Dark matter annihilation radiation in hydrodynamic simulations of Milky Way haloes
Matthieu Schaller, Carlos S. Frenk, Tom Theuns, Francesca Calore, Gianfranco Bertone, Nassim Bozorgnia, Robert A. Crain, Azadeh Fattahi, Julio F. Navarro, Till Sawala, Joop Schaye
备注：
11 pages, 5 figures, accepted for publication in MNRAS, corrected typos
We obtain predictions for the properties of cold dark matter annihilation radiation using high resolution hydrodynamic zoom-in cosmological simulations of Milky Way-like galaxies (APOSTLE project) carried out as part of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) programme. Galactic halos in the simulation have significantly different properties from those assumed in the "standard halo model" often used in dark matter detection studies. The formation of the galaxy causes a contraction of the dark matter halo, whose density profile develops a steeper slope than the Navarro-Frenk-White (NFW) profile between $r\approx1.5$ kpc and $r\approx10$ kpc. At smaller radii, $r\lesssim1.5$ kpc, the halos develop a flatter than NFW slope. This unexpected feature may be specific to our particular choice of subgrid physics model but nevertheless the dark matter density profiles agree within 30% as the mass resolution is increased by a factor 150. The inner regions of the halos are almost perfectly spherical (axis ratios $b/a > 0.97$ within $r=1$ kpc) and there is no offset larger than 45 pc between the centre of the stellar distribution and the centre of the dark halo. The morphology of the predicted dark matter annihilation radiation signal is in broad agreement with $γ$-ray observations at large Galactic latitudes ($b\gtrsim3^\circ$). At smaller angles, the inferred signal in one of our four galaxies is similar to that which is observed but it is significantly weaker in the other three.
The Local Group is a unique environment in which to study the astrophysics of galaxy formation. The proximity of the Milky Way and M31 enhances the frequency of interactions of the low-mass halo population with more massive dark matter haloes, which increases their concentrations and strips them of gas and other material. Some low-mass haloes pass through the haloes of the Milky Way or M31 and are either ejected into the field or exchanged between the two primary hosts. We use high resolution gas-dynamical simulations to describe a new class of field haloes that passed through the haloes of bo…
Stellar streams originating in disrupted dwarf galaxies and star clusters are observed around the Milky Way and nearby galaxies. Such substructures are the important tracers that record how the host haloes have accreted progenitor galaxies. Based on the cosmological context, we investigate the relationship between structural properties of substructures such as length and thinness at $z=0$, and orbits of their progenitors. We model stellar components of a large sample of substructures around Milky Way-sized haloes by combining semi-analytic models with a high-resolution cosmological $N$-body si…
We investigate the build-up of the accreted stellar and dark matter haloes of Milky Way-like galaxies in APOSTLE suite of cosmological hydrodynamics simulations. We show that the stellar halo is made up primarily of stars stripped from a small number of massive dwarfs, most of which are disrupted by the present day. The dark matter halo, on the other hand, is made up primarily of small unresolved subhaloes ($\lesssim 10^6$ M$_{\odot}$) and a ``smooth'' component consisting of particles which were never bound to a subhalo. Despite these differences, the massive dwarfs that make up the majority …
The concordance $Λ$CDM cosmology predicts tens of satellite galaxies distributed in the inner region ($<40\ \lkpc$) of the Milky Way (MW), yet at most $12$ were discovered at present day, including 3 discovered very recently by Dark Energy Survey (DES) and 5 from other surveys (e.g. PanSTARRS, MagLiteS). We use $5$ ultra-high resolution simulations of MW sized dark matter haloes from the $\aqua$ project, combined with $\galf$ semi-analytical galaxy formation model, to investigate properties of the model satellite galaxy population inside $40\ \lkpc$ of MW sized haloes. On average, in each halo…
We calculate the effective $J$-factors, which determine the strength of indirect detection signals from dark matter annihilation, for 25 dwarf spheroidal galaxies (dSphs). We consider several well-motivated assumptions for the relative velocity dependence of the dark matter annihilation cross section: $σ_A v$: $s$-wave (velocity independent), $p$-wave ($σ_A v \propto v^2$), $d$-wave ($σ_A v \propto v^4$), and Sommerfeld-enhancement in the Coulomb limit ($σ_A v \propto 1/v$). As a result we provide the largest and most updated sample of J-factors for velocity-dependent annihilation models. For …
