for the primordial spectral index $n_s$ with respect
to Planck. We show that the mild tension between Planck and ACT is due to the
different pattern in the TE and EE power spectra on multipoles between $350
\lesssim \ell \lesssim 1000$. We also check the impact of marginalizing over
the gravitational lensing information in Planck data, showing that the model
does not solve the CMB lensing anomaly. Future work including higher precision
data from current and upcoming CMB ground-based experiments will be crucial to
test these results. |
Defrosting in an Emergent Galileon Cosmology: We study the transition from an Emergent Galileon condensate phase of the
early universe to a later expanding radiation phase. This "defrosting" or
"preheating" transition is a consequence of the excitation of matter
fluctuations by the coherent Galileon condensate, in analogy to how preheating
in inflationary cosmology occurs via the excitation of matter fluctuations
through coupling of matter with the coherent inflaton condensate. We show that
the "minimal" coupling of matter (modeled as a massless scalar field) to the
Galileon field introduced by Creminelli, Nicolis and Trincherini in order to
generate a scale-invariant spectrum of matter fluctuations is sufficient to
lead to efficient defrosting, provided that the effects of the non-vanishing
expansion rate of the universe are taken into account. If we neglect the
effects of expansion, an additional coupling of matter to the Galileon
condensate is required. We study the efficiency of the defrosting mechanism in
both cases. | An Alternative String Landscape Cosmology: Eliminating Bizarreness: In what has become a standard eternal inflation picture of the string
landscape there are many problematic consequences and a difficulty defining
probabilities for the occurrence of each type of universe. One feature in
particular that might be philosophically disconcerting is the infinite cloning
of each individual and each civilization in infinite numbers of separated
regions of the multiverse. Even if this is not ruled out due to causal
separation one should ask whether the infinite cloning is a universal
prediction of string landscape models or whether there are scenarios in which
it is avoided. If a viable alternative cosmology can be constructed one might
search for predictions that might allow one to discriminate experimentally
between the models. We present one such scenario although, in doing so, we are
forced to give up several popular presuppositions including the absence of a
preferred frame and the homogeneity of matter in the universe. The model also
has several ancillary advantages. We also consider the future lifetime of the
current universe before becoming a light trapping region. |
The anatomy of an extreme starburst within 1.3Gyr of the Big Bang
revealed by ALMA: We present further analysis of the [CII] 158$\mu$m fine structure line and
thermal dust continuum emission from the archetype extreme starburst/AGN group
of galaxies in the early Universe, BRI 1202-0725 at $z=4.7$, using the Atacama
Large Millimeter Array. The group is long noted for having a closely separated
(26kpc in projection) FIR-hyperluminous quasar host galaxy and an optically
obscured submm galaxy (SMG). A short ALMA test observation reveals a rich
laboratory for the study of the myriad processes involved in clustered massive
galaxy formation in the early Universe. Strong [CII] emission from the SMG and
the quasar have been reported earlier by Wagg et al. (2012) based on these
observations. In this letter, we examine in more detail the imaging results
from the ALMA observations, including velocity channel images,
position-velocity plots, and line moment images. We present detections of [CII]
emission from two Ly$\alpha$-selected galaxies in the group, demonstrating the
relative ease with which ALMA can detect the [CII] emission from lower star
formation rate galaxies at high redshift. Imaging of the [CII] emission shows a
clear velocity gradient across the SMG, possibly indicating rotation or a more
complex dynamical system on a scale $\sim 10$kpc. There is evidence in the
quasar spectrum and images for a possible outflow toward the southwest, as well
as more extended emission (a 'bridge'), between the quasar and the SMG,
although the latter could simply be emission from Ly$\alpha$-1 blending with
that of the quasar at the limited spatial resolution of the current
observations. These results provide an unprecedented view of a major merger of
gas rich galaxies driving extreme starbursts and AGN accretion during the
formation of massive galaxies and supermassive black holes within 1.3 Gyr of
the Big Bang. | The DEHVILS Survey Overview and Initial Data Release: High-Quality
Near-Infrared Type Ia Supernova Light Curves at Low Redshift: While the sample of optical Type Ia Supernova (SN Ia) light curves (LCs)
usable for cosmological parameter measurements surpasses 2000, the sample of
published, cosmologically viable near-infrared (NIR) SN Ia LCs, which have been
shown to be good "standard candles," is still $\lesssim$ 200. Here, we present
high-quality NIR LCs for 83 SNe Ia ranging from $0.002 < z < 0.09$ as a part of
the Dark Energy, H$_0$, and peculiar Velocities using Infrared Light from
Supernovae (DEHVILS) survey. Observations are taken using UKIRT's WFCAM, where
the median depth of the images is 20.7, 20.1, and 19.3 mag (Vega) for $Y$, $J$,
and $H$-bands, respectively. The median number of epochs per SN Ia is 18 for
all three bands ($YJH$) combined and 6 for each band individually. We fit 47 SN
Ia LCs that pass strict quality cuts using three LC models, SALT3, SNooPy, and
BayeSN and find scatter on the Hubble diagram to be comparable to or better
than scatter from optical-only fits in the literature. Fitting NIR-only LCs, we
obtain standard deviations ranging from 0.128-0.135 mag. Additionally, we
present a refined calibration method for transforming 2MASS magnitudes to WFCAM
magnitudes using HST CALSPEC stars that results in a 0.03 mag shift in the
WFCAM $Y$-band magnitudes. |
Lagrangian cosmological perturbation theory at shell-crossing: We consider the growth of primordial dark matter halos seeded by three
crossed initial sine waves of various amplitudes. Using a Lagrangian treatment
of cosmological gravitational dynamics, we examine the convergence properties
of a high-order perturbative expansion in the vicinity of shell-crossing, by
comparing the analytical results with state-of-the-art high resolution
Vlasov-Poisson simulations. Based on a quantitative exploration of parameter
space, we study explicitly for the first time the convergence speed of the
perturbative series, and find, in agreement with intuition, that it slows down
when going from quasi one-dimensional initial conditions (one sine wave
dominating) to quasi triaxial symmetry (three sine waves with same amplitude).
In most cases, the system structure at collapse time is, as expected, very
similar to what is obtained with simple one-dimensional dynamics, except in the
quasi-triaxial regime, where the phase-space sheet presents a velocity spike.
In all cases, the perturbative series exhibits a generic convergence behavior
as fast as an exponential of a power-law of the order of the expansion,
allowing one to numerically extrapolate it to infinite order. The results of
such an extrapolation agree remarkably well with the simulations, even at
shell-crossing. | On the use of the local prior on the absolute magnitude of Type Ia
supernovae in cosmological inference: A dark-energy which behaves as the cosmological constant until a sudden
phantom transition at very-low redshift ($z<0.1$) seems to solve the >4$\sigma$
disagreement between the local and high-redshift determinations of the Hubble
constant, while maintaining the phenomenological success of the $\Lambda$CDM
model with respect to the other observables. Here, we show that such a
hockey-stick dark energy cannot solve the $H_0$ crisis. The basic reason is
that the supernova absolute magnitude $M_B$ that is used to derive the local
$H_0$ constraint is not compatible with the $M_B$ that is necessary to fit
supernova, BAO and CMB data, and this disagreement is not solved by a sudden
phantom transition at very-low redshift. We make use of this example to show
why it is preferable to adopt in the statistical analyses the prior on $M_B$ as
an alternative to the prior on $H_0$. The three reasons are: i) one avoids
potential double counting of low-redshift supernovae, ii) one avoids assuming
the validity of cosmography, in particular fixing the deceleration parameter to
the standard model value $q_0=-0.55$, iii) one includes in the analysis the
fact that $M_B$ is constrained by local calibration, an information which would
otherwise be neglected in the analysis, biasing both model selection and
parameter constraints. We provide the priors on $M_B$ relative to the recent
Pantheon and DES-SN3YR supernova catalogs. We also provide a Gaussian joint
prior on $H_0$ and $q_0$ that generalizes the prior on $H_0$ by SH0ES. |
Simulated Analogs of Merging Galaxy Clusters Constrain the Viewing Angle: A key uncertainty in interpreting observations of bimodal merging galaxy
clusters is the unknown angle between the subcluster separation vector and the
plane of the sky. We present a new method for constraining this key parameter.
We find analogs of observed systems in cosmological n-body simulations and
quantify their likelihood of matching the observed projected separation and
relative radial velocities between subclusters, as a function of viewing angle.
We derive constraints on the viewing angle of many observed bimodal mergers
including the Bullet Cluster (1E 0657-558) and El Gordo (ACT-CL J0102-4915). We
also present more generic constraints as a function of projected separation and
relative radial velocity, which can be used to assess additional clusters as
information about them becomes available. The constraints from these two
observables alone are weak (typically $\gtrsim 70-75^\circ$ at 68\% confidence
and $\gtrsim 55-60^\circ$ at 95\% confidence) but incorporate much more
cosmological context than the classical timing argument, marginalizing over
many realizations of substructure, peculiar velocities, and so on. Compared to
the MCMAC code, which implements the timing argument on NFW halos, our
constraints generally predict subcluster separation vectors closer to the plane
of the sky. This is because in realistic mergers the subcluster velocity
vectors are not entirely parallel to the separation vector (i.e, the mergers
are not perfectly head-on). As a result, observation of a nonzero relative
radial velocity does not exclude a separation vector in the plane of the sky,
as it does in the head-on timing argument employed by MCMAC. | Constraints on Dark Energy from New Observations including Pan-STARRS: In this paper, we set the new limits on the equation of state parameter (EoS)
of dark energy with the observations of cosmic microwave background radiation
(CMB) from Planck satellite, the type Ia supernovae from Pan-STARRS and the
baryon acoustic oscillation (BAO). We consider two parametrization forms of
EoS: a constant $w$ and time evolving $w(a)=w_0+w_a(1-a)$. The results show
that with a constant EoS, $w=-1.141\pm{0.075}$ ($68\%~C.L.$), which is
consistent with $\Lambda$CDM at about $2\sigma$ confidence level. For a time
evolving $w(a)$ model, we get $w_0=-1.09^{+0.16}_{-0.18}$ ($1\sigma~C.L.$),
$w_a=-0.34^{+0.87}_{-0.51}$ ($1\sigma~C.L.$), and in this case $\Lambda$CDM can
be comparable with our observational data at $1\sigma$ confidence level. In
order to do the parametrization independent analysis, additionally we adopt the
so called principal component analysis (PCA) method, in which we divide
redshift range into several bins and assume $w$ as a constant in each redshift
bin (bin-w). In such bin-w scenario, we find that for most of the bins
cosmological constant can be comparable with the data, however, there exists
few bins which give $w$ deviating from $\Lambda$CDM at more than $2\sigma$
confidence level, which shows a weak hint for the time evolving behavior of
dark energy. To further confirm this hint, we need more data with higher
precision. |
Observational challenges in dark energy models: Cosmological distances inferred from supernova Ia observations constitute the
most direct and solid evidence for the recently detected accelerated expansion
of the universe. In this contribution, we show some inconsistencies between two
of the main light-curve fitters used for the elaboration of supernova Ia data
sets, opening new observational challenges regarding the use of these
luminosity distances when combined with CMB and BAO data. We also mention
ongoing analysis related to alternative models. The resolution of these
challenges will be crucial for XXI century cosmology. | Understanding WIMP-baryon interactions with direct detection: A Roadmap: We study prospects of dark-matter direct-detection searches for probing
non-relativistic effective theory for WIMP-baryon scattering. We simulate a
large set of noisy recoil-energy spectra for different scattering scenarios
(beyond the standard momentum-independent contact interaction), for Generation
2 and futuristic experiments. We analyze these simulations and quantify the
probability of successfully identifying the operator governing the scattering,
if a WIMP signal is observed. We find that the success rate depends on a
combination of factors: the WIMP mass, the mediator mass, the type of
interaction, and the experimental energy window. For example, for a 20 GeV
WIMP, Generation 2 is only likely to identify the right operator if the
interaction is Coulomb-like, and is unlikely to do so in any other case. For a
WIMP with a mass of 200 GeV or higher, success is almost guaranteed. We also
find that, regardless of the scattering model and the WIMP parameters, a single
Generation 2 experiment is unlikely to successfully discern the momentum
dependence of the underlying operator on its own, but prospects improve
drastically when experiments with different target materials and energy windows
are analyzed jointly. Furthermore, we examine the quality of parameter
estimation and degeneracies in the multi-dimensional parameter space of the
effective theory. We find in particular that the resulting WIMP mass estimates
can be severely biased if data are analyzed assuming the standard
(momentum-independent) operator while the actual operator has
momentum-dependence. Finally, we evaluate the ultimate reach of direct
detection, finding that the prospects for successful operator selection prior
to reaching the irreducible backgrounds are excellent, if the signal is just
below the current limits, but slim if Generation 2 does not report WIMP
detection. |
Coincidence problem within dark energy as a coupled self-interacting
Bose-Einstein gas: A late accelerated expansion of the Universe is obtained from
non-relativistic particles with a short-range attractive interaction, and low
enough temperature to produce a Bose-Einstein condensate; by considering
coupled dark-energy particles, energy is interchanged with dark matter,
allowing it to describe recent acceleration by strengthening its effect. We
show that for a sizable range of parameters, dark energy and dark matter evolve
with similar energy densities, solving the coincidence problem, and in
agreement with the luminosity distance vs redshift, derived from supernova
data. | The cosmic radio dipole: Bayesian estimators on new and old radio
surveys: The cosmic radio dipole is an anisotropy in the number counts of radio
sources, analogous to the dipole seen in the cosmic microwave background (CMB).
Measurements of source counts of large radio surveys have shown that though the
radio dipole is generally consistent in direction with the CMB dipole, the
amplitudes are in tension. These observations present an intriguing puzzle as
to the cause of this discrepancy, with a true anisotropy breaking with the
assumptions of the cosmological principle, invalidating the most common
cosmological models that are built on these assumptions. We present a novel set
of Bayesian estimators to determine the cosmic radio dipole and compare the
results with commonly used methods on the Rapid ASKAP Continuum Survey (RACS)
and the NRAO VLA Sky Survey (NVSS) radio surveys. In addition, we adapt the
Bayesian estimators to take into account systematic effects known to affect
such large radio surveys, folding information such as the local noise floor or
array configuration directly into the parameter estimation. The enhancement of
these estimators allows us to greatly increase the amount of sources used in
the parameter estimation, yielding tighter constraints on the cosmic radio
dipole estimation than previously achieved with NVSS and RACS. We extend the
estimators further to work on multiple catalogues simultaneously, leading to a
combined parameter estimation using both NVSS and RACS. The result is a dipole
estimate that perfectly aligns with the CMB dipole in terms of direction but
with an amplitude that is three times as large, and a significance of
4.8$\sigma$. This new dipole measurement is made to an unprecedented level of
precision for radio sources, which is only matched by recent results using
infrared quasars. |
The Properties of the Interstellar Medium within a Star-Forming Galaxy
at z=2.3: We present an analysis of the molecular and atomic gas emission in the
rest-frame far-infrared and sub-millimetre, from the lensed z=2.3
sub-millimetre galaxy SMM J2135-0102. We obtain very high signal-to-noise
detections of 11 transitions from 3 species and limits on a further 20
transitions from 9 species. We use the 12CO, [CI] and HCN line strengths to
investigate the gas mass, kinematic structure and interstellar medium (ISM)
chemistry, and find strong evidence for a two-phase medium comprising a hot,
dense, luminous component and an underlying extended cool, low-excitation
massive component. Employing photo-dissociation region models we show that on
average the molecular gas is exposed to a UV radiation field that is ~1000 x
more intense than the Milky Way, with star-forming regions having a
characteristic density of n~10^4 /cm^3. These conditions are similar to those
found in local ULIRGs and in the central regions of typical starburst galaxies,
even though the star formation rate is far higher in this system. The 12CO
spectral line energy distribution and line profiles give strong evidence that
the system comprises multiple kinematic components with different conditions,
including temperature, and line ratios suggestive of high cosmic ray flux
within clouds. We show that, when integrated over the galaxy, the gas and
star-formation surface densities appear to follow the Kennicutt-Schmidt
relation, although when compared to high-resolution sub-mm imaging, our data
suggest that this relation breaks down on scales of <100pc. By virtue of the
lens amplification, these observations uncover a wealth of information on the
star formation and ISM at z~2.3 at a level of detail that has only recently
become possible at z<0.1, and show the potential physical properties that will
be studied in unlensed galaxies when ALMA is in full operation. (Abridged). | Probing the Growth of Massive Black Holes with Black Hole-Host Galaxy
Spin Correlations: Supermassive black holes (SMBHs) are commonly found at the centers of their
host galaxies, but their formation still remains an open question. In light of
the tight correlation between the BH mass and the velocity dispersions of the
bulge component of the host galaxy, a BH-host galaxy coevolution scenario has
been established. Such description however still contains many theoretical
uncertainties, including the puzzels about the formation of BH seeds at high
redshifts and the growth channel fueling these seeds. In this work, we
systematically analyze the signatures of different growth channels on MBH
spins. We show that different growth channels can be partially distinguished
with the magnitudes of MBH spins infered from extreme-mass-ratio-inspirals
detected by the Laser Interferometer Space Antenna. In addition, we propose to
measure the correlation between the directions of MBH spins and their host
galaxy spins, which is possible for extreme mass-ratio inspirals happening in
low-redshift galaxies ($z \le 0.3$). With the inclusion of spin direction
correlation different formation channels shall be significantly better
constrained. |
Probing non-Gaussian Stochastic Gravitational Wave Backgrounds with LISA: The stochastic gravitational wave background (SGWB) contains a wealth of
information on astrophysical and cosmological processes. A major challenge of
upcoming years will be to extract the information contained in this background
and to disentangle the contributions of different sources. In this paper we
provide the formalism to extract, from the correlation of three signals in the
Laser Interferometer Space Antenna (LISA), information about the tensor
three-point function, which characterizes the non-Gaussian properties of the
SGWB. This observable can be crucial to discriminate whether a SGWB has a
primordial or astrophysical origin. Compared to the two-point function, the
SGWB three-point function has a richer dependence on the gravitational wave
momenta and chiralities. It can be used therefore as a powerful discriminator
between different models. For the first time we provide the response functions
of LISA to a general SGWB three-point function. As examples, we study in full
detail the cases of an equilateral and squeezed SGWB bispectra, and provide the
explicit form of the response functions, ready to be convoluted with any
theoretical prediction of the bispectrum to obtain the observable signal. We
further derive the optimal estimator to compute the signal-to-noise ratio. Our
formalism covers general shapes of non-Gaussianity, and can be extended
straightaway to other detector geometries. Finally, we provide a short overview
of models of the early universe that can give rise to a non-Gaussian SGWB. | Galaxy-Scale Outflows Driven by Active Galactic Nuclei: We present hydrodynamical simulations of major mergers of galaxies and study
the effects of winds produced by active galactic nuclei (AGN) on interstellar
gas in the AGN's host galaxy. We consider winds with initial velocities ~
10,000 km/s and an initial momentum (energy) flux of ~ tau_w L/c (~ 0.01 tau_w
L), with tau_w ~ 1-10. The AGN wind sweeps up and shock heats the surrounding
interstellar gas, leading to a galaxy-scale outflow with velocities ~ 1000
km/s, peak mass outflow rates comparable to the star formation rate, and a
total ejected gas mass ~ 3 x 10^9 M_sun. Large momentum fluxes, tau_w > 3, are
required for the AGN-driven galactic outflow to suppress star formation and
accretion in the black hole's host galaxy. Less powerful AGN winds (tau_w < 3)
still produce a modest galaxy-scale outflow, but the outflow has little global
effect on the ambient interstellar gas. We argue that this mechanism of AGN
feedback can plausibly produce the high velocity outflows observed in
post-starburst galaxies and the massive molecular and atomic outflows observed
in local ultra-luminous infrared galaxies. Moreover, the outflows from local
ultra-luminous infrared galaxies are inferred to have tau_w ~ 10, comparable to
what we find is required for AGN winds to regulate the growth of black holes
and set the M_BH-sigma relation. We conclude by discussing theoretical
mechanisms that can lead to AGN wind mass-loading and momentum/energy fluxes
large enough to have a significant impact on galaxy formation. |
Lensed Cosmic Microwave Background Constraints on Post-General
Relativity Parameters: The constraints on departures from general relativity (GR) at cosmological
length scales due to cosmic microwave background (CMB) data are discussed. The
departure from GR is measured by the ratio, parameterized as $1 +\varpi_0 (1 +
z)^{-S}$, between the gravitational potentials conventionally appearing in the
geodesic equation and the Poisson equation. Current CMB data indicate
$\varpi_0=1.67^{+3.07}_{-1.87}$ at the 2$\sigma$ confidence level, while $S$
remains unconstrained. The departure from GR affects the lensing conversion of
E-mode into B-mode polarization. Hence, the lensing measurements from a future
CMBpol experiment should be able to improve the constraints to $\varpi_0< 0.30$
for a fiducial $\varpi_0=0$ model and independent of $S$. | Cluster-Void Degeneracy Breaking: Dark Energy, Planck and the Largest
Cluster & Void: Combining galaxy cluster and void abundances breaks the degeneracy between
mean matter density $\Omega_{\rm m}$ and power spectrum normalization
$\sigma_8$. In a first for voids, we constrain $\Omega_{\rm m} = 0.21 \pm 0.10$
and $\sigma_8 = 0.95 \pm 0.21$ for a flat $\Lambda$CDM universe, using
extreme-value statistics on the claimed largest cluster and void. The
Planck-consistent results detect dark energy with two objects, independently of
other dark energy probes. Cluster-void studies also offer complementarity in
scale, density, and non-linearity - of particular interest for testing
modified-gravity models. |
Cosmological model-independent constraints on spatial curvature from
strong gravitational lensing and type Ia supernova observations: Applying the distance sum rule in strong gravitational lensing (SGL) and type
Ia supernova (SN Ia) observations, one can provide an interesting cosmological
model-independent method to determine the cosmic curvature parameter
$\Omega_k$. In this paper, with the newly compiled data sets including 161
galactic-scale SGL systems and 1048 SN Ia data, we place constraints on
$\Omega_k$ within the framework of three types of lens models extensively used
in SGL studies. Moreover, to investigate the effect of different mass lens
samples on the results, we divide the SGL sample into three sub-samples based
on the center velocity dispersion of intervening galaxies. In the singular
isothermal sphere (SIS) and extended power-law lens models, a flat universe is
supported with the uncertainty about 0.2, while a closed universe is preferred
in the power-law lens model. We find that the choice of lens models and the
classification of SGL data actually can influence the constraints on $\Omega_k$
significantly. | Discovery of nine extended ionized gas clouds in a z=0.4 cluster: From deep H-alpha imaging data of Suprime-Cam/Subaru, we discovered nine
extended ionized gas clouds (EIG) around galaxies in Abell 851 cluster (A851)
at z=0.4. We surveyed 30 x 25 arcmin region, and the EIGs were found only near
the cluster center (<2.3 arcmin ~ 750 kpc). The parent galaxies of the EIGs are
star-forming or post-starburst galaxies, all of which are spectroscopically
confirmed members of the cluster. Four out of the nine parent galaxies show
distortion of stellar distribution in the disk, which can be a sign of recent
interaction, and the interaction may have made EIGs. On the other hand, six
parent galaxies (one overlaps those exhibiting distortion) show H-alpha
emission without stars, which implies a ram pressure stripping.The spe ctrum of
the brightest parent galaxy shows a post-starburst signature, and resembles the
H-alpha stripped galaxies found in the Coma cluster. Meanwhile, two brightest
parent galaxies in A851 are more massive than the EIG parent galaxies in the
Coma cluster. This is consistent with "downsizing" of star-forming galaxies,
though it is still in a statistical fluctuation. We also analyzed Suprime-Cam
data of another z=0.39 cluster, CL0024+17, but found no EIGs. The key
difference between A851 and CL0024+17 would be the existence of a subcluster
colliding with the main body of A851, in which six or seven out of the nine
parent galaxies in A851 exist, and the fraction of EIGs in the subcluster is
significantly higher than the main subcluster of A851 and CL0024+17. |
The synergy between the Dark Energy Survey and the South Pole Telescope: The Dark Energy Survey (DES) has recently completed the Science Verification
phase (SV), collecting data over 150 sq. deg. of sky. In this work we analyze
to what extent it is beneficial to supplement the analysis of DES data with CMB
lensing data. We provide forecasts for both DES-SV and for the full survey
covering 5000 sq. deg. We show that data presently available from DES-SV and
SPT-SZ would allow a ~ 8% measurement of the linear galaxy bias in three out of
four redshift bins. We further show that a joint analysis of cosmic shear,
galaxy density and CMB lensing data allows to break the degeneracy between the
shear multiplicative bias, the linear galaxy bias and the normalization of the
matter power spectrum. We show that these observables can thus be self
calibrated to the percent or sub-percent level, depending on the quality of
available data, fraction of overlap of the footprints and priors included in
the analysis. | Astrophysical Tests of Modified Gravity: Chameleon and similar (symmetron and dilation) theories of gravity can
exhibit new and interesting features on cosmological scales whilst screening
the modifications on small scales thereby satisfying solar system tests of
general relativity. This thesis explores the regime between these two scales:
astrophysics. The majority of this thesis is focused on discerning new and
novel astrophysical probes of chameleon gravity in the form of stellar
structure and oscillation tests. These are used to place new constraints on the
theory parameters and the implications of these are discussed, as are the
future prospects for improving them using planned future surveys. The final two
chapters review supersymmetric completions of these theories. |
Green Pea Galaxies and cohorts: Luminous Compact Emission-Line Galaxies
in the Sloan Digital Sky Survey: We present a large sample of 803 star-forming luminous compact galaxies
(LCGs) in the redshift range z = 0.02-0.63, selected from Data Release 7 of the
Sloan Digital Sky Survey (SDSS). The global properties of these galaxies are
similar to those of the so-called "green pea" star-forming galaxies, in the
redshift range z=0.112-0.360 and selected from the SDSS on the basis of their
green color and compact structure. In contrast to green pea galaxies, our LCGs
are selected on the basis of both their spectroscopic and photometric
properties, resulting in a ~10 times larger sample, with galaxies spanning a
redshift range >2 times larger. We find that the oxygen abundances and the
heavy element abundance ratios in LCGs do not differ from those of nearby
low-metallicity blue compact dwarf (BCD) galaxies. The median stellar mass of
LCGs is ~1e9 Msun. However, for galaxies with high EW(Hbeta), >100A, it is only
~7x1e8 Msun. The star formation rate in LCGs varies in the large range of
0.7-60 Msun yr^{-1}, with a median value of ~4 Msun yr^{-1}, a factor of ~3
lower than in high-redshift star-forming galaxies at z>3. The specific star
formation rates in LCGs are extremely high and vary in the range ~1e-9 - 1e-7
yr^{-1}, comparable to those derived in high-redshift galaxies. | On the Nature of Unconfirmed Supernovae: We study the nature of 39 unconfirmed supernovae (SNe) from the sky area
covered by the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8), using
available photometric and imaging data and intensive literature search. We
confirm that 21 objects are real SNe, 2 are Galactic stars, 4 are probable SNe,
and 12 remain unconfirmed events. The probable types for 4 objects are
suggested: 3 SNe are of probable type Ia, and SN 1953H is probable type II SN.
