text
stringlengths 73
2.82k
| category
stringclasses 21
values |
|---|---|
The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable
Star in NGC 2403: We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type
II-narrow (IIn), has photometric and spectroscopic properties unlike those of
normal SNe. Its behavior, instead, is more typical of highly massive stars
which experience the short-lived luminous blue variable (LBV) phase toward the
end of their lives. The star, in fact, most resembles the LBV S Doradus in
outburst. The precursor of SN 2002kg is the irregular, bright blue variable
star 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality
ground-based, multi-band images we can constrain the initial mass of V37 to be
M_ini >~ 40 M_sun. We find that, although the spectra indicate a nitrogen
enhancement, possibly revealing the products of CNO processing by V37 in the
ejecta, the star lacks a substantial LBV nebula. The outburst from SN
2002kg/V37 is not nearly as energetic as the giant eruptions of the eta
Carinae-like variables, such as SN 1954J/V12, also in NGC 2403. SN 2002kg/V37,
however, is among a growing number of ``SN impostors'' exhibiting a broad range
of outburst energetics during a pre-SN phase of massive-star evolution. | astro-ph |
The Distribution of Thermal Pressures in the Interstellar Medium from a
Survey of C I Fine-Structure Excitation: We used the smallest entrance aperture (0.03 arc-sec wide slit) and highest
resolution echelle gratings (E140H and E230H) of STIS on HST to record the
interstellar absorption features for 10 different multiplets of neutral carbon
at a wavelength resolving power of 200,000 in the UV spectra of 21 early-type
stars. We measured the amount of C I in each of its three fine-structure
levels, so that we could determine nT of the absorbing gas and how much it
varies in different regions. To obtain internally consistent results for all
multiplets, we had to modify the transition f-values so that generally weak
transitions were stronger than their published values. The fine-structure
populations indicate that the median thermal pressure for our entire sample is
p/k=2240 cm^-3 K, or slightly higher for temperatures that differ appreciably
from 40 K. About 15% of the gas moving at peculiar velocities shows p/k > 10^4
cm^-3 K, and this fraction drops to 1.5% for quiescent gas. Often, there are
small amounts of gas at p/k > 10^5 cm^-3 K. These ubiquitous wisps of high
pressure material probably arise from small-scale density enhancements created
by converging flows in a turbulent medium. The C I excitations indicate a
barytropic index gamma_eff > 0.90 when the gas is compressed, which is larger
than the value 0.72 expected for material in thermal equilibrium. This
indicates that the regions have a dimension r < 0.01 pc which allows them to
compress very quickly and nearly adiabatically. Appendices of this paper
present evidence that STIS can indeed achieve R = 200,000, and that telluric
oxygen absorption lines are broadened by macroscopic motions. | astro-ph |
Determining Star Formation Rates for Infrared Galaxies: We show that measures of star formation rates (SFRs) for infrared galaxies
using either single-band 24 um or extinction-corrected Paschen-alpha
luminosities are consistent in the total infrared luminosity = L(TIR) ~ 10^10
L_sun range. MIPS 24 micron photometry can yield star formation rates
accurately from this luminosity upward: SFR(M_sun/yr) = 7.8 x 10^-10 L(24 um,
L_sun) from L(TIR) = 5 x 10^9 L_sun to 10^11 L_sun, and SFR = 7.8 x 10^-10 L(24
um, L_sun) x (7.76 x 10^-11 L(24))^0.048 for higher L(TIR). For galaxies with
L(TIR) >= 10^10 L_sun, these new expressions should provide SFRs to within 0.2
dex. For L(TIR) >= 10^11 L_sun, we find that the SFR of infrared galaxies is
significantly underestimated using extinction-corrected Pa-alpha (and
presumably using any other optical or near infrared recombination lines). As a
part of this work, we constructed spectral energy distribution (SED) templates
for eleven luminous and ultraluminous purely star forming infrared galaxies
(LIRGs and ULIRGs) and over the spectral range 0.4 microns to 30 cm. We use
these templates and the SINGS data to construct average templates from 5
microns to 30 cm for infrared galaxies with L(TIR) = 5 x 10^9 to 10^13 L_sun.
All of these templates are made available on line. | astro-ph |
Measuring M31 globular cluster ages and metallicities using both
photometry and spectroscopy: The ages and metallicities of globular clusters play an important role not
just in testing models for their formation and evolution but in understanding
the assembly history for their host galaxies. Here we use a combination of
imaging and spectroscopy to measure the ages and metallicities of globular
clusters in M31, the closest massive galaxy to our own. We use the strength of
the near-infrared calcium triplet spectral feature to provide a relatively age
insensitive prior on the metallicity when fitting stellar population models to
the observed photometry. While the age-extinction degeneracy is an issue for
globular clusters projected onto the disc of M31, we find generally old ages
for globular clusters in the halo of M31 and in its satellite galaxy NGC 205 in
line with previous studies. We measure ages for a number of outer halo globular
clusters for the first time, finding that globular clusters associated with
halo substructure extend to younger ages and higher metallicities than those
associated with the smooth halo. This is in line with the expectation that the
smooth halo was accreted earlier than the substructured halo. | astro-ph |
Light curve analysis of ordinary type IIP supernovae based on
neutrino-driven explosion simulations in three dimensions: Type II-plateau supernovae (SNe IIP) are the most numerous subclass of
core-collapse SNe originating from massive stars. In the framework of the
neutrino-driven explosion mechanism, we study the SN outburst properties for a
red supergiant progenitor model and compare the corresponding light curves with
observations of the ordinary Type IIP SN 1999em. Three-dimensional (3D)
simulations of (parametrically triggered) neutrino-driven explosions are
performed with the (explicit, finite-volume, Eulerian, multifluid
hydrodynamics) code PROMETHEUS, using a presupernova model of a 15 Msun star as
initial data. At approaching homologous expansion, the hydrodynamical and
composition variables of the 3D models are mapped to a spherically symmetric
configuration, and the simulations are continued with the (implicit, Lagrangian
radiation-hydrodynamics) code CRAB to follow the blast-wave evolution during
the SN outburst. Our 3D neutrino-driven explosion model with an explosion
energy of about 0.5x10^51 erg produces Ni-56 in rough agreement with the amount
deduced from fitting the radioactively powered light-curve tail of SN 1999em.
The considered presupernova model, 3D explosion simulations, and light-curve
calculations can explain the basic observational features of SN 1999em, except
for those connected to the presupernova structure of the outer stellar layers.
Our 3D simulations show that the distribution of Ni-rich matter in velocity
space is asymmetric with a strong dipole component that is consistent with the
observations of SN 1999em. The monotonic luminosity decline from the plateau to
the radioactive tail in ordinary SNe IIP is a manifestation of the intense
turbulent mixing at the He/H composition interface. | astro-ph |
Advection-Dominated Accretion Model of Sagittarius A$^*$ and Other
Accreting Black Holes: Viscous rotating accretion flows around black holes become
advection-dominated when the accretion rate $\dot M$ is sufficiently low. Most
of the accretion energy in such flows is stored within the gas and advected
radially inward. The temperature is therefore very high, and much of the
radiation comes out in hard X-rays and $\gamma$-rays. We have constructed an
advection-dominated accretion flow model for the Galactic Center source
Sagittarius A$^*$. The model consists of a $7\times10^5M_\odot$ black hole
accreting at $\dot M=1.2\times10^{-5}\alpha\, M_\odot{\rm yr^{-1}}$, where
$\alpha$ is the usual viscosity parameter. The model spectrum fits the
observations from radio to $\gamma$-rays quite well and explains the unusually
low luminosity of the source. Since the model explicitly makes use of a horizon
at the inner edge to swallow the advected energy, the success of the model
strongly suggests that the central object in Sgr A$^*$ is a black hole. We
further show that, if $\alpha$ is not much smaller than unity, then
advection-dominated models can be applied even to higher luminosity black
holes. The existence of Low and High States in black hole X-ray binaries, and
the abrupt transition between the two states, find a natural explanation. The
models also explain the close similarity in the hard X-ray/$\gamma$-ray spectra
of black hole X-ray binaries and active galactic nuclei. | astro-ph |
A solar-cycle study of coronal rotation: large variations, rapid
changes, and implications for solar wind models: Information on the rotation rate of the corona, and its variation over
latitude and solar cycle, is valuable for making global connections between the
corona and the Sun, for global estimates of reconnection rates, and as a basic
parameter for solar wind modelling. Here, we use a time series of tomographical
maps gained from coronagraph observations between 2007 - 2020 to directly
measure the longitudinal drift of high-density streamers over time. The method
reveals abrupt changes in rotation rates, revealing a complex relationship
between the coronal rotation and the underlying photosphere. The majority of
rates are between -1.0 to +0.5$^\circ$/day relative to the standard Carrington
rate of 14.18$^\circ$/day, although rates are measured as low as
-2.2$^\circ$/day and as high as 1.6$^\circ$/day. Equatorial rotation rates
during the 2008 solar minimum are slightly faster than the Carrington rate,
with an abrupt switch to slow rotation in 2009, then a return to faster rates
in 2017. Abrupt changes and large variations in rates are seen at all
latitudes. Comparison with a magnetic model suggests that periods of equatorial
fast rotation are associated with times when a large proportion of the magnetic
footpoints of equatorial streamers are near the equator, and we interpret the
abrupt changes in terms of the latitudinal distribution of the streamer
photospheric footpoints. The coronal rotation rate is a key parameter for solar
wind models, and variations of up to a degree per day or more can lead to large
systematic errors over forecasting periods of longer than a few days. The
approach described in this paper gives corrected values that can form a part of
future forecasting efforts. | astro-ph |
The drop of the coherence of the lower kHz QPOs is also observed in XTE
J1701-462: We investigate the quality factor and RMS amplitude of the lower kHz QPOs
from XTE J1701-462, a unique X-ray source which was observed in both the
so-called Z and atoll states. Correcting for the frequency drift of the QPO, we
show that, as in all sources for which such a correction can be applied, the
quality factor and RMS amplitude drops sharply above above a critical
frequency. For XTE J1701-462 this frequency is estimated to be ~800 Hz, where
the quality factor reaches a maximum of ~200 (e.g. a value consistent with the
one observed from more classical systems, such as 4U~1636-536). Such a drop has
been interpreted as the signature of the innermost stable circular orbit, and
that interpretation is consistent with the observations we report here. The kHz
QPOs in the Z state are much less coherent and lower amplitude than they are in
the atoll state. We argue that the change of the QPO properties between the two
source states is related to the change of the scale height of the accretion
disk; a prediction of the toy model proposed by barret et al. (2007). As a
by-product of our analysis, we also increased the significance of the upper kHz
QPO detected in the atoll phase up to 4.8 sigma (single trial significance),
and show that the frequency separation (266.5+/-13.1 Hz) is comparable with the
one measured from simultaneous twin QPOs the Z phase. | astro-ph |
The G305 star-forming complex: radio continuum and molecular line
observations: We present 109-115 GHz (3 mm) wide-field spectral line observations of 12^CO,
13^CO and C^18O J=1-0 molecular emission and 5.5 and 8.8 GHz (6 and 3 cm) radio
continuum emission towards the high-mass star forming complex known as G305.
The morphology of G305 is dominated by a large evacuated cavity at the centre
of the complex driven by clusters of O stars surrounded by molecular gas. Our
goals are to determine the physical properties of the molecular environment and
reveal the relationship between the molecular and ionised gas and star
formation in G305. This is in an effort to characterise the star-forming
environment and constrain the star formation history in an attempt to evaluate
the impact of high-mass stars on the evolution of the G305 complex.
Analysis of CO emission in G305 reveals 156 molecular clumps with the
following physical characteristics. The 5.5 and 8.8GHz radio continuum emission
reveals an extended low surface brightness ionised environment within which we
identify 15 large-scale features with a further eight smaller sources projected
within these features. By comparing to mid infrared emission and archival data,
we identify nine HII regions, seven compact HII regions, one UC HII region,
four extended regions. The total integrated flux of the radio continuum
emission at 5.5 GHz is ~180 Jy corresponding to a Lyman continuum output of
2.4x10^50 photons s^-1. We compare the ionised and molecular environment with
optically identified high-mass stars and ongoing star formation, identified
from the literature. Analysis of this dataset reveals a star formation rate of
0.008--0.016 and efficiency of 7--12%, allows us to probe the star formation
history of the region and discuss the impact of high-mass stars on the
evolution of G305. | astro-ph |
Every Flare, Everywhere: An All-Sky Untriggered Search for Astrophysical
Neutrino Transients Using IceCube Data: Recent results from IceCube regarding TXS 0506+056 suggest the presence of
neutrino flares that are not temporally coincident with a significant
corresponding gamma ray flare. Such flares are particularly difficult to
identify, as their presence must be inferred from the temporal distribution of
neutrino data alone. Here we present the results of using a novel method to
search for all such flares across the entire neutrino sky in 10 years of
IceCube data, using both Gaussian and box-shaped flare hypotheses. Unlike for
past searches, that looked for only the most significant neutrino flare in the
data at a given direction, here we implement an algorithm to combine
information from multiple flares associated with a single source candidate.
This represents the most detailed description of the neutrino sky to date,
providing the location and intensity of all neutrino cluster candidates in both
space and time. These results can be used to further constrain potential
populations of transient neutrino sources, serving as a complement to existing
time-integrated and time-dependent methods. | astro-ph |
Internal Dynamics of Globular Clusters: Galactic globular clusters, which are ancient building blocks of our Galaxy,
represent a very interesting family of stellar systems in which some
fundamental dynamical processes have taken place on time scales shorter than
the age of the universe. In contrast with galaxies, these clusters represent
unique laboratories for learning about two-body relaxation, mass segregation
from equipartition of energy, stellar collisions, stellar mergers, and core
collapse. In the present review, we summarize the tremendous developments, as
much theoretical as observational, that have taken place during the last two
decades, and which have led to a quantum jump in our understanding of these
beautiful dynamical systems. | astro-ph |
The Physics of Wind-Fed Accretion: We provide a brief review of the physical processes behind the radiative
driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and
accretion of a fraction of the stellar wind by a compact object, typically a
neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we
describe a program to develop global models of the radiatively-driven
photoionized winds and accretion flows of HMXBs, with particular attention to
the prototypical system Vela X-1. The models combine XSTAR photoionization
calculations, HULLAC emission models appropriate to X-ray photoionized plasmas,
improved models of the radiative driving of photoionized winds, FLASH
time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo
radiation transport. We present two- and three-dimensional maps of the density,
temperature, velocity, ionization parameter, and emissivity distributions of
representative X-ray emission lines, as well as synthetic global Monte Carlo
X-ray spectra. Such models help to better constrain the properties of the winds
of HMXBs, which bear on such fundamental questions as the long-term evolution
of these binaries and the chemical enrichment of the interstellar medium. | astro-ph |
Clustering of 2PIGG galaxy groups with 2dFGRS galaxies: Prompted by indications from QSO lensing that there may be more mass
associated with galaxy groups than expected, we have made new dynamical infall
estimates of the masses associated with 2PIGG groups and clusters. We have
analysed the redshift distortions in the cluster-galaxy cross-correlation
function as a function of cluster membership, cross-correlating z<0.12 2PIGG
clusters and groups with the full 2dF galaxy catalogue. We have made estimates
of the dynamical infall parameter beta and new estimates of the group velocity
dispersions. We first find that the amplitude of the full 3-D redshift space
cross-correlation function, xi_{cg}, rises monotonically with group membership.
