Open AccessGalaxy ecology: groups and low‐density environments in the SDSS and 2dFGRS
Author(s) -
Balogh Michael,
Eke Vince,
Miller Chris,
Lewis Ian,
Bower Richard,
Couch Warrick,
Nichol Robert,
BlandHawthorn Joss,
Baldry Ivan K.,
Baugh Carlton,
Bridges Terry,
Can Russell,
Cole Shaun,
Colless Matthew,
Collins Chris,
Cross Nicholas,
Dalton Gavin,
Propris Roberto De,
Driver Simon P.,
Efstathiou George,
Ellis Richard S.,
Frenk Carlos S.,
Glazebrook Karl,
Gomez Percy,
Gray Alex,
Hawkins Edward,
Jackson Carole,
Lahav Ofer,
Lumsden Stuart,
Maddox Steve,
Madgwick Darren,
Norberg Peder,
Peacock John A.,
Percival Will,
Peterson Bruce A.,
Sutherland Will,
Taylor Keith
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07453.x
Subject(s) - physics , astrophysics , galaxy , velocity dispersion , galaxy group , sigma , star formation , sky , population , astronomy , redshift , redshift survey , galaxy formation and evolution , demography , sociology
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 ( M b J < −19.5) and the Sloan Digital Sky Survey ( M r < −20.6) . We characterize the environment by: (1) Σ 5 , the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) ρ 1.1 and ρ 5.5 , 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, W 0 (Hα). The relative numbers of star‐forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W 0 (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, ρ 5.5 , which is likely independent of the trend with local density, ρ 1.1 . 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.