致密双星的合并（一颗中子星和另一颗中子星或一个黑洞的合并，NSM）被认为是r-过程的有希望的天体物理位置。虽然NSM的平均合并时间尺度似乎超过1亿年，但大多数先前的化学演化模型表明，在[Fe/H] < -2.5的星系晕恒星中观察到的早期出现和[r/Fe]的大分散有利于1- 1千万年的合并时间。我们认为，对于Ishimaru et al.（2015）提出的假设星系晕形成于具有不同恒星形成历史的暗晕集群的模型，情况并非如此。我们提出了一个随机的化学演化模型的subhalos，在该网站的r-过程被假定为主要是NSM与合并的时间尺度为1亿年。考虑到非对称磁源的稀缺性，用蒙特卡罗方法计算了它们在每个次晕中的出现率。我们的研究结果表明，质量较小的subhalos在较低的金属丰度，并产生高度r-过程增强的恒星。这些次晕的集合体在观测到的星系晕中留下了[r/Fe]的大的星-星散射。然而，所观察到的散射的[Sr/Ba]在低金属丰度表明存在一个额外的网站，部分有助于轻中子捕获元素，如Sr的富集。在我们的低质量subhalo模型中发现的低金属丰度的高增强[r/Fe]也定性地再现了最近发现的超微弱矮星系网状II中的恒星的丰度签名。因此，我们的研究结果表明，NSM的主要来源的r-过程元素的星系晕。
英文摘要：
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 histories as suggested by Ishimaru et al. (2015). We present a stochastic chemical evolution model of the subhalos, in which the site of the r-process is assumed to be mainly NSMs with a coalescence timescale of 100 Myr. In view of the scarcity of NSMs, their occurrence in each subhalo is computed with a Monte Carlo method. Our results show that the less massive subhalos evolve at lower metallicities and generate highly r-process-enhanced stars. An assembly of these subhalos leaves behind the large star-to-star scatters of [r/Fe] in the Galactic halo as observed. However, the observed scatters of [Sr/Ba] at low metallicities indicate the presence of an additional site that partially contributes to the enrichment of light neutron-capture elements such as Sr. The high enhancements of [r/Fe] at low metallicities found in our low-mass subhalo models also qualitatively reproduce the abundance signatures of the stars in the recently discovered ultra-faint dwarf galaxy Reticulum II. Therefore, our results suggest NSMs as the dominant sources of r-process elements in the Galactic halo.
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）
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.
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）
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 mat…
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…
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…
Cosmological simulations of the same spiral galaxy: satellite properties, the role of baryonic physics and star formation history in shaping dark matter cores/cusps
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…
ELUCID V. Lighting dark matter halos with galaxies
在最近的一项研究中，我们使用封闭在500 $\mpch$盒中的SDSS DR 7区域北银河系极的星系分布，进行了我们的ELUCID模拟（Wang et al. 2016，ELUCID III）。在这里，我们{ \it光}的暗物质晕和subhalo在模拟与星系的SDSS观测使用一种新的{ \it邻域}丰度匹配方法的重建区域。在我们利用ELUCID模拟中建立的星系-次晕联系来评估星系形成模型之前，我们首先要探索这种联系的可靠性。为此，我们着重讨论了星系的以下几个方面：（1）星系的中心-次晕光度和质量关系，（2）星系的卫星部分，（3）星系的条件光度函数（CLF）和条件恒星质量函数（CSMF），（4）星系的中心-次晕光度和质量关系，（5）星系的卫星部分，（6）星系的条件光度函数（CLF）和条件恒星质量函数（CSMF），（7）星系的条件光度函数（CLF）和条件恒星质量函数（CSMF）。（4）星系与暗物质粒子之间的互相关联函数，其中大部分是对所有红星系和蓝星系群体分别测量的。我们发现，我们的邻域丰度匹配方法准确地再现了中心-暗晕关系，卫星分数，CLF和CSMF和星系的偏差。这些特徴确保了如此建立的星系-次晕连接在限制星系形成过程上非常有用。并对星系-次晕对约束星系形成的三个层次提出了一些建议。从我们的ELUCID模拟中提取的SDSS DR 7区域的星系-晕下链接和晕下合并树可根据要求提供。
Simulations of cold dark matter make robust predictions about the slope and normalization of the dark matter halo and subhalo mass functions on small scales. Recent observational advances utilizing strong gravitational lensing have demonstrated the ability of this technique to place constraints on these quantities on subgalactic scales corresponding to dark matter halo masses of $10^6$--$10^9\mathrm{M}_\odot$. On these scales the physics of baryons, which make up around 17% of the matter content of the Universe but which are not included in pure dark matter N-body simulations, are expected to …
Survival of the most compact: the life and death of satellite halos in self-interacting dark matter
Goethe University（法兰克福歌德大学）；Donostia International Physics Center (DIPC)（圣塞巴斯蒂安国际物理中心）；Ludwig-Maximilians-Universität München（慕尼黑路德维希-马克西米利安大学）；Excellence Cluster ORIGINS（ORIGINS卓越集群）；The University of Texas at Austin（得克萨斯大学奥斯汀分校）；University of California - Irvine（加州大学尔湾分校）
