Journal Article

The ratio of luminous to faint red-sequence galaxies in X-ray and optically selected low-redshift clusters

Diego Capozzi, Chris A. Collins and John P. Stott

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 3, pages 1274-1282
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16220.x
The ratio of luminous to faint red-sequence galaxies in X-ray and optically selected low-redshift clusters

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We study the ratio of luminous to faint red-sequence galaxies in both optically and X-ray selected galaxy clusters in the poorly studied redshift range 0.05 ≤z < 0.19. The X-ray-selected sample consists of 112 clusters based on the ROSAT All-Sky Survey, while the optical sample consists of 266 clusters from the Sloan Digital Sky Survey. Our results are consistent with the presence of a trend in luminous-to-faint ratio with redshift, confirming that downsizing is continuous from high to low redshift.

After correcting for the variations with redshift using a partial Spearman analysis, we find no significant relationship between luminous-to-faint ratio and X-ray luminosity of the host cluster sample, in contrast to recent suggestions. Finally, we investigate the stacked colour–magnitude relations of these samples, finding no significant differences between the slopes for optically and X-ray selected clusters. The colour–magnitude slopes are consistent with the values obtained in similar studies, but not with predictions of theoretical models.

Keywords: galaxies: clusters: general; galaxies: evolution; galaxies: photometry; large-scale structure of Universe

Journal Article.  6747 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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