In addition, we identify the host galaxy of SN 1976N and correct the
offsets/coordinates of SNe 1958E, 1972F, and 1976N. |
On the relativistic mass function and averaging in cosmology: The general relativistic description of cosmological structure formation is
an important challenge from both the theoretical and the numerical point of
views. In this paper we present a brief prescription for a general relativistic
treatment of structure formation and a resulting mass function on galaxy
cluster scales in a highly generic scenario. To obtain this we use an exact
scalar averaging scheme together with the relativistic generalization of
Zel'dovich's approximation (RZA) that serves as a closure condition for the
averaged equations. | Cosmological Consequences of Exponential Gravity in Palatini Formalism: We investigate cosmological consequences of a class of exponential $f(R)$
gravity in the Palatini formalism. By using the current largest type Ia
Supernova sample along with determinations of the cosmic expansion at
intermediary and high-$z$ we impose tight constraints on the model parameters.
Differently from other $f(R)$ models, we find solutions of transient
acceleration, in which the large-scale modification of gravity will drive the
Universe to a new decelerated era in the future. We also show that a viable
cosmological history with the usual matter-dominated era followed by an
accelerating phase is predicted for some intervals of model parameters. |
Erratum: Nonlinear spherical perturbations in quintessence models of
dark energy: We reported results of our study on non-linear spherical perturbations in
quintessence models of dark energy. In the process of some follow up studies we
discovered that a scaling factor in the code used for numerical calculations
that should have been set to unity was set to a large value. Thus the scale of
perturbations was much larger than intended, and for the larger scales the
amplitude of dark matter perturbations was much higher than realistic. We
provide corrected results here in this erratum. We find that there is no change
in the perturbations for dark matter. The amplitude of perturbations in dark
energy is much smaller than presented in the paper. Same holds true for spatial
variation in the equation of state parameter. | Assessing the redshift evolution of massive black holes and their hosts: Motivated by recent observational results that focus on high redshift black
holes, we explore the effect of scatter and observational biases on the ability
to recover the intrinsic properties of the black hole population at high
redshift. We find that scatter and selection biases can hide the intrinsic
correlations between black holes and their hosts, with 'observable' subsamples
of the whole population suggesting, on average, positive evolution even when
the underlying population is characterized by no- or negative evolution. We
create theoretical mass functions of black holes convolving the mass function
of dark matter halos with standard relationships linking black holes with their
hosts. Under these assumptions, we find that the local MBH - sigma correlation
is unable to fit the z = 6 black hole mass function proposed by Willott et al.
(2010), overestimating the number density of all but the most massive black
holes. Positive evolution or including scatter in the MBH - sigma correlation
makes the discrepancy worse, as it further increases the number density of
observable black holes. We notice that if the MBH - sigma correlation at z = 6
is steeper than today, then the mass function becomes shallower. This helps
reproducing the mass function of z = 6 black holes proposed by Willott et al.
(2010). Alternatively, it is possible that very few halos (of order 1/1000)
host an active massive black hole at z = 6, or that most AGN are obscured,
hindering their detection in optical surveys. Current measurements of the high
redshift black hole mass function might be underestimating the density of low
mass black holes if the active fraction or luminosity are a function of host or
black hole mass. Finally, we discuss physical scenarios that can possibly lead
to a steeper MBH - sigma relation at high redshift. |
Cosmological Magnetic Fields from Inflation and Backreaction: We study the backreaction problem in a mechanism of magnetogenesis from
inflation. In usual analysis, it has been assumed that the backreaction due to
electromagnetic fields spoils inflation once it becomes important. However,
there exists no justification for this assumption. Hence, we analyze
magnetogenesis from inflation by taking into account the backreaction. On the
contrary to the naive expectation, we show that inflation still continues even
after the backreaction begins to work. Nevertheless, it turns out that creation
of primordial magnetic fields is significantly suppressed due to the
backreaction. | A Possible Detection of the Cosmic Antineutrino Background in the
Presence of Flavor Effects: Lusignoli and Vignati have recently pointed out that it is in principle
possible to directly detect the cosmic antineutrino background by using the
rather stable isotope holmium-163 as a target, which can decay into
dysprosium-163 via electron capture (EC) with a very small energy release. In
this paper we calculate the rate of the relic antineutrino capture on
holmium-163 nuclei against the corresponding EC decay rate by taking account of
different neutrino mass hierarchies and reasonable values of theta_13. We show
that such flavor effects are appreciable and even important in some cases, and
stress that a calorimetric measurement of the cosmic antineutrino background
might be feasible in the far future. |
The filling factor of intergalactic metals at redshift z=3: Observations of quasar absorption line systems reveal that the z=3
intergalactic medium (IGM) is polluted by heavy elements down to HI optical
depths tau_HI<<10. What is not yet clear, however, is what fraction of the
volume needs to be enriched by metals and whether it suffices to enrich only
regions close to galaxies in order to reproduce the observations. We use gas
density fields derived from large cosmological simulations, together with
synthetic quasar spectra and imposed, model metal distributions to investigate
what enrichment patterns can reproduce the observed median optical depth of CIV
as a function of tau_HI. Our models can only satisfy the observational
constraints if the z=3 IGM was primarily enriched by galaxies that reside in
low-mass (m_tot<10^10 M_sun) haloes that can eject metals out to distances
>10^2 kpc. Galaxies in more massive haloes cannot possibly account for the
observations as they are too rare for their outflows to cover a sufficiently
large fraction of the volume. Galaxies need to enrich gas out to distances that
are much greater than the virial radii of their host haloes. Assuming the
metals to be well mixed on small scales, our modeling requires that the
fractions of the simulated volume and baryonic mass that are polluted with
metals are, respectively, >10% and >50% in order to match observations. | Non-Gaussian Probability Distribution for the CMB Angular Power Spectra?: This is my contribution to Proceedings of the International Workshop on
Cosmic Structure and Evolution, September 23-25, 2009, Bielefeld, Germany. In
my talk I presented some non-Gaussian features of the foreground reduced WMAP
five year full sky temperature maps, which were recently reported in
arXiv:0906.4954 paper by V.Vanchurin. And in these notes I first discuss the
statistics behind this analysis in some detail. Then I describe invaluable
insights which I got from discussions after my talk on the Workshop. And
finally I explain why, in my current opinion, the signal detected in
arXiv:0906.4954 can hardly have something to do with cosmological
perturbations, but rather it presents a fancy measurement of the Milky Way
angular width in the microwave frequency range. |
On the possibility of braneworld quintessential inflation: We examine the possibility of achieving quintessential inflation, where the
same field serves as both inflaton and quintessence, in the context of a
five-dimensional braneworld. Braneworld cosmology provides an appropriate
environment as it permits inflation with much steeper potentials than the
conventional scenario, which is favourable to a late-time quintessence. We
explore a wide space of models, together with contemporary observational data,
to determine in which contexts such a picture is possible. We find that such a
scenario, although attractive, is in fact impossible to achieve for the
potentials studied due to the restrictiveness of current data. | G2C2 I: Homogeneous SDSS photometry for Galactic GCs: We present $g^\prime$ and $z^\prime$ aperture photometry for 96 Galactic
Globular Clusters, making this the largest homogeneous catalog of photometry
for these objects in the SDSS filter system. For a subset of 56 clusters we
also provide photometry in $r^\prime$ and $i^\prime$. We carry out comparisons
with previous photometry as well as with the SDSS dataset. The data will be
useful for a series of applications in Galactic and extragalactic astrophysics.
Future papers will analyse the colour-metallicity relation, colour-magnitude
diagrams, and structural parameters. The compilation of results based on this
dataset will be collected in the Galactic Globular Cluster Catalog (G2C2). |
Cosmology and Fundamental Physics and their Laboratory Astrophysics
Connections: The Decadal Survey of Astronomy and Astrophysics created five panels to
identify the science themes that would define the field's research frontiers in
the coming decade. I will describe the conclusions of one of these, the Panel
on Cosmology and Fundamental Physics, and comment on their relevance to the
discussions at this meeting of the NASA Laboratory Astrophysics community. | Simulations of the Sunyaev-Zel'dovich Power Spectrum with AGN Feedback: We explore how radiative cooling, supernova feedback, cosmic rays and a new
model of the energetic feedback from active galactic nuclei (AGN) affect the
thermal and kinetic Sunyaev-Zel'dovich (SZ) power spectra. To do this, we use a
suite of hydrodynamical TreePM-SPH simulations of the cosmic web in large
periodic boxes and tailored higher resolution simulations of individual galaxy
clusters. Our AGN feedback simulations match the recent universal pressure
profile and cluster mass scaling relations of the REXCESS X-ray cluster sample
better than previous analytical or numerical approaches. For multipoles
$\ell\lesssim 2000$, our power spectra with and without enhanced feedback are
similar, suggesting theoretical uncertainties over that range are relatively
small, although current analytic and semi-analytic approaches overestimate this
SZ power. We find the power at high 2000-10000 multipoles which ACT and SPT
probe is sensitive to the feedback prescription, hence can constrain the theory
of intracluster gas, in particular for the highly uncertain redshifts $>0.8$.
The apparent tension between $\sigma_8$ from primary cosmic microwave
background power and from analytic SZ spectra inferred using ACT and SPT data
is lessened with our AGN feedback spectra. |
Cosmological Constraints from Measurements of Type Ia Supernovae
discovered during the first 1.5 years of the Pan-STARRS1 Survey: We present griz light curves of 146 spectroscopically confirmed Type Ia
Supernovae ($0.03 < z <0.65$) discovered during the first 1.5 years of the
Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is
determined by a combination of on-site measurements of the instrument response
function and observations of spectrophotometric standard stars. We find that
the systematic uncertainties in the photometric system are currently 1.2\%
without accounting for the uncertainty in the HST Calspec definition of the AB
system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia
that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113
PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only SNe and
assuming a constant dark energy equation of state and flatness, yields
$w=-1.120^{+0.360}_{-0.206}\textrm{(Stat)} ^{+0.269}_{-0.291}\textrm{(Sys)}$.
When combined with BAO+CMB(Planck)+$H_0$, the analysis yields $\Omega_{\rm
M}=0.280^{+0.013}_{-0.012}$ and $w=-1.166^{+0.072}_{-0.069}$ including all
identified systematics (see also Scolnic et al. 2014). The value of $w$ is
inconsistent with the cosmological constant value of $-1$ at the 2.3$\sigma$
level. Tension endures after removing either the BAO or the $H_0$ constraint,
though it is strongest when including the $H_0$ constraint. If we include WMAP9
CMB constraints instead of those from Planck, we find
$w=-1.124^{+0.083}_{-0.065}$, which diminishes the discord to $<2\sigma$. We
cannot conclude whether the tension with flat $\Lambda$CDM is a feature of dark
energy, new physics, or a combination of chance and systematic errors. The full
Pan-STARRS1 supernova sample with $\sim\!\!$3 times as many SNe should provide
more conclusive results. | Ultra-low frequency gravitational waves from cosmological and
astrophysical processes: Gravitational waves (GWs) at ultra-low frequencies (${\lesssim
100\,\mathrm{nHz}}$) are key to understanding the assembly and evolution of
astrophysical black hole (BH) binaries with masses $\sim
10^{6}-10^{9}\,M_\odot$ at low redshifts. These GWs also offer a unique window
into a wide variety of cosmological processes. Pulsar timing arrays (PTAs) are
beginning to measure this stochastic signal at $\sim 1-100\,\mathrm{nHz}$ and
the combination of data from several arrays is expected to confirm a detection
in the next few years. The dominant physical processes generating gravitational
radiation at $\mathrm{nHz}$ frequencies are still uncertain. PTA observations
alone are currently unable to distinguish a binary BH astrophysical foreground
from a cosmological background due to, say, a first order phase transition at a
temperature $\sim 1-100\,\mathrm{MeV}$ in a weakly-interacting dark sector.
This letter explores the extent to which incorporating integrated bounds on the
ultra-low frequency GW spectrum from any combination of cosmic microwave
background, big bang nucleosynethesis or astrometric observations can help to
break this degeneracy. |
Cosmology with massive neutrinos I: towards a realistic modeling of the
relation between matter, haloes and galaxies: By using a suite of large box-size N-body simulations that incorporate
massive neutrinos as an extra set of particles, we investigate the impact of
neutrino masses on the spatial distribution of dark matter haloes and galaxies.
We compute the bias between the spatial distribution of dark matter haloes and
the overall matter and cold dark matter distributions using statistical tools
such as the power spectrum and the two-point correlation function. Overall we
find a scale-dependent bias on large scales for the cosmologies with massive
neutrinos. However, our results indicate that the scale-dependence in the bias
is reduced if the latter is computed with respect to the cold dark matter
distribution only. We find that the value of the bias on large scales is
reasonably well reproduced by the Tinker fitting formula once the linear cold
dark matter power spectrum is used, instead of the total matter power spectrum.
We investigate whether scale-dependent bias really comes from purely neutrino's
effect or from nonlinear gravitational collapse of haloes. For this purpose, we
address the $\Omega_\nu$-$\sigma_8$ degeneracy and find that such degeneracy is
not perfect, implying that neutrinos imprint a slight scale dependence on the
large-scale bias. Finally, by using a simple halo occupation distribution (HOD)
model, we investigate the impact of massive neutrinos on the distribution of
galaxies within dark matter haloes. We use the main galaxy sample in the Sloan
Digital Sky Survey II Data Release 7 to investigate if the small-scale galaxy
clustering alone can be used to discriminate among different cosmological
models with different neutrino masses. Our results suggest that different
choices of the HOD parameters can reproduce the observational measurements
relatively well, and we quantify the difference between the values of the HOD
parameters between massless and massive neutrino cosmologies. | Pursuing the Amplitude of Tensor Mode Power Spectrum in Light of BICEP2: In this brief report, we try to constrain general parameterized forms of
scalar and tensor mode power spectra, $P_{s}(k)\equiv
A_s(k/k_0)^{n_s-1+\frac{1}{2}\alpha_s\ln(k/k_0)}$ and $P_{t}(k)\equiv
A_t(k/k_0)^{n_t+\frac{1}{2}\alpha_t\ln(k/k_0)}$ by the recently released BICEP2
data set plus {\it Planck} 2013, WMAP9 and BAO. We loosen the inflationary
consistence relations, and take $A_s$, $n_s$, $A_t$ and $n_t$ as free model
parameters, via the Markov chain Monte Carlo method, the interested model
parameter space was investigated, we obtained marginalized $68\%$ limits on the
interested parameters are: $n_s=0.96339_{-0.00554}^{+0.00560}$,
$n_t=1.70490_{-0.56979}^{+0.56104}$, ${\rm{ln}}(10^{10}
A_s)=3.08682_{-0.02614}^{+0.02353}$ and ${\rm{ln}}(10^{10}
A_t)=3.98376_{-0.54885}^{+0.86045}$. The ratio of the amplitude at the scale
$k=0.002 \text{Mpc} ^{-1}$ is $r=0.01655_{-0.01655}^{+0.00011}$ which is
consistent with the {\it Planck} 2013 result. |
Turbulence Modelling and Stirring Mechanisms in the Cosmological
Large-scale Structure: FEARLESS (Fluid mEchanics with Adaptively Refined Large Eddy SimulationS) is
a numerical scheme for modelling subgrid-scale turbulence in cosmological
adaptive mesh refinement simulations. In this contribution, the main features
of this tool will be outlined. We discuss the application of this method to
cosmological simulations of the large-scale structure. The simulations show
that the production of turbulence has a different redshift dependence in the
intra-cluster medium and the warm-hot intergalactic medium, caused by the
distinct stirring mechanisms (mergers and shock interactions) acting in them.
Some properties of the non-thermal pressure support in the two baryon phases
are also described. | Generalised constraints on the curvature perturbation from primordial
black holes: Primordial black holes (PBHs) can form in the early Universe via the collapse
of large density perturbations. There are tight constraints on the abundance of
PBHs formed due to their gravitational effects and the consequences of their
evaporation. These abundance constraints can be used to constrain the
primordial power spectrum, and hence models of inflation, on scales far smaller
than those probed by cosmological observations. We compile, and where relevant
update, the constraints on the abundance of PBHs before calculating the
constraints on the curvature perturbation, taking into account the growth of
density perturbations prior to horizon entry. We consider two simple
parameterizations of the curvature perturbation spectrum on the scale of
interest: constant and power-law. The constraints from PBHs on the amplitude of
the power spectrum are typically in the range 10^{-2}-10^{-1} with some scale
dependence. |
White dwarfs and revelations: We use the most recent, complete and independent measurements of masses and
radii of white dwarfs in binaries to bound the class of non-trivial modified
gravity theories, viable after GW170817/GRB170817, using its effect on the
mass-radius relation of the stars. We show that the uncertainty in the latest
data is sufficiently small that residual evolutionary effects, most notably the
effect of core composition, finite temperature and envelope structure, must now
accounted for if correct conclusions about the nature of gravity are to be
made. We model corrections resulting from finite temperature and envelopes to a
base Hamada-Salpeter cold equation of state and derive consistent bounds on the
possible modifications of gravity in the stars' interiors, finding that $Y<
0.14$ at 95\% confidence, an improvement of a factor of three with respect to
previous bounds. Finally, our analysis reveals some fundamental degeneracies
between the theory of gravity and the precise chemical makeup of white dwarfs. | Mimetic DBI Inflation in Confrontation with Planck2018 data: We study mimetic gravity in the presence of a DBI-like term which is a
non-canonical setup of the scalar field's derivatives. We consider two general
cases with varying and constant sound speeds and construct the potentials for
both the DBI and Mimetic DBI models. By considering the power-law scale factor
as $a=a_{0}\,t^{n}$, we seek for the observational viability of these models.
We show that, the Mimetic DBI model in some ranges of the parameters space is
free of ghost and gradient instabilities. By studying $r-n_{s}$ and
$\alpha_{s}-n_{s}$ behavior in confrontation with Planck2018 data, we find some
constraints on the model's parameters. We show that for the case with varying
sound speed, although power-law DBI inflation is not consistent with Planck2018
TT, TE, EE+low E+lensing data, but the Mimetic DBI inflation is consistent with
Planck2018 TT, TE, EE+low E+lensing data at 95$\%$ CL, in some ranges of the
model's parameters space as $40\leq n \leq 55$ where the model is
instabilities-free in these ranges of parameters too. For the constant sound
speed, by adopting some sample values of $c_{s}$, we study both DBI and Mimetic
DBI model numerically and find $n\sim 10^{2}$ for DBI model and $n\sim 10$ for
Mimetic DBI model. We also compare the results with Planck2018 TT, TE, EE+low
E+lensing+BK14+BAO data and see that the DBI and Mimetic DBI model with varying
sound speed are ruled out with these joint data. However, these models with
constant sound speed are consistent with Planck2018 TT, TE, EE+low
E+lensing+BK14+BAO data with $n\sim 10^{2}$ for DBI model and $n\sim 10$ for
Mimetic DBI model. In this case, we find some tighter constraints on the
corresponding sound speed. |
The ~0.9 mJy sample: A mid-infrared spectroscopic catalog of 150
infrared-luminous, 24 micron selected galaxies at 0.3<z<3.5: We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR)
luminous galaxies in the Spitzer extragalactic first look survey obtained with
IRS on board Spitzer. The sample is selected to be brighter than ~0.9 mJy at 24
micron and it has a z distribution in the range [0.3,3.5] with a peak at z=1.
It primarily comprises ultraluminous IR galaxies at z>1 and luminous IR
galaxies at z<1, as estimated from their monochromatic 14 micron luminosities.
The number of sources with spectra that are dominated by an active galactic
nucleus (AGN) continuum is 49, while 39 sources have strong, star-formation
related features. For this classification, we used the equivalent width (EW) of
the 11.3 micron polycyclic aromatic hydrocarbon (PAH) feature. Several
intermediate/high z starbursts have higher PAH EW than local ULIRGs. An
increase in the AGN activity is observed with increasing z and luminosity,
based on the decreasing EW of PAHs and the increasing [NeIII]/[NeII] ratio.
Spectral stacking leads to the detection of the 3.3 micron PAH, the H2 0-0 S(1)
and S(3) lines, and the [NeV] line. We observe differences in the flux ratios
of PAHs in the stacked spectra of IR-luminous galaxies with z or luminosity,
which are not due to extinction effects. When placing the observed galaxies on
IR color-color diagrams, we find that the wedge defining AGN comprises most
sources with continuum-dominated spectra, but also contains many starbursts.
