The baryon budget on the galaxy group/cluster boundary

Alastair J.R. Sanderson, Ewan O'Sullivan, Trevor J. Ponman, Anthony H. Gonzalez, Suresh Sivanandam, Ann I. Zabludoff, Dennis Zaritsky

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38 Scopus citations


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 r500 of 0.026 ± 0.003, 0.070 ± 0.005 and 0.096 ± 0.006, respectively, at a corresponding weighted mean M500 of (1.08-0.18+0.21) × 1014 M. Even when accounting for the intracluster stars, four out of five clusters show evidence for a substantial baryon deficit within r500, with baryon fractions (fb) between 50 ± 6 and 59 ± 8 per cent of the universal mean level (i.e. Ωbm), the remaining cluster having fb = 75±11 per cent. For the three clusters where we can trace the hot halo to r500 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-M500 relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r500) remain consistent with the trend with mass published by Gonzalez et al., from which our sample is drawn.

Original languageEnglish (US)
Pages (from-to)3288-3304
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Mar 11 2013


  • Cosmology: observations -X-rays: galaxies: clusters
  • Galaxies: clusters: general
  • Galaxies: evolution
  • Galaxies: stellar content

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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