We use a simple linear-theory infall model to fit xi(sigma, pi) in the range
5<s<40h^{-1}Mpc. We find that the beta versus membership relation for the data
shows a minimum at intermediate group membership n~20 or L~2x10^11h^-2Lsun,
implying that the bias and hence M/L ratios rise by a significant factor (~5x)
both for small groups and rich clusters. However, the mocks show a systematic
shift between the location of the beta minimum and the M/L minimum at
L~10^10h^-2Lsun given by direct calculation using the known DM distribution.
Our overall conclusion is that bias estimates from dynamical infall appear to
support the minimum in star-formation efficiency at intermediate halo masses.
Nevertheless, there may still be significant systematic problems arising from
measuring beta~1/b using large-scale infall rather than M/L using small-scale
velocity dispersions. | astro-ph |
In-flight Calibration of Hitomi Soft X-ray Spectrometer (3) Effective
Area: We present the result of the in-flight calibration of the effective area of
the Soft X-ray Spectrometer (SXS) onboard the Hitomi X-ray satellite using an
observation of the Crab nebula. We corrected for the artifacts when observing
high count rate sources with the X-ray microcalorimeter. We then constructed a
spectrum in the 0.5-20 keV band, which we modeled with a single power-law
continuum attenuated by an interstellar extinction. We evaluated the systematic
uncertainty upon the spectral parameters by various calibration items. In the
2-12 keV band, the SXS result is consistent with the literature values in flux
(2.20 $\pm$ 0.08) $\times$10$^{-8}$ erg s$^{-1}$ cm$^{-2}$ with a 1$\sigma$
statistical uncertainty) but is softer in the power-law index (2.19 $\pm$
0.11). The discrepancy is attributable to the systematic uncertainty of about
$+$6/$-$7% and $+$2/$-$5% respectively for the flux and the power-law index.
The softer spectrum is affected primarily by the systematic uncertainty of the
Dewar gate valve transmission and the event screening. | astro-ph |
Building protoplanetary disks from the molecular cloud: redefining the
disk timeline: We study the formation of the protoplanetary disk by the collapse of a
primordial molecular cloud, and how its evolution leads to the selection of
specific types of planets.
We use a hydrodynamical code that accounts for the dynamics, thermodynamics,
geometry, and composition of the disk to numerically model its evolution as it
is fed by the infalling cloud material. As the mass accretion rate of the disk
onto the star determines its growth, we can calculate the stellar
characteristics by interpolating its radius, luminosity, and temperature over
the stellar mass from pre-calculated stellar evolution models. The density and
midplane temperature of the disk then allow us to model the interactions
between the disk and potential planets and determine their migration.
At the end of the collapse phase, when the disk reaches its maximum mass, it
pursues its viscous spreading, similarly to the evolution from a minimum mass
solar nebula (MMSN). In addition, we establish a timeline equivalence between
the MMSN and a "collapse-formed disk" that would be older by about 2 Myr.
We can save various types of planets from a fatal type-I inward migration: in
particular, planetary embryos can avoid falling on the star by becoming trapped
at the heat transition barriers and at most sublimation lines (except the
silicates one). One of the novelties concerns the possible trapping of putative
giant planets around a few astronomical units from the star around the end of
the infall. Moreover, trapped planets may still follow the traps outward during
the collapse phase and inward after it. Finally, this protoplanetary disk
formation model shows the early possibilities of trapping planetary embryos at
disk stages that are anterior by a few million years to the initial state of
the MMSN approximation. | astro-ph |
Origin of Radially Aligned Magnetic Fields in Young Supernova Remnants: It has been suggested by radio observations of polarized synchrotron
emissions that downstream magnetic field in some young supernova remnants are
oriented radially. We study magnetic field distribution of turbulent supernova
remnant driven by the Richtmyer-Meshkov instability -- in other words, the
effect of rippled shock -- by using three-dimensional magnetohydrodynamics
simulations. We find that the induced turbulence has radially biased
anisotropic velocity dispersion that leads to a selective amplification of the
radial component of the magnetic field. The Richtmyer-Meshkov instability is
induced by the interaction between the shock and upstream density fluctuations.
Future high-resolution polarization observations can distinguish the following
candidates responsible for the upstream density fluctuations: (i) inhomogeneity
caused by the cascade of large-scale turbulence in the ISM so-called the
big-power-law-in-the-sky, (ii) structures generated by the Drury instability in
the cosmic-ray modified shock, and (iii) fluctuations induced by the non-linear
feedback of the cosmic-ray streaming instability. | astro-ph |
Subaru HSC weak lensing of SDSS redMaPPer cluster satellite galaxies:
Empirical upper limit on orphan fractions: Weak gravitational lensing directly probes the matter distribution
surrounding satellite galaxies in galaxy clusters. We measure the weak lensing
signal induced on the shapes of background galaxies around SDSS redMaPPer
cluster satellite galaxies, which have their central galaxies assigned with a
probability $P_{\rm cen}>0.95$ in the redshift range, $0.1\leq z\leq 0.33$. We
use the galaxy shapes from the Subaru Hyper Suprime-Cam (HSC) survey for this
purpose. We bin satellite galaxies by their distance from the cluster centre
and compare it to the signal around a control sample of galaxies which do not
reside in clusters but have similar colours and magnitudes. We explore the
effect of environmental processes on the dark matter mass around satellites. We
see hints of a difference in the mass of the subhalo of the satellite compared
to the halo masses of galaxies in our control sample, especially in the
innermost cluster-centric radial bin ($0.1<r<0.3$ [$h^{-1}\rm Mpc$]). For the
first time, we put an upper limit on the prevalence of orphan galaxies which
have entirely lost their dark matter halos with cluster-centric distances with
the help of our measurements. However, these upper limits could be relaxed if
there is substantial contamination in the satellite galaxy sample. | astro-ph |
Time-resolved multiwavelength observations of the blazar VER J0521+211
from radio to gamma-ray energies: VER J0521+211 (RGB J0521.8+2112) is one of the brightest and most powerful
blazars detected in the TeV gamma-ray regime. It is located at a redshift of
z=0.108 and since its discovery in 2009, VER J0521+211 has exhibited an average
TeV flux exceeding 0.1 times that of the Crab Nebula, corresponding to an
isotropic luminosity of $3\times10^{44}$ erg s$^{-1}$. We present data from a
comprehensive multiwavelength campaign on this object extending between
November 2012 and February 2014, including single-dish radio observations,
optical photometry and polarimetry, UV, X-ray, GeV and TeV gamma-ray data
(VERITAS, MAGIC). Significant flux variability was observed at all wavelengths,
including a long-lasting high state at gamma-ray energies in Fall 2013.
Nightly-resolved spectra at X-ray and TeV energies are be presented, and
emission mechanisms explaining the observed flux and spectral variability are
discussed. | astro-ph |
Reconstruction of Supernova Gravitational Waves Waveforms: Comparing
Three Time-frequency Transform Methods: For supernovae gravitational wave signal analysis which intend to reconstruct
supernova gravitational waves waveforms, we compare the performance of
short-time Fourier transform (STFT), the synchroextracting transform (SET) and
multisynchrosqueezing transform (MSST) by a self-consistent time-frequency
analysis based pipeline. The simulated supernovae waveforms injected into white
noise are identified by a hierarchical clustering method in the time-frequency
map and then reconstructed by the inverse time-frequency transforms. We find
that in terms of signal reconstruction, the SET method performed the best,
especially much better than traditional STFT method in reconstructing signals
from data with white noise when valued the signal-to-noise ratio. While
concerning the quality of time-frequency figures, the MSST method and SET
method have less energy dispersion and were both better than STFT method. The
higher energy dispersion in time-frequency figure of STFT is time consuming in
the clustering process and reduce the accuracy of signal identification. Our
preliminary conclusion is that the SET method is the suitable method for the
supernovae gravitational wave signal analysis pipeline though more tests are
stilled needed. | astro-ph |
Massive Star Cluster Formation and Destruction in Luminous Infrared
Galaxies in GOALS II: An ACS/WFC3 Survey of Nearby LIRGs: We present the results of a Hubble Space Telescope WFC3 near-UV and ACS/WFC
optical study into the star cluster populations of 10 luminous and
ultra-luminous infrared galaxies (U/LIRGs) in the Great Observatories All-Sky
LIRG Survey (GOALS). Through integrated broadband photometry we have derived
ages, masses, and extinctions for a total of 1027 star clusters in galaxies
with $d_{L} <$ 110 Mpc in order to avoid issues related to cluster blending.
The measured cluster age distribution slope of $dN/d\tau \propto \tau^{-0.5 +/-
0.2}$ is steeper than what has been observed in lower-luminosity star-forming
galaxies. Further, differences in the slope of the observed cluster age
distribution between inner- ($dN/d\tau \propto \tau^{-1.07 +/- 0.12}$) and
outer-disk ($dN/d\tau \propto \tau^{-0.37 +/- 0.09}$) star clusters provides
evidence of mass-dependent cluster destruction in the central regions of LIRGs
driven primarily by the combined effect of strong tidal shocks and encounters
with massive GMCs. Excluding the nuclear ring surrounding the Seyfert 1 nucleus
in NGC 7469, the derived cluster mass function (CMF: $dN/dM \propto
M^{\alpha}$) has marginal evidence for a truncation in the power-law (PL) at
$M_{t} \sim 2$x$10^{6} M_{\odot}$ for our three most cluster-rich galaxies,
which are all classified as early-stage mergers. Finally, we find evidence of a
flattening of the CMF slope of $dN/dM \propto M^{-1.42 \pm 0.1}$ for clusters
in late-stage mergers relative to early-stage ($\alpha = -1.65 \pm 0.02$),
which we attribute to an increase in the formation of massive clusters over the
course of the interaction. | astro-ph |
Observations, Thermochemical Calculations, and Modeling of Exoplanetary
Atmospheres: This dissertation as a whole aims to provide means to better understand
hot-Jupiter planets through observing, performing thermochemical calculations,
and modeling their atmospheres. We used Spitzer multi-wavelength
secondary-eclipse observations and targets with high signal-to-noise ratios, as
their deep eclipses allow us to detect signatures of spectral features and
assess planetary atmospheric structure and composition with greater certainty.
Chapter 1 gives a short introduction. Chapter 2 presents the Spitzer
secondary-eclipse analysis and atmospheric characterization of WASP-14b.
WASP-14b is a highly irradiated, transiting hot Jupiter. By applying a Bayesian
approach in the atmospheric analysis, we found an absence of thermal inversion
contrary to theoretical predictions. Chapter 3 describes the infrared
observations of WASP-43b Spitzer secondary eclipses, data analysis, and
atmospheric characterization. WASP-43b is one of the closest-orbiting hot
Jupiters, orbiting one of the coolest stars with a hot Jupiter. The atmospheric
analysis ruled out a strong thermal inversion in its dayside atmosphere.
Chapter 4 presents an open-source Thermochemical Equilibrium Abundances (TEA)
code and its application to several hot Jupiters. TEA calculates the abundances
of gaseous species using the Gibbs free-energy minimization method within an
iterative Lagrangian optimization scheme. The code is written in Python and
available to the community via http://github.com/dzesmin/TEA. Chapter 5
presents my contributions to an open-source Bayesian Atmospheric Radiative
Transfer (BART) code, and its application to WASP-43b. BART characterizes
planetary atmospheres based on the observed spectroscopic information. It
initializes a planetary atmospheric model, performs radiative-transfer
calculations to produce models of planetary spectra, and using a statistical
module compares models with observations. | astro-ph |
The Attenuation of Gamma-Ray Emission in Strongly-Magnetized Pulsars: Gamma-rays from pulsars can be efficiently attenuated in their magnetospheres
via the mechanism of single-photon pair production and also the exotic QED
process of photon splitting, which become prolific in fields approaching the
quantum critical value of $B_{cr}=4.41\times 10^{13}$ Gauss. Recently we have
published results of our modelling of strongly-magnetized $\gamma$-ray pulsars,
which focused on the escape or attenuation of photons emitted near the pole at
the neutron star surface in dipole fields, in a Schwarzschild metric. We found
that pair production and splitting totally inhibit emission above around 10--30
MeV in PSR1509-58, whose surface field is inferred to be as high as
$0.7B_{cr}$. Our model pulsar spectra are consistent with the EGRET upper
limits for PSR1509-58 for a wide range of polar cap sizes. Here we review the
principal predictions of our attenuation analysis, and identify how its
powerful observational diagnostic capabilities relate to current and future
gamma-ray experiments. Diagnostics include the energy of the gamma-ray turnover
and the spectral polarization, which constrain the estimated polar cap size and
field strength, and can determine the relative strength of splitting and pair
creation. | astro-ph |
The DIVING$^{3D}$ Survey -- Deep IFS View of Nuclei of Galaxies -- I.
Definition and Sample Presentation: We present the Deep Integral Field Spectrograph View of Nuclei of Galaxies
(DIVING$^{3D}$) survey, a seeing-limited optical 3D spectroscopy study of the
central regions of all 170 galaxies in the Southern hemisphere with B < 12.0
and |b| > 15 degrees. Most of the observations were taken with the Integral
Field Unit of the Gemini Multi-Object Spectrograph, at the Gemini South
telescope, but some are also being taken with the Southern Astrophysical
Research Telescope (SOAR) Integral Field Spectrograph. The DIVING$^{3D}$ survey
was designed for the study of nuclear emission-line properties, circumnuclear
(within scales of hundreds of pc) emission-line properties, stellar and gas
kinematics and stellar archaeology. The data have a combination of high spatial
and spectral resolution not matched by previous surveys and will result in
significant contributions for studies related to, for example, the statistics
of low-luminosity active galactic nuclei, the ionization mechanisms in
Low-Ionization Nuclear Emission-Line Regions, the nature of transition objects,
among other topics. | astro-ph |
The Fluorescence Detector of the Pierre Auger Observatory - A
Calorimeter for UHECR: The Pierre Auger Observatory is a hybrid detector for ultrahigh energy cosmic
rays (UHECR) with energies above 10$^{18.5}$ eV. Currently the first part of
the Observatory nears completion in the southern hemisphere in Argentina. One
detection technique uses over 1600 water Cherenkov tanks at ground where
samples of secondary particles of extensive air showers (EAS) are detected. The
second technique is a calorimetric measurement of the energy deposited by EAS
in the atmosphere. Charged secondary particles of EAS lose part of their energy
in the atmosphere via ionization. The deposited energy is converted into
excitation of molecules of the air and afterwards partly emitted as
fluorescence light mainly from nitrogen in the wavelength region between 300
and 400 nm. This light is observed with 24 fluorescence telescopes in 4
stations placed at the boundary of the surface array. This setup provides a
combined measurement of the longitudinal shower development and the lateral
particle distribution at ground of the same event. Details on the fluorescence
technique and the necessary atmospheric monitoring will be presented, as well
as first physics results on UHECR. | astro-ph |
High Redshift Radio Galaxies: Laboratories for Massive Galaxy and
Cluster Formation in the early Universe: High redshift radio galaxies are among the largest, most luminous, most
massive, and most beautiful objects in the Universe. They are generally
identified from their radio emission, thought to be powered by accretion of
matter onto supermassive black holes in the nuclei of their host galaxies.
