The lack of tangible evidence for non-gravitational interactions between dark and visible sectors drives the need for exploring new avenues of inferring dark matter properties through purely gravitational probes. In particular, addressing small-scale distribution of dark matter could lead to valuable new insights into its particle nature, either confirming predictions of the collisionless cold dark matter hypothesis or favouring models with suppressed small-scale matter power spectrum. In this work we propose a novel machine learning approach for constraining the abundance of galactic dark matter subhaloes through the analysis of Milky Way's stellar field that has been only recently mapped with sufficient coverage thanks to the Gaia mission. Our method is based on convolutional neural networks which represent a powerful tool for identifying characteristic perturbations in spatial maps of stellar number density and velocity distribution moments. For generating the training data we develop a robust and computationally efficient algorithm, capable of generating mock stellar fields from an arbitrary underlying phase-space distribution of stars. By preforming a preliminary study of the outlined approach on synthetic datasets we demonstrate that sensitivities down to (or even below) $10^8 M_\odot$ could be reached. Furthermore, our results show that the accuracy of the advocated technique crucially depends on the kinematic properties of mapped stars and could be further improved by applying it to abundant stellar populations with particularly low velocity dispersion, such as the galactic thin disc stars.
Dark matter subhalos, predicted in large numbers in the cold dark matter scenario, should have an impact on particle dark matter searches. Recent results show that tidal disruption of these objects in computer simulations is over-efficient due to numerical artifacts and resolution effects. Accounting for these results, we re-estimate the subhalo abundance in the Milky Way using semi-analytical techniques. In particular, we show that the boost factor for gamma rays and cosmic-ray antiprotons is increased by roughly a factor of two.
A Comparison of Galacticus and COZMIC WDM Subhalo Populations
University of Southern California（南加州大学）；The Observatories of the Carnegie Institution for Science（卡内基科学研究所天文台）；UCLA Physics and Astronomy（加州大学洛杉矶分校物理与天文学）
Mergers of compact binaries (of a neutron star and another neutron star or a black hole, NSMs) are suggested to be the promising astrophysical site of the r-process. While the average coalescence timescale of NSMs appears to be > 100 Myr, most of previous chemical evolution models indicate that the observed early appearance and large dispersion of [r/Fe] in Galactic halo stars at [Fe/H] < -2.5 favors shorter coalescence times of 1-10 Myr. We argue that this is not the case for the models assuming the formation of the Galactic halo from clustering of subhalos with different star formation histo…
Dynamical evolution of dark matter subhaloes in the Milky Way: role of the Galactic disc
Institute for Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Center for Cosmology and Computational Astrophysics, Zhejiang University（浙江大学宇宙学与计算天体物理中心）；Institute for Astronomy, University of Vienna（维也纳大学天体物理研究所）
Impact of baryons on the population of Galactic subhalos and implications for dark matter searches
University of Hamburg（汉堡大学）；Instituto de Física Teórica UAM-CSIC, Universidad Autónoma de Madrid（马德里自治大学-西班牙国家研究委员会理论物理研究所）；Universidad Autónoma de Madrid（马德里自治大学）；Universidad de Valencia（瓦伦西亚大学）；Durham University（杜伦大学）
The erasure of Galactic bar resonances by dark matter subhaloes
MIT Kavli Institute For Astrophysics and Space Research（麻省理工学院卡弗里天体物理与空间研究所）；Department of Physics and Astronomy, University College London（伦敦大学学院物理与天文系）；Institute of Astronomy, University of Cambridge（剑桥大学天体物理研究所）
Cold dark matter subhalos are expected to populate galaxies in numbers. If dark matter self-annihilates, these objects turn into prime targets for indirect searches, in particular with gamma-ray telescopes. Incidentally, the Fermi-LAT catalog already contains many unidentified sources that might be associated with subhalos. In this paper, we determine the probability for subhalos to be identified as gamma-ray pointlike sources from their predicted distribution properties. We use a semi-analytical model for the Galactic subhalo population, which, in contrast to cosmological simulations, can be …
We use the suite of Milky Way-like galaxies in the Auriga simulations to determine the contribution to annihilation radiation from dark matter subhalos in three velocity-dependent dark matter annihilation models: Sommerfeld, p-wave, and d-wave models. We compare these to the corresponding distribution in the velocity-independent s-wave annihilation model. For both the hydrodynamical and dark-matter-only simulations, only in the case of the Sommerfeld-enhanced annihilation does the total annihilation flux from subhalos exceed the total annihilation flux from the smooth halo component within the…
Harvard University（哈佛大学）；Massachusetts Institute of Technology（麻省理工学院）
Strong gravitational lensing has emerged as a promising approach for probing dark matter models on sub-galactic scales. Recent work has proposed the subhalo effective density slope as a more reliable observable than the commonly used subhalo mass function. The subhalo effective density slope is a measurement independent of assumptions about the underlying density profile and can be inferred for individual subhalos through traditional sampling methods. To go beyond individual subhalo measurements, we leverage recent advances in machine learning and introduce a neural likelihood-ratio estimator …
The cold dark matter (CDM) scenario predicts that galactic halos should host a huge amount of subhalos possibly lighter than planets, depending on the nature of dark matter. Predicting their abundance and distribution has important implications for dark matter searches and searches for subhalos themselves, as they could provide a decisive test of the CDM paradigm. A major difficulty in subhalo population model building is to account for the gravitational stripping induced by baryons, which strongly impact on the overall dynamics inside galaxies. In this paper, we focus on these "baryonic" tide…
Which Milky Way Streams Make the Best Dark Matter Detectors?
MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡弗里天体物理学与空间研究研究所）；Kavli Institute for Particle Astrophysics and Cosmology, Stanford University（斯坦福大学卡弗里粒子天体物理学与宇宙学研究所）；Department of Physics, Stanford University（斯坦福大学物理系）；SLAC National Accelerator Laboratory（斯坦福直线加速器国家实验室）；The Observatories of the Carnegie Institution for Science（卡内基科学机构天文台）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）
Given recent developments in our understanding of the Large Magellanic Cloud's (LMC) impact on the Milky Way's (MW) dark matter subhalo population, we compare the signatures of dark matter and baryonic physics on subhalos in MW systems with realistic LMC analogs. In particular, we study the effects of self-interacting dark matter (SIDM), warm dark matter (WDM), and the Galactic disk on the peak maximum circular velocity ($V_{\mathrm{peak}}$) function, radial distribution, and spatial distribution of MW and LMC-associated subhalos using cosmological dark matter-only zoom-in simulations of MW+LM…
Challenges in Binary Pulsar Timing Detection of Dark Matter Subhalos
Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台暗物质与空间天文重点实验室）；School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
Within the standard hierarchical structure formation scenario, Milky Way-mass dark matter haloes have hundreds of dark matter subhaloes with mass $\gtrsim 10^8 \, {\rm M_{\odot}}$. Over the lifetime of a galactic disc a fraction of these may pass close to the central region and interact with the disc. We extract the properties of subhaloes, such as their mass and trajectories, from a realistic cosmological simulation to study their potential effect on stellar discs. We find that massive subhalo impacts can generate disc heating, rings, bars, warps, lopsidedness as wells as spiral structures in…
Stringent Constraints On The Dark Matter Annihilation Cross Section From Subhalo Searches With The Fermi Gamma-Ray Space Telescope
银河系的暗物质晕被预测包含了非常大量的较小的次晕。由于暗物质湮灭发生在这样的物体内，最接近的大质量暗晕可能表现为点状或空间扩展的伽马射线源，在其他波长处没有可观测到的对应物。在本文中，我们使用宝瓶座模拟的结果来预测附近的subhalos的分布，并将其与费米伽马射线太空望远镜观测到的不明伽马射线源的特征进行比较。关注最亮的高纬度源，我们利用这种比较来推导出暗物质湮灭截面的极限。对于轻于~200 GeV的暗物质粒子，所得到的极限是迄今为止最强的，比矮星系或银河系中心的观测结果更为严格。我们还推导出独立的限制的基础上缺乏身份不明的伽马射线源与可辨别的空间扩展，但这些限制是一个因素的2-10弱于那些基于点状subhalos。最后，我们注意到10个最亮的高纬度源中有4个呈现出类似的光谱形状，这与30-60 GeV的暗物质粒子湮灭为b夸克相一致，湮灭截面的数量级为sigma v ~（5-10）x 10^-27 cm ^3/s，或8-10 GeV的暗物质粒子湮灭为τ，σ v ~（2.0-2.5）x 10^-27 cm ^3/s。
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 distribution of dark matter (DM) subhalos in our Galaxy remains disputed, leading to varying $γ$-ray and $ν$ flux predictions from their annihilation or decay. In this work, we study how, in the inner Galaxy, subhalo tidal disruption from the Galactic baryonic potential impacts these signals. Based on state-of-the art modeling of this effect from numerical simulations and semi-analytical results, updated subhalo spatial distributions are derived and included in the CLUMPY code. The latter is used to produce a thousand realizations of the $γ$-ray and $ν$ sky. Compared to predictions based o…
We use the IllustrisTNG100 hydrodynamical simulation to study the dependence of the galaxy two-point correlation function on a broad range of secondary subhalo and galactic properties. We construct galaxy mock catalogues adopting a standard sub-halo abundance matching scheme coupled with a secondary assignment between galaxy colour or specific star formation rate and the following subhalo properties: starvation redshift z$_{\rm starve}$, concentration at infall, overdensity $δ_R^{\rm env}$, tidal anisotropy $α_R$, and tidal overdensity $δ_R$. The last two quantities allow us to fully character…
The density variations in thin stellar streams may encode important information on the nature of the dark matter. For instance, if dark matter aggregates into massive sub-halos, these perturbers are expected to scatter stars out of dynamically cold stellar streams, possibly leading to detectable gaps in those structures. Here we re-examine the density variations in the GD-1 stream, using Gaia DR2 astrometry, Pan-STARRS photometry, together with high precision radial velocities measured with the CFHT/ESPaDOnS and VLT/UVES instruments and complemented with public radial velocity catalogs. We sho…
In the standard structure formation scenario based on the cold dark matter paradigm, galactic halos are predicted to contain a large population of dark matter subhalos. While the most massive members of the subhalo population can appear as luminous satellites and be detected in optical surveys, establishing the existence of the low mass and mostly dark subhalos has proven to be a daunting task. Galaxy-scale strong gravitational lenses have been successfully used to study mass substructures lying close to lensed images of bright background sources. However, in typical galaxy-scale lenses, the s…
In a recent study, using the distribution of galaxies in the north galactic pole of SDSS DR7 region enclosed in a 500$\mpch$ box, we carried out our ELUCID simulation (Wang et al. 2016, ELUCID III). Here we {\it light} the dark matter halos and subhalos in the reconstructed region in the simulation with galaxies in the SDSS observations using a novel {\it neighborhood} abundance matching method. Before we make use of thus established galaxy-subhalo connections in the ELUCID simulation to evaluate galaxy formation models, we set out to explore the reliability of such a link. For this purpose, w…
