Journal Article

Compact groups in theory and practice – II. Comparing the observed and predicted nature of galaxies in compact groups

Crystal M. Brasseur, Alan W. McConnachie, Sara L. Ellison and David R. Patton

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 3, pages 1141-1152
Published in print January 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14092.x
Compact groups in theory and practice – II. Comparing the observed and predicted nature of galaxies in compact groups

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We examine the properties of galaxies in compact groups (CGs) identified in a mock galaxy catalogue based upon the Millennium Run simulation. The overall properties of groups identified in projection are in general agreement with the best available observational constraints. However, only ∼30 per cent of these simulated groups are found to be truly compact in three dimensions, suggesting that interlopers strongly affect our observed understanding of the properties of galaxies in CGs. These simulations predict that genuine CG galaxies are an extremely homogeneous population, confined nearly exclusively to the red sequence: they are best described as ‘red and dead’ ellipticals. When interlopers are included, the population becomes much more heterogeneous, due to bluer, star-forming, gas-rich, late-type galaxies incorrectly identified as CG members. These models suggest that selection of members by redshift, such that the line-of-sight velocity dispersion of the group is less than 1000 km s−1, significantly reduces contamination to the 30 per cent level. Selection of members by galaxy colour, a technique used frequently for galaxy clusters, is also predicted to dramatically reduce contamination rates for CG studies.

Keywords: galaxies: evolution; galaxies: general; galaxies: interactions; galaxies: statistics

Journal Article.  10000 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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