The Evolution of the Fractions of Quiescent and Star-forming Galaxies as a Function of Stellar Mass Since z=3: Increasing Importance of Massive, Dusty Star-forming Galaxies in the Early Universe

Using the UltraVISTA DR1 and 3D-HST catalogs, we construct a stellar-mass-complete sample, unique for its combination of surveyed volume and depth, to study the evolution of the fractions of quiescent galaxies, moderately unobscured star-forming galaxies, and dusty star-forming galaxies as a function of stellar mass over the redshift interval $0.2 \le z \le 3.0$. We show that the role of dusty star-forming galaxies within the overall galaxy population becomes more important with increasing stellar mass, and grows rapidly with increasing redshift. Specifically, dusty star-forming galaxies dominate the galaxy population with $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.3$ at $z\gtrsim2$. The ratio of dusty and non-dusty star-forming galaxies as a function of stellar mass changes little with redshift. Dusty star-forming galaxies dominate the star-forming population at $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.0-10.5$, being a factor of $\sim$3-5 more common, while unobscured star-forming galaxies dominate at $\log{(M_{\rm star}/M_{\odot})} \lesssim 10$. At $\log{(M_{\rm star}/M_{\odot})} > 10.5$, red galaxies dominate the galaxy population at all redshift $z<3$, either because they are quiescent (at late times) or dusty star-forming (in the early universe).Comment: 7 pages, 4 figures, 1 table. Accepted by Astrophysical Journal Letters after minor revisio

Spectral classification of emission-line galaxies from the Sloan Digital Sky Survey. I. An improved classification for high redshift galaxies

We study the spectral classification of emission-line galaxies as star-forming galaxies or Active Galactic Nuclei (AGNs). From the Sloan Digital Sky Survey (SDSS) high quality data, we define an improved classification to be used for high redshift galaxies. We classify emission-line galaxies of the SDSS according to the latest standard recipe using [Oiii]5007, [Nii]6584, [Sii]6717+6731, H, and H emission lines. We obtain four classes: star-forming galaxies, Seyfert 2, LINERs, and composites. We then examine where these galaxies fall in the blue diagram used at high redshift (i.e. log([Oiii]5007/H) vs. log([Oii]3726+3729/H).We define new improved boundaries in the blue diagram for star-forming galaxies, Seyfert 2, LINERs, SF/Sy2, and SF-LIN/comp classes. We maximize the success rate to 99.7% for the detection of star-forming galaxies, to 86% for the Seyfert 2 (including the SF/Sy2 region), and to 91% for the LINERs. We also minimize the contamination to 16% in the region of star-forming galaxies. We cannot reliably separate composites from star-forming galaxies and LINERs, but we define a SF/LIN/comp region where most of them fall (64%).Comment: 6 pages, accepted for publication in A&

On the universality of luminosity-metallicity and mass-metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3

We study relations between global characteristics of low-redshift (0 < z < 1) compact star-forming galaxies, including absolute optical magnitudes, Hbeta emission-line luminosities (or equivalently star-formation rates), stellar masses, and oxygen abundances. The sample consists of 5182 galaxies with high-excitation HII regions selected from the SDSS DR7 and SDSS/BOSS DR10 surveys adopting a criterion [OIII]4959/Hbeta > 1. These data were combined with the corresponding data for high-redshift (2 < z < 3) star-forming galaxies. We find that in all diagrams low-z and high-z star-forming galaxies are closely related indicating a very weak dependence of metallicity on stellar mass, redshift, and star-formation rate. This finding argues in favour of the universal character of the global relations for compact star-forming galaxies with high-excitation HII regions over redshifts 0 < z < 3.Comment: 13 pages, 10 figures, accepted for publication in MNRA

Disentangling the role of environmental processes in galaxy clusters

In this work we present the results of a novel approach devoted to disentangle the role of the environmental processes affecting galaxies in clusters. This is based on the analysis of the NUV-r' distributions of a large sample of star-forming galaxies in clusters spanning more than four absolute magnitudes. The galaxies inhabit three distinct environmental regions: virial regions, cluster infall regions and field environment. We have applied rigorous statistical tests in order to analyze both, the complete NUV-r' distributions and their averages for three different bins of r'-band galaxy luminosity down to M_r' ~ -18, throughout the three environmental regions considered. We have identified the environmental processes that significantly affect the star-forming galaxies in a given luminosity bin by using criteria based on the characteristics of these processes: their typical time-scales, the regions where they operate and the galaxy luminosity range for which their effects are more intense. We have found that the high-luminosity (M_r'<=-20) star-forming galaxies do not show significant signs in their star formation activity neither of being affected by the environment in the last ~10^8 yr nor of a sudden quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19) star-forming galaxies appear to be affected by starvation in the virial regions and by the harassment both, in the virial and infall regions. Low-luminosity (-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same environmental processes as intermediate-luminosity star-forming galaxies in a stronger way, as it would be expected for their lower luminosities.Comment: 42 pages, 7 figures, 5 tables; accepted for publication in Ap

