We present the largest publicly available catalog of interacting dwarf galaxies. It includes 177 nearby merging dwarf galaxies of stellar mass M * < 10 10 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 which 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, 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 and, compared to the LMC-SMC, they are generally located at much larger sky-projected distances from their nearest giant neighbor.

We compile a large sample of nearby galaxies that are satellites of hosts using a well known SDSS group catalogue. From this sample, we create an 'ancient infallers' and 'recent infallers' subsample, based on the mean infall time predicted from cosmological simulations for galaxies with their location in phase-space. We compare the stellar mass growth histories of the galaxies in these two subsamples, as determined from multi-wavelength SED fitting that uses a comprehensive library of star formation history shapes derived from cosmological simulations. By simultaneously controlling for satellite stellar mass, and host halo mass, we can clearly see the impact of time spent in their hosts. As we might predict, the ancient infaller population shows clear signs of earlier quenching, especially for lower mass satellites in more massive hosts. More importantly, we find the effects are not limited to massive hosts. We find that hosts which might be considered low mass groups (halo masses ∼10 13 M ) can significantly alter their satellites, even for massive satellites (stellar masses ∼10 10 M ). Intriguingly, we see changes in the mass growth history of the satellites of clusters as early as 8 or 9 Gyr ago, when they had not yet entered the virial radius of their current host. We propose that this could be the result of galaxies being pre-processed in low-mass substructures in the protocluster outskirts, prior to infall.

Context. Dust and its emission is being increasingly used to constrain the evolutionary stage of galaxies. A comprehensive characterization of dust, best achieved in nearby bright galaxies, is thus a highly useful resource. Aims. We aim to characterize the relationship between dust properties (mass, luminosity and temperature) and their relationships with galaxy-wide properties (stellar, atomic and molecular gas mass, and star formation mode). We also aim to provide equations to estimate accurate dust properties from limited observational datasets. Methods. We assemble a sample of 1,630 nearby (z < 0.1) galaxies -over a large range of stellar masses (M * ), star formation rates (SFR) and specific star formation rates (sSFR=SFR/M * ) -for which comprehensive and uniform multi-wavelength observations are available from WISE, IRAS, Planck and/or SCUBA. the characterization of dust emission comes from spectral energy distribution (SED) fitting using Draine & Li dust models, which we parametrize using two components (warm at 45 -70 K and cold at 18 -31 K). The subsample of these galaxies with global measurements of CO and/or HI are used to explore the molecular and/or atomic gas content of the galaxies. Results. The total infrared luminosity (L IR ), dust mass (M dust ) and dust temperature of the cold component (T cold ) form a plane that we refer to as the dust plane. A galaxy's sSFR drives its position on the dust plane: starburst (high sSFR) galaxies show higher L IR , M dust and T cold compared to Main Sequence (typical sSFR) and passive galaxies (low sSFR). Starburst galaxies also show higher specific dust masses (M dust /M * ) and specific gas masses ( M gas /M * ). We confirm earlier findings of an anti-correlation between the dust to stellar mass ratio and M * . We also find different anti-correlations depending on sSFR; the anti-correlation becomes stronger as the sSFR increases, with the spread due to different cold dust temperatures. The dust mass is more closely correlated with the total gas mass (atomic plus molecular) than with the individual atomic and molecular gas masses. Our comprehensive multi wavelength data allows us to define several equations to accurately estimate L IR , M dust and T cold from one or two monochromatic luminosities in the infrared and/or sub-millimeter. Conclusions. It is possible to estimate the dust mass and infrared luminosity from a single monochromatic luminosity within the Rayleigh-Jeans tail of the dust emission, with errors of 0.12 and 0.20 dex, respectively. These errors are reduced to 0.05 and 0.10 dex, respectively, if the dust temperature of the cold component is used. The dust mass is better correlated with the total ISM mass ( M ISM ∝ M dust 0.7 ). For galaxies with stellar masses 8.5 < log(M * / M ⊙ ) < 11.9, the conversion factor between the single monochromatic luminosity at 850 µm and the total ISM mass (α 850 µm ) shows a large scatter (rms = 0.29 dex) and a weak correlation with the L IR . The star formation mode of a galaxy shows a correlation with...

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features such as bars and spiral arms, that lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components: the bright, dominant, diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2% and 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, as well as the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al., in which we investigate the origins of the substructure in such dwarf systems.

In our companion paper (Brought to Light I: Michea et al.), we reveal spectacular spiral-galaxy-like features in deep optical imaging of nine Virgo early-type dwarf galaxies, hidden beneath a dominating smooth stellar disk. Using a new combination of approaches, we find that bar- and spiral-like features contribute 2.2%–6.4% of the total flux within 2 R eff. In this study, we conduct high-resolution simulations of cluster harassment of passive dwarf galaxies. Following close pericenter passages of the cluster core, tidal triggering generates features in our model disks that bear a striking resemblance to the observed features. However, we find the disks must be highly rotationally supported (V peak/σ 0 ∼ 3), much higher than typically observed. We propose that some early-type dwarfs may contain a few percent of their mass in a cold, thin disk that is buried in the light of a hot, diffuse disk and only revealed when they undergo tidal triggering. The red optical colors of our sample do not indicate any recent significant star formation, and our simulations show that very plunging pericenter passages (r peri < 0.25r vir) are required for tidal triggering. Thus, many cluster early-type dwarfs with less-plunging orbits may host a yet-undetected cold stellar disk component. We discuss possible origin scenarios and consider why similar-mass star-forming galaxies in the field are significantly more thin-disk dominated than in our cluster sample.