paper

X-ray Properties of Groups of Galaxies

arXiv:astro-ph/0009379 · doi:10.1146/annurev.astro.38.1.289

Abstract

ROSAT observations indicate that approximately half of all nearby groups of galaxies contain spatially extended X-ray emission. The radial extent of the X-ray emission is typically 50-500 kpc or approximately 10-50% of the virial radius of the group. Diffuse X-ray emission is generally restricted to groups that contain at least one early-type galaxy. X-ray spectroscopy suggests the emission mechanism is most likely a combination of thermal bremsstrahlung and line emission. This interpretation requires that the entire volume of groups be filled with a hot, low-density gas known as the intragroup medium. Higher temperature groups tend to follow the correlations found for rich clusters between X-ray luminosity, temperature, and velocity dispersion. However, groups with temperatures below approximately 1 keV appear to fall off the cluster L-T relationship (and possibly the L-sigma and sigma-T cluster relationships, although evidence for these latter departures is at the present time not very strong.)

45 pages; includes LaTeX text file, 12 ps figures, 1 style file. To appear in Annual Review of Astronomy and Astrophysics, volume 38; minor typos corrected

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