Modeling the evolution of the elements in the Milky Way is a multidisciplinary and challenging task. In addition to simulating the 13 billion years evolution of our Galaxy, chemical evolution simulations must keep track of the elements synthesized and ejected from every astrophysical site of interest (e.g., supernova, compact binary merger). The elemental abundances of such ejecta, which are a fundamental input for chemical evolution codes, are usually taken from theoretical nucleosynthesis calculations performed by the nuclear astrophysics community. Therefore, almost all chemical evolution p…
Galactic disc chemical evolution models generally ignore azimuthal surface density variation that can introduce chemical abundance azimuthal gradients. Recent observations, however, have revealed chemical abundance changes with azimuth in the gas and stellar components of both the Milky Way and external galaxies. To quantify the effects of spiral arm density fluctuations on the azimuthal variations of the oxygen and iron abundances in disc galaxies. We develop a new 2D galactic disc chemical evolution model, capable of following not just radial but also azimuthal inhomogeneities. The density f…
We present Symphony, a compilation of $262$ cosmological, cold-dark-matter-only zoom-in simulations spanning four decades of host halo mass, from $10^{11}$$-$$10^{15}~M_{\mathrm{\odot}}$. This compilation includes three existing simulation suites at the cluster and Milky Way$-$mass scales, and two new suites: $39$ Large Magellanic Cloud-mass ($10^{11}~M_{\mathrm{\odot}}$) and $49$ strong-lens-analog ($10^{13}~M_{\mathrm{\odot}}$) group-mass hosts. Across the entire host halo mass range, the highest-resolution regions in these simulations are resolved with a dark matter particle mass of $\appro…
Galactic chemical evolution (GCE), solar analogues or twins, and peculiarities of the solar composition with respect to the twins are inextricably related. We examine GCE parameters from the literature and present newly derived values using a quadratic fit that gives zero for a Solar age (i.e., 4.6 Gyr). We show how the GCE parameters may be used not only to "correct" abundances to the solar age, but to predict relative elemental abundances as a function of age. We address the question of whether the solar abundances are depleted in refractories and enhanced in volatiles and find that the answ…
We perform a numerical comparison between the fuzzy dark matter model and the cold dark matter model, focusing on formation of satellite galaxy planes around massive galaxies. Such galactic dynamics with controlled initial subhalo configurations are investigated using GADGET2 for the cold dark matter and PyUltraLight for the fuzzy dark matter, respectively. We demonstrate that satellite galaxies in the fuzzy dark matter side have a tendency to form more flattened and corotating satellite systems than in the cold dark matter side mainly due to the dissipation by the gravitational cooling effect…
The goal of the Open Cluster Chemical Abundances and Mapping (OCCAM) survey is to constrain key Galactic dynamic and chemical evolution parameters by the construction and analysis of a large, comprehensive, uniform data set of infrared spectra for stars in hundreds of open clusters. This sixth contribution from the OCCAM survey presents analysis of SDSS/APOGEE Data Release 17 (DR17) results for a sample of stars in 150 open clusters, 94 of which we designate to be "high quality'' based on the appearance of their color-magnitude diagram. We find the APOGEE DR17-derived [Fe/H] values to be in go…
