Dwarf galaxies are ideal laboratories to test dark matter models and alternative theories because their dynamical mass (from observed kinematics) largely outweighs their baryonic mass (from gas and stars). In most star-forming dwarfs, cold atomic gas forms regularly rotating disks extending beyond the stellar component, thus probing the gravitational potential out to the outermost regions. Here I review several aspects of gas dynamics in dwarf galaxies, such as rotation curves, mass models, and noncircular motions. Star-forming dwarfs extend the dynamical laws of spiral galaxies to lower masses, surface densities, and accelerations. The three main dynamical laws of rotation-supported galaxies point to three distinct acceleration scales, which play different physical roles but display the same value, within uncertainties. The small scatter around these dynamical laws implies a tight coupling between baryons and dark matter in galaxies, which will be better understood with next-generation surveys that will enlarge current sample sizes by orders of magnitude.
It has long been speculated that many starburst or compact dwarf galaxies are resulted from dwarf-dwarf galaxy merging, but unequivocal evidence for this possibility has rarely been reported in the literature. We present the first study of deep optical broadband images of a gas-dominated blue compact dwarf galaxy (BCD) VCC848 (Mstar=2e8Msun) which hosts extended stellar shells and thus is confirmed to be a dwarf-dwarf merger. VCC848 is located in the outskirts of the Virgo Cluster. By analyzing the stellar light distribution, we found that VCC848 is the result of a merging between two dwarf ga…
Because the 8 μm polycyclic aromatic hydrocarbon (PAH) emission has been found to correlate with other well-known star formation tracers, it has widely been used as a star formation rate (SFR) tracer. There are, however, studies that challenge the accuracy and reliability of the 8 μm emission as a SFR tracer. Our study, part of the Herschel M33 Extended Survey (HERM33ES) open time key program, aims at addressing this issue by analyzing the infrared emission from the nearby spiral galaxy M33 at the high spatial scale of 75 pc. Combining data from the Herschel Space Observatory and the Spitzer S…
We present tentative evidence for the existence of a dissolved star cluster in the Sextans dwarf spheroidal galaxy. In a sample of six stars, we identify three (possibly four) stars around [Fe/H] =-2.7 that are highly clustered in a multi-dimensional chemical abundance space. The estimated initial stellar mass of the cluster is M*,init = 1.9^+1.5_-0.9 (1.6^+1.2_-0.8)*10^5 Msol assuming a Salpeter (Kroupa) initial mass function (IMF). If corroborated by follow-up spectroscopy, this ancient star cluster at [Fe/H] =-2.7 is the most metal-poor system identified to date. Inspired by this finding, w…
We study the dependence of fragmentation in massive gas-rich galaxy disks at $z > 1$ on feedback model and hydrodynamical method, employing the GASOLINE2 SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. We compare non-cosmological galaxy disk runs with standard blastwave supernovae (SN)feedback, which introduces delayed cooling in order to drive winds, and runs with the new superbubble SN feedback, which produces winds naturally by modelling the detailed physics of SN-driven bubbles and leads to efficient self-regulation of star formation. We find that, with blastwave feed…
One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer (GALEX) ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates o…
We report the discovery of a new dwarf galaxy (NGC6503-d1) during the Subaru extended ultraviolet (XUV) disk survey. It is a likely companion of the spiral galaxy NGC6503. The resolved images, in B, V, R, i, and Halpha, show an irregular appearance due to bright stars with underlying, smooth and unresolved stellar emission. It is classified as the transition type (dIrr/dSph). Its structural properties are similar to those of the dwarfs in the Local Group, with a V absolute magnitude ~ -10.5, half-light radius ~400 pc, and central surface brightness ~25.2. Despite the low stellar surface bright…
We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al. (2004), that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on mode…
Dual AGN are important for understanding galaxy-merger-triggered fueling of black holes and hierarchical growth of structures. The least explored type of dual AGN are those associated with mergers of two dwarf galaxies. According to observations and cosmological simulations, dwarf galaxies are the most abundant type of galaxies in the early Universe and the galaxy merger rate is dominated by dwarfs. However, these mergers are generally too distant to be directly observed, and low-redshift dwarf-dwarf merger-related dual AGN are notoriously hard to find. In this paper, we present the first resu…
The recently discovered dwarf galaxy Perseus I appears to be associated with the dominant plane of non-satellite galaxies in the Local Group (LG). We predict its velocity dispersion and those of the other isolated dSphs Cetus and Tucana to be 6.5, 8.2, and 5.5 km/s, respectively. The NGC 3109 association, including the recently discovered dwarf galaxy Leo P, aligns with the dwarf galaxy structures in the LG such that all known nearby non-satellite galaxies in the northern Galactic hemisphere lie in a common thin plane (rms height 53 kpc; diameter 1.2 Mpc). This plane has an orientation similar…
