We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way mass galaxies that form outside of clusters and eventually sink into them, spiraling in toward central massive objects. Second channel of formation is an in-situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centers of 14 clusters, consistent with observations. 30% of them have external origin while 70% are formed in-situ.
Like massive galaxies, dwarf galaxies are expected to undergo major mergers with other dwarfs. However, the end state of these mergers and the role that merging plays in regulating dwarf star formation is uncertain. Using imaging from the Hyper Suprime-Cam Subaru Strategic program, we construct a sample of dwarf-dwarf mergers and examine the star formation and host properties of the merging systems. These galaxies are selected via an automated detection algorithm from a sample of 6875 spectroscopically selected isolated dwarf galaxies at $z<0.12$ and $\log(M_\star/M_\odot)<9.6$ from the Galaxy…
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。
The tidal tails of globular clusters have been shown to be sensitive to the external tidal field. We investigate how Galactic globular clusters with observed tails are affected by satellite dwarf galaxies by simulating tails in galaxy models with and without dwarf galaxies. The simulations indicate that tidal tails can be subdivided into into three categories based on how they are affected by dwarf galaxies: 1) dwarf galaxies perturb the progenitor cluster's orbit (NGC 4590, Pal 1, Pal 5), 2) dwarf galaxies perturb the progenitor cluster's orbit and individual tail stars (NGC 362, NGC 1851, NG…
We review observational data about a sample of Local Volume objects containing about 1000 galaxies within 11 Mpc of the Milky Way. Dwarf galaxies with stellar masses $M_*/M_{\odot} < 9$ dex make up 5/6 of the sample. Almost 40% of them have their distances measured with high precision using the Hubble Space Telescope. Currently, the LV is the most representative and least selection-affected sample of dwarf galaxies suitable for testing the standard $Λ$CDM paradigm at the shortest cosmological scales. We discuss the H II properties of dwarf galaxies in different environments and the star format…
Despite traditional thinking, an appreciable population of massive black holes may be lurking in dwarf galaxies. Prior to the last decade, nearly all massive black holes were found in the nuclei of giant galaxies and the existence of massive black holes in dwarf galaxies was highly controversial. The field has now been transformed with a growing community of researchers working on a variety of observational studies and theoretical models of dwarf galaxies hosting massive black holes. Work in this area is not only important for a holistic understanding of dwarf galaxy evolution and feedback, bu…
Intermediate-mass black holes (BHs) in local dwarf galaxies are considered the relics of the early seed BHs. However, their growth might have been impacted by galaxy mergers and BH feedback so that they cannot be treated as tracers of the early seed BH population.
Mid-Infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei
在矮星系中寻找活动星系核（AGN）对于我们理解早期宇宙中形成的种子黑洞具有重要意义。在这里，我们测试在低星系质量的活动星系核活动的红外选择方法。我们的母星系样本由斯隆数字巡天中的约18，000个邻近矮星系（M*< 3 x 10^9 Msun，$z<0.055$）组成，在宽视场红外巡天探测器（WISE）发布的AllWISE数据的前三个波段中有重要的探测结果。首先，我们证明了大多数矮星系中的光学选择活动星系核没有被选择为活动星系核使用WISE红外颜色诊断和红外辐射是由宿主星系占主导地位。然后，我们研究了光学选择的成星矮星系的红外特性，发现具有最红红外颜色的星系是最紧凑的，具有蓝色光学颜色，年轻的恒星年龄和大的比恒星形成率。这些结果表明，在使用红外颜色选择矮星系中的活动星系时必须非常小心，因为恒星形成矮星系能够以模仿更明亮活动星系的红外颜色的方式加热尘埃。特别是，一个简单的$\mathrm{W1}-\mathrm{W2}$颜色切割单独不应该被用来选择矮星系的活动星系核。考虑到这些复杂性，我们提出了一个值得后续观测的41个矮星系的样本，这些矮星系落在WISE红外色空间中，通常被更明亮的活动星系核占据。
The Solo (Solitary Local) Dwarf Galaxy survey is a volume limited, wide-field g- and i- band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf galaxies. This set of 44 dwarfs are homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, an analysis of the 12 closest Solo dwarf galaxies accessible from the northern hemisphere is presented, including derivation of their distances, spatial distributions, morphology, and extended structures, including their inner integrated light propert…
