It is commonly believed that most of the stars born in associations decaying with characteristic velocities of stars ~10 km/s. For dwarf galaxies the decay can lead to ejection of stars from the galaxy. The effect is studied for spheroidal and disk dwarf galaxies, and is shown to have substantional observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up to 10^8 M_sol. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of 50% of the stellar mass in galaxies with masses ~10^7 M_sol and the loss of all stars in system with masses 10^5 M_sol, (iv) increase the mass-to-luminosity ratio of the galaxies.
Associations of dwarf galaxies are loose systems composed exclusively of dwarf galaxies. These systems were identified in the Local Volume for the first time more than thirty years ago. We study these systems in the cosmological framework of the $Λ$ Cold Dark Matter ($Λ$CDM) model. We consider the Small MultiDark Planck simulation and populate its dark matter haloes by applying the semi-analytic model of galaxy formation SAG. We identify galaxy systems using a friends of friends algorithm with a linking length equal to $b=0.4 \,{\rm Mpc}\,h^{-1}$, to reproduce the size of dwarf galaxy associat…
The dwarf galaxy distribution surrounding M31 is significantly anisotropic in nature. Of the 30 dwarf galaxies in this distribution, 15 form a disc-like structure and 23 are contained within the hemisphere facing the Milky Way. Using a realistic local potential, we analyse the conditions required to produce and maintain these asymmetries. We find that some dwarf galaxies are required to have highly eccentric orbits in order to preserve the presence of the hemispherical asymmetry with an appropriately large radial dispersion. Under the assumption that the dwarf galaxies originate from a single …
We determined the HI mass function of galaxies in the Ursa Major association of galaxies using a blind VLA-D array survey, consisting of 54 pointings in a cross pattern, covering the centre as well as the outskirts of the Ursa Major volume. The calculated HI mass function has best-fitting Schechter parameters θ^* = 0.19+/-0.11 Mpc^{-3}, log(M^*_{HI}/M_{\odot}) = 9.8+/-0.8 and α = -0.92+/-0.16. The high-mass end is determined by a complementary, targeted WSRT survey, the low-mass end is determined by the blind VLA survey. The slope is significantly shallower than the slopes of the HIPASS (α = -…
Young star clusters in the outer disks of LITTLE THINGS dwarf irregular galaxies
我们研究FUV图像的小东西样本附近的矮不规则（dIrr）和蓝色致密矮（BCD）星系，以确定不同的年轻地区在其遥远的外盘。我们使用银河演化探索者卫星获得的这些数据来确定目前可以识别原位恒星形成的最远半径。FUV节点位于距离星系中心1到8个盘尺度的距离处，年龄<20百万年，质量为20到1 E5太阳能。年轻的星团和OB协会在矮星系的外盘的存在表明，dIrrs确实有恒星形成发生在那里，尽管极端性质的环境。大多数区域的HI表面密度约为1 Msolar per pc 2，尽管HI和分散的老恒星都要远得多。这种有限的密度表明，形成不同OB协会甚至恒星的能力被切断了。我们比较了恒星形成率在FUV地区的平均速率预期在其半径和超越所观察到的气体，使用传统的相关性的气体丰富的地区。局部化速率通常是外部磁盘的预期平均速率的10%。在表面密度小于1 Msolar/pc 2的情况下，恒星的形成（单位为dIrrs）并没有形成明显的星协，或者肯尼卡特-施密特关系式高估了超过这一点的速率。在后一种情况下，在dIrrs的远外部分的恒星盘是来自内部盘的恒星散射的结果。
We present a set of 5 over-densities in spatial-kinematic space previously identified by Kounkel & Covey (2019) that may constitute extended tidal tails associated with the nearby, 400-Myr old Ursa Major association. This sample of 1599 stars have a main-sequence turnoff point consistent with the age of Ursa Major, and might contain its missing low-mass members. It includes 4 candidate white dwarfs with properties that seem consistent with a total age of about 400 Myr, but we estimate from older white dwarf interlopers that about 33% of the sample may be contaminated by random field stars.
