abstract
stringlengths 3
192k
| title
stringlengths 4
857
|
|---|---|
the fornax dwarf spheroidal galaxy is the most massive satellites of the milky way, claimed to be embedded in a huge dark matter halo, and the only among the milky way satellites hosting five globular clusters. interestingly, their estimated masses, ages and positions seem hardly compatible with the presence of a significant dark matter component, as expected in the λcdm scheme. indeed, if fornax would have a cdm halo with a standard density profile, all its globular clusters should have sunk to the galactic centre many gyr ago due to dynamical friction. due to this, some authors proposed that the most massive clusters may have formed out of fornax and later tidally captured. in this paper, we investigate the past evolution of the fornax gc system by using both a recently developed, semi-analytical treatment of dynamical friction and direct n-body simulations of the orbital evolution of the globular clusters within fornax and of fornax galaxy around the milky way. our results suggest that an `in situ' origin for all the clusters is likely if their observed positions are close to their spatial ones and their orbits are almost circular. moreover, the milky way seems to accelerate the gc decay reducing the decay time of 15 per cent. nevertheless, our results indicate that the gcs survival probability exceeds 50 per cent, even in the case of cuspy density profiles. we conclude that more detailed data are required to shed light on the fornax dark matter content, to distinguish between a cuspy or a cored profile. | globular clusters as tracers of the host galaxy mass distribution: the fornax dsph test case |
samples of reliably identified halo wide binaries are scarce. if reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide binaries become a powerful dynamical tool, having provided one of the very few experiments capable of constraining the nature of dark matter in the milky way halo. currently, however, the best available sample of halo wide binaries is confined to the solar neighbourhood, and is plagued by small number statistics at the widest separations. we present the results of a programme aimed to probe the wide binary population of the galactic halo at significantly larger distances, and which informs future searches that could improve the statistics by orders of magnitude. halo stars were taken from the sloan digital sky survey after analysing the galactic orbits of stars in the reduced proper motion diagram. we then select candidate binaries by searching for pairs with small differences in proper motion and small projected separation on the sky. using medium-resolution spectroscopy, a subsample of candidates is validated via radial velocities, finding that about 68 per cent of candidate pairs up to 20 arcsec separation can be considered genuine halo wide binaries, to the limits of the available data. precise parallaxes from gaia confirm that most of our selected pairs have their components at the same distances, independently confirming the robustness of our selection method. these results should prove valuable to guide the optimal assembly of larger catalogues of halo wide binaries from upcoming large databases, e.g. gaia and lsst. | a distant sample of halo wide binaries from sdss |
it has been suggested that a huge amount of baryon resides in the circumgalactic medium (cgm) extending out to the virial radii of galaxies. in this work we attempt to measure the baryon mass in the cgm with a novel method based on the gamma-ray observations of the extended halo of the andromeda galaxy messier 31 (m31). since cosmic-ray particles generated inside the galaxy will eventually escape to the cgm, they will produce gamma-ray emission via the proton-proton collision with the cgm and produce gamma-rays. different from some traditional measurements that are sensitive only to certain metallic ions in specific temperature range, the hadronic gamma-ray flux is sensitive to baryonic gases in all phases and does not rely on the metallicity in the halo, hence the measured gamma-ray flux from the galaxy's halo can be used to constrain the mass of the cgm. by dealing with the cosmic-ray transport in the halo and calculating the hadronic gamma-ray intensity, we find that the total baryon mass contained within the virial radius is less than (1.4-5) × 1010 m⊙ according to the gamma-ray intensity obtained with a model-dependent analysis. it implies that the cgm of andromeda galaxy may not account for more than 30% of the missing baryons, but the result is subject to uncertainties from the gamma-ray intensity upper limit, diffusion coefficient of the cosmic-rays in the halo, as well as the stellar mass and dark matter halo mass of the galaxy. this method will become more constraining provided better understandings on these issues and more sensitive gamma-ray telescopes in the future. | measuring the mass of missing baryons in the halo of andromeda galaxy with gamma-ray observations |
although the standard cosmological model, the so-called λ cold dark matter (λcdm), appears to fit well observations at the cosmological level, it is well known that it possesses several inconsistencies at the galactic scales. in order to address the problems of the λcdm on a small scale, some alternative models have been proposed. among the most popular candidates, the proposal that dark matter in the universe is made of ultralight bosons is a strong candidate today. for this work, we study through an analytical approach the consequences arising from comparing the spitzer photometry and accurate rotation curves catalog observed-baryon acceleration correlation with the scalar field dark matter model. we carry out such analysis either considering the features of galactic halos extracted from structure-formation simulations or considering the existence of other non-dark-matter elements in the whole system (such as baryons or a supermassive black hole). specifically, we address a recent claim that the model is not capable of reproducing a constant surface density in the core, in contrast to what observations suggest for a host of galaxies with different sizes and morphologies. in this direction, we show that this discrepancy can be alleviated once the contributions of non-dark-matter constituents in the whole galactic system are taken into account. additionally, we find that a mass of m ≃ 1.41 × 10-22 ev/c2 is capable of reproducing all of our findings and correctly adjusting the rotation curves coming from the milky way galaxy. | consequences for the scalar field dark matter model from the mcgaugh observed-baryon acceleration correlation |
the shape distortion of the presumed milky way dark matter halo can impact the local density of dark matter and thus the direct detection program. we examine the population of galactic rotation curves measured by sparc and fit them to dark matter haloes that are distorted with a multipole density distribution, finding a significantly better fit with prolate haloes over spherically symmetric ones. this is to be expected since the long-distance rubin flattening v(r)= constant is the natural kepler law due to a filamentary rather than a spherical source. then, elongating the distribution brings about a smaller squared chi, all other things being equal, including the use of several different radial dark matter profiles. the ellipticities that we fit to rotation curve data seem to be much more significant than those computed in cosmological simulations of dark matter haloes. if the milky way's halo would be typical of the spiral-galaxy sparc sample (which we presently ignore), the local dark matter density might currently be overestimated by a factor 2. this would carry on into dark-matter cross-section bounds. | dark-matter halo shapes from fits to sparc galaxy rotation curves |
we study a set of solar neighborhood (d < 3 kpc) stars from gaia data release 2 to determine azimuthal star count differences, i.e., left and right of the line from the galactic center (gc) through the sun - and compare these differences north and south. in this companion paper to gardner et al., we delineate our procedures to remove false asymmetries from sampling effects, incompleteness, and/or interloper populations, as this is crucial to tests of axisymmetry. particularly, we have taken care to make appropriate selections of magnitude, color, in-plane galactocentric radius, and galactic $| b| $ and $| z| $ . we find that requiring parallax determinations of high precision induces sampling biases, so that we eschew such requirements and exclude, e.g., regions around the lines of sight to the magellanic clouds, along with their mirror-image lines of sight, to ensure well-matched data sets. after making conservative cuts, we demonstrate the existence of azimuthal asymmetries and find differences in those, north and south. these asymmetries give key insights into the nature and origins of the perturbations on galactic matter, allowing us to assess the relative influence of the magellanic clouds (lmc and smc), the galactic bar, and other masses on the galactic mass distribution, as described in gardner et al. the asymmetry's radial dependence reveals variations that we attribute to the galactic bar, and it changes sign at a radius of (0.95 ± 0.03)r0, with r0 the sun-gc distance, to give us the first direct assessment of the outer lindblad resonant radius. | probing axial symmetry breaking in the galaxy with gaia data release 2 |
the shape and orientation of dark matter (dm) halos are sensitive to the microphysics of the dm particles, yet in many mass models, the symmetry axes of the milky way's dm halo are often assumed to be aligned with the symmetry axes of the stellar disk. this is well motivated for the inner dm halo, but not for the outer halo. we use zoomed-in cosmological baryonic simulations from the latte suite of fire-2 milky way-mass galaxies to explore the evolution of the dm halo's orientation with radius and time, with or without a major merger with a large magellanic cloud analog, and when varying the dm model. in three of the four cold dm halos we examine, the orientation of the halo minor axis diverges from the stellar disk vector by more than 20° beyond about 30 galactocentric kpc, reaching a maximum of 30°-90°, depending on the individual halo's formation history. in identical simulations using a model of self-interacting dm with σ = 1 cm2 g-1, the halo remains aligned with the stellar disk out to ~200-400 kpc. interactions with massive satellites (m ≳ 4 × 1010 m ⊙ at pericenter; m ≳ 3.3 × 1010 m ⊙ at infall) affect the orientation of the halo significantly, aligning the halo's major axis with the satellite galaxy from the disk to the virial radius. the relative orientation of the halo and disk beyond 30 kpc is a potential diagnostic of self-interacting dm, if the effects of massive satellites can be accounted for. | orientations of dark matter halos in fire-2 milky way-mass galaxies |
we develop a comprehensive study of the gamma-ray flux observed by the high energy stereoscopic system (h.e.s.s.) in 5 regions of the galactic center (gc). motivated by previous works on a possible dark matter (dm) explanation for the tev cut-off observed by h.e.s.s. in the innermost ~ 15 pc of the galaxy, we aim to constrain the dm distribution up to a radius of ~ 450 pc from the gc. in this region, the benchmark approach (e.g. cosmological simulations and galactic dynamics studies) fails to produce a strong prediction of the dm profile. within our proof-of-concept analysis, we use dragon to model the diffuse background emission and determine upper limits on the density distribution of thermal multi-tev weakly interactive massive particles (wimps), compatible with the observed gamma-ray flux. the results are in agreement with the hypothesis of an enhancement of the dm density in the gc with respect to the benchmark navarro-frenk-white (nfw) profile (γ = 1) and allow us to exclude profiles with an inner slope cuspier than γ ≳ 1.3. we also investigate the possibility that such an enhancement could be related to the existence of a dm spike associated with the supermassive black hole sgr a* at the gc. we find out that the existence of an adiabatic dm spike smoothed by the scattering off of wimps by the bulge stars may be consistent with the observed gamma-ray flux if the spike forms on an underlying generalized nfw profile with γ ≲ 0.8, corresponding to a spike slope of γsp-star = 1.5 and spike radius of r sp-stars ~ 25 30 pc. instead, in the extreme case of the instantaneous growth of the black hole, the underlying profile could have up to γ ~ 1.2, a corresponding γsp-inst = 1.4 and r sp-inst ~ 15-25 pc. finally, the results of our analysis of the total dm mass enclosed within the s2 orbit (updated with new gravity data) are less stringent than the spectral analysis. our work aims to guide future studies of the gc region, with both current and next generation of telescopes. in particular, the next cherenkov telescope array will be able to scan the gc region with improved flux sensitivity and angular resolution. | multi-tev dark matter density in the inner milky way halo: spectral and dynamical constraints |
we analyse stellar streams in action-angle coordinates combined with recent local direct acceleration measurements to provide joint constraints on the potential of our galaxy. our stream analysis uses the kullback-leibler divergence with a likelihood analysis based on the two-point correlation function. we provide joint constraints from pulsar accelerations and stellar streams for local and global parameters that describe the potential of the milky way (mw). our goal is to build an "acceleration ladder," where direct acceleration measurements that are currently limited in dynamic range are combined with indirect techniques that can access a much larger volume of the mw. to constrain the mw potential with stellar streams, we consider the palomar 5, orphan, nyx, helmi, and gd1 streams. of the potential models that we have considered here, the preferred potential for the streams is a two-component staeckel potential. we also compare the vertical accelerations from stellar streams and pulsar timing, defining the function $f(z)={\alpha }_{1\mathrm{pulsar}}z-\tfrac{\partial {\rm{\phi }}}{\partial z}$ , where φ is the mw potential determined from stellar streams and α 1 pulsar z is the vertical acceleration determined from pulsar timing observations. our analysis indicates that the oort limit determined from streams is consistently (regardless of the choice of potential) lower than that determined from pulsar timing observations. the calibration we have derived here may be used to correct the estimate of the acceleration from stellar streams. | building an acceleration ladder with tidal streams and pulsar timing |
we propose a new method for determining the shape of the gravitational potential of the dark matter (dm) halo of the milky way (mw) with the galactocentric tangential velocities of a sample of hypervelocity stars (hvss). we compute the trajectories of different samples of hvss in a mw where the baryon distribution is axisymmetric and the dm potential either is spherical or is spheroidal or triaxial with radial-dependent axis ratios. we create ideal observed samples of hvss with known latitudinal components of the tangential velocity, vϑ, and azimuthal component of the tangential velocity, vφ. we determine the shape of the dm potential with the distribution of |vϑ| when the galactic potential is axisymmetric, or with the distribution of |vϑ| and of a function, \bar{v}\varphi , of vφ when the galactic potential is non-axisymmetric. we recover the correct shape of the dm potential by comparing the distribution of |vϑ| and \bar{v}\varphi of the ideal observed sample against the corresponding distributions of mock samples of hvss that traveled in dm halos of different shapes. we use ideal observed samples of ∼800 hvss, which are the largest samples of 4 m⊙ hvss ejected with the hills mechanism at a rate ∼10−4 yr−1, currently outgoing, and located at more than 10 kpc from the galactic center. in our ideal case of galactocentric velocities with null uncertainties and no observational limitations, the method recovers the correct shape of the dm potential with a success rate s ≳ 89% when the galactic potential is axisymmetric, and s > 96% in the explored non-axisymmetric cases. the unsuccessful cases yield axis ratios of the dm potential that are off by ±0.1. the success rate decreases with decreasing size of the hvs sample: for example, for a spherical dm halo, s drops from ∼98% to ∼38% when the sample size decreases from ∼800 to ∼40 hvss. accurate estimates of the success rate of our method applied to real data require more realistic samples of mock observed hvss. nevertheless, our analysis suggests that a robust determination of the shape of the dm potential requires the measure of the galactocentric velocity of a few hundred hvss of robustly confirmed galactocentric origin. | probing the shape of the milky way dark matter halo with hypervelocity stars: a new method |
