Evolution Of Low-mass Galaxies Research Articles

Galaxy Populations in Groups and Clusters: Evidence for a Characteristic Stellar Mass Scale at M ∗ ∼ 109.5 M ⊙

We use the DR9 of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass M h ≥ 1012 M ⊙ and redshift 0.01 ≤ z ≤ 0.08, down to a limiting r-band magnitude of M r = −10 to −12. For given halo masses we measure the CLF for the total populations and for the red and blue populations classified using the (g − z) color. We find a clear faint-end upturn in the CLF of red satellites, with a slope α ≈ −1.8, which is almost independent of halo mass. This faint-end upturn is not seen for the blue and total populations. Our stellar population synthesis modeling shows that (g − z) provides a clean red/blue division and that red group galaxies defined by (g − z) are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at M r ∼ −18, corresponding to M * ∼ 109.5 M ⊙. This scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)−sized halos is in good agreement with the quenched fraction measured for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies and for the stellar mass functions of low-mass galaxies to be observed at high redshift.

Local Group Dwarf Galaxies

AbstractLocal Group dwarf galaxies are a unique astrophysical laboratory because they are the only objects in which we can reliably and precisely characterize the star formation histories of low-mass galaxies going back to the epoch of reionization. There are of order 100 known galaxies less massive than the Small Magellanic Cloud within ~1 Megaparsec of the Milky Way, with a vide variety of star formation history, gas content, and mass to light ratios. In this overview the current understanding of the formation and evolution of low-mass galaxies across cosmic time will be presented, and the possibility of drawing links between the properties of individual systems and the broader Local Group and cosmological context will be discussed. Local Group dwarfs will remain a uniquely powerful testbed to constrain the properties of dark matter and to evaluate the performance of simulations for the foreseeable future.

Galactic Winds in Low-Mass Galaxies

AbstractMass-loss via stellar-feedback driven outflows is predicted to play a critical role in the baryon cycle of low-mass galaxies. However, observational constraints on warm winds are limited as outflows are transient, intrinsically low-surface brightness events and, thus, difficult to detect. Here, we search for outflows in a sample of eleven nearby starburst dwarf galaxies which are strong candidates for outflows. Despite deep H? imaging on galaxies, only a fraction of the sample show evidence of winds. The spatial extent of all detected ionized gas is limited and would still be considered part of the ISM by simulations. These new observations indicate that the physical extent of warm phase outflows is modest and most of the mass will be recycled to the galaxy. The sample is part of the panchromatic STARBurst IRegular Dwarf Survey (STARBIRDS) designed to characterize the starburst phenomenon and its impact on the evolution of low-mass galaxies.

A Catalog of Merging Dwarf Galaxies in the Local Universe

Abstract We present the largest publicly available catalog of interacting dwarf galaxies. It includes 177 nearby merging dwarf galaxies of stellar mass M * < 1010 M ⊙ and redshifts z < 0.02. These galaxies are selected by visual inspection of publicly available archival imaging from two wide-field optical surveys (SDSS-III and the Legacy Survey), and they possess low-surface-brightness features that are likely the result of an interaction between dwarf galaxies. We list UV and optical photometric data that we use to estimate stellar masses and star formation rates. So far, the study of interacting dwarf galaxies has largely been done on an individual basis, and lacks a sufficiently large catalog to give statistics on the properties of interacting dwarf galaxies, and their role in the evolution of low-mass galaxies. We expect that this public catalog can be used as a reference sample to investigate the effects of the tidal interaction on the evolution of star formation, and the morphology/structure of dwarf galaxies. Our sample is overwhelmingly dominated by star-forming galaxies, and they are generally found significantly below the red sequence in the color–magnitude relation. The number of early-type galaxies is only 3 out of 177. We classify them, according to observed low-surface-brightness features, into various categories including shells, stellar streams, loops, antennae, or simply interacting. We find that dwarf–dwarf interactions tend to prefer the low-density environment. Only 41 out of the 177 candidate dwarf–dwarf interaction systems have giant neighbors within a sky-projected distance of 700 kpc and a line-of-sight radial velocity range ±700 km s−1, and compared to the LMC–SMC, they are generally located at much larger sky-projected distances from their nearest giant neighbors.

