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|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|ROSAT observations of compact groups of galaxies|
We have systematically analyzed a sample of 13 new and archival ROSATPosition Sensitive Proportional Counter (PSPC) observations of compactgroups of galaxies: 12 Hickson compact groups plus the NCG 2300 group.We find that approximately two-thirds of the groups have extended X-rayemission and, in four of these, the emission is resolved into diffuseemission from gas at a temperature of kT approximately 1 keV in thegroup potential. All but one of the groups with extended emission have aspiral fraction of less than 50%. The baryon fraction of groups withdiffuse emission is 5%-19%, similar to the values in clusters ofgalaxies. However, with a single exception (HCG 62), the gas-to-stellarmass ratio in our groups has a median value near 5%, somewhat greaterthan the values for individual early-type galaxies and two orders ofmagnitude than in clusters of galaxies. The X-ray luminosities ofindividual group galaxies are comparable to those of similar fieldgalaxies, although the LX-LB relation forearly-type galaxies may be flatter in compact groups than in the field.
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