The comparison of the 11.3 micron PAH EW and the H-band effective radius,
measured from HST data, indicates that sources with EW>2 micron, are typically
more extended than ~3 kpc. However, there is no strong correlation between the
MIR spectral type and the near-IR extent of the sources. [Abridged]. | Massive star formation in Wolf-Rayet galaxies. III: Analysis of the O
and WR populations: (Abridged) We perform a comprehensive multiwavelength analysis of a sample of
20 starburst galaxies that show the presence of a substantial population of
Wolf-Rayet (WR) stars. In this paper we present the analysis of the O and WR
star populations. We study the spatial localization of the WR-rich clusters via
the detection of the blue WR bump (broad He II 4686) and the red WR bump (broad
C IV 5808). We perform a detailed fitting of the nebular and broad emission
lines within these broad features and derive the numbers of WN, WC and O stars
using (i) the standard assumption of constant WR luminosities and (ii)
considering metallicity-dependent WR luminosities. We then compare our results
with the predictions given by evolutionary synthesis models and with previous
empirical results. Aperture effects and the exact positioning of the slit onto
the WR-rich bursts play a fundamental role in their detection. As expected, the
total number of WR stars increases with increasing metallicity, but objects
with 12+log(O/H)<8.2 show a rather constant WR/(WR+O) ratio. The computed
WCE/WNL ratios are different than those empirically found in nearby
star-forming galaxies, indicating that the observed galaxies are experiencing a
strong and very short burst. Considering metallicity-dependent WR luminosities,
our data agree with a Salpeter-like IMF in all regimes. We consider that the
contribution of the WCE stars is not negligible at low metallicities. Although
available models reproduce fairly well the WR properties at high metallicities,
new evolutionary synthesis models for young starbursts including all involved
parameters (age, metallicity, star-formation history, IMF and WR stars
properties such as metallicity-dependent WR luminosities, stellar rotation and
the WR binnary channel) are absolutely needed to perform an appropriate
comparison with the observational data. |
Convergence of halo statistics: code comparison between Rockstar and
CompaSO using scale-free simulations: In this study, we perform a halo-finder code comparison between Rockstar and
CompaSO. Based on our previous analysis aiming at quantifying resolution of
$N$-body simulations by exploiting large (up to $N=4096^3$) simulations of
scale-free cosmologies run using Abacus, we focus on convergence of the HMF,
2PCF and mean radial pairwise velocities of halo centres selected with the
aforementioned two algorithms. We establish convergence, for both Rockstar and
CompaSO, of mass functions at the $1\%$ precision level and of the mean
pairwise velocities (and also 2PCF) at the $2\%$ level. At small scales and
small masses, we find that Rockstar exhibits greater self-similarity, and we
also highlight the role played by the merger-tree post-processing of CompaSO
halos on their convergence. Finally, we give resolution limits expressed as a
minimum particle number per halo in a form that can be directly extrapolated to
LCDM. | Growth of structure in interacting vacuum cosmologies: We examine the growth of structure in three different cosmological models
with interacting dark matter and vacuum energy. We consider the case of
geodesic dark matter with zero sound speed, where the relativistic growing mode
in comoving-synchronous gauge coincides with the Newtonian growing mode at
first order in $\Lambda$CDM. We study corrections to the linearly growing mode
in the presence of interactions and the linear matter growth rate, $f_1$,
contrasting this with the velocity divergence, $f_{rsd}\sigma_8$, observed
through redshift-space distortions. We then derive second-order density
perturbations in these interacting models. We identify the reduced bispectrum
that corresponds to the non-linear growth of structure and show how the shape
of the bispectrum is altered by energy transfer to or from the vacuum. Thus the
bispectrum, or higher-order correlators, might in future be used to identify
dark matter interactions. |
A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255: I. C
IV absorption variability: Broad Absorption Lines indicate gas outflows with velocities from thousands
km/s to about 0.2 the speed of light, which may be present in all quasars and
may play a major role in the evolution of the host galaxy. The variability of
absorption patterns can provide informations on changes of the density and
velocity distributions of the absorbing gas and its ionization status. We
collected 23 photometrical and spectro-photometrical observations at the 1.82m
Telescope of the Asiago Observatory since 2003, plus other 5 spectra from the
literature. We analysed the evolution in time of the equivalent width of the
broad absorption feature and two narrow absorption systems, the correlation
among them and with the R band magnitude. We performed a structure function
analysis of the equivalent width variations. We present an unprecedented
monitoring of a broad absorption line quasar based on 28 epochs in 14 years.
The shape of broad absorption feature shows a relative stability, while its
equivalent width slowly declines until it sharply increases during 2011. In the
same time the R magnitude stays almost constant until it sharply increases
during 2011. The equivalent width of the narrow absorption redwards of the
systemic redshift only shows a decline. The broad absorption behaviour suggests
changes of the ionisation status as the main cause of variability. We show for
the first time a correlation of this variability with the R band flux. The
different behaviour of the narrow absorption system might be due to
recombination time delay. The structure function of the absorption variability
has a slope comparable with typical optical variability of quasars. This is
consistent with variations of the 200 A ionising flux originating in the inner
part of the accretion disk. | Position-dependent power spectrum: a new observable in the large-scale
structure: We present a new observable, position-dependent power spectrum, to measure
the large-scale structure bispectrum in the squeezed configuration, where one
wavenumber is much smaller than the other two. The squeezed-limit bispectrum
measures how the small-scale power spectrum is modulated by a long-wavelength
overdensity, which is due to gravitational evolution and possibly inflationary
physics. We divide a survey into small subvolumes, compute the local power
spectrum and the mean overdensity in each subvolume, and measure the
correlation between them. The correlation measures the integral of the
bispectrum, which is dominated by squeezed configurations if the scale of the
local power spectrum is much smaller than the subvolume size. We use the
separate universe approach to model how the small-scale power spectrum is
affected by a long-wavelength overdensity gravitationally. This models the
nonlinearity of the bispectrum better than the perturbation theory approach.
Not only the new observable is easy to interpret, but it sidesteps the
complexity of the full bispectrum estimation as both power spectrum and mean
overdensity are easier to estimate than the full bispectrum. We report on the
first measurement of the position-dependent correlation function from the
SDSS-III BOSS DR10 CMASS sample. We detect the bispectrum of the CMASS sample,
and constrain their nonlinear bias combining with anisotropic clustering and
weak lensing. We finally study the response of the small-scale power spectrum
to 1-3 long-wavelength overdensities. We compare the separate universe approach
to separate universe simulations to unprecedented accuracy. We test the
standard perturbation theory (SPT) hypothesis that the nonlinear n-point
function is fully predicted by the linear power spectrum at the same time. We
find discrepancies on small scales, which suggest that SPT fails even if it is
calculated to all orders. |
Measurement of the dispersion of radiation from a steady cosmological
source: The `missing baryons' of the near universe are believed to be principally in
a partially ionized state. Although passing electromagnetic waves are dispersed
by the plasma, the effect has hitherto not been utilized as a means of
detection because it is generally believed that a successful observation
requires the background source to be highly variable, \ie~the class of sources
that could potentially deliver a verdict is limited. We argue in two stages
that this condition is not necessary. First, by modeling the fluctuations on
macroscopic scales as interference between wave packets we show that, in
accordance with the ideas advanced by Einstein in 1917, both the behavior of
photons as bosons (\ie~the intensity variance has contributions from Poisson
and phase noise) and the van-Cittert-Zernike theorem are a consequence of
wave-particle duality. Nevertheless, we then point out that in general the
variance on some macroscopic timescale $\tau$ consists of (a) a main
contributing term $\propto 1/\tau$, plus (b) a small negative term $\propto
1/\tau^2$ due to the finite size of the wave packets. If the radiation passes
through a dispersive medium, this size will be enlarged well beyond its vacuum
minimum value of $\Delta t \approx 1/\Delta\nu$, leading to a more negative (b)
term (while (a) remains unchanged) and hence a suppression of the variance
w.r.t. the vacuum scenario. The phenomenon, which is typically at the few parts
in 10$^5$ level, enables one to measure cosmological dispersion in principle.
Signal-to-noise estimates, along with systematic issues and how to overcome
them, will be presented. | Adding helicity to inflationary magnetogenesis: The most studied mechanism of inflationary magnetogenesis relies on the
time-dependence of the coefficient of the gauge kinetic term
$F_{\mu\nu}\,{F}^{\mu\nu}$. Unfortunately, only extremely finely tuned versions
of the model can consistently generate the cosmological magnetic fields
required by observations. We propose a generalization of this model, where also
the pseudoscalar invariant $F_{\mu\nu}\,\tilde{F}^{\mu\nu}$ is multiplied by a
time dependent function. The new parity violating term allows more freedom in
tuning the amplitude of the field at the end of inflation. Moreover, it leads
to a helical magnetic field that is amplified at large scales by
magnetohydrodynamical processes during the radiation dominated epoch. As a
consequence, our model can satisfy the observational lower bounds on fields in
the intergalactic medium, while providing a seed for the galactic dynamo, if
inflation occurs at an energy scale ranging from $10^5$ to $10^{10}$ GeV. Such
energy scale is well below that suggested by the recent BICEP2 result, if the
latter is due to primordial tensor modes. However, the gauge field is a source
of tensors during inflation and generates a spectrum of gravitational waves
that can give a sizable tensor to scalar ratio $r={\cal O}(0.2)$ even if
inflation occurs at low energies. This system therefore evades the Lyth bound.
For smaller values of $r$, lower values of the inflationary energy scale are
required. The model predicts fully helical cosmological magnetic fields and a
chiral spectrum of primordial gravitational waves. |
Searching for large-scale structures around high-redshift radio galaxies
with Herschel: This paper presents the first results of a far-infrared search for
protocluster-associated galaxy overdensities using the SPIRE instrument
on-board the {\it Herschel} Space Observatory. Large ($\sim$400 arcmin$^{2}$)
fields surrounding 26 powerful high-redshift radio galaxies ($2.0 < z < 4.1$;
$L_{\rm 500 MHz} > 10^{28.5}$ WHz$^{-1}$) are mapped at 250, 350 and 500\mic to
give a unique wide-field sample.
On average the fields have a higher than expected, compared to blank fields,
surface density of 500\mic sources within 6 comoving Mpc of the radio galaxy.
The analysis is then restricted to potential protocluster members only, which
are identified using a far-infrared colour selection; this reveals significant
overdensities of galaxies in 2 fields, neither of which are previously known
protoclusters. The probability of finding 2 overdensities of this size by
chance, given the number of fields observed is $5 \times 10^{-4}$.
Overdensities here exist around radio galaxies with $L_{\rm 500 MHz} \gtrsim
10^{29}$ WHz$^{-1}$ and $z < 3$. The radial extent of the average far-infrared
overdensity is found to be $\sim$6 comoving Mpc.
Comparison with predictions from numerical simulations shows that the
overdensities are consistent with having masses $> 10^{14}$Msolar. However, the
large uncertainty in the redshift estimation means that it is possible that
these far-infrared overdensities consist of several structures across the
redshift range searched. | The UV Luminosity Function of star-forming galaxies via dropout
selection at redshifts z ~ 7 and 8 from the 2012 Ultra Deep Field campaign: We present a catalog of high redshift star-forming galaxies selected to lie
within the redshift range z ~ 7-8 using the Ultra Deep Field 2012 (UDF12), the
deepest near-infrared (near-IR) exposures yet taken with the Hubble Space
Telescope. As a result of the increased near-infrared exposure time compared to
previous HST imaging in this field, we probe 0.65 (0.25) mag fainter in
absolute UV magnitude, at z ~ 7 (8), which increases confidence in a
measurement of the faint end slope of the galaxy luminosity function. Through a
0.7 mag deeper limit in the key F105W filter that encompasses or lies just
longward of the Lyman break, we also achieve a much-refined color-color
selection that balances high redshift completeness and a low expected
contamination fraction. We improve the number of drop-out selected UDF sources
to 47 at z ~ 7 and 27 at z ~ 8. Incorporating brighter archival and
ground-based samples, we measure the z ~ 7 UV luminosity function to an
absolute magnitude limit of M_UV = -17 and find a faint end Schechter slope of
\alpha = -1.87+/- 0.18. Using a similar color-color selection at z ~ 8 that
takes account of our newly-added imaging in the F140W filter, and incorporating
archival data from the HIPPIES and BoRG campaigns, we provide a robust estimate
of the faint end slope at z ~ 8, \alpha = -1.94 +/- 0.23. We briefly discuss
our results in the context of earlier work and that derived using the same
UDF12 data but with an independent photometric redshift technique (McLure et al
2012). |
Generalized Non-Commutative Inflation: Non-commutative geometry indicates a deformation of the energy-momentum
dispersion relation $f(E)\equiv\frac{E}{pc}(\neq 1)$ for massless particles.
This distorted energy-momentum relation can affect the radiation dominated
phase of the universe at sufficiently high temperature. This prompted the idea
of non-commutative inflation by Alexander, Brandenberger and Magueijo (2003,
2005 and 2007). These authors studied a one-parameter family of
non-relativistic dispersion relation that leads to inflation: the $\alpha$
family of curves $f(E)=1+(\lambda E)^{\alpha}$. We show here how the
conceptually different structure of symmetries of non-commutative spaces can
lead, in a mathematically consistent way, to the fundamental equations of
non-commutative inflation driven by radiation. We describe how this structure
can be considered independently of (but including) the idea of non-commutative
spaces as a starting point of the general inflationary deformation of
$SL(2,\mathbb{C})$. We analyze the conditions on the dispersion relation that
leads to inflation as a set of inequalities which plays the same role as the
slow roll conditions on the potential of a scalar field. We study conditions
for a possible numerical approach to obtain a general one parameter family of
dispersion relations that lead to successful inflation. | Galaxies at z = 6 - 9 from the WFC3/IR imaging of the HUDF: We present the results of a systematic search for galaxies in the redshift
range z = 6 - 9, within the new, deep, near-infrared imaging of the Hubble
Ultra Deep Field provided by the Wide Field Camera 3 (WFC3) on HST. We have
performed full SED fitting to the optical+infrared photometry of all
high-redshift galaxy candidates detected at greater than 5-sigma in at least
one of the WFC3/IR broad-band filters. After rejection of contaminants, the
result is a sample of 49 galaxies with primary redshift solutions z > 5.9. Our
sample, selected without recourse to specific colour cuts, re-selects all but
the faintest one of the 16 z-drops selected by Oesch et al. (2009), recovers
all 5 of the Y-drops reported by Bouwens et al. (2009), and adds a further 29
galaxy candidates, of which 12 lie beyond z = 6.3, and 4 lie beyond z = 7. We
also present confidence intervals on our photometric redshift estimates, and
caution that acceptable low-redshift (z < 2) solutions exist for 28 out of the
37 galaxies at z > 6.3, and for all 8 galaxy candidates at z > 7.5.
Nevertheless, the very highest redshift candidates appear to be strongly
clustered in the field. We derive new estimates of the ultraviolet galaxy
luminosity function at z = 7 and z = 8. Where our results are most robust, at a
characteristic luminosity M(1500) ~ -19.5 (AB), we find that the comoving
number density of galaxies declines by a factor of ~ 2.5 between z = 6 and z =
7, and by a further factor of ~ 2 by z = 8. These results suggest that it is
difficult for the observed population of high-redshift star-forming galaxies to
achieve reionisation by z ~ 6 without a significant contribution from galaxies
well below the detection limits, plus alterations in the escape fraction of
ionising photons and/or continued vigorous star formation at z > 15. |
The systematics of strong lens modeling quantified: the effects of
constraint selection and redshift information on magnification, mass, and
multiple image predictability: Until now, systematic errors in strong gravitational lens modeling have been
acknowledged but never been fully quantified. Here, we launch an investigation
into the systematics induced by constraint selection. We model the simulated
cluster Ares 362 times using random selections of image systems with and
without spectroscopic redshifts and quantify the systematics using several
diagnostics: image predictability, accuracy of model-predicted redshifts,
enclosed mass, and magnification. We find that for models with $>15$ image
systems, the image plane rms does not decrease significantly when more systems
are added; however the rms values quoted in the literature may be misleading as
to the ability of a model to predict new multiple images. The mass is well
constrained near the Einstein radius in all cases, and systematic error drops
to $<2\%$ for models using $>10$ image systems. Magnification errors are
smallest along the straight portions of the critical curve, and the value of
the magnification is systematically lower near curved portions. For $>15$
systems, the systematic error on magnification is $\sim2\%$. We report no trend
in magnification error with fraction of spectroscopic image systems when
selecting constraints at random; however, when using the same selection of
constraints, increasing this fraction up to $\sim0.5$ will increase model
accuracy. The results suggest that the selection of constraints, rather than
quantity alone, determines the accuracy of the magnification. We note that
spectroscopic follow-up of at least a few image systems is crucial, as models
without any spectroscopic redshifts are inaccurate across all of our
diagnostics. | Microlensing of the broad line region in 17 lensed quasars: When an image of a strongly lensed quasar is microlensed, the different
components of its spectrum are expected to be differentially magnified owing to
the different sizes of the corresponding emitting region. Chromatic changes are
expected to be observed in the continuum while the emission lines should be
deformed as a function of the size, geometry and kinematics of the regions from
which they originate. Microlensing of the emission lines has been reported only
in a handful of systems so far. In this paper we search for microlensing
deformations of the optical spectra of pairs of images in 17 lensed quasars.
This sample is composed of 13 pairs of previously unpublished spectra and four
pairs of spectra from literature. Our analysis is based on a spectral
decomposition technique which allows us to isolate the microlensed fraction of
the flux independently of a detailed modeling of the quasar emission lines.
Using this technique, we detect microlensing of the continuum in 85% of the
systems. Among them, 80% show microlensing of the broad emission lines.
Focusing on the most common lines in our spectra (CIII] and MgII) we detect
microlensing of either the blue or the red wing, or of both wings with the same
amplitude. This observation implies that the broad line region is not in
general spherically symmetric. In addition, the frequent detection of
microlensing of the blue and red wings independently but not simultaneously
with a different amplitude, does not support existing microlensing simulations
of a biconical outflow. Our analysis also provides the intrinsic flux ratio
between the lensed images and the magnitude of the microlensing affecting the
continuum. These two quantities are particularly relevant for the determination
of the fraction of matter in clumpy form in galaxies and for the detection of
dark matter substructures via the identification of flux ratio anomalies. |
Detailed abundance analysis from integrated high-dispersion
spectroscopy: Globular clusters in the Fornax Dwarf Spheroidal: Aims: We describe our newly developed approach to detailed abundance analysis
from integrated-light high-dispersion spectra of star clusters. As a pilot
project, we measure abundances of several elements for three globular clusters
(GCs) in the Fornax dSph, using VLT/UVES spectra. Methods: We divide the
cluster colour-magnitude diagrams into about 100 bins and compute synthetic
spectra for each bin. The individual model spectra are co-added and the
abundances are iteratively adjusted until the best match to the observed
spectra is achieved. Results: We find [Fe/H] = -2.3, -1.4 and -2.1 for Fornax
3, 4 and 5, with +/-0.1 dex uncertainties. Fornax 3 and 5 are thus similar in
metallicity to the most metal-poor Milky Way GCs and fall near the extreme
metal-poor end of the field star metallicity distribution in Fornax. The
[alpha/Fe] ratios, as traced by Ca and Ti, are enhanced with respect to the
Solar composition at the level of about +0.25 dex for Fornax 3 and 5, and
possibly slightly less (about +0.12 dex) for Fornax 4. For all three clusters
the [Mg/Fe] ratio is significantly less elevated than [Ca/Fe] and [Ti/Fe],
possibly an effect of the abundance anomalies that are well-known in Galactic
GCs. We thus confirm that Mg may be a poor proxy for the overall alpha-element
abundances for GCs. The abundance patterns of heavy elements (Y, Ba and Eu)
indicate a dominant contribution to nucleosynthesis from the r-process in all
three clusters, with a mean [Ba/Eu]=-0.7, suggesting rapid formation of the
GCs. Conclusions: Combining our results with literature data for Fornax 1 and
2, four of the five Fornax GCs fall in the range -2.5<[Fe/H]<-2, while Fornax 4
is substantially more metal-rich than the others. The indications that
abundance anomalies are detectable in integrated light are encouraging,
particularly for the prospects of detecting such anomalies in young, massive
star clusters. | LUCIFER@LBT view of star-forming galaxies in the cluster 7C 1756+6520 at
z~1.4: Galaxy clusters are key places to study the contribution of {\it nature}
(i.e. mass, morphology) and {\it nurture} (i.e.environment) in the formation
and evolution of galaxies. Recently, a number of clusters at z$>$1, i.e.
corresponding to the first epochs of the cluster formation, has been discovered
and confirmed spectroscopically. We present new observations obtained with the
{\sc LUCIFER} spectrograph at Large Binocular Telescope (LBT) of a sample of
star-forming galaxies associated with a large scale structure around the radio
galaxy 7C1756+6520 at z=1.42. Combining our spectroscopic data and the
literature photometric data, we derived some of the properties of these
galaxies: star formation rate, metallicity and stellar mass. With the aim of
analyzing the effect of the cluster environment on galaxy evolution, we have
located the galaxies in the plane of the so-called Fundamental Metallically
Relation (FMR), which is known not to evolve with redshift up to z$=2.5$ for
field galaxies, but it is still unexplored in rich environments at low and high
redshift. We found that the properties of the galaxies in the cluster 7C
1756+6520 are compatible with the FMR which suggests that the effect of the
environment on galaxy metallicity at this early epoch of cluster formation is
marginal. As a side study, we also report the spectroscopic analysis of a
bright AGN, belonging to the cluster, which shows a significant outflow of gas. |
Ionization corrections in a multi-phase interstellar medium: Lessons
from a z~2 sub-DLA: We present a high resolution (FWHM=2.7 km/s), high S/N echelle spectrum for
the z = 2.26 QSO J2123-0050 and determine elemental abundances for the z = 2.06
sub-DLA in its line of sight. This high redshift sub-DLA has a complex
kinematic structure and harbours detections of neutral (SI, CI), singly (e.g.
CII, SII) and multiply ionized (e.g. CIV, SiIV) species as well as molecular H
and HD. The plethora of detected transitions in various ionization stages is
indicative of a complex multi-phase structure present in this high redshift
galaxy. We demonstrate that the ionization corrections in this sub-DLA are
significant (up to ~0.7 dex). For example, if no ionization correction is
applied, a super-solar metallicity is derived ([S/H] = +0.36), whereas a single
phase ionization correction reduces this to [S/H] = -0.19. The theoretical
impact of a multi-phase medium is investigated through Cloudy modelling and it
is found that the abundances of Si, S and Fe are always over-estimated (by up
to 0.15 dex in our experiments) if a single-phase is assumed. Therefore,
although Cloudy models improve estimates of metal column densities, the
simplification of a single phase medium leaves a systematic error in the
result, so that even ionization-corrected abundances may still be too high.
Without ionization corrections the properties of this sub-DLA appear to require
extreme scenarios of nucleosynthetic origins. After ionization corrections are
applied the ISM of this galaxy appears to be similar to some of the sightlines
through the Milky Way. | Effect of the Metallicity on the X-ray Emission from the Warm-Hot
Intergalactic Medium: Hydrodynamic simulations predict that a significant fraction of the gas in
the current Universe is in the form of high temperature, highly ionized plasma
emitting and absorbing primarily in the soft X-ray and UV bands, dubbed the
Warm-Hot Intergalactic Medium (WHIM). Its signature should be observable in
red-shifted emission and absorption lines from highly ionized elements. To
determine the expected WHIM emission in the soft X-ray band we used the output
of a large scale hydrodynamic SPH simulation to generate images and spectra
with angular resolution of 14'' and energy resolution of 1 eV. The current
biggest limit of any hydrodynamic simulation in predicting the X-ray emission
comes from metal diffusion. In our investigation, by using four different
models for the WHIM metallicity we have found a strong dependence of the
emission on the model used, with differences up to almost an order of
magnitude. For each model we have investigated the redshift distribution and
angular scale of the emission, confirming that most photons come from redshift
z<1.2 and that the emission has a typical angular scale of less than a few
arcminutes. We also compared our simulations with the few currently available
observations and found that, within the variation of the metallicity models,
our predictions are in good agreement with current constraints on the WHIM
emission, and at this time the weak experimental constraints on the WHIM
emission are not sufficient to exclude any of the models used. |
Radio bursts from superconducting strings: We show that radio bursts from cusps on superconducting strings are linearly
polarized, thus, providing a signature that can be used to distinguish them
from astrophysical sources. We write the event rate of string-generated radio
transients in terms of observational variables, namely, the event duration and
flux. Assuming a canonical set of observational parameters, we find that the
burst event rate can be quite reasonable, e.g., order ten a year for Grand
Unified strings with 100 TeV currents, and a lack of observed radio bursts can
potentially place strong constraints on particle physics models. | Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a
starburst-driven outflow: We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged] |
The EGNoG Survey: Molecular Gas in Intermediate-Redshift Star-Forming
Galaxies: We present the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey,
an observational study of molecular gas in 31 star-forming galaxies from z=0.05
to z=0.5, with stellar masses of (4-30)x10^10 M_Sun and star formation rates of
4-100 M_Sun yr^-1. This survey probes a relatively un-observed redshift range
in which the molecular gas content of galaxies is expected to have evolved
significantly. To trace the molecular gas in the EGNoG galaxies, we observe the
CO(1-0) and CO(3-2) rotational lines using the Combined Array for Research in
Millimeter-wave Astronomy (CARMA). We detect 24 of 31 galaxies and present
resolved maps of 10 galaxies in the lower redshift portion of the survey. We
use a bimodal prescription for the CO to molecular gas conversion factor, based
on specific star formation rate, and compare the EGNoG galaxies to a large
sample of galaxies assembled from the literature. We find an average molecular
gas depletion time of 0.76 \pm 0.54 Gyr for normal galaxies and 0.06 \pm 0.04
Gyr for starburst galaxies. We calculate an average molecular gas fraction of
7-20% at the intermediate redshifts probed by the EGNoG survey. By expressing
the molecular gas fraction in terms of the specific star formation rate and
molecular gas depletion time (using typical values), we also calculate the
expected evolution of the molecular gas fraction with redshift. The predicted
behavior agrees well with the significant evolution observed from z~2.5 to
today. | CMB as a possible new tool to study the dark baryons in galaxies: Baryons constitute about 4% of our universe, but most of them are missing and
we do not know where and in what form they are hidden. This constitute the
so-called missing baryon problem. A possibility is that part of these baryons
are hidden in galactic halos. We show how the 7-year data obtained by the WMAP
satellite may be used to trace the halo of the nearby giant spiral galaxy M31.