Observations show that they are energetic sources of radiation throughout most
of the electromagnetic spectrum, including relativistic plasma, gas and dust,
stars and the active galactic nuclei (AGN). 1 HzRGs are inferred to be
extremely massive, including old stars (up to $\sim$ 10$^{12}$ M$_{\odot}$),
hot gas (up to $\sim$ 10$^{12}$ M$_{\odot}$) and molecular gas (up to $\sim$
10$^{11}$ M$_{\odot}$).Because they are highly luminous and (unlike quasars)
spatially resolvable from the ground, most components of HzRGs provide
important diagnostic information about the spatial distributions of processes
within HzRGs and their environment. The fact that the different constituents
are present in the same objects and that the {\bf {\it interrelationships and
interactions between them}} can be studied make distant radio galaxies unique
laboratories for probing massive galaxy and cluster formation in the early
Universe. | astro-ph |
Fractional amplitude of kilohertz quasi-periodic oscillation from 4U
1728-34: evidence of decline at higher energies: A kilohertz quasi-periodic oscillation (kHz QPO) is an observationally robust
high-frequency timing feature detected from neutron star low-mass X-ray
binaries (LMXBs). This feature can be very useful to probe the superdense core
matter of neutron stars, and the strong gravity regime. However, although many
models exist in the literature, the physical origin of kHz QPO is not known,
and hence this feature cannot be used as a tool yet. The energy dependence of
kHz QPO fractional rms amplitude is an important piece of the jigsaw puzzle to
understand the physical origin of this timing feature. It is known that the
fractional rms amplitude increases with energy at lower energies. At higher
energies, the amplitude is usually believed to saturate, although this is not
established. We combine tens of lower kHz QPOs from a neutron star LMXB 4U
1728-34 in order to improve the signal-to-noise-ratio. Consequently, we, for
the first time to the best of our knowledge, find a significant and systematic
decrease of the fractional rms amplitude with energy at higher photon energies.
Assuming an energy spectrum model, blackbody+powerlaw, we explore if the
sinusoidal variation of a single spectral parameter can reproduce the above
mentioned fractional rms amplitude behavior. Our analysis suggests that the
oscillation of any single blackbody parameter is favored over the oscillation
of any single powerlaw parameter, in order to explain the measured amplitude
behavior. We also find that the quality factor of a lower kHz QPO does not
plausibly depend on photon energy. | astro-ph |
Variations in the slope of the resolved star-forming main sequence: a
tool for constraining the mass of star-forming regions: The correlation between galaxies' integrated stellar masses and star
formation rates (the `star formation main sequence'; SFMS) is a
well-established scaling relation. Recently, surveys have found a relationship
between the star formation rate and stellar mass surface densities on kpc and
sub-kpc scales (the `resolved SFMS'; rSFMS). In this work, we demonstrate that
the rSFMS emerges naturally in FIRE-2 zoom-in simulations of Milky Way-mass
galaxies. We make SFR and stellar mass maps of the simulated galaxies at a
variety of spatial resolutions and star formation averaging time-scales and fit
the rSFMS using multiple methods from the literature. While the absolute value
of the SFMS slope depends on the fitting method, the slope is steeper for
longer star formation time-scales and lower spatial resolutions regardless of
the fitting method employed. We present a toy model that quantitatively
captures the dependence of the simulated galaxies' rSFMS slope on spatial
resolution and use it to illustrate how this dependence can be used to
constrain the characteristic mass of star-forming clumps. | astro-ph |
The Mopra Southern Galactic Plane CO Survey - Data Release 3: We present observations of fifty square degrees of the Mopra carbon monoxide
(CO) survey of the Southern Galactic Plane, covering Galactic longitudes $l =
300$-$350^\circ$ and latitudes $|b| \le 0.5^\circ$. These data have been taken
at 0.6 arcminute spatial resolution and 0.1 km/s spectral resolution, providing
an unprecedented view of the molecular clouds and gas of the Southern Galactic
Plane in the 109-115 GHz $J = 1$-0 transitions of $^{12}$CO, $^{13}$CO,
C$^{18}$O and C$^{17}$O. We present a series of velocity-integrated maps,
spectra and position-velocity plots that illustrate Galactic arm structures and
trace masses on the order of $\sim$10$^{6}$ M$_{\odot}$ per square degree; and
include a preliminary catalogue of C$^{18}$O clumps located between
$l=330$-$340^\circ$. Together with information about the noise statistics of
the survey these data can be retrieved from the Mopra CO website, the PASA data
store and the Harvard Dataverse (doi:10.7910/DVN/LH3BDN ). | astro-ph |
Radio Properties of z>4 Optically-Selected Quasars: We report on two programs to address differential evolution between the
radio-loud and radio-quiet quasar populations at high (z>4) redshift. Both
programs entail studying the radio properties of optically-selected quasars.
First, we have observed 32 optically-selected, high-redshift (z>4) quasars with
the VLA at 6 cm (5 GHz). These sources comprise a statistically complete and
well-understood sample. We detect four quasars above our 3-sigma limit of ~0.15
mJy, which is sufficiently sensitive to detect all radio-loud quasars at the
probed redshift range. Second, we have correlated 134 z>4 quasars, comprising
all such sources that we are aware of as of mid-1999, with FIRST and NVSS.
These two recent 1.4 GHz VLA sky surveys reach 3-sigma limits of approximately
0.6 mJy and 1.4 mJy respectively. We identify a total of 15 z>4 quasars, of
which six were not previously known to be radio-loud. The depth of these
surveys does not reach the radio-loud/radio-quiet demarcation luminosity
density (L(1.4 GHz) = 10^32.5 h(50)^(-2) ergs/s/Hz) at the redshift range
considered; this correlation therefore only provides a lower limit to the
radio-loud fraction of quasars at high-redshift. The two programs together
identify eight new radio-loud quasars at z>4, a significant increase over the
seven currently in the published literature. We find no evidence for radio-loud
fraction depending on optical luminosity for -25 > M_B > -28 at z~2, or for
-26>M_B>-28 at z>4. Our results also show no evolution in the radio-loud
fraction between z~2 and z>4 (-26>M_B>-28). | astro-ph |
Nuclear reactions in hot stellar matter and nuclear surface deformation: Cross-sections for capture reactions of charged particles in hot stellar
matter turn out be increased by the quadrupole surface oscillations, if the
corresponding phonon energies are of the order of the star temperature. The
increase is studied in a model that combines barrier distribution induced by
surface oscillations and tunneling. The capture of charged particles by nuclei
with well-deformed ground-state is enhanced in stellar matter. It is found that
the influence of quadrupole surface deformation on the nuclear reactions in
stars grows, when mass and proton numbers in colliding nuclei increase. | astro-ph |
Recent developments in Laue lens manufacturing and their impact on
imaging performance: We report on recent progress in the development of Laue lenses for
applications in hard X/soft gamma-ray astronomy. Here we focus on the
realization of a sector of such a lens made of 11 bent Germanium crystals and
describe the technological challenges involved in their positioning and
alignment with adhesive-based bonding techniques. The accurate alignment and
the uniformity of the curvature of the crystals are critical for achieving
optimal X-ray focusing capabilities. We have assessed how the errors of
misalignment with respect to the main orientation angles of the crystals affect
the point spread function (PSF) of the image diffracted by a single sector. We
have corroborated these results with simulations carried out with our physical
model of the lens, based on a Monte Carlo ray-tracing technique, adopting the
geometrical configuration of the Laue sector, the observed assembly accuracy
and the measured curvatures of the crystals. An extrapolation of the
performances achieved on a single sector to an entire Laue lens based on this
model has shown that a PSF with half-power-diameter of 4.8 arcmin can be
achieved with current technology. This has the potential to lead to a
significant improvement in sensitivity of spectroscopic and polarimetric
observations in the 50-600 keV band | astro-ph |
Neutrino-heated winds from millisecond proto-magnetars as sources of the
weak r-process: We explore heavy element nucleosynthesis in neutrino-driven winds from
rapidly-rotating, strongly magnetized proto-neutron stars for which the
magnetic dipole is aligned with the rotation axis, and the field is assumed to
be a static force-free configuration. We process the proto-magnetar wind
trajectories calculated by Vlasov et al 2014 through the r-process nuclear
reaction network SkyNet using contemporary models for the evolution of the wind
electron fraction during the proto-neutron star cooling phase. Although we do
not find a successful second or third peak r-process for any rotation period P,
we show that proto-magnetars with P around 1-5 ms produce heavy element
abundance distributions that extend to higher nuclear mass number than from
otherwise equivalent spherical winds (with the mass fractions of some elements
enhanced by factors of 100-1000). The heaviest elements are synthesized by
outflows emerging along flux tubes which graze the closed zone and pass near
the equatorial plane outside the light cylinder. Due to dependence of the
nucleosynthesis pattern on the magnetic field strength and rotation rate of the
proto-neutron star, natural variations in these quantities between core
collapse events could contribute to the observed diversity of the abundances of
weak r-process nuclei in metal-poor stars. Further diversity, including
possibly even a successful third-peak r-process, could be achieved for
misaligned rotators with non-zero magnetic inclination with respect to the
rotation axis. If proto-magnetars are central engines for GRBs, their
relativistic jets should contain a high mass fraction of heavy nuclei of
characteristic average mass number A of order 100, providing a possible source
for ultra-high energy cosmic rays comprised of heavy nuclei with an energy
spectrum that extends beyond the nominal GZK cut-off for protons or iron
nuclei. | astro-ph |
IGR J17329-2731: The birth of a symbiotic X-ray binary: We report on the results of the multiwavelength campaign carried out after
the discovery of the INTEGRAL transient IGR J17329-2731. The optical data
collected with the SOAR telescope allowed us to identify the donor star in this
system as a late M giant at a distance of 2.7$^{+3.4}_{-1.2}$ kpc. The data
collected quasi-simultaneously with XMM-Newton and NuSTAR showed the presence
of a modulation with a period of 6680$\pm$3 s in the X-ray light curves of the
source. This unveils that the compact object hosted in this system is a slowly
rotating neutron star. The broadband X-ray spectrum showed the presence of a
strong absorption ($\gg$10$^{23}$ cm$^{-2}$) and prominent emission lines at
6.4 keV, and 7.1 keV. These features are usually found in wind-fed systems, in
which the emission lines result from the fluorescence of the X-rays from the
accreting compact object on the surrounding stellar wind. The presence of a
strong absorption line around $\sim$21 keV in the NuSTAR spectrum suggests a
cyclotron origin, thus allowing us to estimate the neutron star magnetic field
as $\sim$2.4$\times$10$^{12}$ G. All evidence thus suggests IGR J17329-2731 is
a symbiotic X-ray binary. As no X-ray emission was ever observed from the
location of IGR J17329-2731 by INTEGRAL (or other X-ray facilities) during the
past 15 yr in orbit and considering that symbiotic X-ray binaries are known to
be variable but persistent X-ray sources, we concluded that INTEGRAL caught the
first detectable X-ray emission from IGR J17329-2731 when the source shined as
a symbiotic X-ray binary. The Swift/XRT monitoring performed up to $\sim$3
months after the discovery of the source, showed that it maintained a
relatively stable X-ray flux and spectral properties. | astro-ph |
Digging for the Truth: Photon Archeology with GLAST: Stecker, Malkan and Scully, have shown how ongoing deep surveys of galaxy
luminosity functions, spectral energy distributions and backwards evolution
models of star formation rates can be used to calculate the past history of
intergalactic photon densities for energies from 0.03 eV to the Lyman limit at
13.6 eV and for redshifts out to 6 (called here the intergalactic background
light or IBL). From these calculations of the IBL at various redshifts, they
predict the present and past optical depth of the universe to high energy
gamma-rays owing to interactions with photons of the IBL and the 2.7 K CMB. We
discuss here how this proceedure can be reversed by looking for sharp cutoffs
in the spectra of extragalactic gamma-ray sources such as blazars at high
redshifts in the multi-GeV energy range with GLAST. By determining the cutoff
energies of sources with known redshifts, we can refine our determination of
the IBL photon densities in the past, i.e., the "archeo-IBL", and therefore get
a better measure of the past history of the total star formation rate.
Conversely, observations of sharp high energy cutoffs in the gamma-ray spectra
of sources at unknown redshifts can be used instead of spectral lines to give a
measure of their redshifts. | astro-ph |
Seasonal thaws under mid-to-low pressure atmospheres on Early Mars: Despite decades of scientific research on the subject, the climate of the
first 1.5 Gyr of Mars history has not been fully understood yet. Especially
challenging is the need to reconcile the presence of liquid water for extended
periods of time on the martian surface with the comparatively low insolation
received by the planet, a problem which is known as the Faint Young Sun (FYS)
Paradox. In this paper we use ESTM, a latitudinal energy balance model with
enhanced prescriptions for meridional heat diffusion, and the radiative
transfer code EOS to investigate how seasonal variations of temperature can
give rise to local conditions which are conductive to liquid water runoffs. We
include the effects of the martian dichotomy, a northern ocean with either 150
or 550 m of Global Equivalent Layer (GEL) and simplified CO$_2$ or H$_2$O
clouds. We find that 1.3-to-2.0 bar CO$_2$-dominated atmospheres can produce
seasonal thaws due to inefficient heat redistribution, provided that the
eccentricity and the obliquity of the planet are sufficiently different from
zero. We also studied the impact of different values for the argument of
perihelion. When local favorable conditions exist, they nearly always persist
for $>15\%$ of the martian year. These results are obtained without the need
for additional greenhouse gases (e.g. H$_2$, CH$_4$) or transient
heat-injecting phenomena (e.g. asteroid impacts, volcanic eruptions). Moderate
amounts (0.1 to 1\%) of CH$_4$ significantly widens the parameter space region
in which seasonal thaws are possible. | astro-ph |
The Masses of Nuclear Black Holes in Luminous Elliptical Galaxies and
Implications for the Space Density of the Most Massive Black Holes: Black hole masses predicted from the Mbh-sigma relationship conflict with
those predicted from the Mbh-L relationship for the most luminous galaxies,
such as brightest cluster galaxies (BCGs). This is because stellar velocity
dispersion, sigma, increases only weakly with L for BCGs and other giant
ellipticals. The Mbh-L relationship predicts that the most luminous BCGs may
have Mbh approaching 10^{10}M_sol, while the M-sigma relationship always
predicts Mbh<3X10^9M_sol. We argue that the Mbh-L relationship is a plausible
or even preferred description for BCGs and other galaxies of similar
luminosity. If cores in central stellar density are formed by binary BHs, then
the inner-core cusp radius, r_gamma, may be an independent witness of Mbh.
