Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPhat ELVIS: The inevitable effect of the Milky Ways disk on its dark matter subhaloes
157
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We introduce an extension of the ELVIS project to account for the effects of the Milky Way galaxy on its subhalo population. Our simulation suite, Phat ELVIS, consists of twelve high-resolution cosmological dark matter-only (DMO) zoom simulations of Milky Way-size $Lambda$CDM~ haloes ($M_{rm v} = 0.7-2 times 10^{12} ,mathrm{M}_odot$) along with twelve re-runs with embedded galaxy potentials grown to match the observed Milky Way disk and bulge today. The central galaxy potential destroys subhalos on orbits with small pericenters in every halo, regardless of the ratio of galaxy mass to halo mass. This has several important implications. 1) Most of the $mathtt{Disk}$ runs have no subhaloes larger than $V_{rm max} = 4.5$ km s$^{-1}$ within $20$ kpc and a significant lack of substructure going back $sim 8$ Gyr, suggesting that local stream-heating signals from dark substructure will be rare. 2) The pericenter distributions of Milky Way satellites derived from $mathit{Gaia}$ data are remarkably similar to the pericenter distributions of subhaloes in the $mathtt{Disk}$ runs, while the DMO runs drastically over-predict galaxies with pericenters smaller than 20 kpc. 3) The enhanced destruction produces a tension opposite to that of the classic `missing satellites problem: in order to account for ultra-faint galaxies known within $30$ kpc of the Galaxy, we must populate haloes with $V_mathrm{peak} simeq 7$ km s$^{-1}$ ($M simeq 3 times 10^{7} ,mathrm{M}_odot$ at infall), well below the atomic cooling limit of $V_mathrm{peak} simeq 16$ km s$^{-1}$ ($M simeq 5 times 10^{8} ,mathrm{M}_odot$ at infall). 4) If such tiny haloes do host ultra-faint dwarfs, this implies the existence of $sim 1000$ satellite galaxies within 300 kpc of the Milky Way.
rate research
Read More
The observed population of the Milky Way satellite galaxies offer a unique testing ground for galaxy formation theory on small-scales. Our novel approach was to investigate the clustering of the known Milky Way satellite galaxies and to quantify the amount of substructure within their distribution using a two-point correlation function statistic in each of three spaces: configuration space, line-of-sight velocity space, and four-dimensional phase-space. These results were compared to those for three sets of subhaloes in the Via Lactea II Cold Dark Matter simulation defined to represent the luminous dwarfs. We found no evidence at a significance level above 2-sigma of substructure within the distribution of the Milky Way satellite galaxies in any of the three spaces. The luminous subhalo sets are more strongly clustered than are the Milky Way satellites in all three spaces and over a broader range of scales in four-dimensional phase-space. Each of the luminous subhalo sets are clustered as a result of substructure within their line-of-sight velocity space distributions at greater than 3-sigma significance, whereas the Milky Way satellite galaxies are randomly distributed in line-of-sight velocity space. While our comparison is with only one Cold Dark Matter simulation, the inconsistencies between the Milky Way satellite galaxies and the Via Lactea II subhalo sets for all clustering methods suggest a potential new small-scale tension between Cold Dark Matter theory and the observed Milky Way satellites. Future work will obtain a more robust comparison between the observed Milky Way satellites and Cold Dark Matter theory by studying additional simulations.
The predicted abundance and properties of the low-mass substructures embedded inside larger dark matter haloes differ sharply among alternative dark matter models. Too small to host galaxies themselves, these subhaloes may still be detected via gravitational lensing, or via perturbations of the Milky Ways globular cluster streams and its stellar disk. Here we use the Apostle cosmological simulations to predict the abundance and the spatial and velocity distributions of subhaloes in the range 10^6.5-10^8.5 solar masses inside haloes of mass ~ 10^12 solar masses in LCDM. Although these subhaloes are themselves devoid of baryons, we find that baryonic effects are important. Compared to corresponding dark matter only simulations, the loss of baryons from subhaloes and stronger tidal disruption due to the presence of baryons near the centre of the main halo, reduce the number of subhaloes by ~ 1/4 to 1/2, independently of subhalo mass, but increasingly towards the host halo centre. We also find that subhaloes have non-Maxwellian orbital velocity distributions, with centrally rising velocity anisotropy and positive velocity bias which reduces the number of low-velocity subhaloes, particularly near the halo centre. We parameterise the predicted population of subhaloes in terms of mass, galactocentric distance, and velocities. We discuss implications of our results for the prospects of detecting dark matter substructures and for possible inferences about the nature of dark matter.