Deep UV Luminosity Functions at the Infall Region of the Coma Cluster

We have used deep GALEX observations at the infall region of the Coma cluster to measure the faintest UV luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are measured to M_UV = -10.5 in the GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach the dwarf early-type galaxy population in Coma for the first time. The Schechter faint-end slopes (alpha = -1.39 in both GALEX bands) are shallower than reported in previous Coma UV LF studies owing to a flatter LF at faint magnitudes. A Gaussian-plus-Schechter model provides a slightly better parametrization of the UV LFs resulting in a faint-end slope of ~ -1.15 in both GALEX bands. The two-component model gives faint-end slopes shallower than -1 (a turnover) for the LFs constructed separately for passive and star forming galaxies. The UV LFs for star forming galaxies show a turnover at M_UV ~ -14 owing to a deficit of dwarf star forming galaxies in Coma with stellar masses below M*=10^8 Msun. A similar turnover is identified in recent UV LFs measured for the Virgo cluster suggesting this may be a common feature of local galaxy clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did not identify an excess of passive galaxies as would be expected if the missing dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs for both dwarf passive and star forming galaxies show the same turnover at faint magnitudes. We discuss the possible origin of the missing dwarf star forming galaxies in Coma and their expected properties based on comparisons to local field galaxies.Comment: accepted for publication in Ap

Strongly star forming galaxies in the local Universe with nebular He II 4686 emission

We present a sample of 2865 emission line galaxies with strong nebular He II 4686 emissions in Sloan Digital Sky Survey Data Release 7 and use this sample to investigate the origin of this line in star-forming galaxies. We show that star-forming galaxies and galaxies dominated by an active galactic nucleus form clearly separated branches in the He II 4686/H{\beta} versus [N II] 6584/H{\alpha} diagnostic diagram and derive an empirical classification scheme which separates the two classes. We also present an analysis of the physical properties of 189 star forming galaxies with strong He II 4686 emissions. These star-forming galaxies provide constraints on the hard ionizing continuum of massive stars. To make a quantitative comparison with observation we use photoionization models and examine how different stellar population models affect the predicted He II 4686 emission. We confirm previous findings that the models can predict He II 4686 emission only for instantaneous bursts of 20% solar metallicity or higher, and only for ages of ~ 4 - 5 Myr, the period when the extreme-ultraviolet continuum is dominated by emission from Wolf-Rayet stars. We find however that 83 of the star-forming galaxies (40%) in our sample do not have Wolf-Rayet features in their spectra despite showing strong nebular He II 4686 emission. We discuss possible reasons for this and possible mechanisms for the He II 4686 emission in these galaxies.Comment: 24 pages, 19 figures, accepted for publication in MNRA

The faintest star forming galaxies

I briefly report on the X-ray detection of 10 radio sub-mJy sources in the 2 Ms Chandra observation of the Hubble Deep Field North region. These sources follow the same radio/X-ray luminosities relation which holds for nearby galaxies. Making use of this relation, X-ray number counts from star forming galaxies are predicted from the deep radio Log N-Log S's.Comment: 1 page, 2 figures. Proc. workshop "X-ray surveys in the light of the new observatories" held in Santander (E) 2002. LaTeX, anabs.cls include

Single Star-forming galaxies and Star-forming galaxies in SF+SF and mixed pairs

We compare the SFR of single star-forming galaxies with the SFR of star-forming galaxies in pairs. Volume-limited samples are compared selected from the 2dFGRS, applying a maximum magnitude difference criterion. We show that SF galaxies in SF + SF pairs typically increase their SFR as they get fainter, whereas this does not happen for SF galaxies in mixed (SF + passive) pairs. And we provide evidence that differences between single SF and SF in pairs get more significant when SF galaxies in mixed pairs are excluded from the pair sample. Our analysis confirms that enhanced SFR and the presence of a companion galaxy (on 0.5 h^-1 Mpc scale) are correlated quantities, provided the galaxy is neither too luminous nor too faint, and the triggering galaxy is itself a SF galaxy.Comment: 6 pages, 3 figures, contributed paper, to be published in ''The Evolution of Starbursts'' (Bad Honnef 2004), ed. S. Huettemeister & E. Manthley (Melville:AIP