Using structural parameters derived from a large sample of early-type galaxies
observed by HST, we argue that L is superior to sigma as an indicator of
r_gamma in luminous galaxies. The observed r_gamma-Mbh relationship for 11 core
galaxies with measured Mbh appears to be consistent with the Mbh-L relationship
for BCGs. BCGs have large cores appropriate for their large luminosities that
may be difficult to generate with the modest BH masses inferred from the
Mbh-sigma relationship. Mbh~L may be expected to hold for BCGs, if they were
formed in dissipationless mergers, which should preserve ratio of BH to stellar
mass. This picture appears to be consistent with the slow increase in sigma
with L and the more rapid increase in effective radii with L seen in BCGs. If
BCGs have large BHs commensurate with their luminosities, then the local BH
mass function for Mbh>3X10^9M_sol may be nearly an order of magnitude richer
than that inferred from the Mbh-sigma relationship. The volume density of QSOs
at earlier epochs may favor the predictions from the Mbh-L relationship. | astro-ph |
Correlated timing and spectral behavior of 4U 1705-44: We follow the timing properties of the neutron star low-mass X-ray binary
system 4U 1705-44 in different spectral states, as monitored by the Rossi X-ray
Timing Explorer over about a month. We fit the power density spectra using
multiple Lorentzians. We show that the characteristic frequencies of these
Lorentzians, when properly identified, fit within the correlations previously
reported. The time evolution of these frequencies and their relation with the
parameters of the energy spectra reported in Barret & Olive (2002) are used to
constrain the accretion geometry changes. The spectral data were fitted by the
sum of a blackbody and a Comptonized component and were interpreted in the
framework of a truncated accretion disk geometry, with a varying truncation
radius. If one assumes that the characteristic frequencies of the Lorentzians
are some measure of this truncation radius, as in most theoretical models, then
the timing data presented here strengthen the above interpretation. The soft to
hard and hard to soft transitions are clearly associated with the disk receding
from and approaching the neutron star respectively. During the transitions,
correlations are found between the Lorentzian frequencies and the flux and
temperature of the blackbody, which is thus likely to be coming from the disk.
On the other hand, in the hard state, the characteristic Lorentzians
frequencies which are at the lowest, remained nearly constant despite
significant evolution of the spectra parameters. The disk no longer contributes
to the X-ray emission, and the blackbody is now likely to be emitted by the
neutron star surface which is providing the seed photons for the
Comptonization. | astro-ph |
Prospects for annihilating dark matter from M31 and M33 observations
with the Cherenkov Telescope Array: M31 and M33 are the closest spiral galaxies and the largest members (together
with the Milky Way) of the Local group, which makes them interesting targets
for indirect dark matter searches. In this paper, we present studies of the
expected sensitivity of the Cherenkov Telescope Array (CTA) to an annihilation
signal from weakly interacting massive particles from M31 and M33. We show that
a 100 h long observation campaign will allow CTA to probe annihilation
cross-sections up to $\langle\sigma\upsilon\rangle\approx 5\cdot10^{-25}$
cm$^{3}$s$^{-1}$ for the $\tau^{+}\tau^{-}$ annihilation channel (for M31, at a
DM mass of 0.3 TeV), improving the current limits derived by HAWC by up to an
order of magnitude. We present an estimate of the expected CTA sensitivity, by
also taking into account the contributions of the astrophysical background and
other possible sources of systematic uncertainty. We also show that CTA might
be able to detect the extended emission from the bulge of M31, detected at
lower energies by the Fermi/LAT. | astro-ph |
The Ratio of Helium- to Hydrogen-Atmosphere White Dwarfs: Direct
Evidence for Convective Mixing: We determine the ratio of helium- to hydrogen-atmosphere white dwarf stars as
a function of effective temperature from a model atmosphere analysis of the
infrared photometric data from the Two Micron All Sky Survey combined with
available visual magnitudes. Our study surpasses any previous analysis of this
kind both in terms of the accuracy of the Teff determinations as well as the
size of the sample. We observe that the ratio of helium- to hydrogen-atmosphere
white dwarfs increases gradually from a constant value of ~0.25 between Teff =
15,000 K and 10,000 K to a value twice as large in the range 10,000 > Teff >
8000 K, suggesting that convective mixing, which occurs when the bottom of the
hydrogen convection zone reaches the underlying convective helium envelope, is
responsible for this gradual transition. The comparison of our results with an
approximate model used to describe the outcome of this convective mixing
process implies hydrogen mass layers in the range log M_H/M_tot = -10 to -8 for
about 15% of the DA stars that survived the DA to DB transition near Teff ~
30,000 K, the remainder having presumably more massive layers above log
M_H/M_tot ~ -6. | astro-ph |
Revisiting the Long-Period Transiting Planets from Kepler: Currently, we have only limited means to probe the presence of planets at
large orbital separations. Foreman-Mackey et al. searched for long-period
transiting planets in the Kepler light curves using an automated pipeline.
Here, we apply their pipeline, with minor modifications, to a larger sample and
use updated stellar parameters from Gaia DR2. The latter boosts the stellar
radii for most of the planet candidates found by FM16, invalidating a number of
them as false positives. We identify 15 candidates, including two new ones. All
have sizes from 0.3 to 1 $R_{\rm J}$, and all but two have periods from 2 to 10
yr. We report two main findings based on this sample. First, the planet
occurrence rate for the above size and period ranges is $0.70^{+0.40}_{-0.20}$
planets per Sun-like star, with the frequency of cold Jupiters agreeing with
that from radial velocity surveys. Planet occurrence rises with decreasing
planet size, roughly describable as $dN/d\log R \propto R^{\alpha}$ with
$\alpha = -1.6^{+1.0}_{-0.9}$, i.e., Neptune-sized planets are some four times
more common than Jupiter-sized ones. Second, five out of our 15 candidates
orbit stars with known transiting planets at shorter periods, including one
with five inner planets. We interpret this high incidence rate to mean: (1)
almost all our candidates should be genuine; (2) across a large orbital range
(from $\sim 0.05$ to a few astronomical units), mutual inclinations in these
systems are at most a few degrees; and (3) large outer planets exist almost
exclusively in systems with small inner planets. | astro-ph |
VLT-SINFONI integral field spectroscopy of low-z luminous and
ultraluminous infrared galaxies I. Atlas of the 2D gas structure: We present an atlas of a sample of local (U)LIRGs covering the luminosity
range log(L_IR/L_sun)=11.1-12.4. The atlas is based on near-infrared H and
K-band VLT-SINFONI IFS, and presents the ionised, partially ionised, and warm
molecular gas 2D flux distributions and kinematics over a FoV of 3x3 kpc
(LIRGs) and 12x12kpc (ULIRGs) and with average linear resolutions of 0.2kpc and
0.9kpc, respectively. The different phases of the gas show a wide morphological
variety with the nucleus as the brightest Br_g source for 33% of the LIRGs and
71% of the ULIRGs, whereas all the (U)LIRGs have their maximum H_2 emission in
their nuclear regions. In LIRGs, the ionised gas distribution is dominated by
the emission from the star-forming rings or giant HII regions in the spiral
arms. The Br_g and [FeII] line at 1.644 micron trace the same structures,
although the emission peaks at different locations in some of the objects, and
the [FeII] seems to be more extended and diffuse. The ULIRG subsample contains
mainly pre-coalescence interacting systems. Although the peaks of the molecular
gas emission and the continuum coincide in 71% of the ULIRGs, regions with
intense Pa_a (Br_g) emission tracing luminous star-forming regions located at
distances of 2-4kpc away from the nucleus are also detected, usually associated
with secondary nuclei or tidal tails. The gas kinematics in LIRGs are primarily
due to rotational motions around the centre of the galaxy, although local
deviations associated with radial flows and/or regions of higher velocity
dispersions are present. The ionised and molecular gas share the same
kinematics to first order, showing slight differences in the velocity
amplitudes in some cases, whereas the average velocity dispersions are
compatible within uncertainties. As expected, the kinematics of the ULIRG
subsample is more complex, owing to the interacting nature of the objects of
the sample. | astro-ph |
Clusters of Galaxies as Standard Candles for Global Observational
Cosmology: As the largest gravitationally collapsed objects, and as objects with a
relatively low space density, clusters of galaxies offer one of the best sets
of standard candles for trying to measure basic cosmological parameters such as
the injectivity diameter 2r_{inj} (the shortest distance between two
topologically lensed images of any object, e.g. cluster) and the out-diameter
2r_{+} (the maximum `size' of the Universe). Present constraints indicate that
either of these may be smaller or larger than the horizon diameter. | astro-ph |
Large Observatory for x-ray Timing (LOFT-P): A Probe-classs Mission
Concept Study: LOFT-P is a concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing
mission, based on the LOFT concept originally proposed to ESAs M3 and M4 calls.
LOFT-P requires very large collecting area (>6 m^2, >10x RXTE), high time
resolution, good spectral resolution, broad-band spectral coverage (2-30 keV),
highly flexible scheduling, and an ability to detect and respond promptly to
time-critical targets of opportunity. It addresses science questions such as:
What is the equation of state of ultra dense matter? What are the effects of
strong gravity on matter spiraling into black holes? It would be optimized for
sub-millisecond timing to study phenomena at the natural timescales of neutron
star surfaces and black hole event horizons and to measure mass and spin of
black holes. These measurements are synergistic to imaging and high-resolution
spectroscopy instruments, addressing much smaller distance scales than are
possible without very long baseline X-ray interferometry, and using
complementary techniques to address the geometry and dynamics of emission
regions. A sky monitor (2-50 keV) acts as a trigger for pointed observations,
providing high duty cycle, high time resolution monitoring of the X-ray sky
with ~20 times the sensitivity of the RXTE All-Sky Monitor, enabling
multi-wavelength and multi-messenger studies. A probe-class mission concept
would employ lightweight collimator technology and large-area solid-state
detectors, technologies which have been recently greatly advanced during the
ESA M3 study. Given the large community interested in LOFT (>800 supporters,
the scientific productivity of this mission is expected to be very high,
similar to or greater than RXTE (~2000 refereed publications). We describe the
results of a study, recently completed by the MSFC Advanced Concepts Office,
that demonstrates that LOFT-P is feasible within a NASA probe-class mission
budget. | astro-ph |
The relationship between Class I and Class II methanol masers at high
angular resolution: We have used the Australia Telescope Compact Array (ATCA) to make the first
high resolution observations of a large sample of class~I methanol masers in
the 95-GHz ($8_0$--$7_1$A$^+$) transition. The target sources consist of a
statistically complete sample of 6.7-GHz class~II methanol masers with an
associated 95-GHz class~I methanol maser, enabling a detailed study of the
relationship between the two methanol maser classes at arcsecond angular
resolution. These sources have been previously observed at high resolution in
the 36- and 44-GHz transitions, allowing comparison between all three class~I
maser transitions. In total, 172 95-GHz maser components were detected across
the 32 target sources. We find that at high resolution, when considering
matched maser components, a 3:1 flux density ratio is observed between the 95-
and 44-GHz components, consistent with a number of previous lower angular
resolution studies. The 95-GHz maser components appear to be preferentially
located closer to the driving sources and this may indicate that this
transition is more strongly inverted nearby to background continuum sources. We
do not observe an elevated association rate between 95-GHz maser emission and
more evolved sources, as indicated by the presence of 12.2-GHz class~II masers.
We find that in the majority of cases where both class~I and class~II methanol
emission is observed, some component of the class~I emission is associated with
a likely outflow candidate. | astro-ph |
NICER observations of the Crab pulsar glitch of 2017 November: Context: The Crab pulsar underwent its largest timing glitch on 2017 Nov 8.
The event was discovered at radio wavelengths, and was followed at soft X-ray
energies by observatories, such as XPNAV and NICER. aims: This work aims to
compare the glitch behavior at the two wavelengths mentioned above. Preliminary
work in this regard has been done by the X-ray satellite XPNAV. NICER with its
far superior sensitivity is expected to reveal much more detailed behavior.
methods: NICER has accumulated more than $301$ kilo seconds of data on the Crab
pulsar, equivalent to more than $3.3$ billion soft X-ray photons. These data
were first processed using the standard NICER analysis pipeline. Then the
arrival times of the X-ray photons were referred to the solar system's
barycenter. Then specific analysis was done to study the specific behavior
outlined in the following sections, while taking dead time into account.
results: The variation of the rotation frequency of the Crab pulsar and its
time derivative during the glitch is almost exactly similar at the radio and
X-ray energies. The following properties of the Crab pulsar remain essentially
constant before and after the glitch: the total X-ray flux; the flux, widths,
and peaks of the two components of its integrated profile; and the soft X-ray
spectrum. There is no evidence for giant pulses at X-ray energies. However, the
timing noise of the Crab pulsar shows quasi sinusoidal variation before the
glitch, with increasing amplitude, which is absent after the glitch.
conclusions: Even the strongest glitch in the Crab pulsar appears not to affect
all but one of the properties mentioned above, at either frequency. The fact
that the timing noise appears to change due to the glitch is an important clue
to unravel as this is still an unexplained phenomenon. | astro-ph |
Dark matter in Draco and the Local Group: Implications for direct
detection experiments: We use a cosmological simulation of the Local Group to make quantitative and
speculative predictions for direct detection experiments. Cold dark matter
(CDM) halos form via a complex series of mergers, accretion events and violent
relaxation which precludes the formation of significant caustic features
predicted by axially symmetric collapse. The halo density profiles are combined
with observational constraints on the galactic mass distribution to constrain
the local density of cold dark matter to lie in the range 0.18 <~
rho_CDM(R_solar)/GeV cm^-3 <~ 0.30. In velocity space, coherent streams of dark
matter from tidally disrupted halos fill the halo and provide a tracer of the
merging hierarchy. The particle velocities within triaxial CDM halos cannot be
approximated by a simple Maxwellian distribution and is radially biased at the
solar position. The detailed phase space structure within the solar system will
depend on the early merger history of the progenitor halos and the importance
of major mergers over accretion dominated growth. We follow the formation of a
``Draco'' sized dSph halo of mass 10^8M_solar with several million particles
and high force accuracy. Its internal structure and substructure resembles that
of galactic or cluster mass halos: the density profile has a singular central
cusp and it contains thousands of sub-halos orbiting within its virial radius
demonstrating a self-similar nature to collisionless dark matter
sub-clustering. The singular cores of substructure halos always survive
complete tidal disruption although mass loss is continuous and rapid.
Extrapolating wildly to earth mass halos with velocity dispersion of 1 m s^-1
(roughly equal to the free streaming scale for neutralinos) we find that most
of the dark matter may remain attached to bound subhalos. (Abridged) | astro-ph |
A Census from JWST of Extreme Emission Line Galaxies Spanning the Epoch
of Reionization in CEERS: We present a sample of 1165 extreme emission-line galaxies (EELGs) at 4<z<9
selected using James Webb Space Telescope (JWST) NIRCam photometry in the
Cosmic Evolution Early Release Science (CEERS) program. We use a simple method
to photometrically identify EELGs with Hb + [OIII] (combined) or Ha emission of
observed-frame equivalent width EW >5000 AA. JWST/NIRSpec spectroscopic
observations of a subset (34) of the photometrically selected EELGs validate
our selection method: all spectroscopically observed EELGs confirm our
photometric identification of extreme emission, including some cases where the
SED-derived photometric redshifts are incorrect. We find that the medium-band
F410M filter in CEERS is particularly efficient at identifying EELGs, both in
terms of including emission lines in the filter and in correctly identifying
the continuum between Hb + [OIII] and Ha in the neighboring broad-band filters.