We detect a temperature asymmetry in the M31 halo along the rotation direction
up to about 120 kpc. This could be the first detection of a galactic halo in
microwaves and may open a new way to probe hidden baryons in these relatively
less studied galactic objects using high accuracy CMB measurements. |
Comparison between the Luminosity functions of X-ray and [OIII] selected
AGN: We investigate claims according to which the X-ray selection of AGN is not as
efficient compared to that based on [OIII] selection because of the effects of
X-ray absorption.We construct the predicted X-ray luminosity function both for
all Seyferts as well as separately for Seyfert-1 and Seyfert-2 type galaxies,
by combining the optical AGN [OIII] luminosity functions derived in SDSS with
the corresponding L_X-L_[OIII] relations. These relations are derived from
XMM-Newton observations of all Seyfert galaxies in the Palomar spectroscopic
sample of nearby galaxies after correction for X-ray absorption and optical
reddening. We compare the predicted X-ray luminosity functions with those
actually observed in the local Universe by HEAO-1, RXTE as well as INTEGRAL.
The last luminosity function is derived in the 17-60 keV region and thus is not
affected by absorption even in the case of Compton-thick sources. In the common
luminosity regions, the optically and X-ray selected Seyfert galaxies show
reasonable agreement. We thus find no evidence that the [OIII] selection
provides a more robust tracer of powerful AGN compared to the X-ray. Still, the
optical selection probes less luminous Seyferts compared to the current X-ray
surveys. These low luminosity levels, are populated by a large number of X-ray
unobscured Seyfert-2 galaxies. | Cosmology With Axionic-quintessence Coupled with Dark Matter: We study the possibility of explaining the late time acceleration with an
axion field which is coupled with the dark matter sector of the energy budget
of the Universe. The axion field arises from the Ramond-Ramond sector of the
Type-IIB string theory. We study the background evolution of the Universe as
well as the growth of the matter perturbation in the linear regime. We
subsequently use the observational data from Sn-Ia, BAO measurements,
measurements of the Hubble parameter as well as the observational data for the
growth of the matter perturbation to constrain our model. Our results show that
coupled axion models are allowed to have larger deviation from cosmological
constant by the present observational data. |
Imprints of local lightcone projection effects on the galaxy bispectrum.
III Relativistic corrections from nonlinear dynamical evolution on
large-scales: The galaxy bispectrum is affected on equality scales and above by
relativistic observational effects, at linear and nonlinear order. These
lightcone effects include local contributions from Doppler and gravitational
potential terms, as well as integrated contributions like lensing, together
with all the couplings at nonlinear order. We recently presented the correction
to the galaxy bispectrum from all local lightcone effects up to second order in
perturbations, using a plane-parallel approximation. Here we update our
previous result by including the effects from relativistic nonlinear dynamical
evolution. We show that these dynamical effects make a significant contribution
to the projection effects. | The Growth of Massive Black Holes in Galaxy Merger Simulations with
Feedback by Radiation Pressure: We study the growth of massive black holes (BH) in galaxies using smoothed
particle hydrodynamic simulations of major galaxy mergers with new
implementations of BH accretion and feedback. The effect of BH accretion on gas
in its host galaxy is modeled by depositing momentum at a rate ~ tau L/c into
the ambient gas, where L is the luminosity produced by accretion onto the BH
and tau is the wavelength-averaged optical depth of the galactic nucleus to the
AGN's radiation (a free parameter of our model). The accretion rate onto the BH
is relatively independent of our subgrid accretion model and is instead
determined by the BH's dynamical impact on its host galaxy: BH accretion is
thus self-regulated rather than `supply limited.' We show that the final BH
mass and total stellar mass formed during a merger are more robust predictions
of the simulations than the time dependence of the star formation rate or BH
accretion rate. In particular, the latter depend on the assumed interstellar
medium physics, which determines when and where the gas fragments to form star
clusters; this in turn affects the fuel available for further star formation
and BH growth. Simulations over a factor of ~ 30 in galaxy mass are consistent
with the observed M_BH-sigma relation for a mean optical depth of tau ~ 25.
This requires that most BH growth occur when the galactic nucleus is optically
thick to far-infrared radiation, consistent with the hypothesized connection
between ultra-luminous infrared galaxies and quasars. We find tentative
evidence for a shallower M_BH-sigma relation in the lowest mass galaxies, sigma
< 100 km/s. Our results demonstrate that feedback-regulated BH growth and
consistency with the observed M_BH-sigma relation do not require that BH
feedback terminate star formation in massive galaxies or unbind large
quantities of cold gas. |
Intensity Mapping in the Presence of Foregrounds and Correlated
Continuum Emission: Intensity mapping has attracted significant interest as an approach to
measure the properties of the interstellar medium in typical galaxies at high
redshift. Intensity mapping measures the statistics of surface brightness as a
function of frequency, making it sensitive not only to all line emission of
interest but also radiation from all other sources. Significant effort has gone
into developing approaches that reject foreground contamination. Additionally,
the target galaxies have multiple sources of emission that can complicate the
interpretation of the line brightness. We describe the problem of jointly
estimating correlated continuum emission and cleaning uncorrelated continuum
emission, such as from the Milky Way. We apply these considerations to a
cross-correlation of Planck data with BOSS quasars for a determination of CII
for 2 < z < 3.2. Intensity mapping surveys with few bands have unique
challenges for treating foregrounds and avoiding bias from correlated continuum
emission. We show how a future intensity mapping survey with many bands can
separate line from continuum emission in cross-correlation. | CFHT Legacy Ultraviolet Extension (CLUE): Witnessing Galaxy
Transformations up to 7 Mpc from Rich Cluster Cores: Using the optical data from the Wide component of the CFHT Legacy Survey, and
new ultraviolet data from GALEX, we study the colours and specific star
formation rates (SSFR) of ~100 galaxy clusters at 0.16<z<0.36, over areas
extending out to radii of r~7Mpc. We use a multicolour, statistical background
subtraction method to study the galaxy population at this radius; thus our
results pertain to those galaxies which constitute an excess over the average
field density. We find that the average SSFR, and its distribution, of the
star-forming galaxies (with SFR>0.7 M_sun/yr at z~0.2 and SFR>1.2 M_sun/yr at
z~0.3) have no measurable dependence on the cluster-centric radius, and are
consistent with the field values. However, the fraction of galaxies with SFR
above these thresholds, and the fraction of optically blue galaxies, are lower
for the overdense galaxy population in the cluster outskirts compared with the
average field value, at all stellar masses M*>10^{9.8} M_sun and at all radii
out to at least 7Mpc. Most interestingly, the fraction of blue galaxies that
are forming stars at a rate below our UV detection limit is much higher in all
radial bins around our cluster sample, compared with the general field value.
This is most noticeable for massive galaxies M*>10^{10.7} M_sun; while almost
all blue field galaxies of this mass have detectable star formation, this is
true for less than 20% of the blue cluster galaxies, even at 7Mpc from the
cluster centre. Our results support a scenario where galaxies are pre-processed
in locally overdense regions, in a way that reduces their SFR below our UV
detection limit, but not to zero. |
Joint Cosmic Density Reconstruction from Photometric and Spectroscopic
Samples: We reconstruct the dark matter density field from spatially overlapping
spectroscopic and photometric redshift catalogs through a forward modelling
approach. Instead of directly inferring the underlying density field, we find
the best fitting initial Gaussian fluctuations that will evolve into the
observed cosmic volume. To account for the substantial uncertainty of
photometric redshifts we employ a differentiable continuous Poisson process. In
the context of the upcoming Prime Focus Spectrograph (PFS), we find
improvements in cosmic structure classification equivalent to 50-100\% more
spectroscopic targets by combining relatively sparse spectroscopic with dense
photometric samples. | Dynamical Friction in a Fuzzy Dark Matter Universe: We present an in-depth exploration of the phenomenon of dynamical friction in
a universe where the dark matter is composed entirely of so-called Fuzzy Dark
Matter (FDM), ultralight bosons of mass $m\sim\mathcal{O}(10^{-22})\,$eV. We
review the classical treatment of dynamical friction before presenting analytic
results in the case of FDM for point masses, extended mass distributions, and
FDM backgrounds with finite velocity dispersion. We then test these results
against a large suite of fully non-linear simulations that allow us to assess
the regime of applicability of the analytic results. We apply these results to
a variety of astrophysical problems of interest, including infalling satellites
in a galactic dark matter background, and determine that \emph{(1)}~for FDM
masses $m\gtrsim 10^{-21}\, {\rm eV}\, c^{-2}$, the timing problem of the
Fornax dwarf spheroidal's globular clusters is no longer solved and
\emph{(2)}~the effects of FDM on the process of dynamical friction for
satellites of total mass $M$ and relative velocity $v_{\rm rel}$ should require
detailed numerical simulations for $\left(M/10^9~M_{\odot}\right)
\left(m/10^{-22}~{\rm eV}\right)\left(100~{\rm km}~{\rm s}^{-1}/v_{\rm
rel}\right) \sim 1$, parameters which would lie outside the validated range of
applicability of any currently developed analytic theory, due to transient wave
structures in the time-dependent regime. |
Evidence for Shock-Shock Interaction in the Jet of CTA 102: We have found evidence for interaction between a standing and a traveling
shock in the jet of the blazar CTA 102. Our result is based in the study of the
spectral evolution of the turnover frequency-turnover flux density plane. The
radio/mm light curves were taken during a major radio outburst in April 2006. | The Weight of Emptiness: The Gravitational Lensing Signal of Stacked
Voids: The upcoming new generation of spectroscopic galaxy redshift surveys will
provide large samples of cosmic voids, the distinct, large underdense
structures in the universe. Combining these with future galaxy imaging surveys,
we study the prospects of probing the underlying matter distribution in and
around cosmic voids via the weak gravitational lensing effects of stacked
voids, utilizing both shear and magnification information. The statistical
precision is greatly improved by stacking together a large number of voids
along different lines of sight, even when taking into account the impact of
inherent miscentering and projection effects. We show that Dark Energy Task
Force Stage IV surveys, such as the Euclid satellite and the Large Synoptic
Survey Telescope, should be able to detect the void lensing signal with
sufficient precision from stacking abundant medium-sized voids, thus providing
direct constraints on the matter density profile of voids independent of
assumptions on galaxy bias. |
Learning the Evolution of the Universe in N-body Simulations: Understanding the physics of large cosmological surveys down to small
(nonlinear) scales will significantly improve our knowledge of the Universe.
Large N-body simulations have been built to obtain predictions in the
non-linear regime. However, N-body simulations are computationally expensive
and generate large amount of data, putting burdens on storage. These data are
snapshots of the simulated Universe at different times, and fine sampling is
necessary to accurately save its whole history. We employ a deep neural network
model to predict the nonlinear N-body simulation at an intermediate time step
given two widely separated snapshots. Our results outperform the cubic Hermite
interpolation benchmark method in interpolating N-body simulations. This work
can greatly reduce the storage requirement and allow us to reconstruct the
cosmic history from far fewer snapshots of the universe. | Redshift Evolution in Black Hole-Bulge Relations: Testing CIV-based
Black Hole Masses: We re-examine claims of redshift evolution in black hole-bulge scaling
relations based on lensed quasars. In particular, we refine the black hole mass
estimates using measurements of Balmer lines from near-infrared spectroscopy
obtained with Triplespec at Apache Point Observatory. In support of previous
work, we find a large scatter between Balmer and UV line widths, both MgII
2796, 2803 and CIV 1548, 1550. There is tentative evidence that CIII] 1909,
despite being a blend of multiple transitions, may correlate well with MgII,
although a larger sample is needed for a real calibration. Most importantly, we
find no systematic changes in the estimated BH masses for the lensed sample
based on Balmer lines, providing additional support to the interpretation that
black holes were overly massive compared to their host galaxies at high
redshift. |
The X-ray properties of typical high-redshift radio-loud quasars: We report spectral, imaging, and variability results from four new XMM-Newton
observations and two new Chandra observations of high-redshift (z > 4)
radio-loud quasars (RLQs). Our targets span lower, and more representative,
values of radio loudness than those of past samples of high-redshift RLQs
studied in the X-ray regime. Our spectral analyses show power-law X-ray
continua with a mean photon index, \Gamma =1.74 +/- 0.11, that is consistent
with measurements of lower redshift RLQs. These continua are likely dominated
by jet-linked X-ray emission, and they follow the expected anti-correlation
between photon index and radio loudness. We find no evidence of iron K\alpha ~
emission lines or Compton-reflection continua. Our data also constrain
intrinsic X-ray absorption in these RLQs. We find evidence for significant
absorption (N_H ~ 10^22 cm^-2) in one RLQ of our sample (SDSS J0011+1446); the
incidence of X-ray absorption in our sample appears plausibly consistent with
that for high-redshift RLQs that have higher values of radio loudness. In the
Chandra observation of PMN J221-2719 we detect apparent extended (~ 14 kpc)
X-ray emission that is most likely due to a jet; the X-ray luminosity of this
putative jet is ~2% that of the core. The analysis of a 4.9 GHz VLA image of
PMN J221-2719 reveals a structure that matches the X-ray extension found in
this source. We also find evidence for long-term (450-460 days) X-ray
variability by 80-100% in two of our targets. | Constrained simulations of the local Universe with Modified Gravity: We present a methodology for constructing modified gravity (MG) constrained
simulations of the local Universe using positions and peculiar velocities from
the CosmicFlows data set. Our analysis focuses on the following MG models: the
normal branch of the Dvali-Gabadadze-Porrati (nDGP) model and Hu-Sawicki $f(R)$
model. We develop a model independent methodology for constructing constrained
simulations with any given power spectra and numerically calculated linear
growth functions. Initial conditions (ICs) for a set of constrained simulations
are constructed for the standard cosmological model $\Lambda$CDM and the MG
models. Differences between the model's reconstructed Wiener filtered density
and the resultant simulation density are presented showing the importance for
the generation of MG constrained ICs to study the subtle effects of MG in the
local Universe. These are the first MG constrained simulations ever produced.
The current work paves the way to improved approximate methods for models with
scale-dependent growth functions, such as $f(R)$, and for high-resolution
hydrodynamical MG zoom-in simulations of the local Universe. |
Revisiting the VOS model for monopoles: We revisit the physical properties of global and local monopoles and discuss
their implications in the dynamics of monopole networks. In particular, we
review the Velocity-dependent One-Scale (VOS) model for global and local
monopoles and propose physically motivated changes to its equations. We suggest
a new form for the acceleration term of the evolution equation of the
root-mean-squared velocity and show that, with this change, the VOS model is
able to describe the results of radiation and matter era numerical simulations
of global monopole networks with a single value of the acceleration parameter
$k$, thus resolving the tension previously found in the literature. We also
show that the fact that the energy of global monopoles is not localized within
their cores affects their dynamics and, thus, the Hubble damping terms in the
VOS equations. We study the ultra-relativistic linear scaling regime predicted
by the VOS equations and demonstrate that it cannot be attained either on
radiation or matter eras and, thus, cannot arise from the cosmological
evolution of a global monopole network. We also briefly discuss the
implications of our findings for the VOS model for local monopoles. | The Ysz--Yx Scaling Relation as Determined from Planck and Chandra: SZ clusters surveys like Planck, the South Pole Telescope, and the Atacama
Cosmology Telescope, will soon be publishing several hundred SZ-selected
systems. The key ingredient required to transport the mass calibration from
current X-ray selected cluster samples to these SZ systems is the Ysz--Yx
scaling relation. We constrain the amplitude, slope, and scatter of the Ysz--Yx
scaling relation using SZ data from Planck, and X-ray data from Chandra. We
find a best fit amplitude of \ln (D_A^2\Ysz/CY_X) = -0.202 \pm 0.024 at the
pivot point CY_X=8\times 10^{-5} Mpc^2. This corresponds to a Ysz/Yx-ratio of
0.82\pm 0.024, in good agreement with X-ray expectations after including the
effects of gas clumping. The slope of the relation is \alpha=0.916\pm 0.032,
consistent with unity at \approx 2.3\sigma. We are unable to detect intrinsic
scatter, and find no evidence that the scaling relation depends on cluster
dynamical state. |
Weak Lensing Effect on CMB in the Presence of a Dipole Anisotropy: We investigate weak lensing effect on cosmic microwave background (CMB) in
the presence of dipole anisotropy. The approach of flat-sky approximation is
considered. We determine the functions $\sigma_0^2$ and $\sigma_2^2$ that
appear in expressions of the lensed CMB power spectrum in the presence of a
dipole anisotropy. We determine the correction to B-mode power spectrum which
is found to be appreciable at low multipoles ($l$). However, the temperature
and E-mode power spectrum are not altered significantly. | Mixed constraints to inflationary models: We show how to constrain inflationary models and reheating by using mixed
constraints. In particular we study the physics of the reheating phase after
inflation from observational constraints to the inflationary stage. We show
that it is possible to determine $\omega$, the equation of state during
reheating, by using the reported values of the spectral index and the {\it
full} number of $e$-folds $N(n_s,\omega)= N_H(n_s)+N_{re}(n_s,w)\approx 60$,
which includes the accelerated expansion and the reheating phase. We show that
the reheating number of $e$-folds $N_{re}$ is quite sensitive to this equation
of state. Requiring $N_{re}>0$ and a sensible value for the thermalization
scale $T_{re}$, demands in general a reheating phase with $\omega\neq 0$. We
exemplify the constraints with two particular examples: We show how the
Starobinsky model allows only large values of $T_{re}$ if the reheating phase
is dominated by dust ($w =0$), and if Primordial Black Hole production is
subdominant. For the case of $N=1$ Supergravity inflation, the extra parameter
of the potential provides the necessary freedom to afford lower-scale
thermalization in a dust-like reheating phase and yet our method serves to
determine the rest of the observable parameters. |
Constraints on the Optical Depth to Reionization from Balloon-Borne CMB
Measurements: We assess the uncertainty with which a balloon-borne experiment, nominally
called Tau Surveyor ($\tau S$), can measure the optical depth to reionization
$\sigma(\tau)$ with given realistic constraints of instrument noise and
foreground emissions. Using a $\tau S$ fiducial design with six frequency bands
between 150 and 380 GHz with white and uniform map noise of 7 $\mu$K arcmin,
achievable with a single mid-latitude flight, and including Planck's 30 and 44
GHz data we assess the error $\sigma(\tau)$ obtained with three foreground
models and as a function of sky fraction $f_{\rm sky}$ between 40% and 54%. We
carry out the analysis using both parametric and blind foreground separation
techniques. We compare $\sigma(\tau)$ values to those obtained with low
frequency and high frequency versions of the experiment called $\tau S$-lf and
$\tau S$-hf that have only four and up to eight frequency bands with narrower
and wider frequency coverage, respectively. We find that with $\tau S$ the
lowest constraint is $\sigma(\tau)=0.0034$, obtained for one of the foreground
models with $f_{\rm sky}$=54%. $\sigma(\tau)$ is larger, in some cases by more
than a factor of 2, for smaller sky fractions, with $\tau S$-lf, or as a
function of foreground model. The $\tau S$-hf configuration does not lead to
significantly tighter constraints. Exclusion of the 30 and 44 GHz data, which
give information about synchrotron emission, leads to significant $\tau$
mis-estimates. Decreasing noise by an ambitious factor of 10 while keeping
$f_{\rm sky}$=40% gives $\sigma(\tau) =0.0031$. The combination of
$\sigma(\tau) =0.0034$, BAO data from DESI, and future CMB B-mode lensing data
from CMB-S3/S4 experiments could give $\sigma(\sum m_{\nu}) = 17$ meV. | Gaussian Process Reconstruction of Reionization History: We reconstruct the history of reionization using Gaussian process regression.
Using the UV luminosity data compilation from Hubble Frontiers Fields we
reconstruct the redshift evolution of UV luminosity density and thereby the
evolution of the source term in the ionization equation. This model-independent
reconstruction rules out single power-law evolution of the luminosity density
but supports the logarithmic double power-law parametrization. We obtain
reionization history by integrating ionization equations with the reconstructed
source term. Using optical depth constraint from Planck Cosmic Microwave
Background observation, measurement of UV luminosity function integrated till
truncation magnitude of -17 and -15, and derived ionization fraction from high
redshift quasar, galaxies and gamma-ray burst observations, we constrain the
history of reionization. In the conservative case we find the constraint on the
optical depth as $\tau =0.052\pm0.001\pm0.002$ at 68% and 95% confidence
intervals. We find the redshift duration between 10% and 90% ionization to be
$2.05_{-0.21-0.30}^{+0.11+0.37}$. Longer duration of reionization is supported
if UV luminosity density data with truncation magnitude of -15 is used in the
joint analysis. Our results point out that even in a conservative
reconstruction, a combination of cosmological and astrophysical observations
can provide stringent constraints on the epoch of reionization. |
The X-ray luminous cluster underlying the z = 1.04 quasar PKS1229-021: We present a 100 ks Chandra observation studying the extended X-ray emission
around the powerful z=1.04 quasar PKS1229-021. The diffuse cluster X-ray
emission can be traced out to ~15 arcsec (~120 kpc) radius and there is a drop
in the calculated hardness ratio inside the central 5 arcsec consistent with
the presence of a cool core. Radio observations of the quasar show a strong
core and a bright, one-sided jet leading to the SW hot spot and a second hot
spot visible on the counter-jet side. Although the wings of the quasar PSF
provided a significant contribution to the total X-ray flux at all radii where
the extended cluster emission was detected, we were able to accurately subtract
off the PSF emission using ChaRT and marx simulations. The resulting steep
cluster surface brightness profile for PKS1229-021 appears similar to the
profile for the FRII radio galaxy 3C444, which has a similarly rapid surface
brightness drop caused by a powerful shock surrounding the radio lobes (Croston
et al.). Using a model surface brightness profile based on 3C444, we estimated
the total cluster luminosity for PKS1229-021 to be L_X ~ 2 x 10^{44} erg/s. We
discuss the difficulty of detecting cool core clusters, which host bright X-ray
sources, in high redshift surveys. | The multi-stream flows and the dynamics of the cosmic web: A new numerical technique to identify the cosmic web is proposed. It is based
on locating multi-stream flows, i.e. the places where the velocity field is
multi-valued. The method is local in Eulerian space, simple and computaionally
efficient. This technique uses the velocities of particles and thus takes into
account the dynamical information. This is in contrast with the majority of
standard methods that use the coordinates of particles only. Two quantities are
computed in every mesh cell: the mean and variance of the velocity field. In
the cells where the velocity is single-valued the variance must be equal to
zero exactly, therefore the cells with non-zero variance are identified as
multi-stream flows. The technique has been tested in a N-body simulation of the
\L CDM model. The preliminary analysis has shown that numerical noise does not
pose a significant problem. The web identified by the new method has been
compared with the web identified by the standard technique using only the
particle coordinates. The comparison has shown overall similarity of two webs
as expected, however they by no means are identical. For example, the
isocontours of the corresponding fields have significantly different shapes and
some density peaks of similar heights exhibit significant differences in the
velocity variance and vice versa. This suggest that the density and velocity
variance have a significant degree of independence. The shape of the
two-dimensional pdf of density and velocity variance confirms this proposition.
