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Title:
The colour of galaxies in distant groups
Authors:
Balogh, Michael L.; McGee, Sean L.; Wilman, Dave; Bower, Richard G.; Hau, George; Morris, Simon L.; Mulchaey, J. S.; Oemler, A., Jr.; Parker, Laura; Gwyn, Stephen
Affiliation:
AA(Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada), AB(Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada), AC(Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany), AD(Department of Physics, University of Durham, Durham DH1 3LE), AE(Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia), AF(Department of Physics, University of Durham, Durham DH1 3LE), AG(Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, California, USA), AH(Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, California, USA), AI(Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada), AJ(Canadian Astronomical Data Centre, Herzberg Institute of Astrophysics, Victoria, BC, Canada)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 398, Issue 2, pp. 754-768. (MNRAS Homepage)
Publication Date:
09/2009
Origin:
MNRAS
MNRAS Keywords:
galaxies: clusters: general , galaxies: evolution
DOI:
10.1111/j.1365-2966.2009.15193.x
Bibliographic Code:
2009MNRAS.398..754B

Abstract

We present new optical and near-infrared imaging for a sample of 98 spectroscopically selected galaxy groups at 0.25 < z < 0.55, most of which have velocity dispersions σ < 500kms-1. We use point spread function matched aperture photometry to measure accurate colours for group members and the surrounding field population. The sample is statistically complete above a stellar mass limit of approximately M = 1 × 1010Msolar. The overall colour distribution is bimodal in both the field and group samples; but, at fixed luminosity the fraction of group galaxies populating the red peak is larger, by ~20 +/- 7 per cent, than that of the field. In particular, group members with early-type morphologies, as identified in Hubble Space Telescope imaging, exhibit a tight red sequence, similar to that seen for more massive clusters. Using optical and near-infrared colours, including data from the Spitzer Space Telescope, we show that approximately 20-30 per cent of galaxies on the red sequence may be dust-reddened galaxies with non-negligible star formation and early-spiral morphologies. This is true of both the field and group samples, and shows little dependence on near-infrared luminosity. Thus, the fraction of bright (0.4MK < -22) group members with no sign of star formation or active galactic nuclei activity, as identified by their colours or [OII] emission, is 54 +/- 6 per cent. Our field sample, which includes galaxies in all environments, contains 35 +/- 3 per cent of such inactive galaxies, consistent with the amount expected if all such galaxies are located in groups and clusters. This reinforces our earlier conclusions that dense environments at z <~ 0.5 are associated with a premature cessation of star formation in some galaxies; in particular, we find no evidence for significantly enhanced star formation in these environments. Simple galaxy formation models predict a quenching of star formation in groups that is too efficient, overpopulating the red sequence. Attempts to fix this by increasing the time-scale of this quenching equally for all group members distort the colour distribution in a way that is inconsistent with observations.
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