We present examples of EELGs that could be incorrectly classified at ultra-high
redshift (z>12) as a result of extreme Hb + [OIII] emission blended across the
reddest photometric filters. We compare the EELGs to the broader (sub-extreme)
galaxy population in the same redshift range and find that they are consistent
with being the bluer, high equivalent width tail of a broader population of
emission-line galaxies. The highest-EW EELGs tend to have more compact
emission-line sizes than continuum sizes, suggesting that active galactic
nuclei are responsible for at least some of the most extreme EELGs.
Photometrically inferred emission-line ratios are consistent with ISM
conditions with high ionization and moderately low metallicity, consistent with
previous spectroscopic studies. | astro-ph |
Time-resolved spectroscopy of the peculiar Halpha variable Be star HD
76534: We present time-resolved spectroscopy of the Be star HD 76534, which was
observed to have an Halpha outburst in 1995, when the line went from
photospheric absorption to emission at a level of more than two times the
continuum within 2.5 hours. To investigate the short-term behaviour of the
spectrum of HD 76534 we have obtained 30 spectra within two hours real-time and
searched for variations in the spectrum. Within the levels of statistical
significance, no variability was found. Rather than periodic on short time
scales, the Halpha behaviour seems to be commonly episodic on longer (>1 year)
time scales, as an assessment of the existing data on the Halpha line and the
Hipparcos photometry suggests. HD 76534 underwent only 1 photometric outburst
in the 3 year span that the star was monitored by the Hipparcos satellite. | astro-ph |
Intrinsic errors of the central galactic mass derived from rotation
curves under the influence of a weak non-axisymmetric potential: Rotation curves are often used to estimate the mass distribution of spiral
galaxies, assuming circular rotation of disks. However, non-circular motions
caused by a non-axisymmetric gravitational potential, such as a stellar bar,
may disturb the velocity field, resulting in errors in mass estimation,
especially in the central regions of galaxies, because the line-of-sight
velocity depends on the viewing angles in a non-axisymmetric flow. Observing
rotation curves of edge-on galaxies in time-dependent numerical simulations
from different viewing angles, we obtain errors in the estimation of galactic
mass from the rotation curves. In the most extreme case, the ellipticity of gas
orbits is as high as 0.8 in the central regions, even if the bar potential is
weak. When rotation curves are defined as the highest velocity envelope of
position-velocity diagrams, the mass estimated from the rotation curves is
larger than the true mass by a factor of five for 15% of the viewing angles,
and the ratio between the apparent mass and true mass is less than six for any
viewing angle. The overestimation in mass occurs more frequently than the
underestimation. | astro-ph |
3D Relativistic Magnetohydrodynamic Simulations of Magnetized
Spine-Sheath Relativistic Jets: Numerical simulations of weakly magnetized and strongly magnetized
relativistic jets embedded in a weakly magnetized and strongly magnetized
stationary or weakly relativistic (v = c/2) sheath have been performed. A
magnetic field parallel to the flow is used in these simulations performed by
the new GRMHD numerical code RAISHIN used in its RMHD configuration. In the
numerical simulations the Lorentz factor $\gamma = 2.5$ jet is precessed to
break the initial equilibrium configuration. In the simulations sound speeds
are $\lesssim c/\sqrt 3$ in the weakly magnetized simulations and $\lesssim
0.3c$ in the strongly magnetized simulations. The Alfven wave speed is
$\lesssim 0.07c$ in the weakly magnetized simulations and $\lesssim 0.56c$ in
the strongly magnetized simulations. The results of the numerical simulations
are compared to theoretical predictions from a normal mode analysis of the
linearized relativistic magnetohydrodynamic (RMHD) equations capable of
describing a uniform axially magnetized cylindrical relativistic jet embedded
in a uniform axially magnetized relativistically moving sheath. The theoretical
dispersion relation allows investigation of effects associated with maximum
possible sound speeds, Alfven wave speeds near light speed and relativistic
sheath speeds. The prediction of increased stability of the weakly magnetized
system resulting from c/2 sheath speeds and the stabilization of the strongly
magnetized system resulting from c/2 sheath speeds is verified by the numerical
simulation results. | astro-ph |
Extending the view of ArH+ chemistry in diffuse clouds: One of the surprises of the Herschel mission was the detection of ArH+
towards the Crab Nebula in emission and in absorption towards strong Galactic
background sources. Although these detections were limited to the first
quadrant of the Galaxy, the existing data suggest that ArH+ ubiquitously and
exclusively probes the diffuse atomic regions of the ISM. In this study, we
extend the coverage of ArH+ to other parts of the Galaxy with new observations
of its J = 1-0 transition along seven Galactic sight lines towards bright
sub-mm continuum sources. We aim to benchmark its efficiency as a tracer of
purely atomic gas by evaluating its correlation (or lack there of) with other
well-known atomic and molecular gas tracers. The observations of ArH+ near
617.5 GHz were made feasible with the new, sensitive SEPIA660 receiver on the
APEX 12 m telescope. The two sidebands of this receiver allowed us to observe
p-H2O+ transitions of at 607.227 GHz simultaneously with the ArH+ line. By
analysing the steady state chemistry of OH+ and o-H2O+, we derive on average a
cosmic-ray ionisation rate (CRIR), of 2.3e-16 s^-1 towards the sight lines
studied in this work. Using the derived values of the CRIR and the observed
ArH+ abundances we constrain the molecular fraction of the gas traced by ArH+
to lie below 2e-2 with a median value of 8.8e-4. Combined, our observations of
ArH+, OH+, H2O+, and CH probe different regimes of the ISM, from diffuse atomic
to diffuse and translucent molecular clouds. Over Galactic scales, we see that
the distribution of N(ArH+) is associated with that of N(H), particularly in
the inner Galaxy with potentially even contributions from the warm neutral
medium phase of atomic gas at larger galactocentric distances. We derive an
average o/p-ratio for H2O+ of 2.1, which corresponds to a nuclear spin
temperature of 41 K, consistent with the typical gas temperatures of diffuse
clouds. | astro-ph |
Rotation curves of galaxies in GR: It has been suggested that the observed flat rotation curves of disk galaxies
can be a peculiar effect of General Relativity (GR) rather than evidence for
the presence of dark matter (DM) halos in Newtonian gravity. In Ciotti (2022)
the problem has been quantitatively addressed by using the well known
weak-field, low-velocity gravitomagnetic limit of GR, for realistic exponential
baryonic (stellar) disks. As expected, the resulting GR and Newtonian rotation
curves are indistinguishable, with GR corrections at all radii of the order of
$v^2/c^2\approx 10^{-6}$. Here we list some astrophysical problems that must be
faced if the existence of DM halos is attributed to a misinterpretation of weak
field effects of GR. | astro-ph |
Hybrid magnetized stars within the Field Correlator Method: We present preliminary results of the study of intense magnetic fields
effects on hybrid stars. For the description of the hadronic phase, we use the
relativistic mean field approximation. For the quark matter phase, we employ
the Field Correlator Method formalism. Once the the equation of state is built,
we discuss the pressure anisotropy due the presence of the strong magnetic
field. Finally, we calculate the structure of the compact stars using
magnetized hybrid equations of state and their oscillation modes related with
the emission of gravitational waves. | astro-ph |
Comment on "Nonideal Fields Solve the Injection Problem in Relativistic
Reconnection": Recently, Sironi (PRL, 128, 145102; S22) reported the correlation between
particles accelerated into high energy and their crossings of regions with
electric field larger than magnetic field (E>B regions) in kinetic simulations
of relativistic magnetic reconnection. They claim that electric fields in E>B
regions (for a vanishing guide field) dominate in accelerating particles to the
injection energy. S22 presented test-particle simulations showing that if
particle energies are reset to low energies in E>B regions, efficient injection
is suppressed. This Comment re-examines these claims by analyzing a simulation
resembling the reference case in S22. We show that during crossings E>B
acceleration only contributes a small fraction to the injection energy as E>B
regions only host particles for a short duration. The energization before any
E>B crossings has a comparable contribution, indicating E>B regions are not
unique in pre-accelerating particles. A new test-particle simulation shows that
zero-outing electric fields in E>B regions does not strongly influence the
injection. We suggest that the procedure used in S22 to exclude E>B
acceleration partly removes acceleration outside E>B regions, leading to a
false conclusion. | astro-ph |
The young, tight and low mass binary TWA22AB: a new calibrator for
evolutionary models ? Orbit, spectral types and temperatures determination: Tight binaries discovered in young, nearby associations, with known
distances, are ideal targets to provide dynamical mass measurements to test the
physics of evolutionary models at young ages and very low masses. We report for
the first time the binarity of TWA22, possible new dynamical calibrator for
evolutionary models at young ages. Based on an accurate trigonometric distance
(17.53 +- 0.21 pc) determination, we infer a total dynamical mass of 220 +- 21
MJup for the system. From the resolved near-infrared integral-field
spectroscopy, we find an effective temperature Teff=2900+200-200 K for TWA22 A
and Teff=2900+200-100 K for TWA22 B and surface gravities between 4.0 and 5.5
dex. From our photometry and a M6 +- 1 spectral type for both components, we
find luminosities of log(L/Lsun)=-2.11 +- 0.13 dex and log(L/Lsun)=-2.30 +-
0.16 dex for TWA22 A and B respectively. By comparing these parameters with
evolutionary models, we question the age and the multiplicity of this system.
We also discuss a possible underestimation of the mass predicted by
evolutionary models for young stars close to the substellar boundary. | astro-ph |
The broad line region of narrow-line Seyfert 1 galaxies: We have analyzed new and archival IUE observations of narrow-line Seyfert 1
galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this
sub-group of Active Galactic Nuclei (AGN). We have found broad wings in the
strongest UV emission lines, ruling out the hypothesis that there is no broad
line emission region in this type of objects. Since the similarities in
spectral energy distributions from the far-infrared (FIR) to the soft X rays in
both narrow-line and broad-line Seyfert 1 galaxies do not suggest that the
nuclei of NLS1 are hidden from a direct view, we discuss the possibility that
the line emitting material in NLS1 is optically thin. | astro-ph |
On the nature of bulges in general and of box/peanut bulges in
particular. Input from $N$-body simulations: Objects designated as bulges in disc galaxies do not form a homogeneous
class. I distinguish three types. The classical bulges, whose properties are
similar to those of ellipticals and which form by collapse or merging. Boxy and
peanut bulges, which are seen in near edge-on galaxies and which are in fact
just a part of the bar seen edge-on. Finally disc-like bulges, which result
from the inflow of (mainly) gas to the center-most parts, and subsequent star
formation. I make a detailed comparison of the properties of boxy and peanut
bulges with those of $N$-body bars seen edge-on and answer previously voiced
objections about the links between the two. I also present and analyse
simulations where a boxy /peanut feature is present at the same time as a
classical spheroidal bulge and compare them with observations. Finally, I
propose a nomenclature that can help distinguish between the three types of
bulges and avoid considerable confusion. | astro-ph |
Detection of anisotropic galaxy assembly bias in BOSS DR12: We present evidence of anisotropic galaxy assembly bias in the Baryon
Oscillation Spectroscopic Survey Data Release 12 galaxy sample at a level
exceeding $5\sigma$. We use measurements of the line-of-sight velocity
dispersion $\sigma_\star$ and stellar mass $M_\star$ to perform a simple split
into subsamples of galaxies. We show that the amplitude of the monopole and
quadrupole moments of the power spectrum depend differently on $\sigma_\star$
and $M_\star$, allowing us to split the galaxy sample into subsets with
matching monopoles but significantly different quadrupoles on all scales.
Combining data from the LOWZ and CMASS NGC galaxy samples, we find $>5\sigma$
evidence for anisotropic bias on scales $k<0.15\,h\,\rm{Mpc}^{-1}$. We also
examine splits using other observed properties. For galaxy samples split using
$M_\star$ and projected size $R_0$, we find no significant evidence of
anisotropic bias. Galaxy samples selected using additional properties exhibit
strongly varying degrees of anisotropic assembly bias, depending on which
combination of properties is used to split into subsets. This may explain why
previous searches for this effect using the Fundamental Plane found
inconsistent results. We conclude that any selection of a galaxy sample that
depends on $\sigma_\star$ can give biased and incorrect Redshift Space
Distortion measurements. | astro-ph |
CorrSim: A Multiwavelength Timing Observation Simulator: Studying the rapid variability of many astronomical objects is key to
understanding the underlying processes at play. However, a combination of
limited telescope availability, viewing constraints, and the unpredictable
nature of many sources mean that obtaining data well-suited to this task can be
tricky, especially when it comes to simultaneous multiwavelength observations.