Thus, we conclude that the dynamical information probed by this technique
introduces an additional dimension into analysis of the web. |
Galaxy Kinematics with VIRUS-P: The Dark Matter Halo of M87: We present 2-D stellar kinematics of M87 out to R = 238" taken with the
integral field spectrograph VIRUS-P. We run a large set of axisymmetric,
orbit-based dynamical models and find clear evidence for a massive dark matter
halo. While a logarithmic parameterization for the dark matter halo is
preferred, we do not constrain the dark matter scale radius for an NFW profile
and therefore cannot rule it out. Our best-fit logarithmic models return an
enclosed dark matter fraction of 17.2 +/- 5.0 % within one effective radius
(R_e ~ 100"), rising to 49.4 (+7.2,-8.8) % within 2 R_e. Existing SAURON data
(R < 13"), and globular cluster kinematic data covering 145" < R < 540"
complete the kinematic coverage to R = 47 kpc. At this radial distance the
logarithmic dark halo comprises 85.3 (+2.5,-2.4) % of the total enclosed mass
of 5.7^(+1.3)_(-0.9) X 10^(12) M_sun making M87 one of the most massive
galaxies in the local universe. Our best-fit logarithmic dynamical models
return a stellar mass-to-light ratio of 9.1^(+0.2)_(-0.2) (V-band), a dark halo
circular velocity of 800^(+75)_(-25) kms, and a dark halo scale radius of
36^(+7)_(-3) kpc. The stellar M/L, assuming an NFW dark halo, is well
constrained to 8.20^(+0.05)_(-0.10) (V-band). The stars in M87 are found to be
radially anisotropic out to R ~ 0.5 R_e then isotropic or slightly tangentially
anisotropic to our last stellar data point at R = 2.4 R_e where the anisotropy
of the stars and globular clusters are in excellent agreement. The globular
clusters then become radially anisotropic in the last two modeling bins at R =
3.4 R_e and R = 4.8 R_e. As one of the most massive galaxies in the local
universe, constraints on both the mass distribution of M87 and anisotropy of
its kinematic components strongly informs our theories of early-type galaxy
formation and evolution in dense environments. | Dynamical Mass Measurements of Contaminated Galaxy Clusters Using
Machine Learning: We study dynamical mass measurements of galaxy clusters contaminated by
interlopers and show that a modern machine learning (ML) algorithm can predict
masses by better than a factor of two compared to a standard scaling relation
approach. We create two mock catalogs from Multidark's publicly available
$N$-body MDPL1 simulation, one with perfect galaxy cluster membership
information and the other where a simple cylindrical cut around the cluster
center allows interlopers to contaminate the clusters. In the standard
approach, we use a power-law scaling relation to infer cluster mass from galaxy
line-of-sight (LOS) velocity dispersion. Assuming perfect membership knowledge,
this unrealistic case produces a wide fractional mass error distribution, with
a width of $\Delta\epsilon\approx0.87$. Interlopers introduce additional
scatter, significantly widening the error distribution further
($\Delta\epsilon\approx2.13$). We employ the support distribution machine (SDM)
class of algorithms to learn from distributions of data to predict single
values. Applied to distributions of galaxy observables such as LOS velocity and
projected distance from the cluster center, SDM yields better than a
factor-of-two improvement ($\Delta\epsilon\approx0.67$) for the contaminated
case. Remarkably, SDM applied to contaminated clusters is better able to
recover masses than even the scaling relation approach applied to
uncontaminated clusters. We show that the SDM method more accurately reproduces
the cluster mass function, making it a valuable tool for employing cluster
observations to evaluate cosmological models. |
Stellar Population and Kinematic Profiles in Spiral Bulges & Disks:
Population Synthesis of Integrated Spectra: We present a detailed study of the stellar populations (SPs) and kinematics
of the bulge and inner disk regions of eight nearby spiral galaxies (Sa-Sd)
based on deep Gemini/GMOS data. The long-slit spectra extend to 1-2 disk scale
lengths with S/N/Ang>=50. Several different model fitting techniques involving
absorption-line indices and full spectrum fitting are explored and found to
weigh age, metallicity, and abundance ratios differently. The SPs of spiral
galaxies are not well matched by single episodes of star formation;
representative SPs must involve average SP values integrated over the star
formation history (SFH) of the galaxy. Our "full population synthesis" method
is an optimised linear combination of model templates to the full spectrum with
masking of regions poorly represented by the models. Our spiral bulges follow
the same correlations of increasing light-weighted age and metallicity with
central velocity dispersion as those of elliptical galaxies and early-type
bulges found in other studies, but when SFHs more complex and realistic than a
single burst are invoked, the trend with age is shallower and the scatter much
reduced. In a mass-weighted context, all bulges are predominantly composed of
old and metal-rich SPs. Bulge formation appears to dominated by early processes
that are common to all spheroids, whether they currently reside in disks or
not. While monolithic collapse cannot be ruled out in some cases, merging must
be invoked to explain the SP gradients in most bulges. Further bulge growth via
secular processes or "rejuvenated" star formation generally contributes
minimally to the stellar mass budget. (Abridged) | Contemporary gravitational waves from primordial black holes: Stochastic background of gravitational waves (GW) generated by the
interactions between primordial black holes (PBH) in the early universe and by
PBH evaporation is considered. If PBHs dominated in the cosmological energy
density prior to their evaporation, GWs from the earlier stages (e.g.
inflation) would be noticeably diluted. On the other hand, at the PBH dominance
period they could form dense clusters where PBH binary formation might be
significant. These binaries would be efficient sources of the gravitational
waves. |
Varying alpha from N-body Simulations: We have studied the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) model for the
spatial and temporal variations of the fine structure constant, alpha, with the
aid of full N-body simulations which explicitly and self-consistently solve for
the scalar field driving the alpha-evolution. We focus on the scalar field (or
equivalently alpha) inside the dark matter halos and find that the profile of
the scalar field is essentially independent of the BSBM model parameter. This
means that given the density profile of an isolated halo and the background
value of the scalar field, we can accurately determine the scalar field
perturbation in that halo. We also derive an analytic expression for the
scalar-field perturbation using the Navarro-Frenk-White halo profile, and show
that it agrees well with numerical results, at least for isolated halos; for
non-isolated halos this prediction differs from numerical result by a (nearly)
constant offset which depends on the environment of the halo. | Primordial black hole formation processes with full numerical relativity: See thesis for complete abstract.
Primordial black holes (PBHs) can form in the early universe, and there are
several mass windows in which their abundance today may be large enough to
comprise a significant part of the dark matter density. Additionally, numerical
relativity (NR) allows one to investigate the formation processes of PBHs in
the fully nonlinear strong-gravity regime. In this thesis, we will describe the
use of NR methods to study PBH formation, motivated in particular by open
questions about the nonspherical effects PBH formation in a matter-dominated
early universe.
We demonstrate that superhorizon non-linear perturbations can collapse and
form PBHs via the direct collapse or the accretion collapse mechanisms in a
matter-dominated universe. The heaviest perturbations collapse via the direct
collapse mechanism, while lighter perturbations trigger an accretion process
that causes a rapid collapse of the ambient DM. From the hoop conjecture we
propose an analytic criterion to determine whether a given perturbation will
collapse via the direct or accretion mechanism and we compute the timescale of
collapse. Independent of the formation mechanism, the PBH forms within an efold
after collapse is initiated and with a small initial mass compared to the
Hubble horizon, $M_\textrm{BH} H_0\sim 10^{-2}m_\mathrm{Pl}^2$. Finally, we
find that PBH formation is followed by extremely rapid growth
$M_\textrm{BH}\propto H^{-\beta}$ with $\beta\gg 1$, during which the PBH
acquires most of its mass.
Furthermore, we study the formation of spinning primordial black holes during
an early matter-dominated era. Using non-linear 3+1D general relativistic
simulations, we compute the efficiency of mass and angular momentum transfer in
the process -- which we find to be $\mathcal{O}(10\%)$.
Abstract continues in thesis. |
Fingerprinting Dark Energy II: weak lensing and galaxy clustering tests: The characterization of dark energy is a central task of cosmology. To go
beyond a cosmological constant, we need to introduce at least an equation of
state and a sound speed and consider observational tests that involve
perturbations. If dark energy is not completely homogeneous on observable
scales then the Poisson equation is modified and dark matter clustering is
directly affected. One can then search for observational effects of dark energy
clustering using dark matter as a probe. In this paper we exploit an analytical
approximate solution of the perturbation equations in a general dark energy
cosmology to analyze the performance of next-decade large scale surveys in
constraining equation of state and sound speed. We find that tomographic weak
lensing and galaxy redshift surveys can constrain the sound speed of the dark
energy only if the latter is small, of the order of $c_{s}\lesssim0.01$ (in
units of $c$). For larger sound speeds the error grows to 100% and more. We
conclude that large scale structure observations contain very little
information about the perturbations in canonical scalar field models with a
sound speed of unity. Nevertheless, they are able to detect the presence of
"cold" dark energy, i.e. a dark energy with non-relativistic speed of sound. | LIGO gravitational wave detection, primordial black holes and the
near-IR cosmic infrared background anisotropies: LIGO's discovery of a gravitational wave from two merging black holes (BHs)
of similar masses rekindled suggestions that primordial BHs (PBHs) make up the
dark matter (DM). If so, PBHs would add a Poissonian isocurvature density
fluctuation component to the inflation-produced adiabatic density fluctuations.
For LIGO's BH parameters, this extra component would dominate the small-scale
power responsible for collapse of early DM halos at z>10, where first luminous
sources formed. We quantify the resultant increase in high-z abundances of
collapsed halos that are suitable for producing the first generation of stars
and luminous sources. The significantly increased abundance of the early halos
would naturally explain the observed source-subtracted near-IR cosmic infrared
background (CIB) fluctuations, which cannot be accounted for by known galaxy
populations. For LIGO's BH parameters this increase is such that the observed
CIB fluctuation levels at 2 to 5 micron can be produced if only a tiny fraction
of baryons in the collapsed DM halos forms luminous sources. Gas accretion onto
these PBHs in collapsed halos, where first stars should also form, would
straightforwardly account for the observed high coherence between the CIB and
unresolved cosmic X-ray background in soft X-rays. We discuss modifications
possibly required in the processes of first star formation if LIGO-type BHs
indeed make up the bulk or all of DM. The arguments are valid only if the PBHs
make up all, or at least most, of DM, but at the same time the mechanism
appears inevitable if DM is made of PBHs. |
A Measurement of Gravitational Lensing of the Cosmic Microwave
Background Using SPT-3G 2018 Data: We present a measurement of gravitational lensing over 1500 deg$^2$ of the
Southern sky using SPT-3G temperature data at 95 and 150 GHz taken in 2018. The
lensing amplitude relative to a fiducial Planck 2018 $\Lambda$CDM cosmology is
found to be $1.020\pm0.060$, excluding instrumental and astrophysical
systematic uncertainties. We conduct extensive systematic and null tests to
check the robustness of the lensing measurements, and report a minimum-variance
combined lensing power spectrum over angular multipoles of $50<L<2000$, which
we use to constrain cosmological models. When analyzed alone and jointly with
primary cosmic microwave background (CMB) spectra within the $\Lambda$CDM
model, our lensing amplitude measurements are consistent with measurements from
SPT-SZ, SPTpol, ACT, and Planck. Incorporating loose priors on the baryon
density and other parameters including uncertainties on a foreground bias
template, we obtain a $1\sigma$ constraint on $\sigma_8 \Omega_{\rm
m}^{0.25}=0.595 \pm 0.026$ using the SPT-3G 2018 lensing data alone, where
$\sigma_8$ is a common measure of the amplitude of structure today and
$\Omega_{\rm m}$ is the matter density parameter. Combining SPT-3G 2018 lensing
measurements with baryon acoustic oscillation (BAO) data, we derive parameter
constraints of $\sigma_8 = 0.810 \pm 0.033$, $S_8 \equiv \sigma_8(\Omega_{\rm
m}/0.3)^{0.5}= 0.836 \pm 0.039$, and Hubble constant $H_0 =68.8^{+1.3}_{-1.6}$
km s$^{-1}$ Mpc$^{-1}$. Using CMB anisotropy and lensing measurements from
SPT-3G only, we provide independent constraints on the spatial curvature of
$\Omega_{K} = 0.014^{+0.023}_{-0.026}$ (95% C.L.) and the dark energy density
of $\Omega_\Lambda = 0.722^{+0.031}_{-0.026}$ (68% C.L.). When combining SPT-3G
lensing data with SPT-3G CMB anisotropy and BAO data, we find an upper limit on
the sum of the neutrino masses of $\sum m_{\nu}< 0.30$ eV (95% C.L.). | Spectator Higgs, large-scale gauge fields and the non-minimal coupling
to gravity: Even if the Higgs field does not affect the evolution of the background
geometry, its massive inhomogeneities induce large-scale gauge fields whose
energy density depends on the slow-roll parameters, on the effective scalar
mass and, last but not least, on the dimensionless coupling to the space-time
curvature. Since the non-Abelian gauge modes are screened, the non-minimal
coupling to gravity predominantly affects the evolution of the hypercharge and
electromagnetic fields. While in the case of minimal coupling the obtained
constraints are immaterial, as soon as the coupling increases beyond one fourth
the produced fields become overcritical. We chart the whole parameter space of
this qualitatively new set of bounds. Whenever the limits on the curvature
coupling are enforced, the magnetic field may still be partially relevant for
large-scale magnetogenesis and exceed $10^{-20}$ G for the benchmark scale of
the protogalactic collapse. |
Information gains from Monte Carlo Markov Chains: In this paper, we present a novel method for computing the relative entropy
as well as the expected relative entropy using an MCMC chain. The relative
entropy from information theory can be used to quantify differences in
posterior distributions of a pair of experiments. In cosmology, the relative
entropy has been proposed as an interesting tool for model selection,
experiment design, forecasting and measuring information gain from subsequent
experiments. In contrast to Gaussian distributions, these quantities are not
generally available analytically and one needs to use numerical methods to
estimate them which are certainly computationally expensive. We propose a
method and provide its python package to estimate the relative entropy as well
as expected relative entropy from a posterior sample. We consider the linear
Gaussian model to check the accuracy of our code. Our results indicate that the
relative error is below $0.2\%$ for sample size larger than $10^5$ in the
linear Gaussian model. In addition, we study the robustness of our code in
estimating the expected relative entropy in this model. | Unified Superfluid Dark Sector: We present a novel theory of a unified dark sector, where late-time cosmic
acceleration emerges from the dark matter superfluid framework. The system is
described by a superfluid mixture consisting of two distinguishable states with
a small energy gap, such as the ground state and an excited state of dark
matter. Given their contact in the superfluid, interaction between those states
can happen, converting one state into the other. This long range interaction
within the superfluid couples the two superfluid phonon species through a
cosine potential motivated by Josephson/Rabi interactions. As a consequence of
this potential, a new dynamics of late-time accelerated expansion emerges in
this system, without the need of dark energy, coming from a universe containing
only this two-state DM superfluid. Because the superfluid species are
non-relativistic, their sound speeds remain suitably small throughout the
evolution. We calculate the expansion history and growth of linear
perturbations, and compare the results to $\Lambda$CDM cosmology. For the
fiducial parameters studied here, the predicted expansion and growth function
are close to those of $\Lambda$CDM, but the difference in the predicted growth
rate is significant at late times. The present theory nicely complements the
recent proposal of dark matter superfluidity to explain the empirical success
of MOdified Newtonian Dynamics (MOND) on galactic scales, thus offering a
unified framework for dark matter, dark energy, and MOND phenomenology. |
Current and Future Constraints on Primordial Magnetic Fields: We present new limits on the amplitude of potential primordial magnetic
fields (PMFs) using temperature and polarization measurements of the cosmic
microwave background (CMB) from Planck, BICEP2/Keck Array, POLARBEAR, and
SPTpol. We reduce twofold the 95% CL upper limit on the CMB anisotropy power
due to a nearly-scale-invariant PMF, with an allowed B-mode power at
$\ell=1500$ of $D_{\ell=1500}^{BB} < 0.071 \mu K^2$ for Planck versus
$D_{\ell=1500}^{BB} < 0.034 \mu K^2$ for the combined dataset. We also forecast
the expected limits from soon-to-deploy CMB experiments (like SPT-3G, Adv.
ACTpol, or the Simons Array) and the proposed CMB-S4 experiment. Future CMB
experiments should dramatically reduce the current uncertainties, by one order
of magnitude for the near-term experiments and two orders of magnitude for the
CMB-S4 experiment. The constraints from CMB-S4 have the potential to rule out
much of the parameter space for PMFs. | Structure formation in large-volume cosmological simulations of fuzzy
dark matter: Impact of the non-linear dynamics: An ultra-light bosonic particle of mass around $10^{-22}\,\mathrm{eV}/c^2$ is
of special interest as a dark matter candidate, as it both has particle physics
motivations, and may give rise to notable differences in the structures on
highly non-linear scales due to the manifestation of quantum-physical wave
effects on macroscopic scales, which could address a number of contentious
small-scale tensions in the standard cosmological model, $\Lambda$CDM. Using a
spectral technique, we here discuss simulations of such fuzzy dark matter
(FDM), including the full non-linear wave dynamics, with a comparatively large
dynamic range and for larger box sizes than considered previously. While the
impact of suppressed small-scale power in the initial conditions associated
with FDM has been studied before, the characteristic FDM dynamics are often
neglected; in our simulations, we instead show the impact of the full
non-linear dynamics on physical observables. We focus on the evolution of the
matter power spectrum, give first results for the FDM halo mass function
directly based on full FDM simulations, and discuss the computational
challenges associated with the FDM equations. FDM shows a pronounced
suppression of power on small scales relative to cold dark matter (CDM), which
can be understood as a damping effect due to 'quantum pressure'. In certain
regimes, however, the FDM power can exceed that of CDM, which may be
interpreted as a reflection of order-unity density fluctuations occurring in
FDM. In the halo mass function, FDM shows a significant abundance reduction
below a characteristic mass scale only. This could in principle alleviate the
need to invoke very strong feedback processes in small galaxies to reconcile
$\Lambda$CDM with the observed galaxy luminosity function, but detailed studies
that also include baryons will be needed to ultimately judge the viability of
FDM. |
A quasi-molecular mechanism of formation of hydrogen in the early
Universe -- a scheme of calculation: In our recent papers (Kereslidze et all 2019a, 2021) a non-standard
quasi-molecular mechanism was suggested and applied to treat the cosmological
recombination. It was assumed that in the pre-recombination stage of evolution
of the Universe an electron combined with two neighbouring protons and created
the hydrogen molecular ion, $H_2^+$ in highly excited states, which then
descended into the lower-lying states or dissociated. In this work, we
elaborate the scheme of calculation for free-bound radiative transitions into
attractive states of $H_2^+$ as functions of redshift $z$. Together with the
earlier developed treatment of bound-bound radiative transitions in $H_2^+$,
the elaborated scheme of calculation can be used for the design of a fast and
complete cosmological recombination code. | Real-space density profile reconstruction of stacked voids: We present a non-parametric, model-independent method to reconstruct the
spherical density profiles of void stacks in real space, without redshift-space
distortions. Our method uses the expected spherical symmetry of stacked voids
to build the shape of the spherical density profile of cosmic voids in real
space without any assumption about the cosmological model. We test the
reconstruction algorithm with both a toy model and a full dark matter
simulation. We present the result for the simulation: the reconstruction of the
spherical density profile for a simulated stacked void in real space. We also
present a first application of the algorithm to reconstruct real cosmic void
stacks density profiles in real space from the Sloan Digital Sky Survey (Sutter
et al. 2012b). We discuss capabilities of the algorithm and possible future
improvements. Reconstructed density profiles from real voids open the way to
the study of the spherically averaged dynamical structure of voids. |
All about baryons: revisiting SIDM predictions at small halo masses: We use cosmological hydrodynamic simulations to consistently compare the
assembly of dwarf galaxies in both $\Lambda$ dominated, Cold (CDM) and
Self--Interacting (SIDM) dark matter models. The SIDM model adopts a constant
cross section of 2 $cm^{2}/g$, a relatively large value to maximize its
effects. These are the first SIDM simulations that are combined with a
description of stellar feedback that naturally drives potential fluctuations
able to create dark matter cores. Remarkably, SIDM fails to significantly lower
the central dark matter density at halo peak velocities V$_{max}$ $<$ 30 Km/s.
This is due to the fact that the central regions of very low--mass field halos
have relatively low central velocity dispersion and densities, leading to time
scales for SIDM collisions greater than a Hubble time. CDM halos with V$_{max}$
$<$ 30 km/s have inefficient star formation, and hence weak supernova feedback.
At a fixed 2 cm2/g SIDM cross section, the DM content of very low mass CDM and
SIDM halos differs by no more than a factor of two within 100-200pc. At larger
halo masses ($\sim$ 10$^{10}$ solar masses), the introduction of baryonic
processes creates field dwarf galaxies with dark matter cores and central
DM$+$baryon distributions that are effectively indistinguishable between CDM
and SIDM. Both models are in broad agreement with observed Local Group field
galaxies across the range of masses explored. To significantly differentiate
SIDM from CDM at the scale of faint dwarf galaxies, a velocity dependent cross
section that rapidly increases to values larger than 2 $cm^{2}/g$ for halos
with V$_{max}$ < 25-30 Km/s needs to be introduced. | Structure Formation and the Global 21-cm Signal in the Presence of
Coulomb-like Dark Matter-Baryon Interactions: Many compelling dark matter (DM) scenarios feature Coulomb-like interactions
between DM particles and baryons, in which the cross section for elastic
scattering scales with relative particle velocity as $v^{-4}$. Previous studies
have invoked such interactions to produce heat exchange between cold DM and
baryons and alter the temperature evolution of hydrogen. In this study, we
present a comprehensive study of the effects of Coulomb-like scattering on
structure formation, in addition to the known effects on the thermal history of
hydrogen. We find that interactions which significantly alter the temperature
of hydrogen at Cosmic Dawn also dramatically suppress the formation of galaxies
that source the Lyman-$\alpha$ background, further affecting the global 21-cm
signal. In particular, an interaction cross section at the current
observational upper limit leads to a decrease in the abundance of star-forming
halos by a factor of $\sim 2$ at $z\sim 20$, relative to cold, collisionless
DM. We also find that DM that is 100% millicharged cannot reproduce the depth
and the timing of the reported EDGES anomaly in any part of the parameter
space. These results critically inform modeling of the global 21-cm signal and
structure formation in cosmologies with DM-baryon scattering, with
repercussions for future and upcoming cosmological data analysis. |
The rates and time-delay distribution of multiply imaged supernovae
behind lensing clusters: Time delays of gravitationally lensed sources can be used to constrain the
mass model of a deflector and determine cosmological parameters. We here
present an analysis of the time-delay distribution of multiply imaged sources
behind 17 strong lensing galaxy clusters with well-calibrated mass models. We
find that for time delays less than 1000 days, at z=3.0, their logarithmic
probability distribution functions are well represented by P (log \Delta t)=5.3
x 10^-4 \Delta t^\beta M_250^-2\beta, with \beta=0.77, where M_250 is the
projected cluster mass inside 250 kpc (in 10^14 M_sun), and \beta is the
power-law slope of the distribution. The resultant probability distribution
function enables us to estimate the time-delay distribution in a lensing
cluster of known mass. For a cluster with M_250=2 x 10^14 M_sun, the fraction
of time delays less than 1000 days is approximately 3%. Taking Abell 1689 as an
example, its dark halo and brightest galaxies, with central velocity
dispersions larger than 500 km/s, mainly produce large time delays, while
galaxy-scale mass clumps are responsible for generating smaller time delays. We
estimate the probability of observing multiple images of a supernova in the
known images of Abell 1689. A two-component model of estimating the supernova
rate is applied in this work. For a magnitude threshold of m_AB=26.5, the
yearly rate of Type Ia (core-collapse) supernovae with time delays less than
1000 days is 0.004 +- 0.002 (0.029 +- 0.001). If the magnitude threshold is
lowered to m_AB ~ 27.0, the rate of core-collapse supernovae suitable for time
delay observation is 0.044 +- 0.015 per year. | Cosmology and the Korteweg-de Vries Equation: The Korteweg-de Vries (KdV) equation is a non-linear wave equation that has
played a fundamental role in diverse branches of mathematical and theoretical
physics. In the present paper, we consider its significance to cosmology. It is
found that the KdV equation arises in a number of important scenarios,
including inflationary cosmology, the cyclic universe, loop quantum cosmology
and braneworld models. Analogies can be drawn between cosmic dynamics and the
propagation of the solitonic wave solution to the equation, whereby quantities
such as the speed and amplitude profile of the wave can be identified with
cosmological parameters such as the spectral index of the density perturbation
spectrum and the energy density of the universe. The unique mathematical
properties of the Schwarzian derivative operator are important to the analysis.
A connection with dark solitons in Bose-Einstein condensates is briefly
discussed. |
Using Observations of Distant Quasars to Constrain Quantum Gravity: Aims. The small-scale nature of spacetime can be tested with observations of
distant quasars. We comment on a recent paper by Tamburini et al. (A&A, 533,
71) which claims that Hubble Space Telescope observations of the most distant
quasars place severe constraints on models of foamy spacetime.