the axion is an unusually well motivated dark matter candidate which is the goldstone boson associated with spontaneous breaking of the pq symmetry of qcd. i describe an experiment to search for axions in our galactic halo using a high q resonant cavity coupled to ultra-low-noise receiver electronics. i discuss the analysis of the first production data and present the first results of the experiment. at 90\% confidence ksvz axions of mass 2.9 to 3.3 micro ev are excluded as the dark matter in the halo of our galaxy. this thesis was submitted in 1997 at mit. it has been used as a reference in many subsequent axion experiments, and it has been suggested that it should be placed on the archive as a reference and a resource. i am complying with this request. | a search for halo axions |
we develop a linear perturbative formalism to compute the response of an inhomogeneous stellar disk embedded in a nonresponsive dark matter (dm) halo to various perturbations like bars, spiral arms, and encounters with satellite galaxies. without self-gravity to reinforce it, the response of a fourier mode phase mixes away due to an intrinsic spread in the vertical (ω z ), radial (ω r ), and azimuthal (ω ϕ ) frequencies, triggering local phase-space spirals. the detailed galactic potential dictates the shape of phase spirals: phase mixing occurs more slowly and thus phase spirals are more loosely wound in the outer disk and in the presence of an ambient dm halo. collisional diffusion due to scattering of stars by structures like giant molecular clouds causes superexponential damping of the phase spiral amplitude. the z-vzphase spiral is one-armed (two-armed) for vertically antisymmetric (symmetric) bending (breathing) modes. only transient perturbations with timescales (τ p) comparable to the vertical oscillation period (τz~ 1/ω z ) can trigger vertical phase spirals. each (n, l, m) mode of the response to impulsive (τ p < τ = 1/(nω z+ lω r+ mω ϕ )) perturbations is power-law (~τ p/τ) suppressed, but that to adiabatic (τ p > τ) perturbations is exponentially weak ( $\sim \exp \left[-{\left({\tau }_{{\rm{p}}}/\tau \right)}^{\alpha }\right]$ ) except for resonant (τ → ∞ ) modes. slower (τ p > τz ) perturbations, e.g., distant encounters with satellite galaxies, induce stronger bending modes. sagittarius (sgr) dominates the solar neighborhood response of the milky way (mw) disk to satellite encounters. thus, if the gaia phase spiral was triggered by a mw satellite, sgr is the leading contender. however, the survival of the phase spiral against collisional damping necessitates an impact ~0.6-0.7 gyr ago. | a comprehensive perturbative formalism for phase mixing in perturbed disks. ii. phase spirals in an inhomogeneous disk galaxy with a nonresponsive dark matter halo |
two alternative theories to dark matter are investigated by testing their ability to describe consistently the dynamics of the milky way. the first one refers to a modified gravity theory having a running gravitational constant and the second assumes that dark matter halos are constituted by a bose-einstein condensation (bec). the parameters of each model as well as those characterizing the stellar subsystems of the galaxy were estimated by fitting the rotation curve of the milky way. then, using these parameters, the vertical acceleration profile at the solar position was computed and compared with observations. the modified gravity theory overestimates the vertical acceleration derived from stellar kinematics while predictions of the bec halo model are barely consistent with observations. however, a dark matter halo based on a collisionless fluid satisfies our consistency test, being the best model able to describe equally well the rotation curve and the vertical acceleration of the galaxy. | testing two alternative theories to dark matter with the milky way dynamics |
for the first time, we use the gamma-ray burst monitor (gbm) on-board the fermi satellite to search for sterile neutrino decay lines in the energy range 10-25 kev corresponding to sterile neutrino mass range 20-50 kev. this energy range has been out of reach of traditional x-ray satellites such as chandra, suzaku, xmm-newton, and gamma-ray satellites such as integral. furthermore, the extremely wide field of view of the gbm opens a large fraction of the milky way dark matter halo to be probed. we start with 1601 days worth of gbm data, implement stringent data cuts, and perform two simple line search analyses on the reduced data: in the first, the line flux is limited without background modeling, and in the second, the background is modeled as a power-law. we find no significant excess lines in both our searches. we set new limits on sterile neutrino mixing angles, improving on previous limits by approximately an order of magnitude. better understanding of detector and astrophysical backgrounds, as well as detector response, can further improve the limit. | improved limits on sterile neutrino dark matter from full-sky observations by the fermi-gbm |
directional dark matter detection attempts to measure the direction of motion of nuclei recoiling after having interacted with dark matter particles in the halo of our galaxy. due to earth's motion with respect to the galaxy, the dark matter flux is concentrated around a preferential direction. an anisotropy in the recoil direction rate is expected as an unmistakable signature of dark matter. the average nuclear recoil direction is expected to coincide with the average direction of dark matter particles arriving to earth. here we point out that for a particular type of dark matter, inelastic exothermic dark matter, the mean recoil direction as well as a secondary feature, a ring of maximum recoil rate around the mean recoil direction, could instead be opposite to the average dark matter arrival direction. thus, the detection of an average nuclear recoil direction opposite to the usually expected direction would constitute a spectacular experimental confirmation of this type of dark matter. | inverted dipole feature in directional detection of exothermic dark matter |
recent advancements in astrometry and in cosmological models of dark matter halo growth have significantly changed our understanding of the dynamics of the local group. the most dramatic changes owe to a new picture of the structure and dynamics of the milky way's most massive satellite galaxy, the large magellanic cloud (lmc), which is most likely on its first passage about the milky way and ten times larger in mass than previously assumed. the lmc's orbit through the milky way's dark matter and stellar halo will leave characteristic signatures in both density and kinematics. furthermore, the gravitational perturbations produced by both direct tidal forcing from the lmc and the response of the halo to its passage will together cause significant perturbations to the orbits of tracers of the milky way's dark matter distribution. we advocate for the use of basis field expansion methods to fully capture and quantify these effects. | the lmc vs. the milky way |
in order to explain galactic structures, a self-gravitating system composed of massive fermions in spherical symmetry is considered. the finite mass distribution of such a component is obtained after solving the einstein equation for a thermal and semi-degenerate fermionic gas, described by a perfect fluid in hydrostatic equilibrium and exposed to cutoff effects (e.g. evaporation). within this more general approach a family of density profiles arises, which explains dark matter halo constraints of the galaxy and provides at the same time an alternative to the central black hole scenario in sgr a*. this analysis narrows the allowed particle mass to mc 2 = 48-345 kev. | galactic constraints on fermionic dark matter |
strong dark matter interactions are proposed to alleviate the tension between observations and theoretical predictions in cdm. among different interaction channels, self-interacting dark matter (sidm) models have received considerable attention. however, most models and simulations have so far neglect the contribution of the baryons. in this talk i will present a combination of results from idealized and cosmological sidm simulations where we explore the effect of a baryonic disk/bulge on the shape and density profile of dark matter halos. we find that the inclusion of baryons in the models help alleviate two of the long-standing issues within cdm: i) the diversity of rotation curves on the scale of dwarf galaxies and ii) the high sphericity measured for the dark matter halo of our own milky way. interestingly, the inclusion of the baryonic potential into cosmological simulations within the sidm framework also suggests that the number of subhalos is reduced (compared to dm-only runs), an effect that needs to be considered when comparing theoretical predictions to the abundance of ultra-faint dwarfs observed around our galaxy. | the abundance and dark matter structure of galaxies in self-interacting dark matter models |
stellar streams, produced by the tidal disruption of dwarf galaxies and globular clusters, yield a snapshot of hierarchical structure formation, and are powerful probes of the mass and profile of the milky way's dark matter halo, as well as the formation of its stellar halo. over the last several years, large imaging surveys have increased the number of known stellar streams to over 60. spectroscopic follow-up observations are crucial, not only for confirming the nature of the streams, but also for determining their full 6d kinematics, metallicities, orbits, progenitors, and formation histories. the southern stellar stream spectroscopic survey (s5) began observing the streams recently discovered by the dark energy survey in 2018, and expanded beyond the des footprint in 2019. s5 employs the large fov of aat and high multiplex of 2df+aaomega to obtain kinematic measurements along the spatial extent of the tidal streams. we highlight the most important results from our first observational campaigns, including confirmation of at least seven streams using velocities and metallicities of the members stars. we also report on the serendipitous discovery one of the highest velocity stars in the galaxy, s5-hvs1. this star provides the first direct proof of the hills mechanism, in which one star in a binary pair is captured by a supermassive black hole (in this case, sagittarius a*), while its companion is ejected at extremely high speed. | highlights from the southern stellar stream spectroscopic survey |
we present the results of the shaft experiment to search for axion-like dark matter in the mass range from 12 pev to 12 nev. the experiment is sensitive to the oscillating magnetic field that would be sourced by an axion-like dark matter halo of our galaxy interacting with a strong static magnetic field in the lab. we employ toroidal ferromagnetic cores made of powdered iron-nickel alloy to enhance the static magnetic field by a factor of 24. using superconducting quantum interference devices (squids), we achieve a magnetic sensitivity of 150 at /√{ hz} . this sensitivity allows us to improve, over a part of our mass range, the existing laboratory limits on the electromagnetic coupling of axion-like dark matter, reaching 4 ×10-11gev-1 at 20 pev with 95% confidence level. we acknowledge support from the nsf grant no. 1806557, the heising-simons foundation grant no. 2015-039, the simons foundation grant no. 641332, and the alfred p. sloan foundation grant no. fg-2016-6728. | search for halo axions with ferromagnetic toroids (shaft experiment) |
the gaia mission has transformed our understanding of the milky way halo. in this talk, i will discuss the recent progress made in galactic halo science since the first astrometric gaia data release and future prospects. this includes the discovery and characterization of the last massive merger event (i.e. gaia-enceladus), the influence of the latest accretion event (i.e. the lmc) on the galactic halo, and the first accurate measures of the stellar and dark matter content of the milky way halo. | the galactic halo in the gaia era |
understanding the assembly history and dark matter distribution of our milky way (mw) is a major challenge for astrophysics. thanks to the unique capabilities of hst, proper motions of satellite galaxies, globular clusters and stellar streams have been measured with accuracies of order 0.05 mas/yr ( 10 km/s) at distances of 50-300 kpc. when combined with detailed models of the mw's halo potential, such measurements become high-precision tools to constrain the dark matter mass profile of the mw and compute accurate orbital histories of satellites. however, the mw hosts a pair of massive dwarf galaxies, the lmc and smc, that contribute to its dark matter distribution and change the shape of the potential in a non-symmetrical, time evolving manner. to date, these effects have not been accounted for in existing models of the mw halo. we propose to develop high resolution simulations to quantify the time evolving structure of the mw's dark matter halo owing to the influence of the lmc and smc. these novel models will enable rapid orbital integration of halo objects (satelllites, globular clusters, stellar streams), using high accuracy hst proper motions, while also capturing the complex halo potential resulting from the lmc-smc-mw interaction. the era of high-precision astrometry has arrived, yet we do not currently have an appropriate theoretical framework to study the assembly history of mw-like galaxies in the presence of massive satellite perturbers. our proposed program is thus critical to ongoing hst programs and all efforts to understand the structure and evolution of the dark matter halo of our galaxy and analogous systems like m31 and its massive satellite, m33. | new models of the milky way's dark matter distribution for the era of high precision astrometry |
the local dark matter density encodes valuable information about the local shape of the milky way's dark matter halo near the plane, providing constraints on galaxy formation models, the merger history of the galaxy and even alternative gravity theories. we present an ongoing exploration of the vertical and radial kinematics of stars in the solar vicinity as tracers of the relative contributions of baryons and dark matter to the overall surface mass density of the disk. this work exploits the latest astrometric solution from the gaia mission together with stellar abundances from the apogee survey, which is key to labeling the different population structures in the milky way | anisotropies in the local velocity field of the galactic disk and the local dark matter density |
the extragalactic background light (ebl) is the aggregate emission from all extragalactic sources throughout cosmic time. the cosmic infrared background experiment-1 (ciber-1) is a sounding rocket experiment optimized for probing ebl at near-infrared wavelengths, and it has flown four times from 2009 to 2013. a previous analysis of the fluctuations in ciber-1 second and third flight imager data was interpreted as arising from the intra-halo light (ihl), which is the emission from stars tidally stripped from their host galaxies and redistributed to the dark matter halo during the galaxy merger. in this talk, i will present the recent results on ihl study using ciber-1 fourth flight data. by stacking galaxies in ciber images, we detect the average extended light profile around the galaxies, as well as the non-linear clustering signals. i will conclude with a comparison of our results with the previous stellar halo constraints from ground-based observations in optical bands and hydrodynamic simulations. | studying near-infrared intra-halo light with ciber mission |
methods of measuring distances to objects in our milky way are briefly discussed. they generally base on three principles: of using a standard rod, of standard candle and of column density of interstellar matter. weak and strong points of these methods are presented. the presence of gray extinction towards some objects is suggested which makes the most universal method of standard candle (spectroscopic parallax) very uncertain. hard to say whether gray extinc-tion appears only in the form of circumstellar debris discs or is present also in the general interstellar medium. the application of the method of measuring column densities of interstellar gases suggests that the rotation curve of our milky way system is rather keplerian than flat which creates doubts as to whether any dark matter halo is present around our galaxy. it is emphasized that the most universal method, i.e. that of standard candle, used to estimate distances to cosmological objects, may suffer serious errors because of improper subtraction of extinction effects. | how far is it? distance measurements and their consequences |
a modified circular velocity law is presented for a test body orbiting around a spherically symmetric mass. this law exhibits a distance scale parameter and allows to recover both usual newtonian behaviour for lower distances and a constant velocity limit at large scale. application to the galaxy predicts the known behaviour and also leads to a galactic mass in accordance with the measured visible stellar mass so that additional dark matter inside the galaxy can be avoided. it is also shown that this circular velocity law can be embedded in a geometrical description of space-time within the standard general relativity framework upon relaxing the usual asymptotic flatness condition. this formulation allows to redefine the introduced newtonian scale limit in term of the central mass exclusively. moreover, a satisfactory answer to the galactic escape speed problem can be provided indicating the possibility that one can also get rid of dark matter halo outside the galaxy. | modified circular velocity law |