Researchers can often find themselves tuning observational parameters in
real-time, or may realise later that their observation did not achieve their
goals. Here, we present CorrSim, a program to aid planning of multiwavelength
coordinated observations. CorrSim takes a model of a system (i.e. Power
Spectra, Coherence, and Lags), and returns a simulated multiwavelength
observation, including effects of noise, telescope parameters, and finite
sampling. The goals of this are: (i) To simulate a potential observation (to
inform decisions about its feasibility); (ii) To investigate how different
Fourier models affect a system's variability (e.g. how altering the
frequency-dependent lags between bands can affect data products like
cross-correlation functions); and (iii) To simulate existing data and
investigate its trustworthiness. We outline the methodology behind CorrSim,
show how a variety of parameters (e.g. noise sources, observation length, and
telescope choice) can affect data, and present examples of the software in
action. | astro-ph |
Ground Calibration of Solar X-ray Monitor On-board Chandrayaan-2 Orbiter: Chandrayaan-2, the second Indian mission to the Moon, carries a spectrometer
called the Solar X-ray Monitor (XSM) to perform soft X-ray spectral
measurements of the Sun while a companion payload measures the fluorescence
emission from the Moon. Together these two payloads will provide quantitative
estimates of elemental abundances on the lunar surface. XSM is also expected to
provide significant contributions to the solar X-ray studies with its highest
time cadence and energy resolution spectral measurements. For this purpose, the
XSM employs a Silicon Drift Detector and carries out energy measurements of
incident photons in the 1 -- 15 keV range with a resolution of less than 180 eV
at 5.9 keV, over a wide range of solar X-ray intensities. Extensive ground
calibration experiments have been carried out with the XSM using laboratory
X-ray sources as well as X-ray beam-line facilities to determine the instrument
response matrix parameters required for quantitative spectral analysis. This
includes measurements of gain, spectral redistribution function, and effective
area, under various observing conditions. The capability of the XSM to maintain
its spectral performance at high incident flux as well as the dead-time and
pile-up characteristics have also been investigated. The results of these
ground calibration experiments of the XSM payload are presented in this
article. | astro-ph |
An "Ultrasonic Image" of the Embryonic Universe: CMB Polarization Tests
of the Inflationary Paradigm: This chapter describes how the Cosmic Gravitational Wave Background induces a
specific type of CMB polarization and describes the first experiment dedicated
to testing this most-promising signature of inflation. This experiment, the
Background Imaging of Cosmic Extragalactic Polarization (BICEP) project, has
recently embarked on its third observing season. We show preliminary data from
the BICEP's first season obtained with a novel polarization modulation
mechanism called the "Faraday Rotation Modulator". Our discussion ends with a
description of exciting new technology with the potential to probe inflation
down to the GUT-scale. | astro-ph |
Thermal instabilities in cooling galactic coronae: fuelling star
formation in galactic discs: We investigate the means by which cold gas can accrete onto Milky Way mass
galaxies from a hot corona of gas, using a new smoothed particle hydrodynamics
code, 'SPHS'. We find that the 'cold clumps' seen in many classic SPH
simulations in the literature are not present in our SPHS simulations. Instead,
cold gas condenses from the halo along filaments that form at the intersection
of supernovae-driven bubbles from previous phases of star formation. This
positive feedback feeds cold gas to the galactic disc directly, fuelling
further star formation. The resulting galaxies in the SPH and SPHS simulations
differ greatly in their morphology, gas phase diagrams, and stellar content. We
show that the classic SPH cold clumps owe to a numerical thermal instability
caused by an inability for cold gas to mix in the hot halo. The improved
treatment of mixing in SPHS suppresses this instability leading to a
dramatically different physical outcome. In our highest resolution SPHS
simulation, we find that the cold filaments break up into bound clumps that
form stars. The filaments are overdense by a factor of 10-100 compared to the
surrounding gas, suggesting that the fragmentation results from a physical
non-linear instability driven by the overdensity. This 'fragmenting filament'
mode of disc growth has important implications for galaxy formation, in
particular the role of star formation in bringing cold gas into disc galaxies. | astro-ph |
Soft X-ray in-flight calibration of the ROSAT PSPC: We present an in-flight calibration of the ROSAT PSPC using the incident
spectra of the hot white dwarf HZ43 and the polar AM Her. We derive an absolute
flux calibration of the PSPC using the accurately known soft X-ray spectrum of
HZ43. Corrections to the PSPC response matrix are derived from a comparison of
predicted and observed PSPC spectra of HZ43, supplemented by results for AM
Her. The calibration of the PSPC for photon energies E < 0.28 keV is found to
be accurate to better than 5% refuting earlier reports of a major
miscalibration. Our corrections to the detector response matrices remove
systematic residuals in the pulse height spectra of soft sources. | astro-ph |
Detection of Potential Transit Signals in 17 Quarters of Kepler Data:
Results of the Final Kepler Mission Transiting Planet Search (DR25): We present results of the final Kepler Data Processing Pipeline search for
transiting planet signals in the full 17-quarter primary mission data set. The
search includes a total of 198,709 stellar targets, of which 112,046 were
observed in all 17 quarters and 86,663 in fewer than 17 quarters. We report on
17,230 targets for which at least one transit signature is identified that
meets the specified detection criteria: periodicity, minimum of three observed
transit events, detection statistic (i.e., signal-to-noise ratio) in excess of
the search threshold, and passing grade on three statistical transit
consistency tests. Light curves for which a transit signal is identified are
iteratively searched for additional signatures after a limb-darkened transiting
planet model is fitted to the data and transit events are removed. The search
for additional planets adds 16,802 transit signals for a total of 34,032; this
far exceeds the number of transit signatures identified in prior pipeline runs.
There was a strategic emphasis on completeness over reliability for the final
Kepler transit search. A comparison of the transit signals against a set of
3402 well-established, high-quality Kepler Objects of Interest yields a
recovery rate of 99.8%. The high recovery rate must be weighed against a large
number of false-alarm detections. We examine characteristics of the planet
population implied by the transiting planet model fits with an emphasis on
detections that would represent small planets orbiting in the habitable zone of
their host stars. | astro-ph |
GRB 091127: The cooling break race on magnetic fuel: Using high-quality, broad-band afterglow data for GRB 091127, we investigate
the validity of the synchrotron fireball model for gamma-ray bursts, and infer
physical parameters of the ultra-relativistic outflow. We used multi-wavelength
follow-up observations obtained with GROND and the XRT onboard the Swift
satellite. The resulting afterglow light curve is of excellent accuracy, and
the spectral energy distribution is well-sampled over 5 decades in energy.
These data present one of the most comprehensive observing campaigns for a
single GRB afterglow and allow us to test several proposed emission models and
outflow characteristics in unprecedented detail. Both the multi-color light
curve and the broad-band SED of the afterglow of GRB 091127 show evidence of a
cooling break moving from high to lower energies. The early light curve is well
described by a broken power-law, where the initial decay in the optical/NIR
wavelength range is considerably flatter than at X-rays. Detailed fitting of
the time-resolved SED shows that the break is very smooth with a sharpness
index of 2.2 +- 0.2, and evolves towards lower frequencies as a power-law with
index -1.23 +- 0.06. These are the first accurate and contemporaneous
measurements of both the sharpness of the spectral break and its time
evolution. The measured evolution of the cooling break (nu_c propto t^-1.2) is
not consistent with the predictions of the standard model, wherein nu_c propto
t^-0.5 is expected. A possible explanation for the observed behavior is a time
dependence of the microphysical parameters, in particular the fraction of the
total energy in the magnetic field epsilon_B. This conclusion provides further
evidence that the standard fireball model is too simplistic, and time-dependent
micro-physical parameters may be required to model the growing number of
well-sampled afterglow light curves. | astro-ph |
VLT K-band spectroscopy of massive stars deeply embedded in IRAS sources
with UCHII colours: We have obtained high resolution (R = 10,000) K-band spectra of candidate
young massive stars deeply embedded in (ultra-) compact HII regions (UCHIIs).
In these clusters, three types of objects are identified. The first type (38
objects) consists of ``naked'' OB stars whose K-band spectra are dominated by
photospheric emission. We classify the K-band spectra of the OB-type cluster
members using near-infrared classification criteria. The spectral
classification provides an important constraint on the distance to the embedded
cluster. The ionising power of the population thus derived is compared to the
information obtained from the infrared and radio flux of these sources. In most
cases these two different determinations of the ionising flux are consistent,
from which we conclude that we have identified the ionising star(s) in about
50% of the embedded clusters. The second type (7 objects) are point sources
associated with UCHII radio emission, that exhibit nebular emission lines in
the near-infrared. Six of the objects in this group produce HeI emission
indicative of an embedded O-type star. These objects are more embedded than the
OB stars and probably do not dominate the infrared flux as measured by IRAS.
The third type (20 objects) is characterised by broad (100--200 km/s) Brgamma
emission and no photospheric absorption profiles. Bik et al (2005) show that
these objects are massive YSO candidates surrounded by dense circumstellar
disks. | astro-ph |
The Host Galaxies of Fast-Ejecta Core-Collapse Supernovae: Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN
observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit
wide features indicative of high ejecta velocities (~0.1c). We study the host
galaxies of a sample of 245 low-redshift (z<0.2) core-collapse SN, including 17
SN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous
and dust-obscured z<1.2 LGRBs. We show that, in comparison with SDSS galaxies
having similar stellar masses, the hosts of low-redshift SN Ic-BL and z<1.2
LGRBs have high stellar-mass and star-formation-rate densities. Core-collapse
SN having typical ejecta velocities, in contrast, show no preference for such
galaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN
Ib/Ic and SN II, exhibit high gas velocity dispersions for their stellar
masses. The patterns likely reflect variations among star-forming environments,
and suggest that LGRBs can be used as probes of conditions in high-redshift
galaxies. They may be caused by efficient formation of massive binary
progenitors systems in densely star-forming regions, or, less probably, a
higher fraction of stars created with the initial masses required for a SN
Ic-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for
galaxies with high stellar-mass and star-formation-rate densities cannot be
attributed to a preference for low metal abundances but must reflect the
influence of a separate environmental factor. | astro-ph |
A Radio Nebula Surrounding the Ultra-luminous X-ray Source in NGC 5408: New radio observations of the counterpart of the ultraluminous X-ray source
in NGC 5408 show for the first time that the radio emission is resolved with an
angular size of 1.5 to 2.0 arcseconds. This corresponds to a physical size of
35-46 pc, and rules out interpretation of the radio emission as beamed emission
from a relativistic jet. In addition, the radio spectral index of the
counterpart is well determined from three frequencies and found to be
alpha=-0.8 pm 0.2. The radio emission is likely to be optically-thin
synchrotron emission from a nebula surrounding the X-ray source. The radio
luminosity of the counterpart is 3.8 x 10^34 erg/s and the minimum energy
required to power the nebula is ~1 x 10^49 erg. These values are two orders of
magnitude larger than in any Galactic nebula powered by an accreting compact
object. | astro-ph |
The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic
Giant Branch Bump, and Horizontal Branch Red Clump: Color-magnitude diagrams of globular clusters often exhibit a prominent
horizontal branch (HB) and may also show features such as the red giant branch
(RGB) bump and the asymptotic giant branch (AGB) bump. Stellar evolution theory
predicts that the luminosities of these features will depend on the metallicity
and age of the cluster. We calculate theoretical lines of 2 to 12 Gyr constant
age RGB-bumps and AGB-bumps in the V(HB-Bump)--[Fe/H] diagram, which shows the
brightness difference between the bump and the HB as a function of metallicity.
In order to test the predictions, we identify giant branch bumps in new Hubble
Space Telescope color-magnitude diagrams for 8 SMC clusters. First, we conclude
that the SMC cluster bumps are RGB-bumps. The data for clusters younger than ~6
Gyr are in fair agreement the relative age dependent luminosities of the HB and
RGB-bump. The V(HB-Bump)--[Fe/H] data for clusters older then ~6 Gyr
demonstrate a less satisfactory agreement with our calculations. We conclude
that ~6 Gyr is a lower bound to the age of clusters for which the Galactic
globular cluster, age independent V(HB-Bump)--[Fe/H] calibration is valid.
Application of the V(HB-bump)--[Fe/H] diagram to stellar population studies is
discussed. | astro-ph |
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012
apparition: Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition. | astro-ph |
On the mean field dynamo with Hall effect: We study in the present paper how Hall effect modifies the quenching process
of the electromotive force (e.m.f.) in Mean Field Dynamo (MFD) theories. We
write down the evolution equations for the e.m.f. and for the large and small
scale magnetic helicity, treat Hall effect as a perturbation and integrate the
resulting equations assuming boundary conditions such that the total
divergencies vanish. For force-free large scale magnetic fields, Hall effect
acts by coupling the small scale velocity and magnetic fields. For the range of
parameters considered, the overall effect is a stronger quenching of the e.m.f.
than in standard MHD and a damping of the inverse cascade of magnetic helicity.
In astrophysical environments characterized by the parameters considered here,
Hall effect would produce an earlier quenching of the e.m.f. and consequently a
weaker large scale magnetic field. | astro-ph |
Ultraviolet HST Observations of the Jet in M87: We present new ultraviolet photometry of the jet in M87 obtained from HST
WFPC2 imaging. We combine these ultraviolet data with previously published
photometry for the knots of the jet in radio, optical, and X-ray, and fit three
theoretical synchrotron models to the full data set. The synchrotron models
consistently overpredict the flux in the ultraviolet when fit over the entire
dataset. We show that if the fit is restricted to the radio through ultraviolet
data, the synchrotron models can provide a good match to the data. The break
frequencies of these fits are much lower than previous estimates. The implied
synchrotron lifetimes for the bulk of the emitting population are longer than
earlier work, but still much shorter than the estimated kinematic lifetimes of
the knots. The observed X-ray flux cannot be successfully explained by the
simple synchrotron models that fit the ultraviolet and optical fluxes. We
discuss the possible implications of these results for the physical properties
of the M87 jet. We also observe increased flux for the HST-1 knot that is
consistent with previous results for flaring. This observation fills in a
significant gap in the time coverage early in the history of the flare, and
therefore sets constraints on the initial brightening of the flare. | astro-ph |
Parametrized modified gravity constraints after Planck: We constrain $f(R)$ and chameleon-type modified gravity in the framework of
the Berstchinger-Zukin parametrization using the recent released Planck data,
including both CMB temperature power spectrum and lensing potential power
spectrum. Some other external data sets are included, such as BAO measurements
from the 6dFGS, SDSS DR7 and BOSS DR9 surveys, HST $H_0$ measurement and
supernovae from Union2.1 compilation. We also use WMAP9yr data for consistency
check and comparison. For $f(R)$ gravity, WMAP9yr results can only give quite a
loose constraint on the modified gravity parameter $B_0$, which is related to
the present value of the Compton wavelength of the extra scalar degree of
freedom, $B_0<3.37$ at $95\% {\rm C.L.}$ We demonstrate that this constraint
mainly comes from the late ISW effect. With only Planck CMB temperature
power-spectrum data, we can improve the WMAP9yr result by a factor $3.7$
($B_0<0.91$ at $95\% {\rm C.L.}$). If the Planck lensing potential
power-spectrum data are also taken into account, the constraint can be further
strenghtened by a factor $5.1$ ($B_0<0.18$ at $95\% {\rm C.L.}$). This major
improvement mainly comes from the small-scale lensing signal. Furthermore, BAO,
HST and supernovae data could slightly improve the $B_0$ bound ($B_0<0.12$ at
$95\% {\rm C.L.}$).For the chameleon-type model, we find that the data set
which we used cannot constrain the Compton wavelength $B_0$ and the potential
index $s$ of chameleon field, but can give a tight constraint on the parameter
$\beta_1=1.043^{+0.163}_{-0.104}$ at $95\% {\rm C.L.}$ ($\beta_1=1$ in general
relativity), which accounts for the non-minimal coupling between the chameleon
field and the matter component. In addition, we find that both modified gravity
models we considered favor a relatively higher Hubble parameter than the
concordance LCDM model in general relativity. | astro-ph |
Hydrodynamics of Cloud Collisions in 2D: The Fate of Clouds in a
Multi-phase Medium: We have studied head-on collisions between equal-mass, mildly supersonic
(Mach number 1.5) HI clouds, in a standard Two-phase ISM (T_cl = 74 K, n_cl =
22 cm^-3, \chi = 100). We explore the role of various factors, including the
radiative cooling parameter \eta = t_rad/t_coll (t_coll=R_c/v_c), evolutionary
modifications on the cloud structure (by colliding clouds ``evolved'' through
independent motion within the intercloud medium (WIM)), and the symmetry of the
problem (by colliding initially identical clouds, evolved to different ages
before impact). The presence of bow shocks and ram pressure from material in
the cloud wake, developed during such evolution through the WIM, significantly
alters these interactions with respect to the standard case of non-evolved
clouds.
