A number of nearby dwarf galaxies have globular cluster (GC) candidates that require spectroscopic confirmation. Here, we present Keck telescope spectra for 15 known GCs and GC candidates that may be associated with a host dwarf galaxy and an additional 3 GCs in the halo of M31 that are candidates for accretion from a now-disrupted dwarf galaxy. We confirm six star clusters (of intermediate-to-old age) to be associated with NGC 247. The vast bulk of its GC system remains to be studied spectroscopically. We also confirm the GC candidates in F8D1 and DDO190, finding both to be young star clusters. The three M31 halo GCs all have radial velocities consistent with M31 and are old and very metal-poor. Their ages and metallicities are consistent with accretion from a low-mass satellite galaxy. Finally, three objects are found to be background galaxies – two are projected near NGC 247 and one (candidate GCC7) is near the IKN dwarf. The IKN dwarf thus has only five confirmed GCs but still a remarkable specific frequency of 124.

Nebular Heii emission implies the presence of energetic photons (E≽54 eV). Despite the great deal of effort dedicated to understanding Heii ionization, its origin has remained mysterious, particularly in metal-deficient star-forming galaxies. Unfolding Heii-emitting, metal-poor starbursts at z∼0 can yield insight into the powerful ionization processes occurring in the primordial universe. Here we present a study on the origin of the extended nebular Heii emission in SBS 0335-052E, one of the most metal-poor (Z ∼ 3% Z⊙ Heii-emitter starbursts known locally. Based on optical VLT/MUSE spectroscopic and Chandra X-ray observations, and current stellar models we found that the Heii-ionization budget of SBS 0335-052E can only be produced by peculiar, nearly metal-free ionizing stars (called here “PopIII-like” stars) with a top-heavy initial mass function. This result is in line with recent simulations for PopIII star formation down to z=0.

We report on a study of 9 nearby primitive galaxies observed by Hubble’s COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. By “primitive galaxies,” we mean galaxies having a low stellar mass, and low gas metallicity, , whether they are local or at high redshift. We find that far-UV spectra of these galaxies show evidence of hard radiation, including X-rays. Following Thuan et al. (2004), we identify these galaxies as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of extremely strong X-radiation. Following Heger et al. (2003), we suggest that the accreting black hold is produced by direct collapse of stars having initial masses greater than 50 . The X-radiation produced by black hole disk directly affects the surrounding interstellar medium, and many of these effects are observable in far-UV spectra.

IC 10 as a starburst dwarf galaxy in the Local Group (LG) has a large population of newly formed stars that are massive and intrinsically very bright in comparison with other LG galaxies. Using the Isaac Newton Telescope (INT) with the Wide Field Camera (WFC) in the i-band and V-band, we performed an optical monitoring survey to identify the most evolved asymptotic giant branch stars (AGBs) and red supergiant stars (RSGs) in this star-forming galaxy, which can be used to determine the star formation history (SFH). The E(B - V) as an effective factor for obtaining the precise magnitude of stars is measured for each star using a 2D dust map (SFD98) to obtain a total extinction for each star in both the i-band and V-band. We obtained the photometric catalog for 53579 stars within the area of 0.07 deg2 (13.5 kpc2), of which 762 stars are classified as variable candidates after removing the foreground stars and saturated ones from our catalog. To reconstruct the SFH for IC 10, we first identified 424 long-period variable (LPV) candidates within the area of two half-light radii (2rh) from the center of the galaxy. We estimated the recent star formation rate (SFR) at ∼ 0.32 yr-1 for a constant metallicity Z = 0.0008, showing the galaxy is currently undergoing high levels of star formation. Also, a total stellar mass of is obtained within 2rh for that metallicity.

Understanding the nucleosynthetic origin of nitrogen and the evolution of the N/O ratio in the interstellar medium is crucial for a comprehensive picture of galaxy chemical evolution at high-redshift because most observational metallicity (O/H) estimates are implicitly dependent on the N/O ratio. The observed N/O at high-redshift shows an overall constancy with O/H, albeit with a large scatter. We show that these heretofore unexplained features can be explained by the pre-supernova wind yields from rotating massive stars (M≳10M⊙,ν/νcrit≳0.4). Our models naturally produce the observed N/O plateau, as well as the scatter at low O/H. We find the scatter to arise from varying star formation efficiency. However, the models that have supernovae dominated yields produce a poor fit to the observed N/O at low O/H. This peculiar abundance pattern at low O/H suggests that dwarf galaxies are most likely to be devoid of SNe yields and are primarily enriched by pre-supernova wind abundances.