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at $1<z<1.5$, selected to span a factor $>10$ in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over $\lambda\sim 0.6$--$1.05\mu$m, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes $z^{\prime}<24.25$ and [3.6]$\mu$m$<22.5$, and is therefore statistically complete for stellar masses $M_\ast\gtrsim10^{10.3}M_\odot$, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning $u$ through $K$, in addition to deep IRAC imaging at 3.6$\mu$m. The spectroscopy is $\sim 50$ per cent complete as of semester 17A, and we anticipate a final sample of $\sim 500$ new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

The MaGICC volume: reproducing statistical properties of high-redshift galaxies

We present a cosmological hydrodynamical simulation of a representative volume of the Universe, as part of the Making Galaxies in a Cosmological Context (MaGICC) project. MaGICC uses a thermal implementation for supernova and early stellar feedback. This work tests the feedback model at lower resolution across a range of galaxy masses, morphologies and merger histories. The simulated sample compares well with observations of high redshift galaxies ($z \ge 2$) including the stellar mass - halo mass ($M_\star - M_h$ ) relation, the Galaxy Stellar Mass Function (GSMF) at low masses ($M_\star \lt 5 \times 10^{10} M_\odot$ ) and the number density evolution of low mass galaxies. The poor match of $M_\star - M_h$ and the GSMF at high masses ($M_\star \ge 5 \times 10^{10} M_\odot$ ) indicates supernova feedback is insufficient to limit star formation in these haloes. At $z = 0$, our model produces too many stars in massive galaxies and slightly underpredicts the stellar mass around $L_\star$ mass galaxy. Altogether our results suggest that early stellar feedback, in conjunction with supernovae feedback, plays a major role in regulating the properties of low mass galaxies at high redshift.

A fundamental problem in our understanding of low-mass galaxy evolution

Recent studies have found a dramatic difference between the observed number density evolution of low mass galaxies and that predicted by semi-analytic models. While models accurately reproduce the z=0 number density, they require that the evolution occurs rapidly at early times, which is incompatible with the strong late evolution found observationally. We report here the same discrepancy in two state-of-the-art cosmological hydrodynamical simulations, which is evidence that the problem is fundamental. We search for the underlying cause of this problem using two complementary methods. Firstly, we look for evidence of a different history of today's low mass galaxies in models and observations and we find that the models yield too few young, strongly star-forming galaxies. Secondly, we construct a toy model to link the observed evolution of specific star formation rates (sSFR) with the evolution of the galaxy stellar mass function. We infer from this model that a key problem in both semi-analytic and hydrodynamical models is the presence of a positive instead of a negative correlation between sSFR and stellar mass. A similar positive correlation is found between the specific dark matter halo accretion rate and the halo mass, indicating that model galaxies are growing in a way that follows the growth of their host haloes too closely. It therefore appears necessary to find a mechanism that decouples the growth of low mass galaxies, which occurs primarily at late times, from the growth of their host haloes, which occurs primarily at early times. We argue that the current form of star-formation driven feedback implemented in most galaxy formation models is unlikely to achieve this goal, owing to its fundamental dependence on host halo mass and time. [Abridged]

The slowly evolving role of environment in a spectroscopic survey of star formation in M* &gt; 5 × 108 M⊙ galaxies since z ∼ 1

We present a deep [OII] emission line survey of faint galaxies (22.5<KAB<24) in the Chandra Deep Field South and the FIRES field. With these data we measure the star formation rate (SFR) in galaxies in the stellar mass range 8.85 < log(M*/Msun) < 9.5 at 0.62<z<0.885, to a limit of SFR = 0.1Msun/yr. The presence of a massive cluster (MS1054-03) in the FIRES field, and of significant large scale structure in the CDFS field, allows us to study the environmental dependence of SFRs amongst this population of low-mass galaxies. Comparing our results with more massive galaxies at this epoch, with our previous survey (ROLES) at the higher redshift z=1, and with SDSS Stripe 82 data, we find no significant evolution of the stellar mass function of star-forming galaxies between z=0 and z=1, and no evidence that its shape depends on environment. The correlation between specific star formation rate (sSFR) and stellar mass at z=0.75 has a power-law slope of beta=-0.2, with evidence for a steeper relation at the lowest masses. The normalization of this correlation lies as expected between that corresponding to z=1 and the present day. The global SFR density is consistent with an evolution of the form (1+z)^2 over 0<z<1, with no evidence for a dependence on stellar mass. The sSFR of these star-forming galaxies at z=0.75 does not depend upon the density of their local environment. Considering just high-density environments, the low-mass end of the sSFR-M* relation in our data is steeper than that in Stripe 82 at z=0, and shallower than that measured by ROLES at z=1. Evolution of low-mass galaxies in dense environments appears to be more rapid than in the general field.

Study of Blue Compact Dwarf Galaxies at Redshift 0.2 ~ 0.5 Using SDSS DR7

We present a mass-metallicity (M–Z) relation of 412 blue compact dwarf galaxies at z = 0.2 ~ 0.5 using the Sloan Digital Sky Survey (SDSS) DR7 spectroscopic data. We found a variation of mass-metallicity relations depending on the redshift in which metallicity evolution of low mass galaxies appear to be stronger than that of high mass galaxies. The specific star formation rate (SSFR) shows tight correlation with galaxy mass in the sense that low mass galaxies have substantially high SSFR. We also discuss environmental effect in the SSFR vs galaxy mass relation. At a given mass, merging system shows systematically higher SSFR than isolated one.