In recent years the Sloan Digital Sky Survey has unraveled a new population of ultra-faint dwarf galaxies (UFDs) in the vicinity of the Milky Way (MW) whose origin remains a puzzle. Using a suite of collisionless N-body simulations, we investigate the formation of UFDs in the context of the tidal stirring model for the formation of dwarf spheroidal galaxies in the Local Group (LG). Our simulations are designed to reproduce the tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 10^9 M_sun dark matter (DM) halos. We explore a variety of inner density …
We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters. Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H] ~ -1) and subsolar Mg enhancement ([Mg/Fe] ~ -0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the oth…
We studied the nearby edge-on galaxy NGC4656 and its dwarf low surface brightness companion with the enhanced UV brightness, NGC4656UV, belonging to the interacting system NGC4631/56. Regular photometric structure and relatively big size of NGC4656UV allows to consider this dwarf galaxy as a separate group member rather than a tidal dwarf. Spectral long-slit observations were used to obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us to conclude that this galaxy is the dark-matter dominate…
The dwarf galaxies of the Local Group are believed to be similar to the most abundant galaxies during the epoch of reionization (z>6). As a result of their proximity, there is a wealth of information that can be obtained about these galaxies; however, due to their low surface brightnesses, detecting their progenitors at high redshifts is challenging. We compare the physical properties of these dwarf galaxies to those of galaxies detected at high redshifts using Hubble Space Telescope and Spitzer observations and consider the promise of the upcoming James Webb Space Telescope on the prospects f…
The leading tensions to the collisionless cold dark matter (CDM) paradigm are the "small-scale controversies", discrepancies between observations at the dwarf-galactic scale and their simulational counterparts. In this work we consider methods to infer 3D morphological information on Local Group dwarf spheroidals, and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with mass-to-light ratio $\gtrsim 100 M_\odot/L_\odot$ reflects an oblate morphology. This is discrepant with the dwarf galaxies with mass-to-light ra…
We report the discovery of a new dwarf galaxy, Andromeda XXIX, using data from the recently-released Sloan Digital Sky Survey DR8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15 degrees from M31, with a distance inferred from the tip of the red giant branch of 730kpc+/-75kpc, corresponding to a three dimensional separation from M31 of between 205kpc and 227kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch …
A number of mechanisms have been proposed to connect star-forming dwarf irregular galaxies with the formation of non-star-forming dwarf spheroidal galaxies, but distinguishing between these mechanisms has been difficult. We use the Via Lactea dark matter only cosmological simulations to test two well-motivated simple hypotheses---transformation of irregulars into dwarf spheroidal galaxies by tidal stirring and ram pressure stripping following a close passage to the host galaxy, and transformation via mergers between dwarfs---and predict the radial distribution and inferred formation times of t…
Dwarf Galaxies are the most common objects in the Universe and are believed to contain large amounts of dark matter. There are mainly three morphologic types of dwarf galaxies: dwarf ellipticals, dwarf spheroidals and dwarf irregulars. Dwarf irregular galaxies are particularly interesting in dwarf galaxy evolution, since dwarf spheroidal predecessors could have been very similar to them. Therefore, a mechanism linked to gas-loss in dwarf irregulars should be observed, i.e. ram pressure stripping. In this paper, we study the interaction between the ISM of a dwarf galaxy, and a flowing IGM. We d…
What is the mass of the progenitor of the Sagittarius (Sgr) dwarf galaxy? Here, we reassemble the stellar debris using SDSS and 2MASS data to find the total luminosity and likely mass. We find that the luminosity is in the range 9.6-13.2 x10^7 solar luminosities or M_V ~ -15.1 - 15.5, with 70% of the light residing in the debris streams. The progenitor is somewhat fainter than the present-day Small Magellanic Cloud, and comparable in brightness to the M31 dwarf spheroidals NGC 147 and NGC 185. Using cosmologically motivated models, we estimate that the mass of Sgr's dark matter halo prior to t…
Observations of globular clusters in dwarf galaxies can be used to study a variety of topics, including the structure of dark matter halos and the history of vigorous star formation in low-mass galaxies. We report on the properties of the faint globular cluster (M_V ~ -3.4) in the M31 dwarf galaxy Andromeda I. This object adds to the growing population of low-luminosity Local Group galaxies that host single globular clusters.