For decades, the deceptive simplicity of the radius $R_{\rm e}$, enclosing an arbitrary 50% of a galaxy’s light, has hamstrung the understanding of early-type galaxies (ETGs). Half a century ago, using these ‘effective half-light’ radii from de Vaucouleurs’ $R^{1/4}$ model, Sérsic reported that bright ETGs follow the relation $\mathfrak{M}_B\propto2.5\log R_{\rm e}$; and consequently, one has that $\langle\mu\rangle_{\rm e}\propto2.5\log R_{\rm e}$ and $\mu_{\rm e}\propto2.5\log R_{\rm e}$, where $\mu_{\rm e}$ and $\langle\mu\rangle_{\rm e}$ are the effective surface brightness at $R_{\rm e}$ and the mean effective surface brightness within $R_{\rm e}$, respectively. Sérsic additionally observed an apparent transition which led him to advocate for a division between what he called dwarf and giant ETGs; a belief frequently restated to occur at $\mathfrak{M}_B \approx -18$ mag or $n\approx 2.5$. Here, the location of this false dichotomy in diagrams using ‘effective’ parameters is shown to change by more than 3 mag simply depending on the arbitrary percentage of light used to quantify a galaxy’s size. A range of alternative radii are explored, including where the projected intensity has dropped by a fixed percentage plus a battery of internal radii, further revealing that the transition at $\mathfrak{M}_B\approx -18$ mag is artificial and does not demark a boundary between different physical processes operating on the ETG population.

The above understanding surrounding the effective radius $R_{\rm e}$ is of further importance because quantities such as dynamical mass $\sigma^2R/G$, gravitational-binding energy $GM^2/R$, acceleration $GM/R^2$, and the ‘Fundamental Plane’ also depend on the arbitrary percentage of light used to define R, with implications for dark matter estimates, galaxy formation theories, compact massive galaxies, studies of peculiar velocity flows, and more. Finally, some of the vast literature which has advocated for segregating the ETG population at $\mathfrak{M}_B \approx -18$ mag ($M\approx1$–$2\times10^{10}\,{\rm M}_{\odot}$) is addressed, and it is revealed how this pervasive mindset has spilled over to influence both the classical bulge versus pseudobulge debate and recently also correlations involving supermassive black hole masses.

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 stirring model and mergers of dwarf galaxies. The two scenarios are illustrated with examples from simulations: a comparison between the tidal evolution of dwarfs with cuspy and cored dark matter profiles and the formation of a dwarf spheroidal with prolate rotation.

Galaxies are observed to obey a strict set of dynamical scaling relations. We review these relations for rotationally supported disk galaxies spanning many decades in mass, surface brightness, and gas content. The behavior of these widely varied systems can be summarized with a handful of empirical laws connected by a common acceleration scale.

Using an ultra-deep, untargeted survey with the MUSE integral field spectrograph on the ESO Very Large Telescope, we obtain spectroscopic redshifts to a depth never explored before: galaxies with observed magnitudes m > 30–32. Specifically, we detect objects via Lyman-α emission at 2.9 < z < 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the Hubble Space Telescope, the Hubble Ultra Deep Field. In total, we find more than 100 such objects in 9 square arcminutes at these redshifts, also including a number of sources that are visible only in the HST band that contains Lyman-α. Detailed HST and IRAC stacking analyses confirm the Lyman-α emission as well as the 1216 Å breaks, faint UV continua (MUV ∼ −15), and optical emission lines: these objects are the faintest spectroscopically-confirmed galaxies at high-z. The blue UV continuum slopes and measurements/limits on the equivalent widths of Lyman-α, which in some cases exceeds 300 Å, are consistent with ages < 10 Myr, metallicities < 5% solar, and stellar masses < 107–8 solar masses. The nature of these types of objects is intriguing as they could be the faint star-forming sources of Reionization and could represent the initial (strong) phase of stellar mass growth in galaxies.