In general, in our adiabatic collisions the clouds are disrupted and convert
their gas into a few low density contrast clumps. By contrast, for symmetric
radiative cases we find that the two clouds coalesce, with almost all the
initial kinetic energy radiated away. On the other hand, for both adiabatic and
radiative collisions, asymmetric collisions have a much greater tendency to
disrupt the two clouds. Fragmentation of the clouds may occur, and
instabilities are in general enhanced. In addition, radiative cooling is less
efficient in our asymmetric interactions, so that those parts of the clouds
that initially seem to merge are more likely to re-expand and fade into the
WIM. Since the majority of real cloud collisions should be asymmetric for one
reason or another, we conclude that most gasdynamical diffuse cloud collisions
will be disruptive, at least in the absence of significant self-gravity or of a
significant magnetic field. | astro-ph |
A multi-wavelength analysis of Spitzer selected Coma Cluster galaxies:
star formation rates and masses: We present a thorough study of the specific star formation rates for MIPS
24um selected galaxies in the Coma cluster. We build galaxy spectral energy
distributions using optical (u',g',r',i',z'), Near-infrared (J,H,Ks), and Mid
to Far-infrared (IRAC and MIPS) photometry. New and archival spectra confirm
210 cluster members. Subsequently, the total infrared luminosity, galaxy
stellar mass, and specific star formation rate for the members are determined
by measuring best fit templates. Using an array of complementary diagnostics,
we search for contaminating AGN, but find few. We compare obscured star
formation rates to unobscured rates derived from extinction-corrected H-alpha
emission line measurements. The agreement between these two values leads us to
conclude that there is no evidence for an additionally obscured component. In
our spectroscopic sample, complete to 80% for r' < 19.5, we find that all
starbursts are blue and are dwarfs, having masses < 10^9 solar masses.
Examining the location of these starbursts within the cluster, we confirm that
there is a lower fraction in the cluster core. | astro-ph |
The extreme initial kinetic energy allowed by a collapsing turbulent
core: We present high-resolution hydrodynamical simulations aimed at following the
gravitational collapse of a gas core, in which a turbulent spectrum of velocity
is implemented only initially. We determine the maximal value of the ratio of
kinetic energy to gravitational energy, denoted here by $\left(\frac{E_{\rm
kin} }{E_{\rm grav}}\right)_{\rm max}$, so that the core (i) will collapse
around one free-fall time of time evolution or (ii) will expand unboundedly,
because it has a value of $\frac{E_{\rm kin}}{E_{\rm grav}}$ larger than
$\left( \frac{E_{\rm kin}}{E_{\rm grav}}\right)_{\rm max}$. We consider core
models with a uniform or centrally condensed density profile and with velocity
spectra composed of a linear combination of one-half divergence-free turbulence
type and the other half of a curl-free turbulence type. We show that the
outcome of the core collapse are protostars forming either (i) a multiple
system obtained from the fragmentation of filaments and (ii) a single primary
system within a long filament. In addition, some properties of these protostars
are also determined and compared with those obtained elsewhere. | astro-ph |
A Gaia astrometric view of the open clusters Pleiades, Praesepe and
Blanco 1: Context. Near open clusters as Pleiades, Praesepe and Blanco 1 have been
extensively studied due to their proximity to the Sun. The Gaia data brings the
opportunity to investigate these clusters, since it contains valuable
astrometric and photometric information which can be used to update their
kinematic and stellar properties. Aims. Our goal is to carry out a star
membership study in these nearby open clusters employing an astrometric model
with proper motions and an unsupervised clustering machine learning algorithm
using positions, proper motions and parallaxes. The star members are selected
from the cross-matching between both methods. Methods. We use the Gaia DR3
catalogue to determine star members using two approaches: a classical Bayesian
model and the unsupervised machine learning algorithm DBSCAN. For star members
we build the radial density profiles, the spatial distributions and compute the
King parameters. The ages and metallicities were estimated using the BASE-9
Bayesian software. Results. We identified 958, 744 and 488 star members for the
Pleiades, Praesepe and Blanco 1 respectively. We corrected the distances and
built the spatial distributions, finding that Praesepe and Blanco 1 have
elongated shape structures. The distances, ages and metallicities obtained were
consistent with the reported in the literature. Conclusions. We obtained
catalogues of star members, updated kinematic and stellar parameters for these
open clusters. We found that the proper motions model can find a similar number
of members as the unsupervised clustering algorithm does when the cluster
population form an overdensity in the vector point diagram. It allows to select
an adequate size of the proper motions region to run these methods. Our
analysis found stars that are being directed towards the outskirts of the
Praesepe and Blanco 1, which exhibit elongated shapes. | astro-ph |
Coronagraphic observations of Si X 1430 nm acquired by DKIST/Cryo-NIRSP
with methods for telluric absorption correction: We report commissioning observations of the Si X 1430 nm solar coronal line
observed coronagraphically with the Cryogenic Near-Infrared Spectropolarimeter
(Cryo-NIRSP) at the National Science Foundation's Daniel K. Inouye Solar
Telescope (DKIST). These are the first known spatially resolved observations of
this spectral line, which has strong potential as a coronal magnetic field
diagnostic. The observations target a complex active region located on the
solar northeast limb on 4 March 2022. We present a first analysis of this data,
which extracts the spectral line properties through a careful treatment of the
variable atmospheric transmission that is known to impact this spectral window.
Rastered images are created and compared with EUV observations from the SDO/AIA
instrument. A method for estimating the electron density from the Si X
observations is then demonstrated that makes use of the forbidden line's
density-sensitive emissivity and an emission-measure analysis of the SDO/AIA
bandpass observations. In addition, we derive an effective temperature and
non-thermal line width across the region. This study informs the calibration
approaches required for more routine observations of this promising diagnostic
line. | astro-ph |
Foreground Mismodeling and the Point Source Explanation of the Fermi
Galactic Center Excess: The Fermi Large Area Telescope has observed an excess of ~GeV energy gamma
rays from the center of the Milky Way, which may arise from near-thermal dark
matter annihilation. Firmly establishing the dark matter origin for this excess
is however complicated by challenges in modeling diffuse cosmic-ray foregrounds
as well as unresolved astrophysical sources, such as millisecond pulsars.
Non-Poissonian Template Fitting (NPTF) is one statistical technique that has
previously been used to show that at least some fraction of the GeV excess is
likely due to a population of dim point sources. These results were recently
called into question by Leane and Slatyer (2019), who showed that a synthetic
dark matter annihilation signal injected on top of the real Fermi data is not
recovered by the NPTF procedure. In this work, we perform a dedicated study of
the Fermi data and explicitly show that the central result of Leane and Slatyer
(2019) is likely driven by the fact that their choice of model for the Galactic
foreground emission does not provide a sufficiently good description of the
data. We repeat the NPTF analyses using a state-of-the-art model for diffuse
gamma-ray emission in the Milky Way and introduce a novel statistical
procedure, based on spherical-harmonic marginalization, to provide an improved
description of the Galactic diffuse emission in a data-driven fashion. With
these improvements, we find that the NPTF results continue to robustly favor
the interpretation that the Galactic Center excess is due, in part, to
unresolved astrophysical point sources across the analysis variations that we
have explored. | astro-ph |
Discovery of low-metallicity stars in the central parsec of the Milky
Way: We present a metallicity analysis of 83 late-type giants within the central 1
pc of the Milky Way. K-band spectroscopy of these stars were obtained with the
medium-spectral resolution integral-field spectrograph NIFS on Gemini North
using laser-guide star adaptive optics. Using spectral template fitting with
the MARCS synthetic spectral grid, we find that there is large variation in
metallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity.
About 6\% of the stars have [M/H] $<$ -0.5. This result is in contrast to
previous observations, with smaller samples, that show stars at the Galactic
center have approximately solar metallicity with only small variations. Our
current measurement uncertainties are dominated by systematics in the model,
especially at [M/H] $>$ 0, where there are stellar lines not represented in the
model. However, the conclusion that there are low metallicity stars, as well as
large variations in metallicity is robust. The metallicity may be an indicator
of the origin of these stars. The low-metallicity population is consistent with
that of globular clusters in the Milky Way, but their small fraction likely
means that globular cluster infall is not the dominant mechanism for forming
the Milky Way nuclear star cluster. The majority of stars are at or above solar
metallicity, which suggests they were formed closer to the Galactic center or
from the disk. In addition, our results indicate that it will be important for
star formation history analyses using red giants at the Galactic center to
consider the effect of varying metallicity. | astro-ph |
Radio and Gamma-Ray Constraints on the Emission Geometry and Birthplace
of PSR J2043+2740: We report on the first year of Fermi gamma-ray observations of pulsed
high-energy emission from the old PSR J2043+2740. The study of the gamma-ray
efficiency of such old pulsars gives us an insight into the evolution of
pulsars' ability to emit in gammma rays as they age. The gamma-ray lightcurve
of this pulsar above 0.1 GeV is clearly defined by two sharp peaks,
0.353+/-0.035 periods apart. We have combined the gamma-ray profile
characteristics of PSR J2043+2740 with the geometrical properties of the
pulsar's radio emission, derived from radio polarization data, and constrained
the pulsar-beam geometry in the framework of a Two Pole Caustic and an Outer
Gap model. The ranges of magnetic inclination and viewing angle were determined
to be {alpha,zeta}~{52-57,61-68} for the Two Pole Caustic model, and
{alpha,zeta}~{62-73,74-81} and {alpha,zeta}~{72-83,60-75} for the Outer Gap
model. Based on this geometry, we assess possible birth locations for this
pulsar and derive a likely proper motion, sufficiently high to be measurable
with VLBI. At a characteristic age of 1.2 Myr, PSR J2043+2740 is the third
oldest of all discovered, non-recycled, gamma-ray pulsars: it is twice as old
as the next oldest, PSR J0357+32, and younger only than the recently discovered
PSR J1836+5925 and PSR J2055+25, both of which are at least 5 and 10 times less
energetic, respectively. | astro-ph |
Constraining Ultralight Axions with Galaxy Surveys: Ultralight axions and other bosons are dark matter candidates present in many
high energy physics theories beyond the Standard Model. In particular, the
string axiverse postulates the existence of up to $\mathcal{O}(100)$ light
scalar bosons constituting the dark sector. Considering a mixture of axions and
cold dark matter, we obtain upper bounds for the axion relic density $\Omega_a
h^2 < 0.004$ for axions of mass $10^{-31}\;\mathrm{eV}\leq m_a \leq
10^{-26}\;\mathrm{eV}$ at 95% confidence. We also improve existing constraints
by a factor of over 4.5 and 2.1 for axion masses of $10^{-25}$ eV and
$10^{-32}$ eV, respectively. We use the Fourier-space galaxy clustering
statistics from the Baryon Oscillation Spectroscopic Survey (BOSS) and
demonstrate how galaxy surveys break important degeneracies in the axion
parameter space compared to the cosmic microwave background (CMB). We test the
validity of the effective field theory of large-scale structure approach to
mixed ultralight axion dark matter by making our own mock galaxy catalogs and
find an anisotropic ultralight axion signature in the galaxy quadrupole. We
also observe an enhancement of the linear galaxy bias from 1.8 to 2.4 when
allowing for 5% of the dark matter to be composed of a $10^{-28}$ eV axion in
our simulations. Finally, we develop an augmented interpolation scheme allowing
a fast computation of the axion contribution to the linear matter power
spectrum leading to a 70% reduction of the computational cost for the full
Monte Carlo Markov chains analysis. | astro-ph |
NGC5719/13: interacting spirals forming a counter-rotating stellar disc: (Context) When a galaxy acquires material from the outside, it is likely that
the resulting angular momentum of the accreted material is decoupled from that
of the pre-existing galaxy. The presence of stars counter-rotating with respect
to other stars and/or gas represents an extreme case of decoupling. (Aims)
NGC5719, an almost edge-on Sab galaxy with a prominent skewed dust lane, shows
a spectacular on-going interaction with its face-on Sbc companion NGC5713.
Observations of such interacting systems provide insight into the processes at
work in assembling and reshaping galaxies. (Methods) Studies were made of the
distribution and kinematics of neutral hydrogen in the NGC5719/13 galaxy pair
and the ionised gas and stellar kinematics along the major axis of NGC5719.
(Results) Two HI tidal bridges that loop around NGC5719 and connect to NGC5713,
and two HI tidal tails departing westward from NGC5713 were detected. There is
a correspondence between the HI condensations and the location of clumps of
young stars within and outside the disc of NGC5719. The low-mass satellite
PGC135857 at the tip of the northern tail was detected in HI, and is likely a
by-product of the interaction. The neutral and ionised hydrogen in the disc of
NGC5719 are counter-rotating with respect to the main stellar disc. The
counter-rotating stellar disc contains about 20% of the stars in the system,
and has the same radial extension as the main stellar disc. This is the first
interacting system in which a counter-rotating stellar disc has been detected.
(Conclusions) The data support a scenario where HI from the large reservoir
available in the galaxy's surroundings was accreted by NGC5719 onto a
retrograde orbit and subsequently fuelled the in-situ formation of the
counter-rotating stellar disc. | astro-ph |
Proposal: The Neural Network Telescope: A neural network mechanism that can compensate for poor optical quality was
recently discovered in a biological context. We propose that this mechanism can
and should be adopted for astronomical purposes. This would shift emphasis away
from the quality of the optical equipment to information processing, hence
should decrease the cost and make larger instruments feasible. | astro-ph |
A 2-hr binary period for the black hole transient MAXI J0637-430: We revisit various sets of published results from X-ray and optical studies
of the Galactic black hole (BH) candidate MAXI J0637-430, which went into
outburst in 2019. Combining the previously reported values of peak outburst
luminosity, best-fitting radii of inner and outer accretion disk, viewing
angle, exponential decay timescale and peak-to-peak separation of the He II
4686 disk emission line, we improve the constraints on the system parameters.
We estimate a heliocentric distance d = (8.7 +/- 2.3) kpc, a projected
Galactocentric distance R = (13.2 +/- 1.8) kpc and a height |z| = (3.1 +/- 0.8)
kpc from the Galactic plane. It is the currently known Milky Way BH candidate
located farthest from the Galactic Centre. We infer a BH mass M_1 = (5.1 +/-
1.6) M_{sun}, a spin parameter a* <~ 0.25, a donor star mass M_2 = (0.25 +/-
0.07) M_{sun}, a peak Eddington ratio lambda = 0.17 +/- 0.11 and a binary
period P_{orb} = 2.2^{+0.8}_{-0.6} hr. This is the shortest period measured or
estimated so far for any Galactic BH X-ray binary. If the donor star is a
main-sequence dwarf, such a period corresponds to the evolutionary stage where
orbital shrinking is driven by gravitational radiation and the star has
regained contact with its Roche lobe (low end of the period gap). The three
Galactic BHs with the shortest period (<~3 hr) are also those with the highest
vertical distance from the Galactic plane (>~2 kpc). This is probably because
binaries with higher binding energies can survive faster natal kicks. | astro-ph |
Quadratic genetic modifications: a streamlined route to cosmological
simulations with controlled merger history: Recent work has studied the interplay between a galaxy's history and its
observable properties using "genetically modified" cosmological zoom
simulations. The approach systematically generates alternative histories for a
halo, while keeping its cosmological environment fixed. Applications to date
altered linear properties of the initial conditions such as the mean
overdensity of specified regions; we extend the formulation to include
quadratic features such as local variance, which determines the overall
importance of smooth accretion relative to mergers in a galaxy's history. We
introduce an efficient algorithm for this new class of modification and
demonstrate its ability to control the variance of a region in a
one-dimensional toy model. Outcomes of this work are two-fold: (i) a
clarification of the formulation of genetic modifications and (ii) a proof of
concept for quadratic modifications leading the way to a forthcoming
implementation in cosmological simulations. | astro-ph |
GIARPS High-resolution Observations of T Tauri stars (GHOsT). IV.