Influence of the Void Environment on Chemical Abundances in Dwarf Galaxies and Implications for Connecting Star Formation and Halo Mass
我们研究如何空洞环境影响星系的化学演化，通过比较的氧和氮的丰度的矮星系的空洞与矮星系在密集的地区。利用SDSS DR 7的光谱观测，我们估计了889个空矮星系和672个矮星系在致密区域的氧，氮，氖丰度。一个替代的[OII] 3727的双重发展，允许SDSS矮星系的氧丰度估计在所有的红移与直接Te方法。我们发现，空矮星系有大约相同的氧丰度和Ne/O比，略高的氖丰度，略低的氮丰度和N/O比比在致密的环境中的矮星系。我们的结论是，空洞环境有轻微的影响矮星系的化学演化。我们的质量N/O关系表明，氮的二次生产开始在一个较低的恒星质量在空矮星系比矮星系在密集的环境。我们的矮星系样本显示了sSFR和N/O比之间的强烈反相关性，提供了证据表明，氧是在质量更高的恒星中产生的，而不是合成氮的恒星。较低的N/O比和较小的恒星质量的二次氮生产中看到的空矮星系可能表明延迟的恒星形成和宇宙缩小的大尺度环境的依赖。在空洞矮星系中，氧丰度向稍高的方向转变，这可能是空洞中暗物质晕质量与恒星质量之比大于致密区域的证据。
Fundamental parameters and physical processes leading to the formation of white dwarfs (WDs) may be constrained and refined by discovering WDs in open clusters (OCs). Cluster membership can be utilized to establish the precise distances, luminosities, ages, and progenitor masses of such WDs. We compile a list of probable WDs that are OC members in order to facilitate WD studies that are impractical or difficult to conduct for Galactic field WDs. We use recent catalogs of WDs and OCs that are based on the second data release of the \textit{Gaia} satellite mission (GDR2) to identify WDs that are…
Dwarf galaxies are excellent cosmological probes, because their shallow potential wells make them very sensitive to the key processes that drive galaxy evolution, including baryonic feedback, tidal interactions, and ram pressure stripping. However, some of the key parameters of dwarf galaxies, which help trace the effects of these processes, are still debated, including the relationship between their sizes and masses. We re-examine the Fornax Cluster dwarf population from the point of view of isomass-radius--stellar mass relations (IRSMRs) using the Fornax Deep Survey Dwarf galaxy Catalogue, w…
Recent progress in constraining the massive accretions (>1:10) experienced by the Milky Way (MW) and the Andromeda galaxy (M31) offers an opportunity to understand the dwarf galaxy population of the Local Group. Using zoom-in dark matter-only simulations of MW-mass haloes and concentrating on subhaloes that are thought to be capable of hosting dwarf galaxies, we demonstrate that the infall of a massive progenitor is accompanied with the accretion and destruction of a large number of subhaloes. Massive accreted progenitors do not increase the total number of infalling subhaloes onto a MW-mass h…
The influence of the Cosmic Web on the properties of dwarf galaxies in the Fornax-Eridanus Supercluster
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡皮坦天文研究所）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Universidad Técnica Federico Santa María（费德里科·圣玛丽亚技术大学）
Dark Matter's influence on Evolution of MBHB in Dwarf Galaxies: A Case Study of Leo I dSph
Department of Space Science, Institute of Space Technology（空间科学技术系，太空技术学院）；Space and Astrophysics Research Lab (SARL), National Centre of GIS and Space Applications (NCGSA)（空间与天体物理研究实验室（SARL），国家地理信息与太空应用中心（NCGSA)）
In order to find the possible progenitors of Milky Way globular clusters, we perform orbit integrations to track the orbits of 170 Galactic globular clusters and the eleven classical Milky Way satellite galaxies backwards in time for 11 Gyr in a Milky-Way-plus-satellites potential including the response of the MW to the infall of the Large Magellanic Cloud and the effect of dynamical friction on the satellites. To evaluate possible past associations, we devise a globular-cluster--satellite binding criterion based on the satellite's tidal radius and escape velocity and we test it on globular cl…
Euclid Early Release Observations of the Barnard 30 dark cloud I. Brown dwarfs and planetary mass candidate members at the core of the association
Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心 (CAB)，西班牙国家航空航天技术研究所与科学研究中心）；Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学天文物理实验室，CNRS）；Institut universitaire de France (IUF)（法国大学学院）；Instituto de Astrofísica de Canarias（加那利群岛天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，CEA，CNRS）
Influence of tides and self-gravity on Ultra-Light Dark Matter Bounds from Dwarf Galaxies
CERN（欧洲核子研究组织）；Dipartimento di Fisica, “Sapienza” Università di Roma & Sezione INFN Roma1（罗马第一大学物理系与INFN罗马一分部）；Weizmann Institute of Science（魏茨曼科学研究所）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna, Departamento de Astrofísica（拉各纳大学天体物理学系）
The Scorpius-Centaurus (Sco-Cen) young and nearby massive star-forming region is particularly well suited for extrasolar planet searches with both direct imaging and radial velocity (RV) techniques. The RV search, however, is challenging, as the stars are faster rotators on average than their older stellar counterparts of similar spectral types. Moreover, the RV time series show strong signatures of stellar variability (spots and faculae) and/or stellar pulsations. Our aim is to search for giant planets (GPs) and brown dwarfs at short orbital distances around star members of the Sco-Cen associ…
