NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2018-11-17 T08:50:53 PST
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For refcode 1996ApJ...456...80M:
Retrieve 47 NED objects in this reference.
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Copyright by American Astronomical Society. Reproduced by permission
1996ApJ...456...80M THE INTRAGROUP MEDIUM IN POOR GROUPS OF GALAXIES JOHN S. MULCHAEY The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101-1292 DAVID S. DAVIS University of Alabama, Department of Physics and Astronomy, Tuscaloosa, AL 35487-0324 RICHARD F. MUSHOTZKY NASA/Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 666, Greenbelt, MD 20771 AND DAVID BURSTEIN Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504 Received 1995 April 5; accepted 1995 July 11 ABSTRACT We have used the ROSAT PSPC to search for diffuse, extended X-ray emission in a sample of 14 galaxy groups. A diffuse component was found in four cases. Combining our new analysis with published X-ray observations, we found that a total of 48 galaxy groups of varying size and velocity dispersion have analyzed ROSAT X-ray data. Diffuse, ~1.0 keV X-ray gas is seen in 25 of the 48 groups analyzed, but the true incidence of such an intragroup medium is probably lower, since this sample includes X-ray-discovered groups. X-ray luminosity does not correlate well with the optical richness, blue luminosity, or velocity dispersion of the group. In contrast, there is a strong correlation with the percentage of early-type (E and S0) galaxies. All of the groups with an extended intragroup medium have high percentages of early-type galaxies, and over half of these systems appear to contain no spirals at all. Furthermore, all the X-ray-detected systems contain at least one elliptical with a blue luminosity of L_B_ ~ 5 x 10^10^ L_sun_ or greater. We discuss several possible explanations for the correlation between spiral fraction and the presence of diffuse hot gas, including the idea that the spiral-rich groups represent superpositions of galaxies, that they contain a relatively cool intragroup medium, or that the formation and evolution of spiral-rich groups are fundamentally different from those of elliptical-rich groups. We also use the X-ray observations to estimate the total masses of these systems. There is a large range in the derived gas masses, but in general the mass in the X-ray-emitting gas is comparable to or less than the mass in the galaxies. Despite the large range in gas mass, there is a very narrow range in total group mass, with most of the groups having a mass of ~2 x 10^13^ M_sun_ out to the radius for which X-ray emission is detected by ROSAT. The ratio of observed luminous mass (i.e., galaxies + hot gas) to total inferred mass in poor groups is rather low (~5%-30%), implying that these systems are dominated by dark matter. Subject headings: dark matter - galaxies: clusters: general - galaxies: fundamental parameters - intergalactic medium - X-rays: galaxies
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