Methods. If space is foamy on the Planck scale, photons emitted from distant
objects will accumulate uncertainties in distance and propagation directions
thus affecting the expected angular size of a compact object as a function of
redshift. We discuss the geometry of foamy spacetime, and the appropriate
distance measure for calculating the expected angular broadening. We also
address the mechanics of carrying out such a test. We draw upon our previously
published work on this subject (Christiansen et al. 2011), which carried out
similar tests as Tamburini et al. and also went considerably beyond their work
in several respects.
Results. When calculating the path taken by photons as they travel from a
distant source to Earth, one must use the comoving distance rather than the
luminosity distance. This then also becomes the appropriate distance to use
when calculating the angular broadening expected in a distant source. The use
of the wrong distance measure causes Tamburini et al. to overstate the
constraints that can be placed on models of spacetime foam. In addition, we
consider the impact of different ways of parametrizing and measuring the
effects of spacetime foam. Given the variation of the shape of the point-spread
function (PSF) on the chip, as well as observation-specific factors, it is
important to select carefully -- and document -- the comparison stars used as
well as the methods used to compute the Strehl ratio. | Dark Before Light: Testing the Cosmic Expansion History through the
Cosmic Microwave Background: The cosmic expansion history proceeds in broad terms from a radiation
dominated epoch to matter domination to an accelerated, dark energy dominated
epoch. We investigate whether intermittent periods of acceleration are possible
in the early universe -- between Big Bang nucleosynthesis (BBN) and
recombination and beyond. We establish that the standard picture is remarkably
robust: observations of anisotropies in the cosmic microwave background exclude
any extra period of accelerated expansion between 1 \leq z \lesssim 10^5
(corresponding to 5\times10^{-4}\ {\rm eV} \leq T \lesssim 25\ {\rm eV}). |
Evidence for anisotropy of cosmic acceleration: Observations reveal a `bulk flow' in the local Universe which is faster and
extends to much larger scales than is expected around a typical observer in the
standard $\Lambda$CDM cosmology. This is expected to result in a
scale-dependent dipolar modulation of the acceleration of the expansion rate
inferred from observations of objects within the bulk flow. From a
maximum-likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of
Type Ia supernovae we find that the deceleration parameter, in addition to a
small monopole, indeed has a much bigger dipole component aligned with the CMB
dipole which falls exponentially with redshift $z$: $q_0 = q_\mathrm{m} +
\vec{q}_\mathrm{d}.\hat{n}\exp(-z/S)$. The best fit to data yields
$q_\mathrm{d} = -8.03$ and $S = 0.0262~(\Rightarrow d \sim 100~\mathrm{Mpc})$,
rejecting isotropy ($q_\mathrm{d} = 0$) with $3.9\sigma$ statistical
significance, while $q_\mathrm{m} = -0.157$ and consistent with no acceleration
($q_\mathrm{m} = 0$) at $1.4\sigma$. Thus the cosmic acceleration deduced from
supernovae may be an artefact of our being non-Copernican observers, rather
than evidence for a dominant component of `dark energy' in the Universe. | The Two Phases of Galaxy Formation: Cosmological simulations of galaxy formation appear to show a two-phase
character with a rapid early phase at z>2 during which in-situ stars are formed
within the galaxy from infalling cold gas followed by an extended phase since
z<3 during which ex-situ stars are primarily accreted. In the latter phase
massive systems grow considerably in mass and radius by accretion of smaller
satellite stellar systems formed at quite early times (z>3) outside of the
virial radius of the forming central galaxy. These tentative conclusions are
obtained from high resolution re-simulations of 39 individual galaxies in a
full cosmological context with present-day virial halo masses ranging from 7e11
M_sun h^-1 < M_vir < 2.7e13 M_sun h^-1 and central galaxy masses between 4.5e10
M_sun h^-1 < M_* < 3.6e11 M_sun h^-1. The simulations include the effects of a
uniform UV background, radiative cooling, star formation and energetic feedback
from SNII. The importance of stellar accretion increases with galaxy mass and
towards lower redshift. In our simulations lower mass galaxies ($M_* < 9e10
M_sun h^-1) accrete about 60 per cent of their present-day stellar mass. High
mass galaxy ($M_* > 1.7e11 M_sun h^-1) assembly is dominated by accretion and
merging with about 80 per cent of the stars added by the present-day. In
general the simulated galaxies approximately double their mass since z=1. For
massive systems this mass growth is not accompanied by significant star
formation. The majority of the in-situ created stars is formed at z>2,
primarily out of cold gas flows. We recover the observational result of
archaeological downsizing, where the most massive galaxies harbor the oldest
stars. We find that this is not in contradiction with hierarchical structure
formation. Most stars in the massive galaxies are formed early on in smaller
structures, the galaxies themselves are assembled late. |
Effect of Mask Regions on Weak Lensing Statistics: Sky masking is unavoidable in wide-field weak lensing observations. We study
how masks affect the measurement of statistics of matter distribution probed by
weak gravitational lensing. We first use 1000 cosmological ray-tracing
simulations to examine in detail the impact of masked regions on the weak
lensing Minkowski Functionals (MFs). We consider actual sky masks used for a
Subaru Suprime-Cam imaging survey. The masks increase the variance of the
convergence field and the expected values of the MFs are biased. The bias then
affects the non-Gaussian signals induced by the gravitational growth of
structure. We then explore how masks affect cosmological parameter estimation.
We calculate the cumulative signal-to-noise ratio S/N for masked maps to study
the information content of lensing MFs. We show that the degradation of S/N for
masked maps is mainly determined by the effective survey area. We also perform
simple chi^2 analysis to show the impact of lensing MF bias due to masked
regions. Finally, we compare ray-tracing simulations with data from a Subaru 2
deg^2 survey in order to address if the observed lensing MFs are consistent
with those of the standard cosmology. The resulting chi^2/n_dof = 29.6/30 for
three combined MFs, obtained with the mask effects taken into account, suggests
that the observational data are indeed consistent with the standard LambdaCDM
model. We conclude that the lensing MFs are powerful probe of cosmology only if
mask effects are correctly taken into account. | Kinetic decoupling of WIMPs: analytic expressions: We present a general expression for the values of the average kinetic energy
and of the temperature of kinetic decoupling of a WIMP, valid for any
cosmological model. We show an example of the usage of our solution when the
Hubble rate has a power-law dependence on temperature, and we show results for
the specific cases of kination cosmology and low- temperature reheating
cosmology. |
Beyond Assembly Bias: Exploring Secondary Halo Biases for Cluster-size
Haloes: Secondary halo bias, commonly known as 'assembly bias,' is the dependence of
halo clustering on a halo property other than mass. This prediction of the
Lambda-Cold Dark Matter cosmology is essential to modelling the galaxy
distribution to high precision and interpreting clustering measurements. As the
name suggests, different manifestations of secondary halo bias have been
thought to originate from halo assembly histories. We show conclusively that
this is incorrect for cluster-size haloes. We present an up-to-date summary of
secondary halo biases of high-mass haloes due to various halo properties
including concentration, spin, several proxies of assembly history, and subhalo
properties. While concentration, spin, and the abundance and radial
distribution of subhaloes exhibit significant secondary biases, properties that
directly quantify halo assembly history do not. In fact, the entire assembly
histories of haloes in pairs are nearly identical to those of isolated haloes.
In general, a global correlation between two halo properties does not predict
whether or not these two properties exhibit similar secondary biases. For
example, assembly history and concentration (or subhalo abundance) are
correlated for both paired and isolated haloes, but follow slightly different
conditional distributions in these two cases. This results in a secondary halo
bias due to concentration (or subhalo abundance), despite the lack of assembly
bias in the strict sense for cluster-size haloes. Due to this complexity,
caution must be exercised in using any one halo property as a proxy to study
the secondary bias due to another property. | A conceptual problem for non-commutative inflation and the new approach
for non-relativistic inflationary equation of state: In a previous paper, we connected the phenomenological non-commutative
inflation of Alexander, Brandenberger and Magueijo (2003) and Koh S and
Brandenberger (2007) with the formal representation theory of groups and
algebras and analyzed minimal conditions that the deformed dispersion relation
should satisfy in order to lead to a successful inflation. In that paper, we
showed that elementary tools of algebra allow a group like procedure in which
even Hopf algebras (roughly the symmetries of non-commutative spaces) could
lead to the equation of state of inflationary radiation. In this paper, we show
that there exists a conceptual problem with the kind of representation that
leads to the fundamental equations of the model. The problem comes from an
incompatibility between one of the minimal conditions for successful inflation
(the momentum of individual photons is bounded from above) and the group
structure of the representation which leads to the fundamental inflationary
equations of state. We show that such a group structure, although
mathematically allowed, would lead to problems with the overall consistency of
physics, like in scattering theory, for example. Therefore, it follows that the
procedure to obtain those equations should be modified according to one of two
possible proposals that we consider here. One of them relates to the general
theory of Hopf algebras while the other is based on a representation theorem of
Von Neumann algebras, a proposal already suggested by us to take into account
interactions in the inflationary equation of state. This reopens the problem of
finding inflationary deformed dispersion relations and all developments which
followed the first paper of Non-commutative Inflation. |
Variable partial covering and a relativistic iron line in NGC 1365: We present a complete analysis of the hard X-ray (2-10 keV) properties of the
Seyfert galaxy NGC 1365, based on a 60 ks XMM-Newton observation performed in
January 2004. The two main results are: 1) We detect an obscuring cloud with
N_H~3.5x10^23 cm^(-2) crossing the line of sight in ~25 ks. This implies a
dimension of the X-ray source not larger than a few 10^13 cm and a distance of
the obscuring cloud of the order of 10^16 cm. Adopting the black hole mass
M(BH) estimated from the M(BH)-velocity dispersion relation, the source size is
D_S<20 R_G and the distance and density of the obscuring clouds are
R~3000-10000 R_G and n~10^(10) cm^(-3), i.e. typical values for broad line
region clouds. 2) An iron emission line with a relativistic profile is detected
with high statistical significance. A time integrated fit of the line+continuum
reflection components suggests a high iron abundance (~3 times solar) and an
origin of these components in the inner part (~10 R_G) of the accretion disk,
in agreement with the small source size inferred from the analysis of the
absorption variability. | The Dark Side of QSO Formation at High Redshifts: Observed high-redshift QSOs, at z~6, may reside in massive dark matter (DM)
halos of more than 10^{12} Msun and are thus expected to be surrounded by
overdense regions. In a series of 10 constrained simulations, we have tested
the environment of such QSOs. Comparing the computed overdensities with respect
to the unconstrained simulations of regions empty of QSOs, assuming there is no
bias between the DM and baryon distributions, and invoking an
observationally-constrained duty-cycle for Lyman Break Galaxies, we have
obtained the galaxy count number for the QSO environment. We find that a clear
discrepancy exists between the computed and observed galaxy counts in the Kim
et al. (2009) samples. Our simulations predict that on average eight z~6
galaxies per QSO field should have been observed, while Kim et al. detect on
average four galaxies per QSO field compared to an average of three galaxies in
a control sample (GOODS fields). While we cannot rule out a small number
statistics for the observed fields to high confidence, the discrepancy suggests
that galaxy formation in the QSO neighborhood proceeds differently than in the
field. We also find that QSO halos are the most massive of the simulated volume
at z~6 but this is no longer true at z~3. This implies that QSO halos, even in
the case they are the most massive ones at high redshifts, do not evolve into
most massive galaxy clusters at z=0. |
The Magellanic Bridge as a DLA System: Physical Properties of Cold Gas
toward PKS0312-770: We measure the physical properties of a local multi-component absorption-line
system at V_sol ~ 200 km/s toward the quasar PKS0312-770 behind the Magellanic
Bridge (MB) using Hubble Space Telescope STIS spectroscopy in conjunction with
photoionization modeling. At an impact parameter of ~ 10 kpc from the Small
Magellanic Cloud (SMC), this sightline provides a unique opportunity to probe
the chemical properties and ionization structure in a nearby absorption line
system with a column density of logN(HI) ~ 20.2, at the transition between
Damped Lyman Alpha (DLA) and sub-DLA systems. We find that metallicity of -1.0
< logZ < -0.5 and ionization parameter of -6 < logU < -5 for three
low-ionization components and logU ~ -2.6 for one high-ionization component.
One component at V_sol = 207 km/s shows an alpha-element abundance log(Si/H) ~
-5.0, making it ~ 0.2 dex more metal rich than both SMC H II regions and stars
within the MB and the SMC. The N/Si ratio in this component is log(N/Si) =
-0.3+/-0.1, making it comparable to other N-poor dwarf galaxies and ~ 0.2 dex
lower than H II regions in the SMC. Another component at V_sol = 236 km/s shows
a similar Si/H ratio but has log(N/Si) = -1.0+/-0.2, indicating a nitrogen
deficiency comparable to that seen in the most N-poor DLA systems. These
differences imply different chemical enrichment histories between components
along the same sightline. Our results suggest that, if these absorbers are
representative some fraction of DLA systems, then 1) DLA systems along single
sight-lines do not necessarily represent the global properties of the absorbing
cloud, and b) the chemical composition within a given DLA cloud may be
inhomogeneous. | The connection between radio halos and cluster mergers and the
statistical properties of the radio halo population: We discuss the statistical properties of the radio halo population in galaxy
clusters. Radio bi-modality is observed in galaxy clusters: a fraction of
clusters host giant radio halos while the majority of clusters do not show
evidence of diffuse cluster-scale radio emission. The radio bi-modality has a
correspondence in terms of dynamical state of the hosting clusters showing that
merging clusters host radio halos and follow the well known radio--X-ray
correlation, while more relaxed clusters do not host radio halos and populate a
region well separated from that correlation. These evidences can be understood
in the framework of a scenario where merger-driven turbulence re-accelerate the
radio emitting electrons. We discuss the main statistical expectations of this
scenario underlining the important role of upcoming LOFAR surveys to test
present models. |
Measurement of a Cosmographic Distance Ratio with Galaxy and CMB Lensing: We measure the gravitational lensing shear signal around dark matter halos
hosting CMASS galaxies using light sources at $z\sim 1$ (background galaxies)
and at the surface of last scattering at $z\sim 1100$ (the cosmic microwave
background). The galaxy shear measurement uses data from the CFHTLenS survey,
and the microwave background shear measurement uses data from the {\it Planck}
satellite. The ratio of shears from these cross-correlations provides a purely
geometric distance measurement across the longest possible cosmological lever
arm. This is because the matter distribution around the halos, including
uncertainties in galaxy bias and systematic errors such as miscentering,
cancels in the ratio for halos in thin redshift slices. We measure this
distance ratio in three different redshift slices of the CMASS sample, and
combine them to obtain a $17\%$ measurement of the distance ratio,
$r=0.390^{+0.070}_{-0.062}$ at an effective redshift of $z=0.53$. This is
consistent with the predicted ratio from the {\it Planck} best-fit $\Lambda$CDM
cosmology of $r=0.419$. | A Method for Individual Source Brightness Estimation in Single- and
Multi-band Data: We present a method of reliably extracting the flux of individual sources
from sky maps in the presence of noise and a source population in which number
counts are a steeply falling function of flux. The method is an extension of a
standard Bayesian procedure in the millimeter/submillimeter literature. As in
the standard method, the prior applied to source flux measurements is derived
from an estimate of the source counts as a function of flux, dN/dS. The key
feature of the new method is that it enables reliable extraction of properties
of individual sources, which previous methods in the literature do not. We
first present the method for extracting individual source fluxes from data in a
single observing band, then we extend the method to multiple bands, including
prior information about the spectral behavior of the source population(s). The
multi-band estimation technique is particularly relevant for classifying
individual sources into populations according to their spectral behavior. We
find that proper treatment of the correlated prior information between
observing bands is key to avoiding significant biases in estimations of
multi-band fluxes and spectral behavior, biases which lead to significant
numbers of misclassified sources. We test the single- and multi-band versions
of the method using simulated observations with observing parameters similar to
that of the South Pole Telescope data used in Vieira, et al. (2010). |
Dynamics of entropy perturbations in assisted dark energy with mixed
kinetic terms: We study dynamics of entropy perturbations in the two-field assisted dark
energy model. Based on the scenario of assisted dark energy, in which one
scalar field is subdominant compared with the other in the early epoch, we show
that the entropy perturbations in this two-field system tend to be constant on
large scales in the early epoch and hence survive until the present era for a
generic evolution of both fields during the radiation and matter eras. This
behaviour of the entropy perturbations is preserved even when the fields are
coupled via kinetic interaction. Since, for assisted dark energy, the
subdominant field in the early epoch becomes dominant at late time, the entropy
perturbations can significantly influence the dynamics of density perturbations
in the universe. Assuming correlations between the entropy and curvature
perturbations, the entropy perturbations can enhance the integrated Sachs-Wolfe
(ISW) effect if the signs of the contributions from entropy perturbations and
curvature perturbations are opposite after the matter era, otherwise the ISW
contribution is suppressed. For canonical scalar field the effect of entropy
perturbations on ISW effect is small because the initial value of the entropy
perturbations estimated during inflation cannot be sufficiently large. However,
in the case of k-essence, the initial value of the entropy perturbations can be
large enough to affect the ISW effect to leave a significant imprint on the CMB
power spectrum. | Imprints of the Early Universe on Axion Dark Matter Substructure: Despite considerable experimental progress large parts of the axion-like
particle (ALP) parameter space remain difficult to probe in terrestrial
experiments. In some cases, however, small-scale structure of the ALP dark
matter (DM) distribution is strongly enhanced, offering opportunities for
astrophysical tests. Such an enhancement can be produced by a period of
pre-nucleosynthesis early matter domination (EMD). This cosmology arises in
many ultraviolet completions and generates the correct relic abundance for weak
coupling $f_a\sim 10^{16}$ GeV, ALP masses in the range $10^{-13}$ eV $<m_a <
1$ eV, and without fine-tuning of the initial misalignment angle. This range
includes the QCD axion around $10^{-9}-10^{-8}$ eV. EMD enhances the growth of
ALP small-scale structure, leading to the formation of dense ALP miniclusters.
We study the interplay between the initial ALP oscillation, reheating
temperature, and effective pressure to provide analytic estimates of the
minicluster abundance and properties. ALP miniclusters in the EMD cosmology are
denser and more abundant than in $\Lambda$CDM. While enhanced substructure
generically reduces the prospects of direct detection experiments, we show that
pulsar timing and lensing observations can discover these minihalos over a
large range of ALP masses and reheating temperatures. |
Exponents of non-linear clustering in scale-free one dimensional
cosmological simulations: One dimensional versions of cosmological N-body simulations have been shown
to share many qualitative behaviours of the three dimensional problem. They can
resolve a large range of time and length scales, and admit exact numerical
integration. We use such models to study how non-linear clustering depends on
initial conditions and cosmology. More specifically, we consider a family of
models which, like the 3D EdS model, lead for power-law initial conditions to
self-similar clustering characterized in the strongly non-linear regime by
power-law behaviour of the two point correlation function. We study how the
corresponding exponent \gamma depends on the initial conditions, characterized
by the exponent n of the power spectrum of initial fluctuations, and on a
single parameter \kappa controlling the rate of expansion. The space of initial
conditions/cosmology divides very clearly into two parts: (1) a region in which
\gamma depends strongly on both n and \kappa and where it agrees very well with
a simple generalisation of the so-called stable clustering hypothesis in three
dimensions, and (2) a region in which \gamma is more or less independent of
both the spectrum and the expansion of the universe. We explain the observed
location of the boundary in (n, \kappa) space dividing the "stable clustering"
region from the "universal" region. We compare and contrast our findings to
results in three dimensions, and discuss in particular the light they may throw
on the question of "universality" of non-linear clustering in this context. | SCG0018-4854: a young and dynamic compact group I. Kinematical analysis: Compact groups of galaxies are in particular good laboratories for studying
galaxy interactions and their effects on the evolution of galaxies due to their
high density and low velocity dispersion. SCG0018-4854 is a remarkably high
galaxy density and low velocity dispersion group with evidence of a recent
interaction. We obtained VLT FORS2 optical observations and we present
spectroscopic and photometric evidence of how dramatically galaxy interactions
have affected each of the four member galaxies. We found peculiar kinematics
for each galaxy and evidence of recent star formation. In particular, the gas
and stellar radial velocity curves of two galaxies are irregular with a level
of asymmetry similar to that of other interacting galaxies. We discovered the
presence of a bar for NGC 92 therefore revising a previous morphological
classification and we obtained spectroscopic confirmation of a galactic-scale
outflow of NGC 89. Peculiar kinematics and dynamic consideration lead to a
rough estimate of the age of the latest interaction: 0.2-0.7 Gyr, suggesting
that SCG0018-4854 is a young and dynamical group. |
Cosmology based on $f(R)$ gravity with ${\cal O}(1)$ eV sterile neutrino: We address the cosmological role of an additional ${\cal O}(1)$ eV sterile
neutrino in modified gravity models. We confront the present cosmological data
with predictions of the FLRW cosmological model based on a variant of $f(R)$
modified gravity proposed by one of the authors previously. This viable
cosmological model which deviation from general relativity with a cosmological
constant $\Lambda$ decreases as $R^{-2n}$ for large, but not too large values
of the Ricci scalar $R$ provides an alternative explanation of present dark
energy and the accelerated expansion of the Universe. Various up-to-date
cosmological data sets exploited include Planck CMB anisotropy, CMB lensing
potential, BAO, cluster mass function and Hubble constant measurements. We find
that the CMB+BAO constraints strongly the sum of neutrino masses from above.