The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using HI survey data. Within the virial radius of the Milky Way (224 kpc here), 53 of 55 dwarf galaxies are devoid of gas to limits of M$_{\rm HI}<10^4$ M$_\odot$. Within the virial radius of M31 (266 kpc), 27 of 30 dwarf galaxies are devoid of gas (with limits typically $<10^5$ M$_\odot$). Beyond the virial radii of the Milky Way and M31, the majority of the dwarf galaxies have detected HI gas and have HI masses higher than the limits. When the relationship between gas content and distanc…
We present a study of 41 dwarf galaxies hosting active massive black holes (BHs) using Hubble Space Telescope observations. The host galaxies have stellar masses in the range of $M_\star \sim 10^{8.5}-10^{9.5}~M_\odot$ and were selected to host active galactic nuclei (AGNs) based on narrow emission line ratios derived from Sloan Digital Sky Survey spectroscopy. We find a wide range of morphologies in our sample including both regular and irregular dwarf galaxies. We fit the HST images of the regular galaxies using GALFIT and find that the majority are disk-dominated with small pseudobulges, al…
We report the measured H$α$ fluxes and images of 66 nearby objects observed with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Three of these objects: IC2233, UGC4704, and NGC3432 are late-type spiral galaxies, six objects are distant globular clusters of the M31 galaxy, and the remaining ones are dwarf galaxies. We used the measured H$α$ fluxes to estimate the integrated and specific star-formation rates and analyzed some of the main features of star formation in dwarf galaxies and late-type spirals based on a sample of more than 500 Local volu…
I review the current status of dynamical modelling of dwarf spheroidal galaxies focusing on estimates of their dark matter content. Starting with the simplest methods using the velocity dispersion profiles I discuss the inherent issues of mass-anisotropy degeneracy and contamination by unbound stars. I then move on to methods of increasing complexity, aiming to break the degeneracy, up to recent applications of the Schwarzschild orbit superposition method. The dynamical modelling is placed in the context of possible scenarios for the formation of dwarf spheroidal galaxies, including the tidal …
Using 8.4 years of photometry from the AllWISE/NEOWISE multi-epoch catalogs, we compare the mid-infrared variability properties of a sample of 2197 dwarf galaxies (M_stellar < 2 x 10^9 h^-2 M_sun) to a sample of 6591 more massive galaxies (M_stellar >= 10^10 h^-2 M_sun) matched in mid-infrared apparent magnitude. We find only 2 dwarf galaxies with mid-infrared variability, a factor of ~10 less frequent than the more massive galaxies (p = 6 x 10^-6), consistent with previous findings of optical variability in low-mass and dwarf galaxies using data with a similar baseline and cadence. Within the…
Determining the fraction of nearby dwarf galaxies hosting massive black holes (BHs) can inform our understanding of the origin of "seed" black holes at high redshift. Here we search for signatures of accreting massive BHs in a sample of dwarf galaxies ($M_\star \le 3 \times 10^9~M_\odot$, $z \leq 0.15$) selected from the NASA-Sloan Atlas (NSA) using X-ray observations from the eROSITA Final Equatorial Depth Survey (eFEDS). On average, our search is sensitive to active galactic nuclei (AGNs) in dwarf galaxies that are accreting at $\gtrsim 1%$ of their Eddington luminosity. Of the ${\sim}28,000…
We present the structural parameters of $\sim910$ dwarf elliptical-like galaxies in the local universe ($z\lesssim0.01$) derived from the $r-$band images of the Sloan Digital Sky Survey (SDSS). We examine the dependence of structural parameters on the morphological types (dS0, dE,dE$_{bc}$, dSph, and dE$_{blue}$). There is a significant difference in the structural parameters among the five sub-types if we properly treat the light excess due to nucleation in dSph and dE galaxies. The mean surface brightness within the effective radius ($<μ_{e}>$) of dSph galaxies is also clearly different from…
We study star formation histories (SFHs) of $\simeq500$ dwarf galaxies (stellar mass $M_\ast = 10^5 - 10^9\,M_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher-mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of "satellite vs. central" and "LG vs. individual MWvs. isolated dwarf central." Around the individ…
