Journal Article

How typical is the Coma cluster?

Kevin A. Pimbblet, Samantha J. Penny and Roger L. Davies

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 438, issue 4, pages 3049-3057
Published in print March 2014 | ISSN: 0035-8711
Published online January 2014 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1093/mnras/stt2411
How typical is the Coma cluster?

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Coma is frequently used as the archetype z ∼ 0 galaxy cluster to compare higher redshift work against. It is not clear, however, how representative the Coma cluster is for galaxy clusters of its mass or X-ray luminosity, and significantly, recent works have suggested that the galaxy population of Coma may be in some ways anomalous. In this work, we present a comparison of Coma to an X-ray-selected control sample of clusters. We show that although Coma is typical against the control sample in terms of its internal kinematics (sub-structure and velocity dispersion profile), it has a significantly high (∼3σ) X-ray temperature set against clusters of comparable mass. By de-redshifting our control sample cluster galaxies star formation rates using a fit to the galaxy main-sequence evolution at z < 0.1, we determine that the typical star formation rate of Coma galaxies as a function of mass is higher than for galaxies in our control sample at a confidence level of >99 per cent. One way to alleviate this discrepancy and bring Coma in line with the control sample would be to have the distance to Coma to be slightly lower, perhaps through a non-negligible peculiar velocity with respect to the Hubble expansion, but we do not regard this as likely given precision measurements using a variety of approaches. Therefore, in summary, we urge caution in using Coma as a z ∼ 0 baseline cluster in galaxy evolution studies.

Keywords: galaxies: clusters: general; galaxies: clusters: individual: Coma cluster; galaxies: evolution; X-rays: galaxies: clusters

Journal Article.  5535 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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