the sagittarius dwarf galaxy (sgr) is among the most massive satellites of the milky way and is unique due to its extensive tails of tidally stripped stars. these tails provide strong constraints on the orbital history of sgr, which in turn lend insight into the structure of the milky way's dark matter halo. utilizing the dynamics of sgr for these studies, however, relies on a precise distance measurement to the core. yet past measurements yield a wide range of values (22.0 - 28.4 kpc) with a variation of >25%. through photometry of 3.6μm spitzer data and gloess light curve fitting, we have measured the mean magnitudes of 45 rr lyrae variables in the sgr core. fitting the magnitudes to a period-luminosity relation with a slope of -2.332, we find the distance modulus to be 17.19 ± 0.02 (ran) ± 0.08 (sys) based on zero points derived from hst parallax measurements of five galactic rr lyrae. this yields a mean distance of 27.40 ± 0.21 (ran) ± 1.01 (sys) kpc to the core of sgr. | spitzer merger history and shape of the galactic halo: the distance to the core of the sagittarius dwarf galaxy from the mid-infrared period-luminosity relation for rr lyrae variable stars |
the macro-scale properties of dark matter (dm) haloes, such as shape and orientation, rely on the micro-physics of the dark matter particle. yet the symmetry axes of the milky way's dark matter halo are often assumed to be aligned with the symmetry axes of the stellar disc. while this is the likely case for the inner regions of the dark matter halo, there is no physical reason for the outer dark matter halo to have the same alignment. in this work, we explore the evolution of the dark matter halo orientation in the presence or absence of a major merger with a large magellanic cloud (lmc) analog. we restrict our analysis to various simulated milky way-mass galaxies (1012 m⊙) and their dm haloes from the latte simulation suite. we present orientations of the dark matter axes relative to the stellar disc axes as a function of radius and as a function of time. we conclude that the orientations of the dark matter halo are divergent from the stellar disc axes beyond the stellar disc (>30 kpc), but this trend is not replicated in simulations with self-interacting dark matter (sidm). in terms of lmc-host perturbations, we find in-falling lmc satellites have differential effects on the alignment of the disc axes depending on their mass scales. additionally, there is differential alignment of the halo to lmc analog at the stellar disc and out to the virial radius. our results indicate a dynamic dark matter halo that is responsive to satellite perturbations and anisotropically aligned to the galactic disc. | orientations of dark matter haloes in cdm and sidm latte galaxies |
several multiferroic materials have axion-like modes that resonate with terahertz frequency electromagnetic waves. axions from the local dark matter halo of the galaxy allows such excitations to absorb mid-infrared light with wavelength near 2.44 microns and to raman scatter visible light with wavenumber shift near 4100 inverse centimeters. measuring the location of the peak in the infrared absorption and raman scattering spectra with the resolution of readily available spectrometers would determine the mass of the axion with ten times better precision than the current world average for the mass of the charged particle that carries the weak nuclear force. conversely, such infrared and raman haloscopy gives a fast and easy way to find materials with axion-like excitations. this research was supported in part by the national science foundation under grant no. nsf phy-1748958, by the department of energy under grant no. de-fg02- 00er41132, and by the mainz institute of theoretical physics within the cluster of excellence prisma+ (project id 39083149). | seeing dark matter in multiferroics with infrared and raman haloscopy |
the transition from linear to non-linear structure formation in cosmology is here studied from the point of view of the thermodynamics of self-gravitating fermions. we start by reviewing the principle of maximum entropy production through which such a fermionic system can relax towards spherical equilibrium states able to explain the dark matter (dm) in galaxies. we then analyze the stability, lifetime and morphology of the above configurations, and show that the most general dm profile develops a compact core governed by degeneracy pressure, which is surrounded by an extended halo. for dm particles which are in the range of o(10 100) kev, we apply this theory to the case of the milky way, and show that the compact dm-core explains the dynamics of all the best resolved s-cluster stars orbiting sgra *, without the need of assuming a central black hole (bh). further consequences of this theory regarding open issues in cosmology are outlined, including the problem of formation of supermassive bhs in the early universe. | dark matter fermions:from linear to non-linear structure formation |
the oc stream is a dwarf galaxy stream and is one of the longest and best-measured streams in the galaxy, spanning over 200 degrees on the sky. it extends from the inner milky way (~15 kpc) to the outer halo (~60 kpc), giving us a great tool with which to measure our galaxy's dark matter halo. in addition, portions of the stream pass remarkably close to the lmc (~5 kpc), allowing us to simultaneously measure the properties of our galaxy and the lmc. by combining data from gaia dr3 with the s5 survey, lamost, sdss, and apogee, i will present a 6d view of the stream. in light of this powerful data, we fit the oc stream using a flexible model of the milky way halo and the lmc. in particular, we measure the milky way's mass to a precision of 4% in the middle of the stream's radial extent, ~2.85e11 msun at ~32.4 kpc. we also infer a highly flattened dark matter halo of the milky way, with the data preferring an oblate (q = ~0.55) and prolate (q = ~1.40) halo over a spherical one. interestingly, we find that both of these haloes are producing a similar forcefield in the orbital plane of the oc stream, suggesting they may be attempting to mimic a forcefield which cannot be described with by a flattened halo. we also measure the lmc's dark matter halo. in particular, we find the lmc has a mass of ~1.3e11 msun, which is one sixth the milky way's virial mass. our fits also suggest that the lmc's dark matter halo must extend out to at least ~53 kpc from the lmc, consistent with the lmc being on first approach to the milky way. finally, we find that the oc stream's close passage with the lmc occurs ~300 myr ago. since the oc stream is very sensitive to the lmc's location at this time, this allows us to better constrain the lmc's past orbit up to that time. for the first time, we constrain the amount of dynamical friction the lmc has experienced and find that it is consistent with what is expected given the lmc's substantial dark matter halo. i will end with the future directions of this work and how these results can be used to constrain alternative gravity and alternative dark matter models. | the oc stream's evolution in the dark matter haloes of the milky way and the lmc |
inside the local group, the satellite galaxies of the milky way don't have an isotropic distribution, instead most of them lie on structure almost perpendicular to the plane of the disk of the galaxy, called vpos. at present there is not a theoretical model that correctly explain both the abundance and spatial distribution of these objects within the local group. this work presents a study, using newtonian n-body numerical simulations, on the formation of disk satellites of the milky way (dos) from accretion of dwarf galaxies that fall into the dark matter halo of the milky way following parabolic orbits with initial distances of 4, 2 and 1 mpc. we analysed the morphological properties of dwarfs after 10 gy of fall proposed for interaction with the milky way, the obtained spatial distributions about the plane of the host galaxy and the radial distances at which they are located. we found that, after 10 gy of fall, the structures remain compact while keeping its spherical profile. only associations of dwarf galaxies at distances of 1 mpc manage to enter the halo of the galaxy and could be considered as progenitors of dos. this is supported by the fact that these closest associations are those that had precipitated into the halo of the galaxy, and there are not observed associations of dwarfs at these distances, being the association 14+12 the closest to the milky way at 1.37 mpc. | fall of associations of dwarf galaxies into the milky way halo |
axions saturate the local dark matter halo of the galaxy and have rest energy in the sub-millimeter range. in this frequency range, topological density wave materials, such as, topological insulators in the spin density wave phase (sdw) and weyl semi-metals in the charge density wave phase (cdw), are usually transparent. turning on a magnetic field, however, causes light polarized parallel to the field to couple linearly to modulations of the sdw (cdw) amplitude (phase). the resulting axionic polariton transforms under discrete space-time symmetries in the same way as the axion. rotating the light polarization perpendicular to the magnetic field restores transparency in the absence of axions but gives rise to a measurable excitation amplitude at the observed axion density. | catching axions with density waves |
self-interacting dark matter (sidm) can create sufficiently large cores in dark matter haloes of dwarf galaxies if the self-interaction cross-section is sufficiently large on scales of dwarf galaxies. such a large cross-section can be realized without changing the densities and shapes of cluster-size haloes by introducing a velocity dependent cross-section. lowering the central densities of dwarf-size haloes, however, may change the strength of stellar feedback required to reproduce observed properties of dwarf galaxies such as the luminosity function of the milky way's satellite galaxies. we perform simulations of galaxy formation by employing such a velocity dependent self-interaction cross-section to investigate the coupled effect of sidm and feedback. | structure of dark matter haloes of milky way satellite galaxies in sidm universes |
an excess of gamma rays from the inner galaxy in the fermi lat data has been identified. this emission has been interpreted as a possible signature of the annihilation of dark matter particles, or as originating from a collection of unresolved point sources, such as gamma-ray millisecond pulsars. we explore the clustering properties of the diffuse emission arising from a population of gamma-ray point sources and from the annihilation of dark matter particles in the halo of the galaxy using the 1-pt probability distribution function of counts in pixels (1pt-pdf, the number of pixels with a specified number of counts as a function of counts); this approach is also known as fluctuation analysis or p(d) analysis. we analyze the 1-pt pdf of the gev excess within a +/- 5 degree box around the galactic center. for both dark matter and point sources we adopt the spatial distribution and spectrum to fit the gev excess. we determine the contributions to the 1-pt pdf from the galactic diffuse and isotropic diffuse emission, dark matter, and point sources, and discuss the implications of this analysis for the origin of the gev excess. | dark matter or point sources? utilizing the 1-pt pdf to understand the origin of the gev excess seen by the fermi lat detector |
directly linked to the mass of the dark matter halo where baryons form, the galaxy stellar mass (m_star) is the most important observable parameter to understand galaxy evolution. still, we have not completely figured out how the growth of the stellar mass in galaxies happen. a fundamental problem stands at the fact that galaxies are complex systems with an intricate combination of different structural components such as bulges, discs, and bars. each of these structures may have followed a different formation path, and therefore the separated mass growth of bulges, discs, and bars might hold the key to understand how galaxies evolved with time. in a series of papers, we have applied a new spectro-photometric decomposition code (c2d; méndez-abreu et al. 2019) to a sample of photometrically classified bulge+disc galaxies observed within the califa ifs survey (sánchez et al. 2016). our approach allows us to overcome the general problem of 'structure superposition' in galaxies by separating ifs datacubes, containing the spatial and spectral information, of the individual components shaping the galaxy. the analysis of the independent bulge and disc datacubes opens a new way to analyse their spectroscopic properties. we summarise here our main results on the stellar mass growth of bulges and discs in the nearby universe. | the origin of bulges and discs. the stellar mass growth unveiled using califa spectro-photometric decompositions |
the dark matter halos surrounding milky way-like galaxies that are formed in cosmological simulations are triaxial. these simulated triaxial halos are expected to be slowly rotating with log-normal distribution of pattern speeds centered on ~0.148h km/s/kpc (bailin & steinmetz 2004, apj., 616, 27). stellar streams arising from a satellite experiencing tidal disruption inside such a slowly rotating triaxial halo are expected to be subject to additional forces (e.g. coriolis forces) that affect the structure of the tidal streams. using the python galaxy dynamics package gala (price-whelan, http://gala.adrian.pw) we have generated simulations of tidal streams in a range of triaxial potentials to explore how the structure of milky way's tidal streams, especially the structure of stream bifurcations and the stream orbital plane, are altered by a slow figure rotation of the triaxial dark matter halo. we investigate what can be inferred about halo rotation from current and future data including upcoming data from gaia. this work is supported by nasa-atp award nnx15ak79g to the university of michigan. | using tidal streams to investigate the rotation of the milky way's dark matter halo |
the paper discusses existing methods of distance determinations to bright objects inside our galaxy. possible inaccuracies are considered. measurements of both: distances and radial velocities allow determination of the milky way rotation curve, believed to be at because of the postulated dark matter halo around the galaxy. we demonstrate the rotation curve, based on observations of caii interstellar absorption lines in spectra of ob stars. our high resolution spectra allow to measure both: distances and radial velocities with a high precision - free of the effects of stellar binarity and the line center uncertainties in rapid rotators. the resultant rotation curve of the milky way proves to be much more complex than either "flat" or "keplerian" | distance measurements towards young milky way objects; rotation curve |
the large magellanic cloud (lmc), the most massive satellite of the milky way(mw), is perturbing the dynamics and equilibrium of the mw. understanding thenature and time evolution of these perturbations remains one of the most importantchallenges to the interpretation of 6d phase space measurements of tracers (satel-lites, streams, halo stars) of the dark matter (dm) distribution and assembly historyof the mw. using results from 8 high-resolution n-body simulations, i will describethe main perturbations caused by the lmc: the dm wake, the barycenter displace-ment, and the reflex motion. i show that these perturbations can be detected inboth the kinematics and densities of the stellar halo beyond 50 kpc. furthermore,i will illustrate how the present-day mw-lmc system can be modeled analyticallyusing basis function expansions. i maximize the physical signal in the representa-tion through a comprehensive noise analysis. as a result, the simulations of 10 8 dmparticles representing the distorted mw(mw+lmc) system can be described by ∼236(2067) coefficients. we find that the lmc induces asymmetric perturbations tothe mw's halo, which are inconsistent with oblate, prolate, or triaxial halos. thepresence of the lmc also complicates efforts to recover the underlying shape of themw's halo. i also discuss how the lmc induces clustering of orbital poles of objectsin orbit about the mw. by tracking the evolution of orbital poles for initially ran-dom, steady-state dark matter particles, i find that, after the infall of the lmc, thepresent-day orbital poles of particles , at galactocentric distances beyond =50kpc,cluster near the present-day orbital pole of the lmc. this clustering can be up to afactor of ∼1.3 times higher than the density of orbital poles in an isolated mw haloand is most pronounced after the recent, close (∼50 myr ago, 49 kpc) passage of thelmc. given our location within the disk, particles in the simulation are observedfrom a non-inertial reference frame relative to the outer halo leading to an appar-16ent alignment in their orbital poles. the dm wake induced by the lmc changesthe kinematics of particles in the southern hemisphere. observations of satellitesselected within spatial planes also suffer from a bias, such that measuring orbitalpoles in a great circle in the sky enhances the probability of their orbital poles beingclustered. i expect this scenario to be ubiquitous among hosts that have captured amassive satellite (at least ∼1:10 mass ratio) making a recent (= 1 gyr) pericentricapproach, where the massive satellite will cluster orbital poles of halo tracers. | the effect of the large magellanic cloud on the dark matter halo of the milky way |
