The baryon budget on the galaxy group/cluster boundary

Research output: Contribution to journalArticle


  • A.J.R. Sanderson
  • S. Sivanandam
  • A.I. Zabludoff
  • D. Zaritsky

Colleges, School and Institutes

External organisations

  • Harvard-Smithsonian Center for Astrophysics
  • University of Toronto
  • Embry-Riddle Aeronautical University, Prescott, Arizona 86301 USA
  • School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK


We present a study of the hot gas and stellar content of five optically selected poor galaxy clusters, including a full accounting of the contribution from intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass analysis with XMM-Newton observations. We find weighted mean stellar (including ICL), gas and total baryon mass fractions within r of 0.026 ± 0.003, 0.070 ± 0.005 and 0.096 ± 0.006, respectively, at a corresponding weighted mean M of (1.08) × 10 M. Even when accounting for the intracluster stars, four out of five clusters show evidence for a substantial baryon deficit within r, with baryon fractions (f) between 50 ± 6 and 59 ± 8 per cent of the universal mean level (i.e. Ω/Ω), the remaining cluster having f = 75±11 per cent. For the three clusters where we can trace the hot halo to r we find no evidence for a steepening of the gas density profile in the outskirts with respect to a power law, as seen in more massive clusters. We find that in all cases, the X-ray mass measurements are larger than those originally published on the basis of the galaxy velocity dispersion (σ) and an assumed σ-M relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r) remain consistent with the trend with mass published by Gonzalez et al., from which our sample is drawn.

Bibliographic note

Copyright 2013 Elsevier B.V., All rights reserved.


Original languageEnglish
Pages (from-to)3288-3304
Number of pages17
JournalRoyal Astronomical Society. Monthly Notices
Issue number4
Publication statusPublished - 11 Mar 2013