The stellar and hot gas content of low-mass galaxy clusters

Michael L. Balogh, Pasquale Mazzotta, Richard G. Bower, Vince Eke, Hervé Bourdin, Ting Lu, Tom Theuns

Research output: Contribution to journalArticlepeer-review

29 Scopus citations

Abstract

We analyse the stellar and hot gas content of 18 nearby, low-mass galaxy clusters, detected in redshift space and selected to have a dynamical mass 3 × 1014 < M/M < 6 × 1014 (h= 0.7), as measured from the 2dF Galaxy Redshift Survey. We combine X-ray measurements from both Chandra and XMM with ground-based near-infrared observations from CTIO, Anglo-Australian Telescope and Canada-France-Hawaii Telescope to compare the mass in hot gas and stars to the dynamical mass and state of the clusters. Only 13 of the clusters are detected in X-ray emission, and for these systems we find that a range of 7-20 per cent of their baryonic mass, and <3 per cent of their dynamical mass, is detected in starlight, similar to what is observed in more massive clusters. In contrast, the five undetected clusters are underluminous in X-ray emission, by up to a factor of 10, given their stellar mass. Although the velocity distribution of cluster members in these systems is indistinguishable from a Gaussian, all show subtle signs of being unrelaxed: either they lack a central, dominant galaxy, or the bright galaxy distribution is less concentrated and/or more elongated than the rest of the sample. Thus we conclude that low-mass clusters and groups selected from the velocity distribution of their galaxies exhibit a dichotomy in their hot gas properties. Either they are detected in X-ray, in which case they generally lie on the usual scaling relations, or they are completely undetected in X-ray emission. The non-detections may be partly related to the apparently young dynamical state of the clusters, but it remains a distinct possibility that some of these systems are exceptionally devoid of hot emitting gas as the result of its expulsion or rarefaction.

Original languageEnglish
Pages (from-to)947-959
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume412
Issue number2
DOIs
StatePublished - Apr 2011

Keywords

  • Galaxies: clusters: general

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