the connection between dark matter haloes and galaxies describes the galaxy formation process in the dark matter field. it is crucial for modelling galaxy clustering on small scales and constructing high-fidelity large-scale simulations for galaxies. the early data release (edr) of desi is a powerful dataset for understanding this galaxy-halo relation down to megaparsec scales, with the help of modern large-volume and high-resolution dark matter simulations. the desi edr sample consists of luminous red galaxies (lrgs), emission line galaxies (elgs), and quasi-stellar objects (qsos) in a redshift range of [0.4, 3.5], taken by the mayall 4-m telescope in a few months, with a similar number density as the sdss eboss data accumulated in 4 years. we analyze the galaxy-halo connection of desi edr with unit n-body simulations and a general subhalo abundance matching (sham) algorithm. this algorithm works for all three tracers and takes into account observational systematics like redshift uncertainty and stellar mass completeness. we detect the quenching of elg star formation and qso black-hole activity in a dense environment, and massive lrgs are found to be complete. the redshift uncertainty plays a role for lrgs and qsos at 10-20mpc/h but elgs are immune to it on megaparsec scales. similar studies using different sham and halo occupation distribution (hod) methods and with alternative simulations report more properties of the desi tracer. for instance, the average number of satellites of lrgs and qsos increases as their host halo mass, while elg satellites illustrate the opposite trend. in addition, there is no evidence of assembly bias for lrgs and qsos. besides, desi elgs do not include the most luminous oii emitters for z<0.8. it's supported by the director, office of science, office of high energy physics of the us doe under contract de-ac02-05ch11231, and by the national energy research scientific computing center under the same contract; additional support is provided by the us nsf division of astronomical sciences under contract ast-0950945 to nsf national optical-infrared astronomy research laboratory; the science and technologies facilities council of the uk; the gordon and betty moore foundation; the heising-simons foundation; cea of france; conacyt of mexico; micinn of spain, and by desi member institutions. | desi early data release: galaxy-dark-matter-halo connection |
the dark matter halos that surround milky way-like galaxies in cosmological simulations are, to first order, triaxial. such halos are predicted to exhibit steady figure rotation with a median pattern speed 0.15h km/s/kpc ~ 0.15h radian/gyr. the pattern speeds predicted by cosmological cdm simulations are so small that it is largely unimportant for galaxy evolution and very difficult to detect. we present a new way to detect figure rotation in the milky way halo using the morphology and 3-d velocities of stars in tidal streams, such as the kinematical data that are being obtained by gaia and large multi-fiber spectroscopic milky way surveys like desi. we show using simulations of a sagittarius-like polar tidal stream in triaxial dark matter halos with different shapes that when the halos are rotated about one of the three principal axes, figure rotation produces warps and misalignments of the planes of the leading and trailing arms of the stream. for pattern speeds typical of cosmological halos we demonstrate, for the first time, that a sagittarius-like tidal stream would be altered to a degree that is detectable with current observations. we also quantify the effects of figure rotation on the observed kinematics of thinner and shorter tidal streams. this discovery will potentially allow for a future measurement of figure rotation of the milky way's dark halo, perhaps enabling the first evidence of this relatively unexplored prediction of cdm. this work is funded in part by nasa grants nnx15ak79g and 80nssc20k0509 and a micde catalyst grant. | using tidal streams to probe the figure rotation of the milky way's dark matter halo |
the length asymmetry of the tidal stellar stream palomar 5 could have been caused by a past encounter(s) with the galactic bar, thus limiting its use as a probe for structures in the dark matter halo of the milky way. | mind the galactic bar |
galaxies live in dark matter haloes and hence the galaxy properties are majorly defined by the properties of the haloes. thus the environmental dependence of dark matter halo properties prompts a correlation between galaxy properties and the environment. more insights into these environmental correlations are crucial for the better understanding of the galaxy formation. the objective of this thesis is to explore the environmental dependence of galaxy properties using robust statistical tools on galaxies from redshift surveys and simulations. we study the environmental dependence of luminosities in optical, near-infrared, and mid-infrared bands, as well as stellar mass and star formation rate. for that, we use a set of galaxy samples from the gama and sdss galaxy surveys and the cosmodc2 mock galaxy catalogue. we measure two-point correlation function and marked correlation function using the above-mentioned properties as marks. using these measurements, we show which among the properties is the strongest tracer of the environment in which the galaxies live. we also demonstrate which photometric passband best serves as a proxy for stellar mass and star formation rate in the absence thereof. in this thesis, we also test whether the survey flux limit influences the clustering results. furthermore, we verify how well the cosmodc2 mock catalogue - the state-of-the-art mock catalogue prepared to mimic the galaxy and large-scale structure properties in the future legacy survey of space and time (lsst) - reproduces the environmental dependence of galaxy properties observed in gama and we find significant discrepancies. | environmental dependence of galaxy properties using marked statistics |
glon sky survey is a data acquisition method of 21 cm neutral hydrogen spectrum. recently, the author has conducted a series of studies on the data of the glon sky survey. after transforming and analyzing the data, the author found that in the region of the center of the milky way galaxy, the linear velocity of galactic rotation increases with the distance away from the center. for the region 15 light-years away, the linear velocity of rotation remains almost unchanged. by transforming the variation of velocity with radius into the chart, it can be found that there are deviations in the early galactic rotation structure model. for the newly proposed combined exponential and isothermal model, there is a high degree of agreement. the model confirms that there is a huge dark matter halo at the outer edge of the galaxy. the weak gravitational interaction between dark matter halo and visible matter affects the current rotational structure of the galaxy. | research on the galaxy rotation model based on 21 cm hydrogen spectrum |
the stars of the s-cluster orbiting the galactic center provide one of the best astrophysical observables to infer the gravitational potential generated by the central source sgr a*, traditionally assumed to be a black hole (bh). an alternative model for sgr a* is the ruffini- argüelles-rueda (rar) model, based on a self-gravitating system of neutral fermions in the framework of general relativity. it predicts the existence of a dense core of highly degenerate fermions able to mimic the bh, which is surrounded by a more dilute atmosphere that is consistent with the dark matter (dm) halo of the galaxy. in this work we study the dynamics of the most important star in the s-cluster, assuming that it moves around the compact dm core predicted by the rar model. for the first time we fit the orbital parameters of the s-2 star with a markov chain monte carlo (mcmc) technique, and compare the results with the ones obtained in the bh paradigm. | testing the nature of sgr a* with the s-2 star orbit data |
in the outer reaches of galaxies, stars dont move quite how they should. is this deviation due to mysterious dark matter? or is something else at work? in a recent study, scientists turn to elliptical galaxies in search of new clues.weirdness in galactic fringestwo rotating galaxies are shown with their rotation curves in this animated gif. based on the distribution of visible matter, we would expect to see inner stars moving fast and outer stars moving slowly, producing a rotation curve like whats seen on the left. instead, we see stars moving with the same speed, producing the flat rotation curve seen on the right. [ingo berg]usually, things that orbit do so in predictable ways. in our solar system, for instance, planets orbit the sun following predictable laws of gravitation: close-in planets speed along quickly, whereas planets farther out move more slowly.you might think that galaxies would work the same way. since most of a galaxys visible mass is concentrated at its center just like most of our solar systems mass (the sun) is at its center we would expect stars near the center of a galaxy to orbit quickly, and stars in the galaxys outermost fringes to orbit very slowly. instead, we see that stars throughout galaxies move at roughly the same speeds: galaxies have flat rotation curves.artists illustration of the distribution of dark matter in the halo surrounding the visible disk of the milky way galaxy. [eso/l. calada]dark matter? or a gravitational misunderstanding?what drives this weird behavior? the most widely accepted explanation is dark matter: the idea that theres a lot of matter in a galaxy that isnt concentrated in its center we just cant see it. this dark matter is distributed in a wide halo around the galaxy, and its gravitational tug causes outer stars to orbit faster than they would under the influence of the visible matter alone.but dark matter isnt the only possible explanation for galactic rotation curves: an alternative, modified newtonian dynamics (mond), was first introduced nearly 40 years ago. the mond hypothesis contends that dark matter isnt needed to explain galaxy rotation curves because our understanding of gravity is wrong.according to mond, normal newtonian gravitation applies in regions where acceleration is large say, in the case of the moon orbiting the earth, planets orbiting a solar system, or in the inner regions of a galaxy. but gravity behaves slightly differently in regions where acceleration is small like in the outer reaches of galaxies.critical accelerationhow can we test mond as a theory? one clue is whether individual galaxies stray from expected gravitational behavior at a consistent acceleration scale some fundamental value of acceleration that effectively marks the transition from the newtonian regime to the mond regime. if, instead of a universal acceleration scale, we find a large amount of scatter in how galaxies deviate, that would rule out the mond hypothesis.the authors elliptical galaxy sample is consistent with a universal acceleration scale of g = 1.2 x 10-10 m/s2 which is consistent with the acceleration scale previously found for spiral galaxies. [chae et al. 2020]a universal acceleration scale has, in fact, been found in previous studies that explored the observed radial acceleration of spiral galaxies. now, in a study led by kyu-hyun chae (sejong university, republic of korea), scientists have demonstrated that this same scale appears to extend to a sample of elliptical galaxies as well.chae and collaborators study is important because it shows that both galaxies supported by rotation (spirals) and those supported by pressure (ellipticals) behave the same way. these two independent measures underscore the universality of how galaxies acceleration deviates from whats predicted from visible matter alone and suggest that mond isnt out of the running just yet.citationon the presence of a universal acceleration scale in elliptical galaxies, kyu-hyun chae et al 2020 apjl 903 l31. doi:10.3847/2041-8213/abc2d3 | searching for universal acceleration |
we describe an algorithm that can fit the properties of the dwarf galaxy progenitor of a tidal stream, given the properties of that stream. we show that under ideal conditions (the milky way potential, the orbit of the dwarf galaxy progenitor, and the functional form of the dwarf galaxy progenitor are known exactly), the density and angular width of stars along the stream can be used to constrain the mass and radial profile of both the stellar and dark matter components of the progenitor dwarf galaxy that was ripped apart to create the stream. our provisional fit for the parameters of the dwarf galaxy progenitor of the orphan stream indicates that it is less massive and has fewer stars than previous works have indicated. | streams and the milky way dark matter halo |
the macro-scale properties of dark matter (dm) halos, including their shape and orientation, are sensitive to the micro-physics of the dark matter particle. yet in many cases, the symmetry axes of the milky way's dark matter halo are often assumed to be aligned with the symmetry axes of the stellar disk when modeling the mass distribution. while this is well-motivated for the inner regions of the dark matter halo, there is no obvious reason for the outer dark matter halo to have the same alignment, given the large difference in dynamical times. in this work, we use zoomed cosmological-baryonic simulations from the fire-2 suite to explore the evolution of the dark matter halo's orientation with radius and time, in the presence or absence of a major merger with a large magellanic cloud (lmc) analog, and when varying the dark matter model. in three of the four cdm halos we examine, the orientation of the halo minor axis diverges from that of the stellar disk by more than 20 degrees beyond about 30 kpc galactocentric. the angular offset between the halo and disk symmetry axes reaches a maximum of 30-90 degrees depending on the individual halo's formation history. in simulations with identical initial conditions but assuming a model of self-interacting dark matter (sidm) with σ = 1 cm2 g-1, the halo remains aligned with the stellar disk to much larger radii, out to ~200-400 kpc. interactions with massive satellites affect the orientation of the halo relative to the disk significantly (i.e. above the stochastic variation in halos without perturbers) for perturber masses ≳ 4 × 1010 m⊙ at pericenter (≳ 3.3 × 1010 m⊙ at infall), inducing a varying degree of alignment of the halo's major axis to the satellite galaxy from the stellar disk out to the virial radius. our results indicate that the relative orientation of the halo and disk beyond 30 kpc can in principle be used as a diagnostic of dm self-interaction, but only if the effects of massive merging satellites can be properly accounted for. | orientations of dark matter halos in cdm and sidm latte galaxies |
nimble (non-parametric jeans modeling with b-splines) inferrs the cumulative mass distribution of a gravitating system from full 6d phase space coordinates of its tracers via spherical jeans modeling. it models the milky way's dark matter halo using gaia and dark energy spectroscopic instrument milky way survey (desi mws) data. nimble includes a basic inverse modeling jeans routine that assumes perfect and complete data is available and a more complex forward modeling jeans routine that deconvolves observational effects (uncertainties and limited survey volume) characteristic of gaia and the desi-mws. it also includes tools for generating simple equilibrium model galaxies using agama (ascl:1805.008) and imposing mock gaia+desi errors on 6d phase space input data. | nimble: non-parametric jeans modeling with b-splines |
the mass and cumulative mass profile of the milky way's dark matter halo is a fundamental property of the galaxy, and yet these quantities remain poorly constrained and span almost two orders of magnitude in the literature. there are a variety of methods to measure the mass of the milky way, and a common way to constrain the mass uses kinematic information of satellite objects (e.g. globular clusters) orbiting the galaxy. one reason precise estimates of the mass and mass profile remain elusive is that the kinematic data of the globular clusters are incomplete; for some both line-of-sight and proper motion measurements are available (i.e. complete data), and for others there are only line-of-sight velocities (i.e. incomplete data). furthermore, some proper motion measurements suffer from large measurement uncertainties, and these uncertainties can be difficult to take into account because they propagate in complicated ways. past methods have dealt with incomplete data by using either only the line-of-sight measurements (and throwing away the proper motions), or only using the complete data. in either case, valuable information is not included in the analysis. during my phd research, i have been developing a coherent hierarchical bayesian method to estimate the mass and mass profile of the galaxy that 1) includes both complete and incomplete kinematic data simultaneously in the analysis, and 2) includes measurement uncertainties in a meaningful way. in this presentation, i will introduce our approach in a way that is accessible and clear, and will also present our estimates of the milky way's total mass and mass profile using all available kinematic data from the globular cluster population of the galaxy. | bayesian mass estimates of the milky way: inferring the mass profile from globular cluster kinematics |