AMAZE

We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z>3 by means of deep near-IR spectroscopy. Gas metallicities are measured, for an initial sample of nine star forming galaxies at z~3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z~3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z~3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z>3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems.

The Invisible Hand: Star Formation Triggered by Runaway Black Holes

The presence of intergalactic star-forming regions within galaxy clusters shows that stars may form well away from a host galaxy. On larger scales, the existence of distorted isolated galaxies hosting star formation, apparently triggered by unseen companions, challenges our understanding of galaxy interactions and evolution. Moreover, most galaxies contain one or more massive central black holes that can be ejected by gravitational-radiation-induced recoil or by gravitational slingshot. In this Letter we examine the effect of a runaway supermassive black hole (RSMBH) passage through the intergalactic medium using the impulse approximation. Even if ejected at high speed, our analytical estimate indicates that SMBHs are able to ignite star formation efficiently in the wake of their trajectories. Cluster-bound RSMBHs may control intergalactic star formation and have substantial influence on the evolution of low-mass galaxies. Star formation induced by RSMBHs or, as we dub it, the invisible-hand mechanism may have had a very relevant role during the quasar epoch when most SMBHs formed.

The Origin, Evolution, and Classification of Field and Cluster Galaxy Populations

In this thesis I address the formation and evolution of lowmass galaxies and investigate their importance in the general galaxy evolution/formation process. Currently favored models of galaxy formation, such as cold dark matter (CDM), suggest that the first galaxies to form in the universe have low masses and sizes, similar to modern dwarf galaxies, that later merge to form more massive systems. The most common galaxies in the nearby universe are dwarf ellipticals in clusters that could be descendants of these early galaxies. This thesis addresses two questions related to these objects: (1) Are the dwarf elliptical galaxies seen in clusters an old primordial population that survived since their initial formation, or are these dwarfs the end product of some evolutionary dynamical process? (2) Do galaxy mergers occur in the universe, and if so, how does this merging evolve through time? To determine whether dwarf elliptical galaxies are an old cluster population, kinematic, structural, and photometric information for these objects was obtained using the WisconsinIndiana-Yale-NOAO 3.5 m telescope. Radial velocities of dwarf elliptical galaxies in the Virgo Cluster suggest that these objects are not an old cluster population but were accreted sometime in the past (C. J. Conselice, J. S. Gallagher III, & R. F. G. Wyse 2001, ApJ, 559, 791). Kinematics also demonstrate that these objects could have originated from a more massive progenitor. Photometry of dwarf elliptical galaxies in the Perseus Cluster further suggests that the stellar populations of these objects are old, with little to no recent star formation or population gradients. The broadband UBR colors of these objects are also consistent with color differences originating from metallicity. Low-mass galaxies in the Perseus Cluster however do not follow the color-magnitude relationship found for the giant elliptical galaxies, with some too red and others too blue for their magnitudes. Through comparisons with LCDM models of galaxy formation, I show that the blue lowmass cluster objects in Perseus are consistent with being old CDM galaxies. Low-mass cluster galaxies that are redder than the color-magnitude relationship are shown to be composed of stars with high metallicities. These red low-mass cluster galaxies must have very high mass-to-light ratios near 250 in solar units or must be the remnants of higher mass galaxies whose stellar material was stripped during high-speed impulsive interactions with other cluster galaxies. To address the issue of galaxy mergers, I develop and use a morphological system to identify robustly, and unambiguously, objects undergoing major mergers (C. J. Conselice, M. A. Bershady, & A. Jangren 2000, ApJ, 529, 886; C. J. Conselice, M. A. Bershady, & J. S. Gallagher III 2000, A&A, 354, L21). This system uses an asymmetry index, such that galaxies undergoing mergers have asymmetry values , with the A 1 0.35 range of possible values being 0–2. When this is applied to the galaxies in the Hubble Deep Field–North, an increase with redshift of galaxies undergoing major mergers is found. Depending on the method of computation, the merger fraction evolution out to can be characterized as , where m m z ∼ 3.5 f p (1 z) ranges from 1 to 2.5. The best fit gives a variable m, such that . m p 2.96 0.32z I also investigate the properties of a nearby massive central cluster galaxy, NGC 1275 in the Perseus Cluster, whose unusual properties and structural aspects can be partially accounted for by recent and past mergers (C. J. Conselice, J. S. Gallagher III, & R. F. G. Wyse 2001, AJ, 122, 2281). Finally, after summarizing the results of this thesis, as well as previous work, I present a new galaxy classification system according to which all galaxies can be fitted based on the three most salient properties that drive galaxy evolution: dissipation, star formation, and galaxy interactions.