This excludes values $\lambda\sim 1$ for which distinctive cosmological
features of the model are mostly pronounced as compared to the $\Lambda$CDM
model, since then free streaming damping of perturbations due to neutrino rest
masses is not sufficient to compensate their extra growth occurring in $f(R)$
gravity. Thus, we obtain $\lambda>8.2$ ($2\sigma$) with cluster systematics and
$\lambda>9.4$ ($2\sigma$) without that. In the latter case we find for the
sterile neutrino mass
$0.47\,\,\rm{eV}$$\,<\,$$m_{\nu,\,\rm{sterile}}$$\,<\,$$1\,\,\rm{eV}$
($2\sigma$) assuming the active neutrinos are massless, not significantly
larger than in the standard $\Lambda$CDM with the same data set:
$0.45\,\,\rm{eV}$$\,<\,$$m_{\nu,\,\rm{sterile}}$$\,<\,$$0.92\,\,\rm{eV}$
($2\sigma$). However, a possible discovery of a sterile neutrino with the mass
$m_{\nu,\,\rm{sterile}} \approx 1.5\,$eV motivated by various anomalies in
neutrino oscillation experiments would favor cosmology based on $f(R)$ gravity
rather than the $\Lambda$CDM model. | The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active
Galactic Nuclei in the Southern Survey: We present a catalog of 191 extragalactic sources detected by the Atacama
Cosmology Telescope (ACT) at 148 GHz and/or 218 GHz in the 2008 Southern
survey. Flux densities span 14-1700 mJy, and we use source spectral indices
derived using ACT-only data to divide our sources into two sub-populations: 167
radio galaxies powered by central active galactic nuclei (AGN), and 24 dusty
star-forming galaxies (DSFGs). We cross-identify 97% of our sources (166 of the
AGN and 19 of the DSFGs) with those in currently available catalogs. When
combined with flux densities from the Australian Telescope 20 GHz survey and
follow-up observations with the Australia Telescope Compact Array, the
synchrotron-dominated population is seen to exhibit a steepening of the slope
of the spectral energy distribution from 20 to 148 GHz, with the trend
continuing to 218 GHz. The ACT dust-dominated source population has a median
spectral index of 3.7+0.62-0.86, and includes both local galaxies and sources
with redshifts as great as 5.6. Dusty sources with no counterpart in existing
catalogs likely belong to a recently discovered subpopulation of DSFGs lensed
by foreground galaxies or galaxy groups. |
Quantized fields and gravitational particle creation in f(R) expanding
universes: The problem of cosmological particle creation for a spatially flat,
homogeneous and isotropic Universes is discussed in the context of f(R)
theories of gravity. Different from cosmological models based on general
relativity theory, it is found that a conformal invariant metric does not
forbid the creation of massless particles during the early stages (radiation
era) of the Universe. | Detectability of Small-Scale Dark Matter Clumps with Pulsar Timing
Arrays: We examine the capability of pulsar timing arrays (PTAs) to detect very
small-scale clumps of dark matter (DM), which are a natural outcome of the
standard cold dark matter (CDM) paradigm. A clump streaming near the Earth or a
pulsar induces an impulsive acceleration to encode residuals on pulsar timing
data. We show that, assuming the standard abundance of DM clumps predicted by
the CDM model, small-scale DM clumps with masses from $\sim 10^{-11} M_\odot$
to $\sim 10^{-8} \ M_\odot$ can be detectable by a PTA observation for a few
decades with ${\cal O}(100)$ of pulsars with a timing noise of ${\cal O}(10)$
ns located at $\gtrsim 3$ kpc away from the Galactic center, as long as these
mass scales are larger than the cutoff scale of the halo mass function that is
determined by the particle nature of DM. Our result suggests that PTAs can
provide a unique opportunity for testing one of the most fundamental
predictions of the CDM paradigm. In addition, the detections and non-detections
can constrain the cutoff mass scale inherent to the DM model. |
Anthropic Bounds on Lambda from the No-Boundary Quantum State: We show that anthropic selection emerges inevitably in the general framework
for prediction in quantum cosmology. There the predictions of anthropic
reasoning depend on the prior implied by the universe's quantum state. To
illustrate this we compute the probabilities specified by the no-boundary wave
function for our observations at the present time of the values of Lambda and Q
in an inflationary landscape model in which both quantities vary. Within the
anthropic range of values the no-boundary state yields an approximately flat
distribution on Lambda and strongly favors small values of Q. This restores
Weinberg's successful prediction of Lambda. | Evidence of patchy hydrogen reionization from an extreme Ly$α$
trough below redshift six: We report the discovery of an extremely long ($\sim$110 Mpc/$h$) and dark
($\tau_{\rm eff} \gtrsim 7$) Ly$\alpha$ trough extending down to $z \simeq 5.5$
towards the $z_{\rm em} \simeq 6.0$ quasar ULAS J0148+0600. We use these new
data in combination with Ly$\alpha$ forest measurements from 42 quasars at $4.5
\le z_{\rm em} \le 6.4$ to conduct an updated analysis of the line-of-sight
variance in the intergalactic Ly$\alpha$ opacity over $4 \le z \le 6$. We find
that the scatter in transmission among lines of sight near $z \sim 6$
significantly exceeds theoretical expectations for either a uniform ultraviolet
background (UVB) or simple fluctuating UVB models in which the mean free path
to ionizing photons is spatially invariant. The data, particularly near $z
\simeq 5.6$-5.8, instead require fluctuations in the volume-weighted hydrogen
neutral fraction that are a factor of 3 or more beyond those expected from
density variations alone. We argue that these fluctuations are most likely
driven by large-scale variations in the mean free path, consistent with
expectations for the final stages of inhomogeneous hydrogen reionization. Even
by $z \simeq 5.6$, however, a large fraction of the data are consistent with a
uniform UVB, and by $z \sim 5$ the data are fully consistent with opacity
fluctuations arising solely from the density field. This suggests that while
reionization may be ongoing at $z \sim 6$, it has fully completed by $z \sim
5$. |
Overconfidence in Photometric Redshift Estimation: We describe a new test of photometric redshift performance given a
spectroscopic redshift sample. This test complements the traditional comparison
of redshift {\it differences} by testing whether the probability density
functions $p(z)$ have the correct {\it width}. We test two photometric redshift
codes, BPZ and EAZY, on each of two data sets and find that BPZ is consistently
overconfident (the $p(z)$ are too narrow) while EAZY produces approximately the
correct level of confidence. We show that this is because EAZY models the
uncertainty in its spectral energy distribution templates, and that post-hoc
smoothing of the BPZ $p(z)$ provides a reasonable substitute for detailed
modeling of template uncertainties. Either remedy still leaves a small surplus
of galaxies with spectroscopic redshift very far from the peaks. Thus, better
modeling of low-probability tails will be needed for high-precision work such
as dark energy constraints with the Large Synoptic Survey Telescope and other
large surveys. | Measurement on the cosmic curvature using the Gaussian process method: Inflation predicts that the Universe is spatially flat. The Planck 2018
measurements of the cosmic microwave background anisotropy favour a spatially
closed universe at more than 2$\sigma$ confidence level. We use model
independent methods to study the issue of cosmic curvature. The method
reconstructs the Hubble parameter $H(z)$ from cosmic chronometers data with the
Gaussian process method. The distance modulus is then calculated with the
reconstructed function $H(z)$ and fitted by type Ia supernovae data. Combining
the cosmic chronometers and type Ia supernovae data, we obtain
$\Omega_{k0}h^2=0.102\pm 0.066$ which is consistent with a spatially flat
universe at the 2$\sigma$ confidence level. By adding the redshift space
distortions data to the type Ia supernovae data with a proposed novel model
independent method, we obtain $\Omega_{k0}h^2=0.117^{+0.058}_{-0.045}$ and no
deviation from $\Lambda$CDM model is found. |
Zoomed high-resolution simulations of Multi-coupled Dark Energy: cored
galaxy density profiles at high redshift: We perform for the first time high-resolution zoom-in re-simulations of
individual halos in the context of the Multi-coupled Dark Energy (McDE)
scenario, which is characterised by the existence of two distinct dark matter
particle species with opposite couplings to a Dark Energy scalar field. We
compare the structural properties of the simulated halos to the standard
Lambda-CDM results. The zoomed-in initial conditions are set up using a
specifically designed code called ZInCo that we publicly release along with the
present paper. Our numerical results allow to investigate in detail and with
unprecedented resolution the halo segregation process that characterises McDE
cosmologies from its very early stages. In particular, we find that in contrast
to what could be inferred from previous numerical analysis at lower resolution,
the segregation process is already in place at redshifts as high as z ~ 7. Most
remarkably, we find that the subsequent evolution of the segregation leads to
the formation of cored total matter density profiles with a core size that
progressively increases in time. The shape of the cored profiles can be
accurately predicted as the superposition of two NFW profiles with an
increasing offset, thereby confirming the interpretation of the simulations
results in terms of the segregation of the two dark matter components of the
halo as a consequence of their different coupling to the Dark Energy field. | Reconciling cosmic dipolar tensions with a gigaparsec void: Recent observations indicate a $4.9\sigma$ tension between the CMB and quasar
dipoles. This tension challenges the cosmological principle. We propose that if
we live in a gigaparsec scale void, the CMB and quasar dipolar tension can be
reconciled. This is because we are unlikely to live at the center of the void.
And a 15% offset from the center will impact the quasars and CMB differently in
their dipolar anisotropies. As we consider a large and thick void, our setup
can also ease the Hubble tension. |
The size of the Universe according to the Poincare dodecahedral space
hypothesis: One of the FLRW models that best fits the WMAP sky maps of the CMB is the
Poincare dodecahedral space. The optimal fit of this model to WMAP data was
recently found using an optimal cross-correlation method, but the systematic
error in the estimate of the matched-circle angular radius \alpha, or
equivalently, the (comoving) size of the Universe 2\rinj (twice the injectivity
radius), might be much higher than the random error. In order to increase the
falsifiability of the model, it would be useful to reduce the uncertainty in
this estimate and to estimate the fraction of the sky where multiply imaged
gravitationally bound objects should potentially be detectable. "Matched discs"
are defined in order to describe a useful subset of multiply imaged objects.
The cross-correlation method at \ltapprox 1 \hGpc is applied to WMAP 7-year
data in order to improve the estimate of \alpha. The improved matched-circle
radius estimate is \alpha = 23 \pm 1.4 deg, where the uncertainty represents
systematic error dependent on the choices of galactic mask and all-sky map.
This is equivalent to 2\rinj = 18.2\pm 0.5 \hGpc for matter density parameter
Omega_m=0.28\pm 0.02. The lowest redshift of multiply imaged objects is
z=106\pm18. Multiply imaged high overdensity (rare) peaks visible during
200>z>106 should be present in matched discs of radius 14.8\pm2.3 deg. The
accuracy in the matched circle radius estimate is considerably improved by
using the higher resolution signal. The predicted matched discs (over
200>z>106) project to about 20% of the full sky. Since any object located
exactly in the discs would be multiply imaged at equal redshifts, evolutionary
effects would be small for objects that are nearly located in the discs. | Black hole variability and the star formation-AGN connection: Do all
star-forming galaxies host an AGN?: We investigate the effect of active galactic nucleus (AGN) variability on the
observed connection between star formation and black hole accretion in
extragalactic surveys. Recent studies have reported relatively weak
correlations between observed AGN luminosities and the properties of AGN hosts,
which has been interpreted to imply that there is no direct connection between
AGN activity and star formation. However, AGNs may be expected to vary
significantly on a wide range of timescales (from hours to Myr) that are far
shorter than the typical timescale for star formation (>~100 Myr). This
variability can have important consequences for observed correlations. We
present a simple model in which all star-forming galaxies host an AGN when
averaged over ~100 Myr timescales, with long-term average AGN accretion rates
that are perfectly correlated with the star formation rate (SFR). We show that
reasonable prescriptions for AGN variability reproduce the observed weak
correlations between SFR and L_AGN in typical AGN host galaxies, as well as the
general trends in the observed AGN luminosity functions, merger fractions, and
measurements of the average AGN luminosity as a function of SFR. These results
imply there may be a tight connection between AGN activity and SFR over galaxy
evolution timescales, and that the apparent similarities in rest-frame colors,
merger rates, and clustering of AGNs compared to "inactive" galaxies may be due
primarily to AGN variability. The results provide motivation for future deep,
wide extragalactic surveys that can measure the distribution of AGN accretion
rates as a function of SFR. |
A model independent measure of the large scale curvature of the Universe: Cosmological distances as a function of redshift depend on the effective
curvature density via the effect on the geometrical path of photons from large
scale spatial curvature and its effect on the expansion history, H(z).
Cosmological time, however, depends on the expansion history only. Therefore,
by combining distance and lookback time observations (or other estimates of the
expansion history), it is possible to isolate the geometrical curvature
contribution and measure the curvature in a model independent way, i.e., free
from assumptions about the energy content of the universe.
We investigate two different approaches to accomplish this task; the
differential and the integral approach. The differential approach requires, in
addition to distances, derivatives of distance with respect to redshift as well
as knowledge of the expansion history. The integral approach is based on
measuring the integral of the inverse of the expansion history via measurements
of cosmic time as derived, e.g., from galaxy ages.
In this paper, we attempt to constrain the large scale curvature of the
Universe using distances obtained from observations of Type Ia supernovae
together with inferred ages of passively evolving galaxies and Hubble parameter
estimates from the large scale clustering of galaxies. Current data are
consistent with zero spatial curvature, although the uncertainty on the
curvature density is of order unity. Future data sets with on the order of
thousands of Type Ia supernovae distances and galaxy ages will allow us to
constrain the curvature density with an uncertainty of less than 0.1 at the 95%
confidence level. | Understanding the non-linear clustering of high redshift galaxies: We incorporate the non-linear clustering of dark matter halos, as modelled by
Jose et al. (2016) into the halo model to better understand the clustering of
Lyman break galaxies (LBGs) in the redshift range $z=3-5$. We find that, with
this change, the predicted LBG clustering increases significantly on
quasi-linear scales ($0.1 \leq r\,/\,h^{-1} \,{\rm Mpc} \leq 10$) compared to
that in the linear halo bias model. This in turn results in an increase in the
clustering of LBGs by an order of magnitude on angular scales $5" \leq \theta
\leq 100"$. Remarkably, the predictions of our new model on the whole remove
the systematic discrepancy between the linear halo bias predictions and the
observations. The correlation length and large scale galaxy bias of LBGs are
found to be significantly higher in the non-linear halo bias model than in the
linear halo bias model. The resulting two-point correlation function retains an
approximate power-law form in contrast with that computed using the linear halo
bias theory. We also find that the non-linear clustering of LBGs increases with
increasing luminosity and redshift. Our work emphasizes the importance of using
non-linear halo bias in order to model the clustering of high-z galaxies to
probe the physics of galaxy formation and extract cosmological parameters
reliably. |
Reionization of the Intergalactic Medium: After recombination the cosmic gas was left in a cold and neutral state.
However, as the first stars and black holes formed within early galactic
systems, their UV and X-ray radiation induced a gradual phase transition of the
intergalactic gas into the warm and ionized state we currently observe. This
process is known as cosmic reionization. Understanding how the energy
deposition connected with galaxy and star formation shaped the properties of
the intergalactic gas is one of the primary goals of present-day cosmology. In
addition, reionization back reacts on galaxy evolution, determining many of the
properties of the high-redshift galaxy population that represent the current
frontier of our discovery of the cosmos. In these two Lectures we provide a
pedagogical overview of cosmic reionization and intergalactic medium and of
some of the open questions in these fields. | Testing f(R) gravity with the simulated data of gravitational waves from
the Einstein Telescope: In this paper we analyze the implications of gravitational waves (GWs) as
standard sirens on the modified gravity models by using the third-generation
gravitational wave detector, i.e., the Einstein Telescope. Two viable models in
$f(R)$ theories within the Palatini formalism are considered in our analysis
($f_{1}(\mathcal{R})=\mathcal{R}-\frac{\beta}{\mathcal{R}^{n}}$ and
$f_{2}(\mathcal{R})=\mathcal{R}+\alpha\ln{\mathcal{R}}-\beta$), with the
combination of simulated GW data and the latest electromagnetic (EM)
observational data (including the recently released Pantheon type Ia supernovae
sample, the cosmic chronometer data, and baryon acoustic oscillation distance
measurements). Our analysis reveals that the standard sirens GWs, which provide
an independent and complementary alternative to current experiments, could
effectively eliminate the degeneracies among parameters in the two modified
gravity models. In addition, we thoroughly investigate the nature of
geometrical dark energy in the modified gravity theories with the assistance of
$Om(z)$ and statefinder diagnostic analysis. The present analysis makes it
clear-cut that the simplest cosmological constant model is still the most
preferred by the current data. However, the combination of future naturally
improved GW data most recent EM observations will reveal the consistency or
acknowledge the tension between the $\Lambda$CDM model and modified gravity
theories. |
Bayesian evidence of non-standard inflation: isocurvature perturbations
and running spectral index: Bayesian model comparison penalizes models with more free parameters that are
allowed to vary over a wide range, and thus offers the most robust method to
decide whether some given data require new parameters. In this paper, we ask a
simple question: do current cosmological data require extensions of the
simplest single-field inflation models? Specifically, we calculate the Bayesian
evidence of a totally anti-correlated isocurvature perturbation and a running
spectral index of the scalar curvature perturbation. These parameters are
motivated by recent claims that the observed temperature anisotropy of the
cosmic microwave background on large angular scales is too low to be compatible
with the simplest inflation models. Both a subdominant, anti-correlated cold
dark matter isocurvature component and a negative running index succeed in
lowering the large-scale temperature power spectrum. We show that the
introduction of isocurvature perturbations is disfavored, whereas that of the
running spectral index is only moderately favored, even when the BICEP2 data
are included in the analysis without any foreground subtraction. | Mid-Infrared Variability from the Spitzer Deep, Wide-Field Survey: We use the multi-epoch, mid-infrared Spitzer Deep, Wide-Field Survey to
investigate the variability of 474,179 objects in 8.1 deg^2 of the NDWFS Bootes
field. We perform a Difference Image Analysis of the four available epochs
between 2004 and 2008, focusing on the deeper 3.6 and 4.5 micron bands. We find
that 1.1% of the studied sample meet our standard selection criteria for being
classed as a variable source. We require that the 3.6 and 4.5 micron
light-curves are strongly correlated (r>0.8) and that their joint variance
exceeds that for all sources with the same magnitude by 2 sigma. We then
examine the mid-IR colors of the variable sources and match them with X-ray
sources from the XBootes survey, radio catalogs, 24 micron-selected AGN
candidates, and spectroscopically identified AGNs from the AGN and Galaxy
Evolution Survey (AGES). Based on their mid-IR colors, most of the variable
sources are AGNs (76%), with smaller contributions from stars (11%), galaxies
(6%), and unclassified objects. Most of the stellar, galaxy and unclassified
sources are false positives. For our standard selection criteria, 11-12% of the
mid-IR counterparts to X-ray sources, 24 micron-selected AGN candidates and
spectroscopically identified AGNs show variability. Mid-IR AGN variability can
be well described by a single power-law structure function with a power-law
index of 0.5 at both 3.6 and 4.5 microns, and an amplitude of 0.1 mag on
rest-frame time scales of 2 years. The variability amplitude is higher for
shorter rest-frame wavelengths and lower luminosities. (Abridged) |
New Constraints on variations of the fine structure constant from CMB
anisotropies: We demonstrate that recent measurements of Cosmic Microwave Background
temperature and polarization anisotropy made by the ACBAR, QUAD and BICEP
experiments substantially improve the cosmological constraints on possible
variations of the fine structure constant in the early universe. This data,
combined with the five year observations from the WMAP mission yield the
constraint alpha/alpha_0 = 0.987 \pm 0.012 at 68% c.l.. The inclusion of the
new HST constraints on the Hubble constant further increases the accuracy to
alpha/alpha_0 = 1.001 \pm 0.007 at 68% c.l., bringing possible deviations from
the current value below the 1% level and improving previous constraints by a
factor 3. | On the amount of peculiar velocity field information in supernovae from
LSST and beyond: Peculiar velocities introduce correlations between supernova magnitudes,
which implies that the supernova Hubble diagram residual carries information on
both the matter power spectrum at the present time and its growth rate. By a
combination of brute-force exact computations of likelihoods and Fisher matrix
analysis, we investigate how this information, which comes from supernova data
only, depends on different survey parameters such as covered area, depth, and
duration. We show that, for a survey like The Rubin Observatory Legacy Survey
of Space and Time (LSST) and a fixed redshift depth, the same observing time
provides the same cosmological information whether one observes a larger area,
or a smaller area during more years. We also show that although the peculiar
velocity information is peaked in the range $z \in [0, 0.2]$, there is yet
plenty of information in $z \in [0.2, 0.5]$, and for very high supernova number
densities there is even more information in the latter range. We conclude that,
after 5 years, LSST could measure $\sigma_8$ with an uncertainty of 0.17 with
the current strategy, and that this could be improved to 0.09 if the supernova
completeness is improved to 20%. Moreover, we forecast results considering the
extra parameter $\gamma$, and show that this creates a non-linear degeneracy
with $\sigma_8$ that makes the Fisher matrix analysis inadequate. Finally, we
discuss the possibility of achieving competitive results with the current
Zwicky Transient Facility. |
Full-sky bispectrum in redshift space for 21cm intensity maps: We compute the tree-level bispectrum of 21cm intensity mapping after
reionisation. We work in the directly observable angular and redshift space,
focusing on equal-redshift correlations and thin redshift bins, for which the
lensing contribution is negligible. We demonstrate the importance of the
contributions from redshift-space distortions which typically dominate the
result. Taking into account the effects of telescope beams and foreground
cleaning, we estimate the signal to noise and show that the bispectrum is
detectable by both SKA in single-dish mode and HIRAX in interferometer mode,
especially at the lower redshifts in their respective ranges. | Gauge invariance and non-Gaussianity in Inflation: We clarify the role of gauge invariance for the computation of quantum
non-Gaussian correlators in inflation. A gauge invariant generating functional
for n-point functions is given and the special status of the spatially flat
gauge is pointed out. We also comment on the relation between gauge
transformations, field redefinitions, the choice of $t={\rm const}$
hypersurfaces and the use of boundary terms in computations of non-Gaussianity. |
Spectroscopic failures in photometric redshift calibration: cosmological
biases and survey requirements: We use N-body-spectro-photometric simulations to investigate the impact of
incompleteness and incorrect redshifts in spectroscopic surveys to photometric
redshift training and calibration and the resulting effects on cosmological
parameter estimation from weak lensing shear-shear correlations. The photometry
of the simulations is modeled after the upcoming Dark Energy Survey and the
spectroscopy is based on a low/intermediate resolution spectrograph with
wavelength coverage of 5500{\AA} < {\lambda} < 9500{\AA}. The principal
systematic errors that such a spectroscopic follow-up encounters are
incompleteness (inability to obtain spectroscopic redshifts for certain
galaxies) and wrong redshifts. Encouragingly, we find that a neural
network-based approach can effectively describe the spectroscopic
incompleteness in terms of the galaxies' colors, so that the spectroscopic
selection can be applied to the photometric sample. Hence, we find that
spectroscopic incompleteness yields no appreciable biases to cosmology,
although the statistical constraints degrade somewhat because the photometric
survey has to be culled to match the spectroscopic selection. Unfortunately,
wrong redshifts have a more severe impact: the cosmological biases are
intolerable if more than a percent of the spectroscopic redshifts are
incorrect. Moreover, we find that incorrect redshifts can also substantially
degrade the accuracy of training set based photo-z estimators. The main problem
is the difficulty of obtaining redshifts, either spectroscopically or
photometrically, for objects at z > 1.3. We discuss several approaches for
reducing the cosmological biases, in particular finding that photo-z error
estimators can reduce biases appreciably. | The Atacama Cosmology Telescope: Cosmology from Galaxy Clusters Detected
via the Sunyaev-Zel'dovich Effect: We present constraints on cosmological parameters based on a sample of
Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave
survey by the Atacama Cosmology Telescope. The cluster sample used in this
analysis consists of 9 optically-confirmed high-mass clusters comprising the
high-significance end of the total cluster sample identified in 455 square
degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive
systems to reduce the degeneracy between unknown cluster astrophysics and
cosmology derived from SZ surveys. We describe the scaling relation between
cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the
values of the parameters in this fit with conservative priors gives sigma_8 =
0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological
model with WMAP 7-year priors on cosmological parameters. This gives a modest
improvement in statistical uncertainty over WMAP 7-year constraints alone.
Fixing the scaling relation between cluster mass and SZ signal to a fiducial
relation obtained from numerical simulations and calibrated by X-ray
observations, we find sigma_8 = 0.821 +/- 0.044 and w = -1.05 +/- 0.20. These
results are consistent with constraints from WMAP 7 plus baryon acoustic
oscillations plus type Ia supernoava which give sigma_8 = 0.802 +/- 0.038 and w
= -0.98 +/- 0.053. A stacking analysis of the clusters in this sample compared
to clusters simulated assuming the fiducial model also shows good agreement.
These results suggest that, given the sample of clusters used here, both the
astrophysics of massive clusters and the cosmological parameters derived from
them are broadly consistent with current models. |
Mass Accretion and its Effects on the Self-Similarity of Gas Profiles in
the Outskirts of Galaxy Clusters: Galaxy clusters exhibit remarkable self-similar behavior which allows us to
establish simple scaling relationships between observable quantities and
cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray
observations suggest that self-similarity may be broken in the outskirts of
galaxy clusters. In this work, we analyze a mass-limited sample of massive
galaxy clusters from the Omega500 cosmological hydrodynamic simulation to
investigate the self-similarity of the diffuse X-ray emitting intracluster
medium (ICM) in the outskirts of galaxy clusters. We find that the
self-similarity of the outer ICM profiles is better preserved if they are
normalized with respect to the mean density of the universe, while the inner
profiles are more self-similar when normalized using the critical density.
However, the outer ICM profiles as well as the location of accretion shock
around clusters are sensitive to their mass accretion rate, which causes the
apparent breaking of self-similarity in cluster outskirts. We also find that
the collisional gas does not follow the distribution of collisionless dark
matter perfectly in the infall regions of galaxy clusters, leading to 10%
departures in the gas-to-dark matter density ratio from the cosmic mean value.
Our results have a number implications for interpreting observations of galaxy
clusters in X-ray and through the Sunyaev-Zel'dovich effect and their
application to cluster cosmology. | Effect of Priomordial non-Gaussianities on Galaxy Clusters Scaling
Relations: Galaxy clusters are a valuable source of cosmological information. Their
formation and evolution depends on the underlying cosmology and on the
statistical nature of the primordial density fluctuations. In this work we
investigate the impact of primordial non-gaussianities (PNG) on the scaling
properties of galaxy clusters. We performed a series of cosmological
hydrodynamic N-body simulations featuring adiabatic gas physics and different
levels of non-Gaussian initial conditions within the $\Lambda$CDM framework. We
focus on the T-M, S-M, Y-M and Yx-M scalings relating the total cluster mass
with temperature, entropy and SZ cluster integrated pressure that reflect the
thermodynamical state of the intra-cluster medium. Our results show that PNG
have an impact on cluster scalings laws. The mass power-law indexes of the
scalings are almost unaffected by the existence of PNG but the amplitude and
redshift evolution of their normalizations are clearly affected. The effect is
stronger for the evolution of the Y-M and Yx-M normalizations, which change by
as much as 22% and 16% when $f_{NL}$ varies from -500 to 500, respectively.
These results are consistent with the view that positive/negative $f_{NL}$
affect cluster profiles due to an increase/decrease of cluster concentrations.