the axion was introduced over forty years ago to explain the apparent symmetry of the strong nuclear force under time-reversal tand space inversion p. later, it became a leading dark matter candidate when laboratory searches indicated its decay constant is large compared to the electroweak symmetry breaking scale. yet, the most sensitive direct searches for axions in the local dark matter halo of the galaxy using radio-frequency electromagnetic cavities have yielded no positive results. in this talk we argue that measurements of the muon magnetic moment at the level of precision currently achieved using muon beams in storage rings can directly detect such axions in a couple runs provided the axion mass lies in the near-infrared regime and the beam cross-section can be increased to 10 cm2 while keeping fixed the number of muons in the beam. we give a symmetry argument that leads to a mass in this range provided axions form the bulk of the dark matter in the observable universe. finally, we show that axions saturate the dark matter density in the local halo by evaluating their contribution to the t and p breaking decay of the long-lived neutral k meson into a pair of charged pions. | weighing the axion with muon haloscopy |
the keplerian distribution of velocities is not observed in the rotation of large scale structures, such as found in the rotation of spiral galaxies. the deviation from keplerian distribution provides compelling evidence of the presence of non-luminous matter i.e. called dark matter. there are several astrophysical motivations for investigating the dark matter in and around the galaxy as halo. in this work we address various theoretical and experimental indications pointing towards the existence of this unknown form of matter. amongst its constituents neutrino is one of the most prospective candidates. we know the neutrinos oscillate and have tiny masses, but there are also signatures for existence of heavy and light sterile neutrinos and possibility of their mixing. altogether, the role of neutrinos is of great interests in cosmology and understanding dark matter. | dark matter and neutrinos |
based on the recently discovered correlations between the half-light radii and dark matter halo parameters of milky way dwarf spheroidal galaxies, we infer the initial distributions of baryonic and dark matter in the first galaxies. | inferring the initial mass distributions of the first galaxies from observed correlations between the half-light radii and dark matter halo parameters of milky way dwarf spheroidals |
dark matter and dark energy comprise most of the energy density of the universe; however, we know very little about either of them. we have only seen their effects on astrophysics and cosmology, and these remain the best ways to test these theories. i have focused my dissertation on testing various dark matter and dark energy theories with astrophysical data. this includes work testing verlinde's emergent gravity theory with dwarf galaxies, higher-dimensional dark energy theories with gravitational waves, self-interacting dark matter with galaxy warps, and modified gravity theories of dark matter with baryonic acoustic oscillations. in this talk, i will focus on just one of these projects: how self-interacting dark matter can be constrained with galaxy warps. for some types of self-interactions, the passage of a galaxy through some background dark matter overdensity will cause a separation of centroids between the collisionless stars and the dark matter halo of the galaxy, which will be experiencing a drag force due to self-interactions. for stars arranged in a disk, this would cause a u-shaped warp of the disk. we have looked for these u-shaped warps in the sloan digital sky survey and have used this to place competitive constraints on the self-interaction cross section. | constraining self-interacting dark matter with galaxy warps |
for over three decades cosmological simulations have predicted the properties of dark matter in the cold dark matter (cdm) paradigm. most observational efforts have focused on verifying the small-scale predictions of cdm. despite significant advances in understanding the milky way in the context of the prevailing lcdm paradigm, the fundamental parameters describing the large-scale properties of the dark matter in our galaxy (e.g. its total mass and its 3d shape) are very uncertain. since it is impossible to directly observe dark matter, the best way of mapping its distribution is through dynamical analysis of motions of tracer populations, such as halo stars and globular clusters. we are at a unique moment in time when the availability and quality of data for modeling the 3d structure of galactic dark matter greatly surpass the accuracy and flexibility of the dynamical modeling tools . the goals of this proposal are two fold. first we will improve the flexibility of a recently developed dynamical modeling code (distribution function (df) fitting using orbital actions) and apply it to the astrometric data currently being obtained by the european space agency s gaia astrometric satellite to determine fundamental properties of the milky way's dark matter halo: (a) its total mass and density profile; (b) its three dimensional shape and its variation with radius. to ensure the robustness of our code and to assess the sensitivity of the results to disequilibrium in the milky way (due to recently discovered impacts on the disk and perturbations in the halo) we will apply the code to a large sample of publicly available mock gaia data. the second goal of this proposal is to explore the possibility of testing, for the first time, a prediction of lcdm that has been known for over two decades: triaxial dark matter halos should have extremely slow figure rotation. our recent work shows that stellar tidal streams can be sensitive probes of such figure rotation. our team has the ideal combination of expertise in dynamical modeling, simulations, and statistical data analysis that is necessary to achieve our goals. collaborator vasiliev has developed a state-of-the-art, publicly available galactic dynamics package agama which enables the efficient compution of actions in general axisymmetric potentials. he will update agama so that it can efficiently and robustly compute actions in triaxial systems following a method for which proof-of-concept has already been demonstrated. we will enhance agama's speed and efficiency by gpu acceleration, which is necessary to deal with the extremely large gala data sets. collaborator hattori has developed a new df fitting code, igalapagos (based on agama), that use observed kinematical data from gaia to simultaneously model the df of the stellar halo and constrain the shape of the dark matter halo potential. hattori will implement the triaxial action finder from agama to measure triaxiality and its variation with radius. pi valluri has significant prior experience with dynamical modeling, and analysis of simulated stellar and dark matter halos. she recently discovered that the predicted figure rotation of dark matter halos is measurable with tidal streams and will use simulations and bayesian inference modeling to measure this for the milky way. this multifaceted approach to robustly model the exquite quality data from the gaia space mission will allow us to not only determine some of the fundamental large-scale properties of our galaxy's large halo, but it will allow us to test predictions of lcdm and understand our home galaxy in a cosmological context, meeting one of the major objectives of nasa's astrophysics program. | exploring the nature of dark matter with gaia |
we propose to measure the proper motion (pm) of m31 stars to unprecedented precision, using multi-epoch hst data of seven acs/wfc fields. our first goal is to measure m31's mean tangential motion with a precision nearly triple that of the previous hst and gaia measurements. the better-determined center-of-mass (com) motion of m31 will be essential for refining models of the local universe, the orbits of objects in m31's halo, the total dark matter halo masses of the milky way (mw) and m31, and the evolution and fate of the mw. second, we will clearly resolve the internal kinematics of m31 with pms. we will obtain useful precision for multiple structural components and even the brighter individual stars. we will measure the bulk flows between cold components such as m31's disk and giant stream, and resolve the tangential velocity dispersion in m31's hot halo. third, we will obtain the pm of m32 for the first time. this will provide crucial information about m32's orbit, evolution, and interactions with m31. in particular, we will test scenarios where it is the stripped remnant of a major merger, responsible for shaping many of m31's properties. gaia (which can only measure young m31 disk stars) cannot undertake the differential pm investigations proposed here, and would require many more years of data to compete with our expected m31 com motion. based on previous works, the pm accuracies required for our scientific goals are well within reach of hst's demonstrated capabilities. hst's 2012 m31 bulk pm measurements were highly publicized, but due to hst's longevity it is now possible to address many new questions that were previously out of reach. | resolved proper motions of m31 and the m31-m32 interaction |
every field observed more than once by the wfirst telescope is an astrometric survey. this includes the high-latitude survey fields, which span several thousand square degrees. the large synoptic space telescope will identify rr lyrae stars with extremely accurate distance measurements to beyond the virial radius of the milky way, so that in fields observed by wfirst over multiple epochs, these stars will have complete six-dimensional phase space coordinates throughout the milky way's dark halo. using synthetic surveys of cosmological mock stellar halos, we show how wfirst proper motions will connect tidal streams in the outer halo with the map of the inner halo produced by gaia, and how these connections can constrain the shape and mass of the milky way's dark matter halo. | wfirst: mapping the milky way’s dark matter halo with wfirst astrometry |
an excess of gamma rays from the inner galaxy in the fermi lat data has been identified. this emission has been interpreted as a possible signature of the annihilation of dark matter particles, or as originating from a collection of unresolved point sources, such as gamma-ray millisecond pulsars. we explore the clustering properties of the diffuse emission arising from a population of gamma-ray point sources and from the annihilation of dark matter particles in the halo of the galaxy using the 1-pt probability distribution function of counts in pixels (1pt-pdf, the number of pixels with a specified number of counts as a function of counts); this approach is also known as fluctuation analysis or p(d) analysis. we analyze the 1-pt pdf of the gev excess within a +/- 5 degree box around the galactic center. for both dark matter and point sources we adopt the spatial distribution and spectrum to fit the gev excess. we determine the contributions to the 1-pt pdf from the galactic diffuse and isotropic diffuse emissions, dark matter, and point sources, and discuss the implications of this analysis for the origin of the gev excess. | dark matter or point sources? utilizing the 1-pt pdf to understand the origin of the gev excess seen by the fermi lat detector |
the current cosmological paradigm predicts that dark matter halos are triaxial overall, but oblate in regions where baryons dominate. however recent measurements of the shape of the milky way dark matter halo find it to be very triaxial with a shape and orientation that are significantly at odds with theoretical predictions. the esa’s gaia satellite will soon map the entire milky way giving us six phase-space coordinates, ages and abundances for hundreds of thousands of halo stars. i will report progress on a new code based on the schwarzschild orbit superposition method and orbital frequency mapping, to determine the global shape of the milky way's dark matter halo using field stars from gaia. this technique will simultaneously yield the self-consistent phase-space distribution function of the stellar halo in the inner 20-30kpc region. detailed analysis of correlations between the chemical abundances, ages and orbits of halo stars in this distribution function will enable us to extract clues to the formation history of the milky way that are encoded in orbital properties of halo stars. | using accurate phase space coordinates of ~100,00 halo field stars to constrain the milky way halo |
x-ray observations of nearby clusters and galaxies have reported an unexpected x-ray line around 3.5 kev. this line has received significant attention due to its possible explanation through decaying dark matter; in particular, decaying sterile neutrino models, with a sterile neutrino mass around 7 kev, provide a good fit to the available data. we use over 30 ms of xmm-newton blank-sky observations to search for evidence of the 3.5 kev line consistent with arising from decaying dark matter within the ambient halo of the milky way. we find the strongest limits to-date on the lifetime of dark matter in this mass range, strongly disfavoring the possibility that the 3.5 kev line originates from dark matter decay. this research was supported by the doe under contracts desc00012567 and desc0013999. i am also supported by the miller institute for basic research in science at the university of california, berkeley. | evidence the 3.5 kev line is not from dark matter decay |
with its observations over 2/3 of the sky every day, the high altitude water cherenkov (hawc) observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. dark matter annihilation and decay in the dark matter halo of the milky way galaxy should produce gamma-ray signals which are spatially extended on the sky. we present a limits on the dark matter annihilation cross-section and decay lifetime from hawc observations of the galactic halo from 15 months of hawc data. these are some of the most robust limits on tev and pev dark matter and are largely insensitive to the dark matter morphology. in particular, we show that these limits can constrain dark matter models in which pev icecube neutrinos are explained by dark matter which primarily decays into hadrons. | searches for dark matter in the galactic halo with the high altitude water cherenkov observatory |
we incorporate milky way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the galactic center extended gamma-ray excess (gce) detected by the fermi gamma ray space telescope. the range of particle annihilation rate and masses expand when including these unknowns. however, two of the most precise empirical determinations of the milky way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. accordingly, we accurately quantify this tension in a joint likelihood analysis. we determine which particle dark matter models are favored in the case of a high local dark matter density scenario and in the case where dark matter differentiates between the gc and dwarfs, specifying what part of the parameter space for such models is most favored. intended for the focus session on the gev excess. | implications of tension between observations of the bright galactic center excess and dim dwarf galaxies |
one of the most exciting recent results in the field of dark matter indirect searches has been the discovery of an excess emission in gamma rays from the galactic centre above the standard astrophysical background. we show that current hydrodynamic simulations, namely simulated milky way-like galaxies within the “evolution and assembly of galaxies and their environments” (eagle) project, challenge the possibility to interpret the gev excess as due to annihilation of dark matter particles in the halo if the milky way. | the fermi gev excess: challenges for the dark matter interpretation |
the axion is a hypothetical elementary particle arising in the 1970's from an elegant solution to the strong cp problem in quantum chromo dynamics. light qcd axions (masses <10-3 ev/c2) would have extraordinarily feeble interactions with normal matter and radiation, and these axions have the properties of an ideal dark-matter candidate. axions have been searched for since their inception. however, light axions constituting dark matter are so feebly coupled that it is only recently that detection technology has advanced to where such axions might be detected. several large searches are in the construction and commissioning phase, with new projects in the development phase. there are also concepts for new detector technologies aimed at improving the sensitivity and axion mass-reach. these searches would have the potential to detect even the more pessimistically-coupled dark-matter axions should they contribute a fraction of the local milky way dark-matter halo. this talk discusses the dark-matter axion experimental landscape and the prospects for their discovery. supported by the u.s. department of energy, office of high energy physics. | searching for dark-matter axions |