We present a semi-analytic model of isolated dwarf galaxy evolution and use it to study the build-up of observed correlations between dwarf galaxy properties. We analyse the evolution using models with averaged and individual halo mass assembly histories in order to determine the importance of stochasticity on the present-day properties of dwarf galaxies. The model has a few free parameters, but when these are calibrated using the halo mass - stellar mass and stellar mass-metallicity relations, the results agree with other observed dwarf galaxy properties remarkably well. Redshift evolution sh…
We report the discovery of a new faint dwarf galaxy, GHOSTS I, using HST/ACS data from one of our GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disk, and Star clusters) fields. Its detected individual stars populate an approximately one magnitude range of its luminosity function (LF). Using synthetic color-magnitude diagrams (CMDs) to compare with the galaxy's CMD, we find that the colors and magnitudes of GHOSTS I's individual stars are most consistent with being young helium-burning and asymptotic giant branch stars at a distance of 12 +/- 2 Mpc. Morphologically, GHOSTS I appears to…
Nearby dwarf galaxies are local analogues of high-redshift and metal-poor stellar populations. Most of these systems ceased star formation long ago, but they retain signatures of their past that can be unraveled by detailed study of their resolved stars. Archaeological examination of dwarf galaxies with resolved stellar spectroscopy provides key insights into the first stars and galaxies, galaxy formation in the smallest dark matter halos, stellar populations in the metal-free and metal-poor universe, the nature of the first stellar explosions, and the origin of the elements. Extremely large t…
Solitary dwarf galaxy groups as tracers of dark matter halos in the local Universe
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；State Key Laboratory of Radio Astronomy and Technology（射电天文学与技术国家重点实验室）；School of Astronomy, University of Chinese Academy of Sciences（中国科学院大学天文学院）
The demographics of dwarf galaxy populations have long been in tension with predictions from the Cold Dark Matter (CDM) paradigm. If primordial density fluctuations were scale-free as predicted, dwarf galaxies should themselves host dark matter subhaloes, the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as satellites of more massive galaxies, and there is observational and theoretical evidence to suggest that these satellites at z=0 were captured by the massive host halo as a group. However, the evolution of …
We report the detection of 388 pulsating variable stars (and some additional miscellaneous variables) in the Carina dSph galaxy over an area covering the full visible extent of the galaxy and extending a few times beyond its photometric (King) tidal radius along the direction of its major axis. Included in this total are 340 newly discovered dwarf Cepheids which are mostly located ~2.5 magnitudes below the horizontal branch and have very short periods (<0.1 days) typical of their class and consistent with their location on the upper part of the extended main sequence of the younger populations…
We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently-released SDSS DR8. The galaxy is a likely satellite of Andromeda, and, at a separation of $365^{+17}_{-1}$ kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is $650^{+150}_{-80}$ kpc, and analysis of its structure and luminosity show that it has an absolute magnitude of $M_V = -8.5^{+0.4}_{-1.0}$ and half-light radius of $r_h = 210^{+60}_{-50}$ pc, similar to many other faint Local Group dwarfs. With presently-available imaging we are unable to determine if the…
We present deep stellar photometry of the Boötes I dwarf spheroidal galaxy in g and i band filters, taken with the Dark Energy Camera at Cerro Tololo in Chile. Our analysis reveals a large, extended region of stellar substructure surrounding the dwarf, as well as a distinct over-density encroaching on its tidal radius. A radial profile of the Boötes I stellar distribution shows a break radius indicating the presence of extra-tidal stars. These observations strongly suggest that Boötes I is experiencing tidal disruption, although not as extreme as that exhibited by the Hercules dwarf spheroidal…