The mass to luminosity ratio of the dwarf satellite galaxies in the Milky Way suggests that these dwarf galaxies may contain substantial dark matter. The dark matter at the dense region such as within or at the vicinity of the centres of these dwarf galaxies may undergo the process of self annihilation and produce $γ$-rays as the end product. The satellite borne $γ$-ray telescope such as Fermi-LAT reported the detection of $γ$-rays from around 45 Dwarf Spheroidals (dSphs) of Milky Way. In this work, we consider particle dark matter models described in the literature and after studying their ph…
We use six, high-resolution $Λ$CDM simulations of galaxy formation to study how emission from dark matter annihilation is affected by baryonic processes. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, and stellar and halo masses comparable to those of the Milky Way. They resolve dark matter structures with mass above $\sim 10^6$ $\rm M_{\odot}$ and are each available in both full-physics and dark-matter-only versions. In the full-physics case, formation of the stellar galaxy enhances annihilation radiation from the dominant smooth component of …
The Milky Way halo is the brightest source of dark matter annihilation on the sky. Indeed, the potential strength of the Galactic dark matter signal can supersede that expected from dwarf galaxies and galaxy groups even in regions away from the Inner Galaxy. In this paper, we present the results of a search for dark matter annihilation in the smooth Milky Way halo for $|b| > 20^\circ$ and $r < 50^\circ$ using 413 weeks of Fermi Pass 8 data within the energy range of $\sim$0.8-50 GeV. We exclude thermal dark matter with mass below $\sim$70 GeV that annihilates to $b\bar{b}$ at the 95% confidenc…
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 $Λ$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…
We study the impact of the dark matter velocity distribution modelling on signals from velocity-dependent dark matter annihilation in Milky Way dwarf spheroidal galaxies. Using the high resolution APOSTLE simulations, we identify analogues corresponding to Milky Way dwarf spheroidal galaxies, and from these directly determine the dark matter pair-wise relative velocity distribution, and compare to best-fitting Maxwell-Boltzmann distribution models. For three velocity-dependent annihilation models, p-wave, d-wave, and the Sommerfeld model, we quantify the errors introduced when using the Maxwel…
Ultrafaint dwarf galaxies ($M_\star\lesssim10^{5-6}\,{\rm M}_\odot$) are relics of an early phase of galaxy formation. They contain some of the oldest and most metal-poor stars in the Universe which likely formed before the epoch of hydrogen reionisation. These galaxies are so faint that they can only be detected as satellites of the Milky Way. They are so small that they are just barely resolved in current cosmological hydrodynamics simulations. Here we combine very high resolution cosmological $N$-body simulations with a semi-analytic model of galaxy formation to study the demographics and s…
We study high-resolution hydrodynamic simulations of Milky Way type galaxies obtained within the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) project, and identify the those that best satisfy observational constraints on the Milky Way total stellar mass, rotation curve, and galaxy shape. Contrary to mock galaxies selected on the basis of their total virial mass, the Milky Way analogues so identified consistently exhibit very similar dark matter profiles inside the solar circle, therefore enabling more accurate predictions for indirect dark matter searches. We find in par…
We determine the dark matter pair-wise relative velocity distribution in a set of Milky Way-like halos in the Auriga and APOSTLE simulations. Focusing on the smooth halo component, the relative velocity distribution is well-described by a Maxwell-Boltzmann distribution over nearly all radii in the halo. We explore the implications for velocity-dependent dark matter annihilation, focusing on four models which scale as different powers of the relative velocity: Sommerfeld, s-wave, p-wave, and d-wave models. We show that the J-factors scale as the moments of the relative velocity distribution, an…
The DORCHA suite: nature, nurture, and the phase space distribution of the Milky Way's high redshift progenitors today
Facultad de Físicas, Multidisciplinary Unit for Energy Science, Universidad de Sevilla（塞维利亚大学物理学院能源科学多学科单元）；School of Physics, University of Melbourne（墨尔本大学物理学院）；ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)（ARC三维全天体物理学卓越中心（ASTRO 3D））；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）