the origin of the satellite disc of the milky way (dos or vpos) and m31 (gpoa) remains an open problem in astrophysics (klypling, kravtsov, & valenzuela, 1999; pawlowski, kroupa, & jerjen, 2013). this paper presents a study on the possible formation of the milky way satellite disc from an association of dwarf galaxies that infall into the milky way dark matter halo in parabolic orbits. for this, we performed newtonian numerical simulations of n-bodies taking values for the initial distances of 4, 2 and 1 mpc. morphological properties of dwarfs were analyzed after a simulation time of 10 gy, proposed for the interaction with the milky way, taking into account: the distributions obtained around the plane of the host galaxy, the distances to which the dwarfs are located, their density profiles and their velocity dispersion. one results is that, after 10 gy of fall, the structures remain compact maintaining their morphological properties, with better results when the halo of dark matter that envelops them is included. only associations of dwarf galaxies located at distances of 1 mpc these manage to enter the halo of the galaxy. this is supported by the fact that these closest associations are those that have fallen in towards the halo of the galaxy, which is why no associations of dwarfs are observed at these distances in the local group, the closet association being 14+12 at a distance of 1.37 mpc from the milky way (tully, 2006). | infall of associations of dwarf galaxies into the milky way halo |
a wealth of astrophysical and cosmological observational evidence shows that the matter content of the universe is made of about 85$\%$ of non-baryonic dark matter. huge experimental efforts have been deployed to look for the direct detection of dark matter via their scattering on target nucleons, their production in colliders, and their indirect detection via their annihilation products. inelastic scattering of high-energy cosmic rays off dark matter particles populating the milky way halo would produce secondary gamma rays in the final state from the decay of the neutral pions produced in such interactions, providing a new avenue to probe dark matter properties. we compute here the sensitivity for h.e.s.s.-like observatory, a current-generation ground-based cherenkov telescopes, to the expected gamma-ray flux from collisions of galactic cosmic rays and dark matter in the center of the milky way. we also derive sensitivity prospects for the upcoming cherenkov telescope array (cta) and southern wide-field gamma-ray observatory (swgo). the expected sensitivity allows us to probe a poorly-constrained range of dark matter masses so far, ranging from kev to sub-gev, and provide complementary constraints on the dark matter-proton scattering cross section traditionally probed by deep underground direct dark matter experiments. | sensitivity to kev-mev dark matter from cosmic-ray scattering with current and the upcoming ground-based arrays cta and swgo |
our current understanding of how dark matter (dm) is distributed within the milky way (mw) halo, particularly in the solar neighborhood, is based on either careful studies of the local stellar orbits or model assumptions on the global shape of the mw halo. in this work, we undertake a study of external galaxies, with the intent of providing insight to the dm distribution in mw-analog galaxies. for this, we carefully select a sample of galaxies similar to the mw, based on maximum atomic hydrogen (hi) rotational velocity (v=200-280 km s^{-1}) and morphological type (sab-sbc) criteria. with a need for deep, highly-resolved hi, our resulting sample is composed of 5 galaxies from the viva and things surveys. to perform our baryonic analysis, we use deep spitzer mid-ir images at 3.6 and 4.5 {\mu}m from the s4g survey. based on the dynamical three-dimensional modeling software 3d-barolo, we construct rcs and derive the gas and stellar contributions from the galaxyś gaseous- and stellar-disks mass surface density profiles. through a careful decomposition of their rotation curves into their baryonic (stars, gas) and dm components, we isolate the dm contribution by using an mcmc-based approach. based on the sunś location and the mwś r_{25}, we define the corresponding location of the solar neighborhood in these systems. we put forward a window for the dm density (\rho=0.21-0.46 gev cm^{-3}) at these galactocentric distances in our mw analog sample, consistent with the values found for the mwś local dm density, based on more traditional approaches found in the literature. | dark matter distribution in milky way-analog galaxies |
stellar streams are sensitive tracers of the gravitational potential, which is typically assumed to be static in the inner galaxy. however, massive mergers like gaia-sausage-enceladus can impart torques on the stellar disk of the milky way that result in the disk tilting at rates of up to 10-20 deg/gyr. here, we demonstrate the effects of disk tilting on the morphology and kinematics of stellar streams. through a series of numerical experiments, we find that streams with nearby apocenters $(r_{\rm apo} \lesssim 20~\rm{kpc})$ are sensitive to disk tilting, with the primary effect being changes to the stream's on-sky track and width. interestingly, disk tilting can produce both more diffuse streams and more narrow streams, depending on the orbital inclination of the progenitor and the direction in which the disk is tilting. our model of pal 5's tidal tails for a tilting rate of 15 deg/gyr is in excellent agreement with the observed stream's track and width, and reproduces the extreme narrowing of the trailing tail. we also find that failure to account for a tilting disk can bias constraints on shape parameters of the milky way's local dark matter distribution at the level of 5-10%, with the direction of the bias changing for different streams. disk tilting could therefore explain discrepancies in the milky way's dark matter halo shape inferred using different streams. | slant, fan, and narrow: the response of stellar streams to a tilting galactic disk |
recent measurements of muon spin precession confirm a long-standing tension with the standard model of particle physics. we argue that axions from the local dark matter halo of the galaxy are responsible for the tension. the argument yields a percent level prediction for the mass of the axion provided that dark matter is made of axions. an analysis of charge asymmetry in kaon decays suggests that at least in the local halo dark matter is made of axions and that axions from the local halo are responsible for the observed violation by these reactions of the combined charge conjugation and spatial inversion symmetry operation. a tabletop experiment to directly detect dark matter in the form of axions with the predicted mass is proposed. | weighing the axion with muon haloscopy |
we report the detection of a 282 $^{+34}_{-31}$ pc-sized core in the center of milky way dark matter halo at $68\%$ confidence level by using the micro-lensing event rate sky map data from the optical gravitational lensing experiment (ogle) survey. we apply the spacial information of the micro-lensing sky map and model it with the detailed milky way dark matter halo core/cusp profile, and the fraction of dark matter in the form of mini dark matter structure (mdms, $f_{\rm mdms}=\omega_{\rm mdms}/\omega_{\rm dm}$), e.g. primordial black hole, earth-mass subhalos, floating planets and so on. we find that this sky map can constrain both $f_{\rm mdms}$ and the core size simultaneously without strong degeneracy while fully considering mass function of milky way stellar components from both the bulge and disk. | a $\\sim$300 pc-sized core of milky way dark matter halo constrained from the ogle micro-lensing sky map |
ecosystems are responding to climate change and increasing atmospheric co2 concentrations. interactions between these factors have rarely been assessed experimentally during and after extreme climate events despite their predicted increase in intensity and frequency and their negative impact on primary productivity and soil carbon stocks. here, we document how a grassland exposed to a forecasted 2050s climate shows a remarkable recovery of ecosystem carbon uptake after a severe drought and heat wave, this recovery being amplified under elevated co2. over the growing season, elevated co2 entirely compensated for the negative impact of extreme heat and drought on net carbon uptake. this study highlights the importance of incorporating all interacting factors in the predictions of climate change impacts. | elevated co2 maintains grassland net carbon uptake under a future heat and drought extreme |
the colorado ultraviolet transit experiment (cute) is a 6u nasa cubesat carrying on-board a low-resolution, near-ultraviolet (2479-3306 å) spectrograph. it has a cassegrain telescope with a rectangular primary to maximize the collecting area, given the shape of the satellite bus, and an aberration correcting grating to improve the image quality, and thus spectral resolution. cute, launched on the of 2021 september 27th to a low earth orbit, is designed to monitor transiting extra-solar planets orbiting bright, nearby stars to improve our understanding of planet atmospheric escape and star-planet interaction processes. we present here the cute autonomous data reduction pipeline, developed for reducing cute data. the pipeline has been structured with a modular approach, which also considers scalability and adaptability to other missions carrying on-board a long-slit spectrograph. the cute data simulator has been used to generate synthetic observations used for developing and testing the pipeline functionalities. the pipeline has been tested and updated employing flight data obtained during commissioning and initial science operations of the mission. | the autonomous data reduction pipeline for the cute mission |
the absorption of stellar radiation observed by hd 209458b in the resonant lines of o i and c ii has not yet been satisfactorily explained. we apply a 2d hydrodynamic multi-fluid model that self-consistently describes the expanding planetary wind, driven by stellar xuv radiation and influenced by tidal forces and the surrounding stellar wind. according to this model, hd 209458b has a hydrogen-dominated plasmasphere, expanding beyond the roche lobe, in the form of two supersonic streams that propagate toward and away from the star. the species heavier than hydrogen and helium are dragged in the escaping material streams and accelerated up to 50 km s-1. our simulations show that, assuming solar abundances, o i and c ii produce absorption due to the doppler resonance mechanism at the level of 6%-10%, which is consistent with the observations. most of this absorption takes place in the streams. the transit depth in the o i and c ii lines is unaffected by the stellar wind, unless it is strong enough to form a compact bowshock around the planet and able to redirect all the escaping material to the tail. in this case, the absorption profile becomes asymmetric due to the prominent blueshifted attenuation. thus, the spectroscopic measurements enable probing of the planetary wind character, as well as the strength of the stellar wind. the computed absorption at wavelengths of the si iii, mg i, and mg ii lines at solar abundances appears to be much stronger, compared to the observations. this possibly indicates that si and mg may be under-abundant in the upper atmosphere of hd 209458b. | modeling of absorption by heavy minor species for the hot jupiter hd 209458b |
the magnetic fields of the solar system's planets provide valuable insights into their interiors and can have dramatic consequences for the evolution of their atmospheres and interaction with the solar wind. however, we have little direct knowledge of magnetic fields in exoplanets. here we present a method for detecting magnetic fields in the atmospheres of close-in exoplanets based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. this methodology has been successfully applied for exploring magnetic fields in solar coronal filaments. strong absorption signatures (transit depths on the order of a few percent) in the 1083 nm line have recently been observed for several close-in exoplanets. we show that in the conditions in these escaping atmospheres, metastable helium atoms should be optically pumped by the starlight and, for field strengths more than a few × 10-4 g, should align with the magnetic field. this results in linearly polarized absorption at 1083 nm that traces the field direction (the hanle effect), which we explore by both analytic computation and the hazel numerical code. the linear polarization √{{q}^{2}+{u}^{2}}/i ranges from ∼10-3 in optimistic cases down to a few × 10-5 for particularly unfavorable cases, with very weak dependence on field strength. the line-of-sight component of the field results in a slight circular polarization (the zeeman effect), also reaching v/i∼ few × {10}^{-5}({b}_{\parallel }/10 g). we discuss the detectability of these signals with current (spirou) and future (extremely large telescope) high-resolution infrared spectropolarimeters, and we briefly comment on possible sources of astrophysical contamination. | detecting magnetic fields in exoplanets with spectropolarimetry of the helium line at 1083 nm |
we estimate the contribution of the molecular hydrogen dissociation processes, which are induced by the extreme uv radiation and the accompanying flux of photoelectrons, to the formation of a fraction of suprathermal atomic hydrogen in the h2 → h transition region and the corresponding escape flux from the extended upper atmosphere of an exoplanet—the hot neptune gj 436b (gliese 436b). we calculate the formation rate and the energy spectrum of hydrogen atoms, which are formed with the excess of kinetic energy when h2 dissociates. with a numerical stochastic model of a hot planetary corona, we study at the molecular level the kinetics and transfer of suprathermal hydrogen atoms in the extended upper atmosphere and calculate the nonthermal escape flux. the escape flux has been estimated as 3.0 × 1012 cm-2 s-1 for moderate activity of the star in the uv-radiation range, from which an upper estimate for the rate of the atmospheric loss caused by the h2 dissociation processes has been found at 7.8 × 108 g s-1. the calculated value is within a range of approximately 3.7 × 106 to 1.1 × 109 g s-1 for the estimates of the possible atmospheric loss rate obtained in observations of the exoplanet gj 436b. the rate of the atmospheric loss due to suprathermal hydrogen atoms, which was estimated in calculations for the exoplanet gj 436b, may be considered as a mean value, since the calculations were performed for the conditions corresponding to moderate uv-radiation activity of the star and the smallest values of the probabilities for predissociation of the excited electron levels of a h2 molecule. we recommend this source of suprathermal hydrogen atoms to be included to the current aeronomic models of physical and chemical processes in the upper atmospheres of hot exoplanets. | nonthermal atmospheric loss of the exoplanet gj 436b due to h2 dissociation processes |
observations of extended atmospheres around hot planets have generated exciting results concerning the dynamics of escaping planetary material. the configuration of the escaping planetary gas can result in asymmetric transit features, producing both pre- and post-transit absorption in specific atomic transitions. measuring the velocity and strength of the absorption can provide constraints on the mass loss mechanism, and potentially clues to the interactions between the planet and the host star. here we present a search for hα absorption in the circumplanetary environments of the hot planets kelt-3 b and gj 436 b. we find no evidence for absorption around either planet at any point during the two separate transit epochs for which each system was observed. we provide upper limits on the radial extent and density of the excited hydrogen atmospheres around both planets. the null detection for gj 436 b contrasts with the strong lyα absorption measured for the same system, suggesting that the large cloud of neutral hydrogen is almost entirely in the ground state. the only confirmed exoplanetary hα absorption to date has been made around the active star hd 189733 b. kelt-3 and gj 436 are less active than hd 189733, hinting that exoplanet atmospheres exposed to euv photons from active stars are better suited for detection of hα absorption. | a search for hα absorption around kelt-3 b and gj 436 b |
