Serendipitous XMM-Newton discovery of a cluster of galaxies at z = 0.28

Fabio Gastaldello, David A. Buote, Philip J. Humphrey, Luca Zappacosta, Marc S. Seigar, Aaron J. Barth, Fabrizio Brighenti, William G. Mathews

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


We report the discovery of a galaxy cluster serendipitously detected as an extended X-ray source in an offset observation of the group NGC 5044. The cluster redshift, z = 0.281, determined from the optical spectrum of the brightest cluster galaxy, agrees with that inferred from the X-ray spectrum using the Fe Ka complex of the hot ICM (z = 0.27 ± 0.01). Based on the 50 ks XMM-Newton observation, we find that within a radius of 383 kpc the cluster has an unabsorbed X-ray flux fX(0.5-2 keV) = (3.34 -0.13+0.08) × 10-13 ergs cm-2 s-1, a bolometric X-ray luminosity LX = (2.21 0.19+0.34) × 1044 ergs s-1, kT = 3.57±0.12 ke V, and metallicity 0.60 ± 0.09 Z. The cluster obeys the scaling relations for LX and T observed at intermediate redshift. The mass derived from an isothermal NFW model fit is Mvir = 3.89 ± 0.35 × 1014 M, with a concentration parameter, c = 6.7 ± 0.4, consistent with the range of values expected in the concordance cosmological model for relaxed clusters. The optical properties suggest this could be a "fossil cluster."

Original languageEnglish (US)
Pages (from-to)923-926
Number of pages4
JournalAstrophysical Journal
Issue number2 I
StatePublished - Jun 20 2007


  • Galaxies: clusters: general
  • X-rays: general

Fingerprint Dive into the research topics of 'Serendipitous XMM-Newton discovery of a cluster of galaxies at z = 0.28'. Together they form a unique fingerprint.

Cite this