We report on the discovery and chemical abundance analysis of the first CEMP-r/s star detected in the Sagittarius dwarf Spheroidal Galaxy, by means of UVES high resolution spectra. The star, found in the outskirts of Sgr dSph, along the main body major axis, is a moderately metal poor giant (T$_{eff}$=4753 K, log g=1.75, [Fe/H]=-1.55), with [C/Fe]=1.13 placing it in the so-called "high-carbon band", and strong s-process and r-process enrichment ([Ba/Fe]=1.4, [Eu/Fe]=1.01). Abundances of 29 elements from C to Dy were obtained. The chemical pattern appears to be best fitted by a scenario where a…
Context. The Sagittarius (Sgr) dwarf galaxy is merging with the Milky Way, and the study of its globular clusters (GCs) is important to understand the history and outcome of this ongoing process. Aims. Our main goal is to characterize the GC system of the Sgr dwarf galaxy. This task is hampered by high foreground stellar contamination, mostly from the Galactic bulge. Methods. We performed a GC search specifically tailored to find new GC members within the main body of this dwarf galaxy using the combined data of the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-infrared survey …
We report discovery of a dwarf galaxy in the Leo Triplet. Analysis of the neutral hydrogen distribution shows that it rotates independently of the tidal tail of NGC 3628, with a radial velocity gradient of 35-40 km s$^{-1}$ over approximately 13 kpc. The galaxy has a very high neutral gas content, explaining large part of its total dynamic mass - suggesting small dark matter content. As it is located at the tip of the gaseous tail, this strongly suggests its tidal origin. Should it be the case, it would be one of the most confident and closest (to the Milky Way) detections of a tidal dwarf gal…
We study a gas rich merging dwarf system KUG 0200-096. Deep optical image reveals an optically faint tail with a length of 20 kpc, giving a visual impression of tidal antenna similar to NGC 4038/39. The interacting dwarf galaxies have B-band absolute magnitudes -18.06 and -16.63 mag. We identify a young stellar clump of stellar mass of 2$\times$10$^{7}$ M$_{\sun}$ at the tip of the antenna, possibly a Tidal Dwarf Galaxy (TDG). The putative TDG candidate is quite blue with $g-r$ color index of -0.07 mag, whereas the interacting dwarf galaxies have $g-r$ color indices 0.29 and 0.19 mag. The TDG …
Dwarf galaxies are affected by all the evolutionary processes normally at work in galaxies of any mass. As fainter and less massive galaxies, however, dwarf galaxies are particularly susceptible to environmental mechanisms that can more easily perturb these systems. Importantly, the presence of nearby large galaxies are expected to have a profound effect on dwarf galaxies. Gravitational (especially tidally-induced) effects from the large galaxy can cause mass to be lost from the dwarf, and the passage of the dwarf through the gaseous medium surrounding the large galaxy can additionally cause t…
We present our discovery and analysis of dwarf galaxies in the NGC 3585 galaxy group by the KMTNet Supernova Program. Using deep stack images reaching $\simeq$ 28 mag arcsec$^{-2}$ in $BVI$, we discovered 46 dwarf galaxy candidates distributed in a 7 square degree field. The dwarf galaxy candidates exhibit central surface brightness as faint as $μ_{0,V} = 26.2$ mag arcsec$^{-2}$, with effective radii larger than 150 pc and total absolute magnitudes brighter than $M_V \approx -10$ mag, if at the distance of NGC 3585. The dwarf galaxy surface number density decreases with projected distance from…
We present newly discovered dwarf galaxy candidates in deep and wide-field images of NGC 1291 obtained with the Korea Microlensing Telescope Network. We identify 15 dwarf galaxy candidates by visual inspection. Using imaging simulations, we demonstrate that the completeness rate of our detection is greater than 70% for the central surface brightness value of $μ_{0,R}\lesssim26$ mag arcsec$^{-2}$ and for magnitudes $M_R\lesssim-10$ mag. The structural and photometric properties of the dwarf galaxy candidates appear to be broadly consistent with those of ordinary dwarf galaxies in nearby groups …
Ultra Compact Dwarf Galaxies (UCDs) and dwarf galaxy nuclei have many common properties, such as internal velocity dispersions and colour-magnitude trends, suggesting tidally stripped dwarf galaxies as a possible UCD origin. However, UCDs typically have sizes more than twice as large as nuclei at the same luminosity. We use a GPU-enabled version of the particle-mesh code \textsc{superbox} to study the possibility of turning nucleated dwarf galaxies into UCDs by tidally stripping them in a Virgo-like galaxy cluster. We find that motion in spherical potentials, where close passages happen many t…