hydrogen and helium transmission signals trace the upper atmospheres of hot gas-giant exoplanets, where the incoming stellar extreme ultraviolet and x-ray fluxes are deposited. further, for the hottest stars, the near-ultraviolet excitation of hydrogen in the balmer continuum may play a dominant role in controlling the atmospheric temperature and driving photoevaporation. kelt-9 b is the archetypal example of such an environment as it is the hottest gas-giant exoplanet known to date (teq ∼ 4500 k) and orbits an a0v-type star. studies of the upper atmosphere and escaping gas of this ultra-hot jupiter have targeted the absorption in the balmer series of hydrogen (n1 = 2 → n2 > 2). unfortunately, the lowermost metastable helium state that causes the triplet absorption at 1083 å is not sufficiently populated for detection. this is due to the low extreme-ultraviolet and x-ray fluxes from the host star, and to its high near-ultraviolet flux, which depopulates this metastable state. here, we present evidence of hydrogen absorption in the paschen series in the transmission spectrum of kelt-9 b observed with the high-resolution spectrograph carmenes. specifically, we focus on the strongest line covered by its near-infrared channel, paβ at 12 821.6 å (n1 = 3 → n2 = 5). the observed absorption shows a contrast of (0.53 −0.13+0.12)%, a blueshift of −14.8 −3.2+3.5 km s−1, and a full width at half maximum of 31.9−8.3+11.8 km s−1. the observed blueshift in the absorption feature could be explained by day-to-night circulation within the gravitationally bound atmosphere or, alternatively, by paβ absorption originating in a tail of escaping gas moving toward the observer as a result of extreme atmospheric evaporation. this detection opens a new window for investigating the atmospheres of ultra-hot jupiters, providing additional constraints of their temperature structure, mass-loss rates, and dynamics for future modeling of their scorching atmospheres. | detection of paschen β absorption in the atmosphere of kelt-9 b. a new window into the atmospheres of ultra-hot jupiters |
we develop platypos (planetary photoevaporation simulator), a python code to perform planetary photoevaporative mass-loss calculations for close-in planets with hydrogen-helium envelopes atop earth-like rocky cores. with physical and model parameters as input, platypos calculates the atmospheric mass loss and with it the radius evolution of a planet over time, taking into account also the thermal cooling and subsequent radius evolution of the planet. in particular, we implement different stellar activity evolution tracks over time. our setup allows for a prediction of whether a planet can hold on to a significant fraction of its atmosphere, or fully evaporates, leaving behind only the bare rocky core. the user supplies information about the star-planet system of interest, which includes planetary and host star parameters, as well as the star's rotational and thus activity evolution. in addition, several details for the evaporative mass-loss rate estimation can be chosen. this includes the effective absorption cross-section for high energy photons, the evaporation efficiency, and the hydrodynamic escape model. | estimating photoevaporative mass loss of exoplanets with platypos |
we propose a new method to estimate ion escape from unmagnetized planets that combines observations and models. assuming that upstream solar wind conditions are known, a computer model of the interaction between the solar wind and the planet is executed for different ionospheric ion production rates. this results in different amounts of mass loading of the solar wind. we then obtain the ion escape rate from the model run that best fits observations of the bow shock location. as an example of the method, we estimate the heavy-ion escape from mars on 1 march 2015 to be 2×1024 ions s−1, using a hybrid plasma model and observations by the mars atmosphere and volatile evolution (maven) and mars express (mex) missions. this method enables studies on how escape depends on different parameters as well as studies on escape rates during extreme solar wind conditions; moreover, the technique is applicable to studies of escape in the early solar system and at exoplanets. | estimating ion escape from unmagnetized planets |
numerous exoplanets with masses ranging from earth to neptune and radii larger than earth have been found through observations. these planets possess atmospheres that range in mass fractions from 1% to 30%, reflecting the diversity of atmospheric mass fractions. such diversities are supposed to be caused by differences in the formation processes or evolution. here, we consider head-on giant impacts onto planets causing atmosphere losses in the later stage of their formation. we perform smoothed particle hydrodynamic simulations to study the impact-induced atmosphere loss of young super-earths with 10%-30% initial atmospheric mass fractions. we find that the kinetic energy of the escaping atmosphere is almost proportional to the sum of the kinetic impact energy and self-gravitational energy released from the merged core. we derive the relationship between the kinetic impact energy and the escaping atmosphere mass. the giant impact events for planets of comparable masses are required in the final stage of the popular scenario of rocky planet formation. we show it results in a significant loss of the atmosphere, if the impact is a head-on collision with comparable masses. this latter fact provides a constraint on the formation scenario of rocky planets with substantial atmospheres. | giant impact events for protoplanets: energetics of atmospheric erosion by head-on collision |
one of the most well-studied exoplanets to date, hd 189733 b, stands out as an archetypal hot jupiter with many observations and theoretical models aimed at characterizing its atmosphere, interior, host star, and environment. we report here on the results of an extensive campaign to observe atmospheric escape signatures in hd 189733 b using the hubble space telescope and its unique ultraviolet capabilities. we have found a tentative, but repeatable in-transit absorption of singlyionized carbon (c ii, 5.2% ± 1.4%) in the epoch of june-july/2017, as well as a neutral hydrogen (h i) absorption consistent with previous observations. we model the hydrodynamic outflow of hd 189733 b using an isothermal parker wind formulation to interpret the observations of escaping c and o nuclei at the altitudes probed by our observations. our forward models indicate that the outflow of hd 189733 b is mostly neutral within an altitude of ~2 r p and singly ionized beyond that point. the measured in-transit absorption of c ii at 1335.7 å is consistent with an escape rate of ~1.1 × 1011 g s-1, assuming solar c abundance and an outflow temperature of 12,100 k. although we find marginal neutral oxygen (o i) in-transit absorption, our models predict an in-transit depth that is only comparable to the size of measurement uncertainties. a comparison between the observed lyα transit depths and hydrodynamics models suggests that the exosphere of this planet interacts with a stellar wind at least 1 order of magnitude stronger than solar. | hydrodynamic atmospheric escape in hd 189733 b: signatures of carbon and hydrogen measured with the hubble space telescope |
photoevaporation is a potential explanation for several features within exoplanet demographics. atmospheric escape observed in young neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this evolution and at what times they dominate. au mic b is one such exoplanet, slightly larger than neptune (4.19 r ⊕). it closely orbits a 23 myr pre-main-sequence m dwarf with an orbital period of 8.46 days. we obtained two visits of au mic b at lyα with hubble space telescope (hst)/space telescope imaging spectrograph. one flare within the first hst visit is characterized and removed from our search for a planetary transit. we present a nondetection in our first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. the outflow absorbed ~30% of the star's lyα blue wing 2.5 hr before the planet's white-light transit. we estimate that the highest-velocity escaping material has a column density of 1013.96 cm-2 and is moving 61.26 km s-1 away from the host star. au mic b's large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes, rendering it temporarily unobservable. our time-variable lyα transit ahead of au mic b could also be explained by an intermediate stellar wind strength from au mic that shapes the escaping material into a leading tail. future lyα observations of this system will confirm and characterize the unique variable nature of its lyα transit, which, combined with modeling, will tune the importance of stellar wind and photoionization. | the variable detection of atmospheric escape around the young, hot neptune au mic b |
the 2006 guinsaugon landslide in saint bernard, southern leyte, is one of the largest known landslides in the philippines in recent history. it consists of a 15-20 million m3 rockslide-debris avalanche from an approximately 675 m high mountain weakened by continuous movement of the philippine fault. the catastrophic guinsaugon landslide killed 1221 people and displaced 19 000 residents over its 4.5 km path. to investigate the present-day morphology of the scar and potential failure that may occur, analysis of a 5 m resolution insar-derived digital elevation model was conducted using coltop3d and matterocking software, leading to the generation of a landslide hazard map for the province of southern leyte in central philippines. the dip and dip direction of discontinuity sets that contribute to gravitational failure in mountainous areas of the province were identified and measured using a lower schmidt-lambert color scheme. after measurement of the morpho-structural orientations, potential sites of failure were analyzed. conefall was then utilized to compute the extent of rock mass runout. results of the analysis show instability in the scarp area of the 2006 guinsaugon landslide and in adjacent slopes because of the presence of steep discontinuities that range from 45 to 60°. apart from the 2006 guinsaugon landslide site, runout models simulated farther rock mass extent in its adjacent slopes, revealing a high potential for fatal landslides to happen in the municipality of saint bernard. concerned agencies may use maps produced in the same manner as this study to identify possible sites where structurally controlled landslides can occur. in a country like the philippines, where fractures and faults are common, this type of simulated hazard maps would be useful for disaster prevention and facilitate disaster risk reduction efforts for landslide-susceptible areas. | hazard mapping related to structurally controlled landslides in southern leyte, philippines |
4 debris avalanches pose some of the most destructive geologic hazards that threaten both 5 urban and rural populations around the world. on 20 september 2018, villages in naga city, 6 cebu, philippines, were devastated by a landslide that claimed 78 lives with 6 missing, joining 7 other catastrophic landslides in the country like the 1628 iriga and the 2006 guinsaugon debris 8 avalanches. understanding the mechanism of these gargantuan landslides and their correct 9 nomenclature are useful for hazard prevention and mitigation. in this study, we compare the 10 deposit characteristics of the naga city landslide with analog models and well-known historical 11 debris avalanche events/deposits in the philippines to understand factors that led to the landslide 12 disaster in naga city. physical characteristics obtained from aerial and satellite imagery, ground 13 surveys, recorded footage, borehole data, and lithologic maps provided a detailed dataset for 14 analyzing the conditions that led to the mass movement and the observed characteristics of 15 the naga landslide deposits. comparison with analog models of hummock formation and the 16 description of historical debris avalanche deposits show striking similarities, which were used 17 to demonstrate that the naga landslide was a rockslide-debris avalanche. the equations of 18 corominas (1996) and dade and huppert (1998) for long-runout rockfalls support this analysis. 19 the naga landslide event is an example of a well-documented debris avalanche, complete with 20 all the characteristics of this type of rapid mass movement. it is consistent with the descriptions 21 found in the literature with respect to its deposit features and mechanical behavior as de.ned by 22 laboratory models and empirically-derived equations. this study helps us understand historical 23 and future long-runout debris avalanches in order for scientists and authorities to .nd ways to 24 save lives. unfortunately, there was lack of appropriate hazards assessment on the site, which 25 had warnings in the form of the development of fractures at the headscarp of the landslide, a 26 month prior to the disaster. | anatomy of the naga city landslide and comparison with historical debris avalanches and analog models |
the rotation of the interplanetary magnetic field (imf) provides details of the escape mechanism that varies with the interaction between the intrinsic magnetic field and the imf. a multispecies magnetohydrodynamic simulation is conducted on a mars-like planet under the conditions of a weak intrinsic magnetic field and the imf rotating by 180° over 12 hr, which is comparable to the coronal mass ejection (cme) time scale. the total ion escape rate increases from ∼5 × 1023 s-1 to ∼3 × 1025 s-1 during the imf rotation from due north (parallel to the assumed intrinsic magnetic field) to due south (antiparallel to the assumed intrinsic magnetic field). the escape rate increases significantly with the imf rotating from due north to clock angles of 45°-75°, followed by a gentle increase until the imf rotates to due south. the trigger for the large increase is multiple reconnections in the magnetospheric flank region, and the subsequent increase is due to the expansion of the reconnection area into the equatorial region. the imf mass loading in the ionosphere is also responsible for the gentle increase with imf clock angles above 90° in addition to the flank reconnection. the imf rotation is a general feature for a cme. exoplanets orbiting in the vicinity of m-dwarfs might be frequently affected by imf rotation, as they could be exposed to severe stellar winds such as in cme environments, and the current study could be helpful for future planned observations of the exoplanetary environment. | enhanced ion escape rate during imf rotation under weak intrinsic magnetic field conditions on a mars-like planet |
we investigate the atmospheric and magnetospheric conditions of the massive, close-in exoplanet υ andromedae b (hereafter ups and b). in particular, we explore whether radio emission can be produced by the cyclotron maser instability (cmi), and whether this emission can escape from its source region. for this, we compare the local cyclotron frequency to the local plasma frequency. the planetary mass has a decisive impact on both of these frequencies: the cyclotron frequency depends on the (mass-dependent) estimate of the planetary magnetic moment, and the plasma frequency is determined by the (gravity-dependent) atmospheric profile. for this reason, the planetary mass is one of the decisive parameters determining whether the cmi can operate efficiently. as the precise planetary mass is unknown in the case of ups and b, we compare the plasma conditions for a range of hypothetical masses of the planet in order to determine at which mass the atmosphere becomes 'compact', i.e. is not strongly extended, and thus provides favourable conditions for the cmi. in the case of detected planetary radio emission, this approach can provide a new way to constrain the mass of an exoplanet for which only a minimum mass is known. | can radio emission escape from the magnetosphere of υ andromedae b - a new method to constrain the minimum mass of hot jupiters |
we estimated the contribution of reactions of exothermic photochemistry, namely, the dissociation of molecular hydrogen, by extreme uv radiation and the accompanying flux of photoelectrons, to the formation of a fraction of suprathermal atomic hydrogen in the h2 → h transition region of the extended upper atmosphere of an exoplanet—the hot sub-neptune π men c and the formation of the corresponding escape flux from the atmosphere. we calculate the formation rate and the energy spectrum of hydrogen atoms, which are formed with the excess of kinetic energy when h2 dissociates. with a numerical stochastic model of a hot planetary corona, we study at the molecular level the kinetics and transfer of suprathermal hydrogen atoms in the extended upper atmosphere and calculate the nonthermal escape flux. the escape flux has been estimated as 2.5 × 1012 cm-2 s-1 for moderate activity of the star in the uv-radiation range, from which an upper estimate for the rate of the atmospheric loss caused by the h2 dissociation processes has been found at 6.7 × 108 g s-1. the calculated value is close to the estimates of the possible atmospheric loss rate obtained in observations of the exoplanet π men c in the range no higher than 1.0 × 109 g s-1. the rate of the atmospheric loss due to suprathermal hydrogen atoms, which was estimated in calculations for the exoplanet π men c, may be considered as a mean value, since the calculations were performed for the conditions corresponding to moderate uv-radiation activity of the star and the smallest values of the probabilities for predissociation of the excited electron levels of a h2 molecule. we recommend this source of suprathermal hydrogen atoms to be included to the current aeronomic models of physical and chemical processes in the upper atmospheres of hot exoplanets. | nonthermal atmospheric loss of the sub-neptune π men c due to exothermic photochemistry |