We present a comprehensive search for the 3.5 keV line, using $sim$51 Ms of archival Chandra observations peering through the Milky Ways Dark Matter Halo from across the entirety of the sky, gathered via the Chandra Source Catalog Release 2.0. We consider the datas radial distribution, organizing observations into four data subsets based on angular distance from the Galactic Center. All data is modeled using both background-subtracted and background-modeled approaches to account for the particle instrument background, demonstrating statistical limitations of the currently-available $sim$1 Ms of particle background data. A non-detection is reported in the total data set, allowing us to set an upper-limit on 3.5 keV line flux and constrain the sterile neutrino dark matter mixing angle. The upper-limit on sin$^2$(2$theta$) is $2.58 times 10^{-11}$ (though systematic uncertainty may increase this by a factor of $sim$2), corresponding to the upper-limit on 3.5 keV line flux of $2.34 times 10^{-7}$ ph s$^{-1}$ cm$^{-2}$. These limits show consistency with recent constraints and several prior detections. Non-detections are reported in all radial data subsets, allowing us to constrain the spatial profile of 3.5 keV line intensity, which does not conclusively differ from Navarro-Frenk-White predictions. Thus, while offering heavy constraints, we do not entirely rule out the sterile neutrino dark matter scenario or the more general decaying dark matter hypothesis for the 3.5 keV line. We have also used the non-detection of any unidentified emission lines across our continuum to further constrain the sterile neutrino parameter space.
I present the mean metallicity distribution of stars in the Milky Way Galaxy based on photometry from the Sloan Digital Sky Survey. I utilize an empirically calibrated set of stellar isochrones developed in previous work to estimate the metallicities of individual stars to a precision of $0.2$ dex for reasonably bright stars across the survey area. I also obtain more precise metallicity estimates using priors from the $Gaia$ parallaxes for relatively nearby stars. Close to the Galactic mid-plane ($|Z|<2$ kpc), a mean metallicity map reveals deviations from the mirror symmetry between the northern and southern hemispheres, displaying wave-like oscillations. The observed metallicity asymmetry structure is almost parallel to the Galactic mid-plane, and coincides with the previously known asymmetry in the stellar number density distribution. This result reinforces the previous notion of the plane-parallel vertical waves propagating through the disk, in which a local metallicity perturbation from the mean vertical metallicity gradient is induced by the phase-space wrapping of stars in the $Z$-$V_Z$ plane. The maximum amplitude of the metallicity asymmetry ($Delta$[Fe/H]$sim0.05$) implies that these stars have been pulled away from the Galactic mid-plane by an order of $Delta|Z|sim80$ pc as a massive halo substructure such as the Sagittarius dwarf galaxy plunged through the Milky Way. This work provides evidence that the $Gaia$ phase-space spiral may continue out to $|Z|sim1.5$ kpc.
The growing trove of precision astrometric observations from the Gaia space telescope and other surveys is revealing the structure and dynamics of the Milky Way in ever more exquisite detail. We summarize the current status of our understanding of the structure and the characteristics of the Milky Way, and we review the emerging picture: the Milky Way is evolving through interactions with the massive satellite galaxies that stud its volume, with evidence pointing to a cataclysmic past. It is also woven with stellar streams, and observations of streams, satellites, and field stars offer new constraints on its dark matter, both on its spatial distribution and its fundamental nature. The recent years have brought much focus to the study of dwarf galaxies found within our Galaxys halo and their internal matter distributions. In this review, we focus on the predictions of the cold dark matter paradigm at small mass scales through precision astrometric measurements, and we summarize the modern consensus on the extent to which small-scale probes are consistent with this paradigm. We note the discovery prospects of these studies, and also how they intertwine with probes of the dynamics and evolution of the Milky Way in various and distinct ways.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