We present spatially resolved kinematic measurements of AGN-driven outflows in dwarf galaxies in the stellar mass range $\sim6\times10^8 - 9\times10^9 M_\odot$, selected from SDSS DR7,8 and followed up with Keck/LRIS spectroscopy. We find spatially extended ($\sim 1$ half light radius), high velocity ionized gas outflows ($W_{80}$ up to $\sim2000\,\rm{km\,s}^{-1}$) in 13/50 dwarf galaxies with and without AGN. Outflow velocities in all 13 galaxies exceed the escape velocities of their halos. Nine of these 13 galaxies are classified as AGN according to their narrow line flux ratios. Of these, s…
When interpreted within the standard framework of Newtonian gravity and dynamics, the kinematics of stars and gas in dwarf galaxies reveals that most of these systems are completely dominated by their dark matter halos. These dwarf galaxies are thus among the best astrophysical laboratories to study the structure of dark halos and the nature of dark matter. We review the properties of the dwarf galaxies of the Local Group from the point of view of stellar dynamics. After describing the observed kinematics of their stellar components and providing an overview of the dynamical modelling techniqu…
Though smooth, extended spheroidal stellar outskirts have long been observed around nearby dwarf galaxies, it is unclear whether dwarfs generically host an extended stellar halo. We use imaging from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) to measure the shapes of dwarf galaxies out to four effective radii for a sample of dwarfs at 0.005<z<0.2 and 10^7<M_star/M_sun<10^9.6. We find that dwarfs are slightly triaxial, with a <B/A> >~ 0.75 (where the ellipsoid is characterized by three principle semi-axes constrained by C<=B<=A). At M_star>10^8.5 M_sun, the galaxies grow from thick…
We report the result of searching for globular clusters (GCs) around 55 Milky Way satellite dwarf galaxies within the distance of 450 kpc from the Galactic Center except for the Large and Small Magellanic Clouds and the Sagittarius dwarf. For each dwarf, we analyze the stellar distribution of sources in Gaia DR2, selected by magnitude, proper motion, and source morphology. Using the kernel density estimation of stellar number counts, we identify eleven possible GC candidates. Crossed-matched with existing imaging data, all eleven objects are known either GCs or galaxies and only Fornax GC 1-6 …
We compare and contrast the stellar structures of isolated Local Group dwarf galaxies, as traced by their oldest stellar populations, with the satellite dwarf galaxies of the Milky Way and M31. All Local Group dwarfs with Mv < -6 and surface brightness < 26.5 mags. per square arcsec. are considered, taking advantage of measurements from surveys that use similar observations and analysis techniques. For the isolated dwarfs, we use the results from Solitary Local (Solo) Dwarf Galaxy Survey. We begin by confirming that the structural and dynamical properties of the two satellite populations are n…
We use archival Herschel data to examine the singly ionized carbon ([CII]) content of 14 star forming dwarf galaxies in the Virgo cluster. We use spectral energy distribution (SED) fits to far infrared, mid infrared, near infrared, optical and ultraviolet data to derive the total infrared continuum (TIR) for these galaxies. We compare the [CII]/TIR ratio for dwarf galaxies in the central part of Virgo to those in the southern part of the cluster and to galaxies with similar TIR luminosities and metallicities in the Herschel Dwarf Galaxy Survey (DGS) sample of field dwarf galaxies to look for s…
Detecting the seed black holes from which quasars formed is extremely challenging; however, those seeds that did not grow into supermassive should be found as intermediate-mass black holes (IMBHs) of 100-10$^5$ M$_{\odot}$ in local dwarf galaxies. The use of deep multiwavelength surveys has revealed that a population of actively accreting IMBHs (low-mass AGN) exists in dwarf galaxies at least out to $z\sim$3. The black hole occupation fraction of these galaxies suggests that the early Universe seed black holes formed from direct collapse of gas, which is reinforced by the possible flattening o…