in this work, numerical estimates of the rate of nonthermal loss of the atmosphere of a hot exoplanet due to exothermic photochemical processes are obtained. as an example, calculations were made for the h2 → h transition region of the upper atmosphere of the hot neptune gj 3470b in the altitude range 1.6-2.05 rp. from the obtained energy spectrum of the flux of suprathermal hydrogen atoms formed due to the processes of dissociation of h2 molecules and escaping from the atmosphere through the upper boundary of the transition region, an estimate equal to 3.4 × 1013 cm-2 s-1 was derived for the numerical escape flux in the planet-star direction under conditions of a moderate level of stellar activity. this calculated value of the numerical escape flux of suprathermal hydrogen atoms is close to the value of the numerical flux of thermal hydrogen atoms calculated by the jeans formula for the data of the aeronomic model and equal to 3.3 × 1013 cm-2 s-1. the calculated atmospheric mass loss flux averaged over the illuminated hemisphere of the upper atmosphere is 9.5 × 109 g/s at the upper boundary of the transition region. it can be concluded that nonthermal processes in the modeling of exoplanet atmospheres should be considered as one of the important factors determining the atmospheric mass loss, especially for hot exoplanets from the families of sub-neptunes and super-earths. | nonthermal atmospheric losses for the exoplanet gj 3470b |
the 23 myr system v1298 tau hosts four transiting planets and is a valuable laboratory for exploring the early stages of planet evolution soon after formation of the star. we observe the innermost planet, v1298 tau c, during transit using lbt pepsi to obtain high spectral resolution characterization of escaping material near the h-α line. we find no strong evidence for atmospheric material escaping at the orbital velocity of the planet. instead, we find a deep stellar feature that is variable on the few percent level, similar to a previous observation of the planet and can be explained by stellar activity. we attempted to monitor the broadband optical transit with lbt mods but do not achieve the precision needed to characterize the atmosphere or improve the ephemeris. | h-α variability of v1298 tau c |
the colorado ultraviolet transit experiment cubesat mission aims to observe atmospheric escape from a dozen or more exoplanets by monitoring them in the near-ultraviolet, explains principal investigator kevin france. | exploring extreme exoplanets |
atmospheric escape is an important sector in the evolution of planetary atmosphere, and its energy is mainly originated from the radiation of the host star at the high energy band. the radiation flux drops dramatically with the increase of orbital distance, there is a large difference of planetary atmospheric escape in different orbits, so it is necessary to study the impact of orbital distance on the atmospheric escape of an exoplanet. we consider the radiation transfer and the photochemical reactions of multiple kinds of particles to study the variation of planetary atmospheric escape with the orbital distance by using a 1-d hydrodynamic model. due to the large differences of the spectra of host stars in different evolution stages, the astrophysical plasma emission code (apec) in the x-ray spectral fitting package (xspec) is used to obtain the spectra of solar-type stars with different ages as the input spectra of the model. the results indicate that the escape rates of the exoplanets in different orbits are different significantly, and the escape mechanism is converted from the drastic hydrodynamic escape into the moderate jeans escape as the orbital distance increases, the smaller the planetary gravitational potential, the younger the star-planet system, the larger the distance of this conversion. the correlation between the escape rate and the radiation flux decreases for the short-period exoplanets in a younger star-planet system. it is shown that the classical energy-limited escape theory is not suitable for this kind of exoplanets. these results have enriched the studies on the atmospheric escape of exoplanets, especially, extended the studies on the escape mechanism and energy conversion under different orbital distances and stellar ages. | effect of orbital distance on the atmospheric escape of exoplanets |
we adapted a multispecies escape model, developed for close-in extrasolar planets, to calculate the escape rates of ch4 and n2 from pluto. in the absence of escape, ch4 should overtake n2 as the dominant species below the exobase. the ch4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for pluto lead to a nearly constant mixing ratio of less than 1% below the exobase. in this case the ch4 escape rate is only 5-10% of the n2 escape rate. observations of the ch4 profile by the new horizons/alice spectrograph can constrain the ch4 escape rate and provide a unique test for escape models. | on the escape of ch4 from pluto's atmosphere |
sodium and potassium signatures in transiting exoplanets can be challenging to isolate from the stellar absorption lines. here, these challenges are discussed in the framework of solar system observations, and transits of mercury in particular. radiation pressure is important for alkali gas dynamics in close-orbiting exoplanets since the d lines are efficient at resonant scattering. when the star-planet velocity is ≳10 km/s, eccentric exoplanets experience more than an order of magnitude higher radiation pressures, aiding atmospheric escape and producing a larger effective cross-section for absorbing starlight at the phase of transit. the doppler shift also aids in isolating the planetary signature from the stellar photosphere's absorption. only one transiting exoplanet, hd 80606b, is presently thought to have both this requisite doppler shift and alkali absorption. radiation pressure on a planetary exosphere naturally produces blue-shifted absorption, but at levels insufficient to account for the extreme doppler shifts that have been inferred from potassium transit measurements of this system. in the absence of clear mechanisms to generate such a strong wind, it is described how this characteristic could arise from an exomoon-magnetosphere interaction, analogous to io-jupiter. at low contrasts presented here, follow-up transit spectra of hd 80606b cannot rule out a potassium jet or atmospheric species with a broad absorption structure. however, it is evident that line absorption within the imaging passbands fails to explain the narrow-band photometry that has been reported in-transit. new observations of energetic alkalis produced by the io-jupiter interaction are also presented, which illustrate that energetic sodium doppler structure offers a more valuable marker for the presence of an exomoon than potassium. | doppler-shifted alkali d absorption as indirect evidence for exomoons |
the population of known low- to intermediate-mass exoplanets shows a large spread in densities, which is believed to be due to the diversity of planetary atmospheres and thus controlled by planetary atmospheric mass loss. one of the main drivers of long-term atmospheric escape is the absorption of high-energy xuv radiation from the host star. for main sequence solar-like stars, rotation and xuv radiation are closely connected, with faster rotating stars being xuv brighter and with both rotation and xuv decreasing with time. this evolution, however, does not follow a unique path, as stars born with the same mass and metallicity can have widely different initial rotation rates. this non-uniqueness holds up to about 1 gyr, while atmospheric escape from exoplanets is strongest. the atmospheric mass loss through this period is often deciding the future of the planet and its position in the observed population. therefore, the diversity of possible stellar histories can be an uncertain factor affecting the predictions of population studies. here, i explore its relevance for different planets and different host stars. | stellar rotation and its connection to the evolution of hydrogen-dominated atmospheres of exoplanets |
driven by the high energy radiation of host stars, atmospheric escape is very important for planet evolution. while the flux drops dramatically with the increase of orbital distance, it is essential to study the impacts of orbital distance on atmospheric escape. we consider the hydrodynamic escape of exoplanets driven by the xuv (x-ray and extreme-ultraviolet) radiation of their host stars. we aim to study the mass-loss rate, the transition of escape mechanism, the structures of temperature and velocity, based on a one-dimensional hydrodynamic model which includes radiative transfer processes and photochemical reactions. as the stellar xuv emission varies with the stellar evolution, we use xspec (x-ray spectral fitting package) to construct the xuv spectra of solar-type stars at different ages. we find that with the increase of orbital distance, the mass-loss rates drop significantly, and when the stellar xuv flux is too small to preserve the hydrodynamic escape, it will turn to jeans escape. this transition occurs in larger distance for younger and smaller planets. for young planets, hydrodynamic escape can occur in 1-2 au. for very young and close-in planets, the relation between mass-loss rate and stellar flux is not as significant as planets that are not close to their host stars, and the energy-limited equation can lead to large overestimate. | the impacts of orbital distance on exoplanetary atmospheric escape |
the known populations of super-earths and sub-neptunes with orbital periods less than ~100 days have been shaped by atmospheric evaporation, leading to the observed radius valley near 1.7 earth radii. however, it is currently unclear what the dominant mass loss mechanism is for these planets. the two likely culprits are photoevaporation by the host star's high energy radiation and core-powered evaporation, where the latent heat of formation in the planet's core causes the atmosphere to expand and escape. distinguishing between these two mass loss mechanisms will require much more precise exoplanet radii statistics or, alternatively, measurements of mass loss for planets of varying ages and incident high energy flux. we propose to address this critical question by using cos to observe the transit of the ~20 million year old planet au mic b and measure its mass loss rate in uv metal lines of carbon, silicon, and oxygen. au mic is the brightest pre-main sequence star known to host a transiting planet and offers a unique opportunity to detect the planet's atmosphere at very high signal-to-noise in a number of uv mass loss indicators. furthermore, information from the uv metal lines is complementary to absorption in the hydrogen lyman-alpha line, which is heavily attenuated by the ism. the metal lines trace material from the base of the thermosphere, whereas lyman-alpha samples the highly extended unbound exosphere. measurements of young planet evaporation rates are vital benchmarks for atmospheric evolution models and au mic b is currently the best known exoplanet to perform such an experiment. | measuring mass loss via metal lines from the very young planet au mic b |
exoplanets orbiting close to their parent stars have been observed to lose a fraction of their atmosphere into space: they "evaporate." the escape of atmospheric gas is due to the large x-ray to ultraviolet (xuv) energy input from the nearby host-star into the upper atmosphere of the planet. evaporation is characterized through the transit observations of escaping atoms and ions, like hydrogen atoms at lyman-α, ionized or neutral carbon, oxygen, and magnesium in the uv. detailed modeling of this phenomenon has to take into account a large number of important physical processes, like the interactions of the upper atmosphere with the stellar environment, radiation pressure, photoionization, self-shielding, charge exchanges, and magnetic interactions with the stellar wind. massive evaporation can lead some gaseous exoplanets to lose a large fraction of their atmosphere and undergo a significant change in their nature. as a result, some short period, small exoplanets are potentially the remnant of former more massive planets. evaporation is thus an important process that sculpts the structure of planetary systems with a significant and measurable effect on exoplanets at short orbital distances. | characterizing evaporating atmospheres of exoplanets |
we are moving from an era of exoplanet discovery into an era of exoplanet characterization, but small, potentially-rocky planets orbiting bright, nearby stars that are suitable for atmospheric characterization studies are relatively scarce. here we propose to obtain time series spectroscopy using wfc3/ir to test for detectable atmospheric signatures of the three recently-discovered small planets (r=0.7, 1.3, and 1.4 rearth) orbiting the nearby (10.6 pc), bright (h = 7.4) m3 dwarf l 98-59, the second closest transiting multiplanet system. the equilibrium temperatures for the outer two planets are close to or less than the h2 molecular escape temperature, raising the possibility of hydrogen-dominated atmospheres. we propose to obtain one transit for each of the outer two planets to test for hydrogen-dominated atmospheres. for the innermost sub-earth-sized planet, due to its low expected gravity, a hydrogen atmosphere would be highly vulnerable to atmospheric escape. however, a water-dominated atmosphere is much more resilient, so we propose five transits of the innermost planet to test for a cloud-free water-dominated atmosphere. the host star is particularly quiet with no detected flares or rotational modulation, allowing a comparison between small planets orbiting an active late m-dwarf (trappist-1) and those around a quiet early m-dwarf (l 98-59), and pave the path for atmospheric characterization of the l 98-59 planets with jwst. | searching for secondary atmospheres in a system of benchmark worlds |
we present concept and laboratory demonstration of high-contrast apodization baffle for instruments to be carried on exploration missions of the solar system. the primary science objective of the high-contrast baffle is to reveal escape of atmosphere on mars, while other faint objects around blight sources are potential targets. we diverted heritages studied for exoplanet science and instrumentation to this work. the apodization in this work is realized by edge with microscopic gaussian shaped structure. a simulation to confirm the concept and design of the high-contrast apodization baffle was carried out. then, a baffle which was consisting of transparent flat substrate and thin film of aluminum on it was manufactured. the experiment was executed with he-ne laser with wavelength of 633 nm. as the result, it was demonstrated that the apodization by the gaussian edge is significantly working to improve the contrast. achieved contrast is better than 10-6.5 and 10-8 in θ > 0.5 degree and θ > 1 degree, respectively. these results satisfy the requirement for remote sensing of the atmospheric less on mars. | high-contrast apodization baffle for instruments onboard solar system exploration missions |
in july 2015, we announced the discovery of the super-earth hd 219134b, orbiting a v = 5.57 star 6.5-pc away from us motalebi et al. 2015. it was the brightest and closest transiting system known so far. the density of hd 219134b is compatible with a rocky planet, possibly containing a large amount of volatile species. the planet receives high stellar irradiation, which could significantly erode its atmosphere. estimates indicate that this 4.5 earth-mass object should nonetheless retain a substantial atmosphere. hd 219134b lies sufficiently far from its star to allow the formation of a hydrogen cloud with a detectable coma. we observed it at three different epochs in the far ultraviolet (fuv) using the hst/stis allowing us to detect, for the first time, a possible atmospheric escape from a super-earth. the detection of escaping hydrogen is revealed by a redshifted absorption in the lyman alpha line. those observations also show that hd 219134 has, by far, the brightest lyman alpha emission among all measured transiting exoplanet host stars, which make it possible to observe it at high resolution with the stis/e140h grating. the high-resolution observations allow us to reconstruct the intrinsic lyman alpha line of the star with unprecedented constrains for a planetary system. the stellar flux in this region is used as a proxy to assess the entire energy deposit of the star in the atmosphere of the planet, which is controlling the atmospheric escape mechanism. as the intrinsic line is absorbed by the deuterium and hydrogen of the interstellar medium (ism), it also allows us to probe the deuterium-to-hydrogen ratio of the local ism. as deuterium is only produced during the big bang and destroyed in the stars (astration process), this ratio is a key ingredient for cosmological simulations and in understanding the evolution of galaxies by evaluation of the birth/death rates of stars. | lyman alpha observations of the hd 219134 system: deuterium-to-hydrogen ratio of the local ism and the exosphere of the super-earth hd 219134b |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.