We present catalogs of calibrated photometry and spectroscopic redshifts in the Extended Groth Strip, intended for studies of photometric redshifts (photo-z's). The data includes ugriz photometry from CFHTLS and Y-band photometry from the Subaru Suprime camera, as well as spectroscopic redshifts from the DEEP2, DEEP3 and 3D-HST surveys. These catalogs incorporate corrections to produce effectively matched-aperture photometry across all bands, based upon object size information available in the catalog and Moffat profile point spread function fits. We test this catalog with a simple machine lea…
We announce the discovery of the Crater 2 dwarf galaxy, identified in imaging data of the VST ATLAS survey. Given its half-light radius of ~1100 pc, Crater 2 is the fourth largest dwarf in the Milky Way, surpassed only by the LMC, SMC and the Sgr dwarf. With a total luminosity of $M_V\approx-8$, this satellite galaxy is also one of the lowest surface brightness dwarfs. Falling under the nominal detection boundary of 30 mag arcsec$^{-2}$, it compares in nebulosity to the recently discovered Tuc 2 and Tuc IV and UMa II. Crater 2 is located ~120 kpc from the Sun and appears to be aligned in 3-D w…
Nearby, low-metallicity dwarf starburst galaxies hosting active galactic nuclei (AGNs) offer the best local analogs to study the early evolution of galaxies and their supermassive black holes (BHs). Here we present a detailed multi-wavelength investigation of star formation and BH activity in the low-metallicity dwarf-dwarf galaxy merger Mrk 709. Using Hubble Space Telescope H$α$ and continuum imaging combined with Keck spectroscopy, we determine that the two dwarf galaxies are likely in the early stages of a merger (i.e., their first pass) and discover a spectacular $\sim 10$ kpc-long string …
We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semi-analytic model for galaxy formation on the level 2 Aquarius dark matter simulations. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the st…
Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. It is therefore a crucial task to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based $V$ and $i$-band Subaru Suprime Cam photometry with a completeness of $i=27$ mag, we measure the tip of the red giant branch distance for the dwarf galaxy [TT2009] 25. This dwarf resides in the field around the Milky Way-analog NGC 891. By using a Bayesian approach, we measure a distance of $10.28^{+1.17}_{-1.73}$ Mpc, which i…
We present the metallicities and carbon abundances of four newly discovered metal-poor stars with $ -2.2 <$ [Fe/H] $< -1.6$ in the Sagittarius dwarf spheroidal galaxy. These stars were selected as metal-poor member candidates using a combination of public photometry from the SkyMapper Southern Sky Survey and proper motion data from the second data release from the Gaia mission. The SkyMapper filters include a metallicity-sensitive narrow-band $v$ filter centered on the Ca II K line, which we use to identify metal-poor candidates. In tandem, we use proper motion data to remove metal-poor stars …
We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than being only the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from colour-magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be a…
Feeding and Feedback in Dwarf Galaxies (FeeD) -- I. Evidence of nuclear ultra-fast and galaxy-scale outflows in the dwarf galaxy Arp 151
Christ University（基督大学）；Indian Institute of Astrophysics（印度天体物理研究所）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所（ICE，CSIC））；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚太空研究学院（IEEC））；Raman Research Institute（拉曼研究所）
A faint dwarf irregular galaxy has been discovered in the HST/ACS field of LV J1157+5638. The galaxy is resolved into individual stars, including the brightest magnitude of the red giant branch. The dwarf is very likely a physical satellite of LV J1157+5638.The distance modulus of LV J1157+5638 using the tip of the red giant branch (TRGB) distance indicator is 29.82+-0.09 mag (D = 9.22+-0.38 Mpc). The TRGB distance modulus of LV J1157+5638 sat is 29.76+-0.11 mag (D = 8.95+-0.42 Mpc). The distances to the two galaxies are consistent within the uncertainties. The projected separation between the…
We have surveyed a complete extent of Leo A - an apparently isolated gas-rich low-mass dwarf irregular galaxy in the Local Group. The $B$, $V$, and $I$ passband CCD images (typical seeing $\sim$0.8") were obtained with Subaru Telescope equipped with Suprime-Cam mosaic camera. The wide-field ($20' \times 24'$) photometry catalog of 38,856 objects ($V \sim 16-26$ mag) is presented. This survey is also intended to serve as "a finding chart" for future imaging and spectroscopic observation programs of Leo A.
