X-ray overluminous elliptical galaxies: A new class of mass concentrations in the universe?

A. Vikhlinin, B.R. McNamara, Allan Hornstrup, H. Quintana, W. Forman, C. Jones, M. Way

Research output: Contribution to journalJournal articleResearchpeer-review


We detect four isolated, X-ray overluminous [L-x > 2 x 10(43) (h/0.5)(-2) ergs s(-1)] elliptical galaxies (OLEGs) in our 160 deg(2) ROSAT PSPC survey. The extent of their X-ray emission, total X-ray luminosity, total mass, and mass of the hot gas in these systems corresponds to poor clusters, and the optical luminosity of the central galaxies (M-R<-22.5 + 5 log h) is comparable to that of cluster cD galaxies. However, there are no detectable fainter galaxy concentrations around the central elliptical galaxy. The estimated mass-to-light ratio within the radius of detectable X-ray emission is in the range of 250-450 M./L., which is 2-3 times higher than typically found in clusters or groups. These objects can be the result of galaxy merging within a group. OLEGs must have been undisturbed for a very long time, which makes them the ultimate examples of systems in hydrostatic equilibrium. The number density of OLEGs is n = 2.4(-1.2)(+3.1) x 10(-7) (h/0.5)(-3) Mpc(-3) at the 90% confidence level. They comprise 20% of all clusters and groups of comparable X-ray luminosity, and nearly all field galaxies brighter than M-R = -22.5. The estimated contribution of OLEGs to the total mass density in the universe is close to that of T > 7 keV clusters.
Original languageEnglish
JournalAstrophysical Journal
Issue number1
Pages (from-to)L1-L4
Publication statusPublished - 1999


  • cosmology : observations
  • dark matter
  • X-rays : galaxies
  • galaxies : clusters : general

Fingerprint Dive into the research topics of 'X-ray overluminous elliptical galaxies: A new class of mass concentrations in the universe?'. Together they form a unique fingerprint.

Cite this