Accretion properties of the Taurus-Auriga young association: In the framework of the GIARPS@TNG High-resolution Observations of T Tauri
stars (GHOsT) project, we study the accretion properties of 37 Classical T
Tauri Stars of the Taurus-Auriga star forming region (SFR) with the aim of
characterizing their relation with the properties of the central star, of jets
and disk winds, and of the global disk structure, in synergy with complementary
ALMA millimiter observations. We derive stellar parameters, optical veiling,
accretion luminosity ($\rm L_{acc}$) and mass accretion rate ($\rm \dot
M_{acc}$) in a homogeneous and self-consistent way using high-resolution
spectra acquired at the Telescopio Nazionale Galileo with the HARPS-N and GIANO
spectrographs, and flux-calibrated based on contemporaneous low-resolution
spectroscopic and photometric ancillary observations. The $\rm L_{acc}$-$\rm
L_{\star}$, $\rm \dot{M}_{acc}$-$\rm M_{\star}$ and $\rm \dot{M}_{acc}$-$\rm
M_{disk}$ relationships of the Taurus sample are provided and compared with
those of the coeval SFRs of Lupus and Chamaeleon I. Our results demonstrate the
potential of contemporaneous optical and near-infrared high-resolution
spectroscopy to simultaneously provide precise measurements of stellar and
accretion/wind properties of young stars. | astro-ph |
Automated Lensing Learner: Automated Strong Lensing Identification with
a Computer Vision Technique: Forthcoming surveys such as the Large Synoptic Survey Telescope (LSST) and
Euclid necessitate automatic and efficient identification methods of strong
lensing systems. We present a strong lensing identification approach that
utilizes a feature extraction method from computer vision, the Histogram of
Oriented Gradients (HOG), to capture edge patterns of arcs. We train a
supervised classifier model on the HOG of mock strong galaxy-galaxy lens images
similar to observations from the Hubble Space Telescope (HST) and LSST. We
assess model performance with the area under the curve (AUC) of a Receiver
Operating Characteristic (ROC) curve. Models trained on 10,000 lens and
non-lens containing images images exhibit an AUC of 0.975 for an HST-like
sample, 0.625 for one exposure of LSST, and 0.809 for 10-year mock LSST
observations. Performance appears to continually improve with the training set
size. Models trained on fewer images perform better in absence of the lens
galaxy light. However, with larger training data sets, information from the
lens galaxy actually improves model performance, indicating that HOG captures
much of the morphological complexity of the arc finding problem. We test our
classifier on data from the Sloan Lens ACS Survey and find that small scale
image features reduces the efficiency of our trained model. However, these
preliminary tests indicate that some parameterizations of HOG can compensate
for differences between observed mock data. One example best-case
parameterization results in an AUC of 0.6 in the F814 filter image with other
parameterization results equivalent to random performance. | astro-ph |
Of `Cocktail Parties' and Exoplanets: The characterisation of ever smaller and fainter extrasolar planets requires
an intricate understanding of one's data and the analysis techniques used.
Correcting the raw data at the 10^-4 level of accuracy in flux is one of the
central challenges. This can be difficult for instruments that do not feature a
calibration plan for such high precision measurements. Here, it is not always
obvious how to de-correlate the data using auxiliary information of the
instrument and it becomes paramount to know how well one can disentangle
instrument systematics from one's data, given nothing but the data itself. We
propose a non-parametric machine learning algorithm, based on the concept of
independent component analysis, to de-convolve the systematic noise and all
non-Gaussian signals from the desired astrophysical signal. Such a `blind'
signal de-mixing is commonly known as the `Cocktail Party problem' in
signal-processing. Given multiple simultaneous observations of the same
exoplanetary eclipse, as in the case of spectrophotometry, we show that we can
often disentangle systematic noise from the original light curve signal without
the use of any complementary information of the instrument. In this paper, we
explore these signal extraction techniques using simulated data and two data
sets observed with the Hubble-NICMOS instrument. Another important application
is the de-correlation of the exoplanetary signal from time-correlated stellar
variability. Using data obtained by the Kepler mission we show that the desired
signal can be de-convolved from the stellar noise using a single time series
spanning several eclipse events. Such non-parametric techniques can provide
important confirmations of the existent parametric corrections reported in the
literature, and their associated results. Additionally they can substantially
improve the precision exoplanetary light curve analysis in the future. | astro-ph |
Venus Observations at 40 and 90 GHz with CLASS: Using the Cosmology Large Angular Scale Surveyor, we measure the
disk-averaged absolute Venus brightness temperature to be 432.3 $\pm$ 2.8 K and
355.6 $\pm$ 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz,
respectively. At both frequency bands, these are the most precise measurements
to date. Furthermore, we observe no phase dependence of the measured
temperature in either band. Our measurements are consistent with a
CO$_2$-dominant atmospheric model that includes trace amounts of additional
absorbers like SO$_2$ and H$_2$SO$_4$. | astro-ph |
A Kiloparsec-Scale Binary Active Galactic Nucleus Confirmed by the
Expanded Very Large Array: We report the confirmation of a kpc-scale binary active galactic nucleus
(AGN) with high-resolution radio images from the Expanded Very Large Array
(EVLA). SDSS J150243.1+111557 is a double-peaked [O III] AGN at z = 0.39
selected from the Sloan Digital Sky Survey. Our previous near-infrared adaptive
optics imaging reveals two nuclei separated by 1.4" (7.4 kpc), and our optical
integral-field spectroscopy suggests that they are a type-1--type-2 AGN pair.
However, these data alone cannot rule out the single AGN scenario where the
narrow emission-line region associated with the secondary is photoionized by
the broad-line AGN in the primary. Our new EVLA images at 1.4, 5.0, and 8.5 GHz
show two steep-spectrum compact radio sources spatially coincident with the
optical nuclei. The radio power of the type-2 AGN is an order-of-magnitude in
excess of star-forming galaxies with similar extinction-corrected [O II] 3727
luminosities, indicating that the radio emission is powered by accretion.
Therefore, SDSS J150243.1+111557 is one of the few confirmed kpc-scale binary
AGN systems. Spectral-energy-distribution modeling shows that SDSS
J150243.1+111557 is a merger of two ~10^{11} M_sun galaxies. With both black
hole masses around 10^8 Msun, the AGNs are accreting at ~10 times below the
Eddington limit. | astro-ph |
INTEGRAL and Swift observations of the Be X-ray binary 4U 1036-56 (RX
J1037.5-5647) and its possible relation with gamma-ray transients: We present timing, spectral, and long-term temporal analysis of the high mass
X-ray binary (HMXB) 4U 1036-56 using INTEGRAL and Swift observations. We show
that it is a weak hard X-ray source spending a major fraction of the time in
quiescence, and only occasionally characterized by X-ray outbursts. The
outburst activity we report here lasts several days, with a dynamic range
spanned by the luminosity in quiescence and in outburst as high as ~30. We
report the detection of pulse period at 854.75+/-4.39 s during an outburst,
which is consistent with previous measurements. Finally, we analyze the
possibility of 4U 1036--56's association with the unidentified transient
gamma-ray sources AGL J1037--5708 & GRO J1036--55, as prompted by its
positional correlation. | astro-ph |
Are spectral and timing correlations similar in different spectral
states in black hole X-ray binaries?: We study the outbursts of the black hole X-ray binaries MAXI J1659-152, SWIFT
J1753.5--0127 and GX 339-4 with the Swift X-ray Telescope. The bandpass of the
X-ray Telescope has access to emission from both components of the accretion
flow: the accretion disk and the corona/hot flow. This allows a correlated
spectral and variability study, with variability from both components of the
accretion flow. We present for the first time, a combined study of the
evolution of spectral parameters (disk temperature and radius) and timing
parameters (frequency and strength) of all power spectral components in
different spectral states. Comparison of the correlations in different spectral
states shows that the frequency and strength of the power spectral components
exhibit dependencies on the disk temperature that are different in the
(low-)hard and the hard-intermediate states; most of these correlations that
are clearly observed in the hard-intermediate state (in MAXI J1659-152 and GX
339-4) are not seen in the (low-)hard state (in GX 339-4 and SWIFT
J1753.5-0127). Also, the responses of the individual frequency components to
changes in the disk temperature are markedly different from one component to
the next. Hence, the spectral-timing evolution cannot be explained by a single
correlation that spans both these spectral states. We discuss our findings in
the context of the existing models proposed to explain the origin of
variability. | astro-ph |
Progress on the SOXS transients chaser for the ESO-NTT: SOXS (Son Of X-Shooter) is a single object spectrograph offering a
simultaneous spectral coverage from U- to H-band, built by an international
consortium for the 3.58-m ESO New Technology Telescope at the La Silla
Observatory. It is designed to observe all kind of transients and variable
sources discovered by different surveys with a highly flexible schedule
maintained by the consortium, based on the Target of Opportunity concept. SOXS
is going to be a fundamental spectroscopic partner for any kind of imaging
survey, becoming one of the premier transient follow-up instruments in the
Southern hemisphere. This paper gives an updated status of the project, when
the instrument is in the advanced phase of integration and testing in Europe,
prior to the activities in Chile. | astro-ph |
Modeling Strong Lenses from Wide-Field Ground-Based Observations in KiDS
and GAMA: Despite the success of galaxy-scale strong gravitational lens studies with
Hubble-quality imaging, the number of well-studied strong lenses remains small.
As a result, robust comparisons of the lens models to theoretical predictions
are difficult. This motivates our application of automated Bayesian lens
modeling methods to observations from public data releases of overlapping large
ground-based imaging and spectroscopic surveys: Kilo-Degree Survey (KiDS) and
Galaxy and Mass Assembly (GAMA), respectively. We use the open-source lens
modeling software PyAutoLens to perform our analysis. We demonstrate the
feasibility of strong lens modeling with large-survey data at lower resolution
as a complementary avenue to studies that utilize more time-consuming and
expensive observations of individual lenses at higher resolution. We discuss
advantages and challenges, with special consideration given to determining
background source redshifts from single-aperture spectra and to disentangling
foreground lens and background source light. High uncertainties in the best-fit
parameters for the models due to the limits of optical resolution in
ground-based observatories and the small sample size can be improved with
future study. We give broadly applicable recommendations for future efforts,
and with proper application this approach could yield measurements in the
quantities needed for robust statistical inference. | astro-ph |
Revisited Mass-Radius relations for exoplanets below 120 Earth masses: The masses and radii of exoplanets are fundamental quantities needed for
their characterisation. Studying the different populations of exoplanets is
important for understanding the demographics of the different planetary types,
which can then be linked to planetary formation and evolution. We present an
updated exoplanet catalog based on reliable, robust and as much as possible
accurate mass and radius measurements of transiting planets up to 120
$M_{\oplus}$. The resulting mass-radius (M-R) diagram shows two distinct
populations, corresponding to rocky and volatile-rich exoplanets which overlap
in both mass and radius. The rocky exoplanet population shows a relatively
small density variability and ends at mass of $\sim25 M_{\oplus}$, possibly
indicating the maximum core mass that can be formed. We use the composition
line of pure-water to separate the two populations, and infer two new empirical
M-R relations based on this data: $ M = (0.9 \pm 0.06) \ R^{(3.45 \pm 0.12)}$
for the rocky population, and $ M = (1.74 \pm 0.38) \ R^{(1.58 \pm 0.10)}$ for
the volatile-rich population. While our results for the two regimes are in
agreement with previous studies, the new M-R relations better match the
population in the transition-region from rocky to volatile-rich exoplanets,
which correspond to a mass range of 5-25 $M_{\oplus}$ and a radius range of 2-3
$R_{\oplus}$. | astro-ph |
Validation of HD 183579b using archival radial velocities: a
warm-neptune orbiting a bright solar analog: As exoplanetary science matures into its third decade, we are increasingly
offered the possibility of pre existing, archival observations for newly
detected candidates. This is particularly poignant for the TESS mission, whose
survey spans bright, nearby dwarf stars in both hemispheres, which are
precisely the types of sources targeted by previous radial velocity (RV)
surveys. On this basis, we investigated whether any of the TESS Objects of
Interest (TOIs) coincided with such observations, from which we find 18 single
planet candidate systems. Of these, one exhibits an RV signature that has the
correct period and phase matching the transiting planetary candidate with a
false alarm probability of less than 1 percent. After further checks, we
exploit this fact to validate HD 183579b (TOI-1055b). This planet is less than
4 Earth Radii and has better than 33 percent planetary mass measurements, thus
advancing the TESS primary objective of finding 50 such worlds. We find that
this planet is amongst the most accessible small transiting planets for
atmospheric characterization. Our work highlights that the efforts to confirm
and even precisely measure the masses of new transiting planet candidates need
not always depend on acquiring new observations - that in some instances these
tasks can be completed with existing data. | astro-ph |
A new calculation of Earth-skimming very- and ultra-high energy tau
neutrinos: Cosmic neutrinos above a PeV are produced either within astrophysical sources
or when ultra-high energy cosmic rays interact in transit through the cosmic
background radiation. Detection of these neutrinos will be essential for
understanding cosmic ray acceleration, composition and source evolution. By
using the Earth as a tau neutrino converter for upward-going extensive air
showers from tau decays, balloon-borne and space-based instruments can take
advantage of a large volume and mass of the terrestrial neutrino target. The
theoretical inputs and uncertainties in determining the tau lepton exit
probabilities and their translation to detection acceptance will be discussed
in the context of a new calculation we have performed. We quantify the
experimental detection capability based on our calculation, including using the
Probe of Extreme Multi-Messenger Astrophysics (POEMMA) concept study response
parameters for optical air Cherenkov detection. These case studies are used to
illustrate the features and uncertainties in upward tau air shower detection. | astro-ph |
On the distribution of collisionless particles in local potential well: The distribution of collisionless particles with infinite motion in the
presence of a local potential well is discussed. Such distribution is important
for interpretation of results of dark matter searches. The relationship
n/v=const, where n and v are respectively number density and velocity of
particles, is derived for particles crossing a local potential well. The limits
of application of this relationship are specified. | astro-ph |
Mauna Kea Sky Transparency from CFHT SkyProbe Data: Nighttime sky transparency statistics on Mauna Kea are reported based on data
from the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the
period beginning with the start of MegaCam wide-field optical imager operations
in 2003, and continuing for almost three years. Skies were clear enough to
observe on 76% of those nights; attenuations were less than 0.2 magnitudes up
to 60% of the time. An empirical model of cloud attenuation and duration is
presented allowing us to further characterize the photometric conditions. This
is a good fit tothe SkyProbe data, and indicates that Mauna Kea skies are truly
photometric (without cloud) an average of 56% of the time, with moderate
seasonal variation. Continuous monitoring of transparency during the night is
necessary to overcome fluctuations in attenuation due to thin cloud. | astro-ph |
Subsets and Splits