RR Lyrae variables are powerful tools to study their host stellar populations. Globular clusters and dwarf galaxies are old and usually host this type of variables. With a growing number of low luminosity objects discovered in the halo of the Milky Way, classifying stars clusters and galaxies has become more challenging. In this study, we examine the properties of RR Lyrae stars in globular clusters and dwarf galaxies in the Local Group. We construct a catalog of RR Lyrae variables in the Local Group globular clusters and dwarf galaxies from previously published data and compare the properties of RR Lyrae variables between those two types of stellar systems. Our goal is to search for a physical difference in the properties of RR Lyrae variables in those two classes of stellar systems. We also analyze the global trend of RRLs in these systems to understand more about their formation and evolution history.

We present results of a multiwavelength study of the isolated dual AGN system Was 49. Observations show that the dominant component in this interacting system, Was 49a, is a spiral galaxy, while Was 49b is hosted in a dwarf galaxy located at 8 kpc from the nucleus of Was 49a, at the edge of its disk. The intriguing fact about this system is the luminosity of their corresponding AGNs. While Was 49a hosts a low luminosity Seyfert 2 with Lbol˜1043 erg s–1, Was 49b has a Seyfert 2 with Lbol ˜ 1045 erg s–1, in the luminosity range of Quasars. Furthermore, estimates of the black hole and host galaxy masses of Was 49b indicate a black hole significantly more massive than one would expect from scaling relations. This result is in contrast with findings that the most luminous merger-triggered AGNs are found in major mergers and that minor mergers predominantly enhance AGN activity in the primary galaxy.

Interactions and mergers between dwarf galaxies are mostly gas-rich and should be marked by an intense star formation activity. But these processes, which are expected to be common at earlier times, are very difficult to observe at low redshifts. To investigate that, we look in the Sloan Digital Sky Survey (SDSS) for compact groups that contain one luminous compact galaxy (LCG) with very high specific star formation rate (sSFR) and at least two other blue galaxies. We found 24 groups that satisfy these criteria, among which 12 groups have SDSS spectroscopic data for at least 2 member galaxies. Here we want to investigate, using the tidal strength estimator Q, how interactions between neighbouring galaxies affect the sSFR and concentration of each LCG. Statistical tests reveal a correlation between Q and their sSFR, indicating that tidal forces between neighbouring galaxies might be inducing bursts of star formation in the LCGs.

The gas evolution of a typical Dwarf Spheroidal Galaxy is investigated by means of 3D hydrodynamic simulations, taking into account the feedback of type II and Ia supernovae, the outflow of an Intermediate Massive Black Hole (IMBH) and a static cored dark matter potential. When the IMBH’s outflow is simulated in an homogeneous medium a jet structure is created and a small fraction of the gas is pushed away from the galaxy. No jet structure can be seen, however, when the medium is disturbed by supernovae, but gas is still pushed away. In this case, the main driver of the gas removal are the supernovae. The interplay between the stellar feedback and the IMBH’s outflow should be taken into account.

In this work, we performed two distinct non-cosmological, three-dimensional hydrodynamic simulations that evolved the gas component of a galaxy similar to the classical dwarf spheroidal galaxy Ursa Minor. Both simulations take into account types II and Ia supernovae feedback constrained by chemical evolution models, while ram-pressure stripping mechanism is added into one of them considering an intergalactic medium and a galactic velocity that resemble what is observed nowadays for the Ursa Minor galaxy. Our results show no difference in the amount of gas left inside the galaxy until 400 Myr of evolution. Moreover, the ram-pressure wind was stalled and inverted by thermal pressure of the interstellar medium and supernovae feedback during the same interval.

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 – 105 M⊙ 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 ˜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 of the black hole-galaxy scaling relations at the low-mass end. This scenario is however challenged by the finding that AGN feedback can have a strong impact on dwarf galaxies, which implies that low-mass AGN in dwarf galaxies might not be the untouched relics of the early seed black holes. This has important implications for seed black hole formation models.

