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For refcode 1989ApJ...344...57R:
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Copyright by American Astronomical Society. Reproduced by permission
1989ApJ...344...57R GROUPS OF GALAXIES IN THE CENTER FOR ASTROPHYSICS REDSHIFT SURVEY MASSIMO RAMELLA Osservatorio Astronomico di Trieste AND MARGARET J. GELLER AND JOHN P. HUCHRA Harvard-Smithsonian Center for Astrophysics Received 1988 November 8; accepted 1989 February 1 ABSTRACT We apply an objective group identification algorithm described by Huchra and Geller to the Center for Astrophysics redshift survey complete to m_B(0)_ = 15.5 over the right ascension range 8^h^ <= {alpha} <= 17^h^ and declination range 26.5^deg^ <= {delta} < 38.5^deg^. We extract a catalog of 128 groups with three or more members; 92 of these groups constitute our "statistical sample." Simulations of the geometry of large-scale structure indicate that >~30% of the groups with three or four members are probably an artifact of the geometry. The median velocity dispersion for the 36 groups in the "statistical sample" with five or more members is {sigma}_v_ = 228 km s^-1^, and the median M/L_B(0)_ is 178h M_sun_/L_sun_, where the Hubble constant H_0_ is 100h km s^-1^ Mpc^-1^ (we take h = 1 unless otherwise indicated). The median parameters for the 92 group sample are similar. The sample contains seven Abell clusters; the physical properties of these clusters overlap substantially with those of groups. In fact, the distinction between groups and clusters is not generally apparent on the basis of selection of systems in redshift space. Comparison of the distribution of group centers with the distribution of all of the galaxies in the survey shows qualitatively that groups trace the large-scale structure in the region. The physical properties of groups may be related to the details of the large-scale structure. Groups reextracted from the earlier CfA survey complete to m_B(0)_ = 14.5 have a significantly lower median velocity dispersion, {sigma}_v_ = 131 km s^-1^, than the groups in the 15.5 survey. About 58% of the groups in the m_B(0)_ <= 15.5 survey contains three or more galaxies brighter than L^*^, the characteristic luminosity in the Schechter form of the luminosity function; in contrast, 77% of the groups in the 14.5 survey have fewer than three members brighter than L^*^. The difference in the group catalogs is probably largely a result of the properties of large-scale structures and their location relative to the survey limits. Subject headings: galaxies: clustering - galaxies: redshifts
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