We report the detection of a pair of dwarf galaxies at $z\!=\!0.30$ which may be in the early stages of an interaction. Both galaxies have stellar masses of $<10^{9}M_\odot$, and display a projected separation of $\sim\!29$kpc and a physical separation of $\sim\!240$kpc. Evidence of ongoing star formation has been found in both galaxies, with neither one showing an enhanced star-formation rate that would be expected if they were already interacting. One galaxy displays a disturbed morphology but shows ordered gas rotation, which may reflect a previous minor merger event in the recent history o…
As galaxy simulations increase in resolution more attention is being paid towards the evolution of dwarf galaxies and how the simulations compare to observations. Despite this increasing resolution we are however, far away from resolving the interactions of satellite dwarf galaxies and the hot coronae which surround host galaxies. We describe a new method which focuses only on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo will alter the chemodynamical evolution of dwarf galaxies. Using this method we examine how a dwarf, similar to Sextans…
The remarkable 1994 discovery of the Sagittarius dwarf galaxy (Sgr) revealed that, together with the Magellanic Clouds (MCs), there are at least three major dwarf galaxies, each with a total mass of order 10^10 - 10^11 solar masses, falling onto the Galaxy in the present epoch. Beyond a Galactic radius of 300 kpc, dwarfs tend to retain their gas. At roughly 50 kpc, the MCs have experienced substantial gas stripping as evidenced by the Magellanic Stream which extends from them. Since Sgr experienced star formation long after it fell into the Galaxy, it is interesting to explore just how and whe…
We report the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep imaging with Subaru/Hyper Suprime-Cam. MADCASH J074238+652501-dw lies $\sim$35 kpc in projection from NGC 2403, a dwarf spiral galaxy at $D$$\approx$3.2 Mpc. This new dwarf has $M_{g} = -7.4\pm0.4$ and a half-light radius of $168\pm70$ pc, at the calculated distance of $3.39\pm0.41$ Mpc. The color-magnitude diagram reveals no evidence of young stellar populations, suggesting that MADCASH J074238+652501-dw is an old, metal-poor dwarf similar to low luminosity dw…
We introduce the Solitary Local Dwarfs Survey (Solo), a wide field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multi-band imaging from CFHT/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than Mv = -18 situated beyond the nominal virial radius of the Milky Way and M31 (>300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius Dwarf Irregular Galaxy (Sag DIG), one of t…
It is of broad interest for galaxy formation theory to carry out a full inventory of the numbers and properties of dwarf galaxies in the Local Volume, both satellites and isolated ones. Ultra-deep imaging in wide areas of the sky with small amateur telescopes can help to complete the census of these hitherto unknown low surface brightness galaxies, which cannot be detected by the current resolved stellar population and HI surveys. We report the discovery of Donatiello I, a dwarf spheroidal galaxy located one degree from the star Mirach (Beta And) in a deep image taken with an amateur telescope…
We undertook a search for new dwarf galaxies in the vicinity of relatively isolated nearby galaxies with distances $D < 12$ Mpc and stellar masses in the $2\times10^{11}-3\times10^8~M_{\odot}$ interval, using the data from the DESI Legacy Imaging Surveys. Around the 46 considered Local Volume galaxies, $67$ new candidates for satellites of these galaxies were found. About half of them are classified as spheroidal dwarfs of low surface brightness. The new galaxies are included in the Local Volume database (LVGDB), which now contains 1421 objects, being 63% more than the Updated Nearby Galaxy Ca…
The low-mass low-surface brightness (LSB) disc galaxy Arakelian 18 (Ark 18) resides in the Eridanus void and because of its isolation represents an ideal case to study the formation and evolution mechanisms of such a galaxy type. Its complex structure consists of an extended blue LSB disc and a bright central elliptically-shaped part hosting a massive off-centered star-forming clump. We present the in-depth study of Ark 18 based on observations with the SCORPIO-2 long-slit spectrograph and a scanning Fabry-Perot interferometer at the Russian 6-m telescope complemented by archival multi-wavelen…
The Arecibo Galaxy Environment Survey (AGES) has detected a nearby HI source at a heliocentric velocity of +363 km/s . The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey (SDSS) data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object : 1) It is within the Local Group, in which case its HI properties are comparable with recently discovered ultra-compact high velocity clouds; 2) It is just behind the Local Group, in which case its optical characteristic…
Dwarf galaxies make ideal laboratories to test galaxy evolution paradigms and cosmological models. Detailed studies of dwarfs across the spectrum allow us to gauge the efficacy of astrophysical processes at play in the lowest mass halos such as gas accretion, feedback, turbulence and chemical enrichment. Future observational studies will deliver unprecedented insights on the orbits of dwarf companions around the Milky Way, on their star formation histories and on the 3-D internal motions of their stars. Over large volumes, we will assess the impact of local environment on baryon cycling and st…