The ubiquity of star-forming dwarf galaxies (SFDG) in the local Universe allows us to trace their evolution in all type of environments, from voids to rich clusters. SFDGs in low-density regions are still assembling their mass, they often show peculiar gas morphology and kinematics, likely associated to external gas accretion or galaxy interactions, and they can experience strong bursts of star formation. The most metal-poor SFDGs are found in the field and they are unique laboratories to investigate the star formation process in the low-metallicity regime, at conditions similar to their high-redshift analogues. On the other hand, SFDGs in intermediate- and high-density environments provide a key to understand the processes that remove their interstellar medium (ISM) and suppress star formation, leading to the different types of gas-poor early-type dwarfs. We review the most recent results on the properties of SFDGs at low and high galaxy densities focusing in particular on the impact of a cluster environment on their ISM components (dust, molecular, atomic and ionised gas). We analyse the population of SFDGs in the nearest rich clusters: Virgo, which is still in the process of assembly, and Fornax, which is more dynamically evolved, more compact and denser. We discuss how the different evolutionary stage of the two structures affects the properties of SFDGs.

Half-dozen of extreme representatives of void dwarf galaxy population were found in our study of evolutionary status of a hundred galaxies in the nearby Lynx-Cancer void. They are very gas-rich, extremely low-metallicity [7.0 < 12 + log(O/H) < ∼ 7.3] objects, with blue colours of outer parts. The colours indicate the ages of the oldest visible stellar population of one to a few Gyr. They all are intrinsically faint, mostly Low Surface Brightness dwarfs, with MB range of –9.5m to –14m. Thus, their finding is a subject of the severe observational selection. The recent advancement in search for such objects in other nearby voids resulted in doubled their total number. We summarize all available data on this group of unusual void dwarf galaxies and discuss them in the general context of very low metallicity galaxies and their possible formation and evolutionary scenarios.

The evolution of galaxies is driven by the birth and death of stars. AGB stars are at the end points of their evolution and therefore their luminosities directly reflect their birth mass; this enables us to reconstruct the star formation history. These cool stars also produce dust grains that play an important role in the temperature regulation of the interstellar medium (ISM), chemistry, and the formation of planets. These stars can be resolved in all of the nearby galaxies. Therefore, the Local Group of galaxies offers us a superb near-field cosmology site. Here we can reconstruct the formation histories, and probe the structure and dynamics, of spiral galaxies, of the many dwarf satellite galaxies surrounding the Milky Way and Andromeda, and of isolated dwarf galaxies. It also offers a variety of environments in which to study the detailed processes of galaxy evolution through studying the mass-loss mechanism and dust production by cool evolved stars. In this paper, I will first review our recent efforts to identify mass-losing Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) in Local Group galaxies and to correlate spatial distributions of the AGB stars of different mass with galactic structures. Then, I will outline our methodology to reconstruct the star formation histories using variable pulsating AGB stars and RSGs and present the results for rates of mass–loss and dust production by pulsating AGB stars and their analysis in terms of stellar evolution and galaxy evolution.

We study how the void environment affects the chemical evolution of galaxies by comparing the metallicity of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate oxygen and nitrogen abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. A substitute for the [OII] λ3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the direct method. We find that void dwarf galaxies have about the same oxygen abundances and slightly lower N/O ratios than dwarf galaxies in denser environments. The lower N/O ratios seen in void dwarf galaxies may indicate both delayed star formation and a dependence of cosmic downsizing on the large-scale environment. Similar oxygen abundances in the two dwarf galaxy populations might be evidence of larger ratios of dark matter halo mass to stellar mass in voids.

To investigate molecular composition of low-metallicity environments, we conducted spectral line survey observations in the 3 mm band toward three dwarf galaxies, the Large Magellanic Cloud, IC 10, and NGC 6822 with the Mopra 22 m, the Nobeyama 45 m and the IRAM 30 m, respectively. The rotational transitions of CCH, HCN, HCO+, HNC, CS, SO, 13CO, and 12CO were detected in all three galaxies. We found that the spectral intensity patterns are similar to one another regardless of star formation activities. Compared with Solar-metallicity environments, the molecular compositions of dwarf galaxies are characterized by (1) deficient nitrogen-bearing molecules and (2) enhanced CCH and suppressed CH3OH. These are interpreted (1) as a direct consequence of the lower elemental abundance of nitrogen, and (2) as a consequence of extended photon dominated regions in cloud peripheries due to the lower abundance of dust grains, respectively.