At low values of $f_{NL}$, as suggested by present Planck constraints on a
scale invariant $f_{NL}$, the impact on the scalings normalizations is only a
few percent, which is small when compared with the effect of additional gas
physics and other cosmological effects such as dark energy. However if $f_{NL}$
is in fact a scale dependent parameter, PNG may have larger positive/negative
amplitudes at clusters scales and therefore our results suggest that PNG should
be taken into account when galaxy cluster data is used to infer cosmological
parameters or to asses the constraining power of future cluster surveys. |
MILCANN : A neural network assessed tSZ map for galaxy cluster detection: We present the first combination of thermal Sunyaev-Zel'dovich (tSZ) map with
a multi-frequency quality assessment of the sky pixels based on Artificial
Neural Networks (ANN) aiming at detecting tSZ sources from sub-millimeter
observations of the sky by Planck. We construct an adapted full-sky ANN
assessment on the fullsky and we present the construction of the resulting
filtered and cleaned tSZ map, MILCANN. We show that this combination allows to
significantly reduce the noise fluctuations and foreground residuals compared
to standard tSZ maps. From the MILCANN map, we constructed the HAD tSZ source
catalog that consists of 3969 sources with a purity of 90\%. Finally, We
compare this catalog with ancillary catalogs and show that the galaxy-cluster
candidates in the HAD catalog are essentially low-mass (down to $M_{500} =
10^{14}$ M$_\odot$) high-redshift (up to $z \leq 1$) galaxy cluster candidates. | A Hybrid Deep Learning Approach to Cosmological Constraints From Galaxy
Redshift Surveys: We present a deep machine learning (ML)-based technique for accurately
determining $\sigma_8$ and $\Omega_m$ from mock 3D galaxy surveys. The mock
surveys are built from the AbacusCosmos suite of $N$-body simulations, which
comprises 40 cosmological volume simulations spanning a range of cosmological
models, and we account for uncertainties in galaxy formation scenarios through
the use of generalized halo occupation distributions (HODs). We explore a trio
of ML models: a 3D convolutional neural network (CNN), a power-spectrum-based
fully connected network, and a hybrid approach that merges the two to combine
physically motivated summary statistics with flexible CNNs. We describe best
practices for training a deep model on a suite of matched-phase simulations and
we test our model on a completely independent sample that uses previously
unseen initial conditions, cosmological parameters, and HOD parameters. Despite
the fact that the mock observations are quite small
($\sim0.07h^{-3}\,\mathrm{Gpc}^3$) and the training data span a large parameter
space (6 cosmological and 6 HOD parameters), the CNN and hybrid CNN can
constrain $\sigma_8$ and $\Omega_m$ to $\sim3\%$ and $\sim4\%$, respectively. |
Scalar perturbations in cosmological models with quark nuggets: In this paper we consider the Universe at the late stage of its evolution and
deep inside the cell of uniformity. At these scales, the Universe is filled
with inhomogeneously distributed discrete structures (galaxies, groups and
clusters of galaxies). Supposing that a small fraction of colored objects
escaped hadronization and survived up to now in the form of quark-gluon nuggets
(QNs), and also taking into account radiation, we investigate scalar
perturbations of the FRW metrics due to inhomogeneities of dustlike matter as
well as fluctuations of QNs and radiation. In particular, we demonstrate that
the nonrelativistic gravitational potential is defined by the distribution of
inhomogeneities/fluctuations of both dustlike matter and QNs. Consequently, QNs
can be distributed around the baryonic inhomogeneities (e.g., galaxies) in such
a way that it can solve the problem of the flatness of the rotation curves. We
also show that the fluctuations of radiation are caused by both the
inhomogeneities in the form of galaxies and the fluctuations of quark-gluon
nuggets. Therefore, if QNs exist, the CMB anisotropy should contain also the
contributions from QNs. Additionally, the spatial distribution of the radiation
fluctuations is defined by the gravitational potential. All these results look
physically reasonable. | Non-congruent Phase Transitions in Cosmic Matter and in the Laboratory: Non-congruence appears to be the most general form of phase transition in
cosmic matter and in the laboratory. In terrestrial applications
noncongruencemeans coexistence of phases with different chemical composition in
systems consisting of two (or more) chemical elements. It is just the case for
all phase transitions in high-temperature chemically reactive mixtures, which
are typical for uranium-bearing compounds in many nuclear energy devices, both
contemporary and perspective. As for cosmic matter, most of real and
hypothetical phase transitions without nuclear reactions, i.e., those in the
interiors of giant planets (solar and extrasolar), those in brown dwarfs and
other sub-stellar objects, as well as in the outer crust of compact stars, are
very plausible candidates for such type of phase transformations. Two exotic
phase transitions, the gas-liquid phase transition in dense nuclear matter and
the quark-hadron transition occuring in the interior of compact stars as well
as in high-energy heavy-ion collisions are under discussion as the most extreme
example of hypothetical non-congruence for phase transformations in High Energy
Density Matter. |
Probing the cool ISM in galaxies via 21cm HI absorption: Recent targeted studies of associated HI absorption in radio galaxies are
starting to map out the location, and potential cosmological evolution, of the
cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21
cm absorption profiles often show two distinct spectral-line components:
narrow, deep lines arising from cold gas in the extended disc of the galaxy,
and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al.
2011). Here, we present results from a targeted search for associated HI
absorption in the youngest and most recently-triggered radio AGN in the local
universe (Allison et al. 2012b). So far, by using the recently commissioned
Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011),
we have detected two new absorbers and one previously-known system. While two
of these show both a broad, shallow component and a narrow, deep component (see
Fig. 1), one of the new detections has only a single broad, shallow component.
Interestingly, the host galaxies of the first two detections are classified as
gas-rich spirals, while the latter is an early-type galaxy. These detections
were obtained using a spectral-line finding method, based on Bayesian
inference, developed for future large-scale absorption surveys (Allison et al.
2012a). | The cosmological dependence of halo and galaxy assembly bias: One of the main predictions of excursion set theory is that the clustering of
dark matter haloes only depends on halo mass. However, it has been long
established that the clustering of haloes also depends on other properties,
including formation time, concentration, and spin; this effect is commonly
known as halo assembly bias. We use a suite of gravity-only simulations to
study the dependence of halo assembly bias on cosmology; these simulations
cover cosmological parameters spanning 10$\sigma$ around state-of-the-art
best-fitting values, including standard extensions of the $\Lambda$CDM paradigm
such as neutrino mass and dynamical dark energy. We find that the strength of
halo assembly bias presents variations smaller than 0.05 dex across all
cosmologies studied for concentration and spin selected haloes, letting us
conclude that the dependence of halo assembly bias upon cosmology is
negligible. We then study the dependence of galaxy assembly bias (i.e. the
manifestation of halo assembly bias in galaxy clustering) on cosmology using
subhalo abundance matching. We find that galaxy assembly bias also presents
very small dependence upon cosmology ($\sim$ 2$\%$-4$\%$ of the total
clustering); on the other hand, we find that the dependence of this signal on
the galaxy formation parameters of our galaxy model is much stronger. Taken
together, these results let us conclude that the dependence of halo and galaxy
assembly bias on cosmology is practically negligible. |
Measuring the Inflaton Coupling in the CMB: We study the perspectives to extract information about the microphysical
parameters that governed the reheating process after cosmic inflation from CMB
data. We identify conditions under which the inflaton coupling to other fields
can be constrained for a given model of inflation without having to specify the
details of the particle physics theory within which this model is realised.
This is possible when the effective potential during reheating is approximately
parabolic, and when the coupling constants are smaller than an upper bound that
is determined by the ratios between the inflaton mass and the Planck mass or
the scale of inflation. We consider scalar, Yukawa, and axion-like interactions
and estimate that these conditions can be fulfilled if the inflaton coupling is
comparable to the electron Yukawa coupling or smaller, and if the inflaton mass
is larger than $10^5$ GeV. Constraining the order of magnitude of the coupling
constant requires measuring the scalar-to-tensor ratio at the level of
$10^{-3}$, which is possible with future CMB observatories. Such a measurement
would provide an important clue to understand how a given model of inflation
may be embedded into a more fundamental theory of nature. | Feedback and the Structure of Simulated Galaxies at redshift z=2: We study the properties of simulated high-redshift galaxies using
cosmological N-body/gasdynamical runs from the OverWhelmingly Large Simulations
(OWLS) project. The runs contrast several feedback implementations of varying
effectiveness: from no-feedback, to supernova-driven winds to powerful
AGN-driven outflows. These different feedback models result in large variations
in the abundance and structural properties of bright galaxies at z=2. We find
that feedback affects the baryonic mass of a galaxy much more severely than its
spin, which is on average roughly half that of its surrounding dark matter halo
in our runs. Feedback induces strong correlations between angular momentum
content and galaxy mass that leave their imprint on galaxy scaling relations
and morphologies. Encouragingly, we find that galaxy disks are common in
moderate-feedback runs, making up typically ~50% of all galaxies at the centers
of haloes with virial mass exceeding 1e11 M_sun. The size, stellar masses, and
circular speeds of simulated galaxies formed in such runs have properties that
straddle those of large star-forming disks and of compact early-type galaxies
at z=2. Once the detailed abundance and structural properties of these rare
objects are well established it may be possible to use them to gauge the
overall efficacy of feedback in the formation of high redshift galaxies. |
Blazars in hard X-rays: Although blazars are thought to emit most of their luminosity in the
gamma-ray band, there are subclasses of them very prominent in hard X-rays.
These are the best candidates to be studied by Simbol-X. They are at the
extremes of the blazar sequence, having very small or very high jet powers. The
former are the class of TeV emitting BL Lacs, whose synchrotron emission often
peaks at tens of keV or more. The latter are the blazars with the most powerful
jets and have high black hole masses accreting at high (i.e. close to
Eddington) rates. These sources are predicted to have their high energy peak
even below the MeV band, and therefore are very promising candidates to be
studied with Simbol-X. | Fuzzy Dark Matter Dynamics and the Quasiparticle Hypothesis: Dark matter may be composed of ultra-light bosons whose de Broglie wavelength
in galaxies is of order 1 kpc. The standard model for this fuzzy dark matter
(FDM) is a complex scalar field that obeys the Schr\"odinger-Poisson equations.
The wavelike nature of FDM leads to fluctuations in the gravitational field
that can pump energy into the stellar components of a galaxy. Heuristic
arguments and theoretical analyses suggest that these fluctuations can be
modelled by replacing FDM with a system of quasiparticles (QPs). We test this
hypothesis by comparing self-consistent simulations of a Schr\"odinger field
with those using a system of QPs in one spatial dimension. Simulations of pure
FDM systems allow us to derive a phenomenological relation between the number
of QPs that is required to model FDM with a given de Broglie wavelength. We
also simulate systems of FDM and stars and find that the FDM pumps energy into
the stars whether it is described by QPs or a Schr\"odinger field with the FDM
adiabatically contracting and the stellar system adiabatically expanding.
However, we find that QPs overestimate dynamical heating. |
A survey of lens spaces and large-scale CMB anisotropy: The cosmic microwave background (CMB) anisotropy possesses the remarkable
property that its power is strongly suppressed on large angular scales. This
observational fact can naturally be explained by cosmological models with a
non-trivial topology. The paper focuses on lens spaces L(p,q) which are
realised by a tessellation of the spherical 3-space S^3 by cyclic deck groups
of order p<=72. The investigated cosmological parameter space covers the
interval Omega_tot \in [1.001,1.05]. Several spaces are found which have CMB
correlations on angular scales theta >= 60^\circ suppressed by a factor of two
compared to the simply connected S^3 space. The analysis is based on the S
statistics, and a comparison to the WMAP 7yr data is carried out. Although the
CMB suppression is less pronounced than in the Poincare dodecahedral space,
these lens spaces provide an alternative worth for follow-up studies. | Testing the theory of gravity with DESI: estimators, predictions and
simulation requirements: Shortly after its discovery, General Relativity (GR) was applied to predict
the behavior of our Universe on the largest scales, and later became the
foundation of modern cosmology. Its validity has been verified on a range of
scales and environments from the Solar system to merging black holes. However,
experimental confirmations of GR on cosmological scales have so far lacked the
accuracy one would hope for -- its applications on those scales being largely
based on extrapolation and its validity sometimes questioned in the shadow of
the unexpected cosmic acceleration. Future astronomical instruments surveying
the distribution and evolution of galaxies over substantial portions of the
observable Universe, such as the Dark Energy Spectroscopic Instrument (DESI),
will be able to measure the fingerprints of gravity and their statistical power
will allow strong constraints on alternatives to GR.
In this paper, based on a set of $N$-body simulations and mock galaxy
catalogs, we study the predictions of a number of traditional and novel
estimators beyond linear redshift distortions in two well-studied modified
gravity models, chameleon $f(R)$ gravity and a braneworld model, and the
potential of testing these deviations from GR using DESI. These estimators
employ a wide array of statistical properties of the galaxy and the underlying
dark matter field, including two-point and higher-order statistics,
environmental dependence, redshift space distortions and weak lensing. We find
that they hold promising power for testing GR to unprecedented precision. The
major future challenge is to make realistic, simulation-based mock galaxy
catalogs for both GR and alternative models to fully exploit the statistic
power of the DESI survey and to better understand the impact of key systematic
effects. Using these, we identify future simulation and analysis needs for
gravity tests using DESI. |
Cosmic voids and the kinetic analysis. II. Link to Hubble tension: We consider a principal problem, that of the possible dominating role of
self-consistent gravitational interaction in the formation of cosmic
structures: voids and their walls in the local Universe. It is in the context
of the Hubble tension as a possible indication of the difference in the
descriptions of the late (local) and early (global) Universe. The kinetic
Vlasov treatment enables us to consider the evolution of gravitating structures
where the fundamental role has the modified gravitational potential with a
cosmological constant, leading to the prediction of a local flow with a Hubble
parameter that is nonidentical to that of the global Hubble flow. The Poisson
equation for a potential with an additional repulsive term, including an
integral equation formulation, is analyzed, and we predict the appearance of
multiply connected two-dimensional gravitating structures and voids in the
local Universe. The obvious consequence of the developed mechanism is that the
cosmological constant poses a natural scaling for the voids, along with the
physical parameters of their local environment, which can be traced in
observational surveys. | Detecting the Cold Spot as a Void with the Non-Diagonal Two-Point
Function: The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could
be due to the existence of an anomalously large spherical (few hundreds Mpc/h
radius) underdense region, called a "Void" for short. Such a structure would
have an impact on the CMB also at high multipoles l through Lensing. This would
then represent a unique signature of a Void. Modeling such an underdensity with
an LTB metric, we show that the Lensing effect leads to a large signal in the
non-diagonal two-point function, centered in the direction of the Cold Spot,
such that the Planck satellite will be able to confirm or rule out the Void
explanation for the Cold Spot, for any Void radius with a Signal-to-Noise ratio
of at least O(10). |
Supermassive Black Holes from Ultra-Strongly Self-Interacting Dark
Matter: We consider the cosmological consequences if a small fraction ($f\lesssim
0.1$) of the dark matter is ultra-strongly self-interacting, with an elastic
self-interaction cross-section per unit mass $\sigma\gg1\ \mathrm{cm^{2}/g}$.
This possibility evades all current constraints that assume that the
self-interacting component makes up the majority of the dark matter.
Nevertheless, even a small fraction of ultra-strongly self-interacting dark
matter (uSIDM) can have observable consequences on astrophysical scales. In
particular, the uSIDM subcomponent can undergo gravothermal collapse and form
seed black holes in the center of a halo. These seed black holes, which form
within several hundred halo interaction times, contain a few percent of the
total uSIDM mass in the halo. For reasonable values of $\sigma f$, these black
holes can form at high enough redshifts to grow to $\sim10^9 M_\odot$ quasars
by $z \gtrsim 6$, alleviating tension within the standard $\Lambda$CDM
cosmology. The ubiquitous formation of central black holes in halos could also
create cores in dwarf galaxies by ejecting matter during binary black hole
mergers, potentially resolving the "too big to fail" problem. | Weak Lensing Minima and Peaks: Cosmological Constraints and the Impact
of Baryons: We present a novel statistic to extract cosmological information in weak
lensing data: the lensing minima. We also investigate the effect of baryons on
the cosmological constraints from peak and minimum counts. Using the
\texttt{MassiveNuS} simulations, we find that lensing minima are sensitive to
non-Gaussian cosmological information and are complementary to the lensing
power spectrum and peak counts. For an LSST-like survey, we obtain $95\%$
credible intervals from a combination of lensing minima and peaks that are
significantly stronger than from the power spectrum alone, by $44\%$, $11\%$,
and $63\%$ for the neutrino mass sum $\sum m_\nu$, matter density $\Omega_m$,
and amplitude of fluctuation $A_s$, respectively. We explore the effect of
baryonic processes on lensing minima and peaks using the hydrodynamical
simulations \texttt{BAHAMAS} and \texttt{Osato15}. We find that ignoring
baryonic effects would lead to strong ($\approx 4 \sigma$) biases in inferences
from peak counts, but negligible ($\approx 0.5 \sigma$) for minimum counts,
suggesting lensing minima are a potentially more robust tool against baryonic
effects. Finally, we demonstrate that the biases can in principle be mitigated
without significantly degrading cosmological constraints when we model and
marginalize the baryonic effects. |
IDCS J1426.5+3508: Cosmological implications of a massive, strong
lensing cluster at Z = 1.75: The galaxy cluster IDCS J1426.5+3508 at z = 1.75 is the most massive galaxy
cluster yet discovered at z > 1.4 and the first cluster at this epoch for which
the Sunyaev-Zel'Dovich effect has been observed. In this paper we report on the
discovery with HST imaging of a giant arc associated with this cluster. The
curvature of the arc suggests that the lensing mass is nearly coincident with
the brightest cluster galaxy, and the color is consistent with the arc being a
star-forming galaxy. We compare the constraint on M200 based upon strong
lensing with Sunyaev-Zel'Dovich results, finding that the two are consistent if
the redshift of the arc is z > 3. Finally, we explore the cosmological
implications of this system, considering the likelihood of the existence of a
strongly lensing galaxy cluster at this epoch in an LCDM universe. While the
existence of the cluster itself can potentially be accomodated if one considers
the entire volume covered at this redshift by all current high-redshift cluster
surveys, the existence of this strongly lensed galaxy greatly exacerbates the
long-standing giant arc problem. For standard LCDM structure formation and
observed background field galaxy counts this lens system should not exist.
Specifically, there should be no giant arcs in the entire sky as bright in
F814W as the observed arc for clusters at z \geq 1.75, and only \sim 0.3 as
bright in F160W as the observed arc. If we relax the redshift constraint to
consider all clusters at z \geq 1.5, the expected number of giant arcs rises to
\sim15 in F160W, but the number of giant arcs of this brightness in F814W
remains zero. These arc statistic results are independent of the mass of IDCS
J1426.5+3508. We consider possible explanations for this discrepancy. | Numerically reconstructing the geometry of the Universe from data: We give an outline of an algorithm designed to reconstruct the background
cosmological metric within the class of spherically symmetric dust universes
that may include a cosmological constant. Luminosity and age data are used to
derive constraints on the geometry of the universe up to a redshift of $z =
1.75$. It is shown that simple radially inhomogeneous void models that are
sometimes used as alternative explanations for the apparent acceleration of the
late time Universe cannot be ruled out by these data alone. |
Primordial non-Gaussianities: This contribution gives an overview on primordial non-Gaussianities from a
theoretical perspective. After presenting a general formalism to describe
nonlinear cosmological perturbations, several classes of models, illustrated
with examples, are discussed: multi-field inflation with non-standard
Lagrangians, modulaton fields, curvaton fields. In the latter case, a special
emphasis is put on the isocurvature perturbations, which could leave a specific
signature in non-Gaussianities. | Testing cosmic opacity with the combination of strongly lensed and
unlensed supernova Ia: In this paper, we present a scheme to investigate the opacity of the Universe
in a cosmological-model-independent way, with the combination of current and
future measurements of type Ia supernova sample and galactic-scale strong
gravitational lensing systems with SNe Ia acting as background sources. The
observational data include the current newly-compiled SNe Ia data (Pantheon
sample) and simulated sample of SNe Ia observed by the forthcoming Large
Synoptic Survey Telescope (LSST) survey, which are taken for luminosity
distances ($D_L$) possibly affected by the cosmic opacity, as well as strongly
lensed SNe Ia observed by the LSST, which are responsible for providing the
observed time-delay distance ($D_{\Delta t}$) unaffected by the cosmic opacity.
Two parameterizations, $\tau(z)=2\beta z$ and $\tau(z)=(1+z)^{2\beta}-1$ are
adopted for the optical depth associated to the cosmic absorption. Focusing on
only one specific type of standard cosmological probe, this provides an
original method to measure cosmic opacity at high precision. Working on the
simulated sample of strongly lensed SNe Ia observed by the LSST in 10 year
$z$-band search, our results show that, with the combination of the current
newly-compiled SNe Ia data (Pantheon sample), there is no significant deviation
from the transparency of the Universe at the current observational data level.
Moreover, strongly lensed SNe Ia in a 10 year LSST $z$-band search would
produce more robust constraints on the validity of cosmic transparency (at the
precision of $\Delta\beta=10^{-2}$), with a larger sample of unlensed SNe Ia
detected in future LSST survey. We have also discussed the ways in which our
methodology could be improved, with the combination of current and future
available data in gravitational wave (GW) and electromagnetic (EM) domain. |
Testing black hole no-hair theorem with OJ287: We examine the ability to test the black hole no-hair theorem at the 10%
level in this decade using the binary black hole in OJ287. In the test we
constrain the value of the dimensionless parameter q that relates the scaled
quadrupole moment and spin of the primary black hole: q2 = -q 2 . At the
present we can say that q = 1 \pm 0.3 (one), in agreement with General
Relativity and the no-hair theorems. We demonstrate that this result can be
improved if more observational data is found in historical plate archives for
the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019
outbursts will be crucial in improving the accuracy of the test. Space-based
photometry is required in 2019 July due the proximity of OJ287 to the Sun at
the time of the outburst. The best situation would be to carry out the
photometry far from the Earth, from quite a different vantage point, in order
to avoid the influence of the nearby Sun. We have considered in particular the
STEREO space mission which would be ideal if it has a continuation in 2019 or
LORRI on board the New Horizons mission to Pluto. | Structure formation in a nonlocally modified gravity model: We study a nonlocally modified gravity model proposed by Deser and Woodard
which gives an explanation for current cosmic acceleration. By deriving and
solving the equations governing the evolution of the structure in the Universe,
we show that this model predicts a pattern of growth that differs from standard
general relativity (+dark energy) at the 10-30% level. These differences will
be easily probed by the next generation of galaxy surveys, so the model should
be tested shortly. |
Constraining the Statistics of Population III Binaries: We perform a cosmological simulation in order to model the growth and
evolution of Population III (Pop III) stellar systems in a range of host
minihalo environments. A Pop III multiple system forms in each of the ten
minihaloes, and the overall mass function is top-heavy compared to the
currently observed initial mass function in the Milky Way. Using a sink
particle to represent each growing protostar, we examine the binary
characteristics of the multiple systems, resolving orbits on scales as small as
20 AU. We find a binary fraction of ~36%, with semi-major axes as large as 3000
AU. The distribution of orbital periods is slightly peaked at < 900 yr, while
the distribution of mass ratios is relatively flat. Of all sink particles
formed within the ten minihaloes, ~50% are lost to mergers with larger sinks,
and ~50% of the remaining sinks are ejected from their star-forming disks. The
large binary fraction may have important implications for Pop III evolution and
nucleosynthesis, as well as the final fate of the first stars. | Directional axion detection: We develop a formalism to describe extensions of existing axion haloscope
designs to those that possess directional sensitivity to incoming dark matter
axion velocities. The effects are measurable if experiments are designed to
have dimensions that approach the typical coherence length for the local axion
field. With directional sensitivity, axion detection experiments would have a
greatly enhanced potential to probe the local dark matter velocity
distribution. We develop our formalism generally, but apply it to specific
experimental designs, namely resonant cavities and dielectric disk haloscopes.
We demonstrate that these experiments are capable of measuring the daily
modulation of the dark matter signal and using it to reconstruct the
three-dimensional velocity distribution. This allows one to measure the Solar
peculiar velocity, probe the anisotropy of the dark matter velocity ellipsoid
and identify cold substructures such as the recently discovered streams near to
Earth. Directional experiments can also identify features over much shorter
timescales, potentially facilitating the mapping of debris from axion
miniclusters. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.