Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

Abstract

We analyse the observed correlation between galaxy environment and Hα emission‐line strength, using volume‐limited samples and group catalogues of 24 968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (MbJ< −19.5) and the Sloan Digital Sky Survey (Mr < −20.6). We characterize the environment by: (1) Σ5, the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) ρ1.1 and ρ5.5, three‐dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 and 5.5 Mpc, respectively. We find that star‐forming and quiescent galaxies form two distinct populations, as characterized by their Hα equivalent width, W0(Hα). The relative numbers of star‐forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W0(Hα) amongst the star‐forming population is independent of environment. The fraction of star‐forming galaxies shows strong sensitivity to the density on large scales, ρ5.5, which is likely independent of the trend with local density, ρ1.1. We use two differently selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for σ= 200–1000 km s‐1. Even in the lowest‐density environments, no more than ∼70 per cent of galaxies show significant Hα emission. Based on these results, we conclude that the present‐day correlation between star formation rate and environment is a result of short‐time‐scale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy–galaxy interactions.

OMEGA – OSIRIS Mapping of Emission-line Galaxies in A901/2: II. – Environmental influence on integrated star formation properties and AGN activity

“…We sample higher Hα fluxes than in Paper I as a consequence of the improved sky subtraction that we apply here (see Section 3). The WHα distribution is broadly compatible with the one found by Balogh et al (2004a). For equivalent widths larger than ∼ 30Å, the distribution declines steeply, following a power law with slope −2.3, and reaching as high as ∼ 300Å.…”

“…This result agrees with the findings of Poggianti et al (2008), Vulcani et al (2010) and Paccagnella et al (2016), but contradicts the conclusions of Balogh et al (2004a), Verdugo, Ziegler & Gerken (2008) and Bamford et al (2008), who suggest this transition has to be relatively fast. We attribute this discrepancy, at least partially, to differences in the definition of the star-forming galaxy samples these studies are based on and the range of environments they explore.…”

Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-phase Metallicity Gradients: The Effects of Ram Pressure Stripping

“…Numerous studies have established that galaxy clusters have significantly larger fractions of elliptical and S0-type galaxies relative to the field galaxy populations (Dressler 1980;Poggianti et al 1999; Van der Wel 2008). Galaxies in local galaxy clusters have lower star-formation rates and are deficient in both the molecular and atomic gas compared to field galaxies Balogh et al 2004;Chung et al 2009;Hughes & Cortese 2009;Cortese et al 2011;Boselli et al 2014a;Odekon et al 2016;Brown et al 2017). The removal of the cold/hot gas reservoir for an infalling galaxy via ram pressure stripping (RPS; Gunn & Gott 1972) by the hot diffuse intracluster medium (ICM) can explain some of the differences between cluster and field galaxies such as lower gas fraction and lower star formation rates in cluster galaxies (Abramson et al 2011;Chung et al 2009;Boselli et al 2014b).…”

A DEEP, WIDE-FIELD Hα SURVEY OF NEARBY CLUSTERS OF GALAXIES: DATA

“…The most complete emission-line surveys of the local universe have come from objective prism studies (e.g., Gallego et al 1997;Salzer et al 2001;Moss & Whittle 2000Gronwall et al 2004;Bongiovanni et al 2005;Jangren et al 2005) or multi-fiber surveys such as SDSS and the Two-Degree Field (2dF) survey (e.g., Gómez et al 2003;Hopkins et al 2003;Balogh et al 2004;Brinchmann et al 2004). The prism and fiber spectra have the advantage of uniform coverage over large areas of sky and redshift depth, sufficient to estimate the local cosmological star formation density (e.g., Gallego et al 1995).…”