Browsing by Author "GOURGOULHON, E"

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    GROUPS OF GALAXIES WITHIN 80 MPC .1. GROUPING HIERARCHICAL METHOD AND STATISTICAL PROPERTIES
    (1992) GOURGOULHON, E; CHAMARAUX, P; FOUQUE, P
    A hierarchial algorithm, similar to Tully's (1987) one, has been devised and applied to an all-sky sample of 4143 galaxies comprising all the objects with an apparent diameter D25 larger than 100 arcsec and having known recession velocities smaller than 6000 km s-1 (i.e. closer than 80 Mpc, with H0 = 75 km s-1 Mpc-1). This sample is at least 84% complete to these limits of diameter and redshift. The hierarchy is built on the mass density of the aggregates progressively formed by the method, corrected for the loss of faint galaxies with the distance; this correction represents the main improvement upon Tully's treatment. In the method, a group is defined as an entity having an average luminosity density higher than 8 10(9) L(B). Mpc-3, chosen as to ensure that the group is gravitationally bound and does not follow the Hubble expansion. 264 groups of at least three members have been identified in this way, among which 82 have more than five members and are located at distances lower than 40 Mpc. Our sample represents the deepest and richest collection of groups homogeneous over both hemispheres and whose global properties do not present significant biases with the distance; it can thus be used confidently for a variety of statistical studies. A first quick analysis of the sample leads to the following main conclusions: (i) almost all the crossing times are lower than H0(-1), which confirms the bound nature of our groups; (ii) the median virial mass to blue luminosity ratio of the groups is 74 M. L(B).-1, a high value, but lower than those obtained in previous studies; (iii) we confirm clearly the increasing of the M/L ratio with the group size, a result which can be taken as an indication of the presence of dark matter around galaxies to a distance of 500 kpc.
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    GROUPS OF GALAXIES WITHIN 80 MPC .2. THE CATALOG OF GROUPS AND GROUP MEMBERS
    (1992) FOUQUE, P; GOURGOULHON, E; CHAMARAUX, P; PATUREL, G
    This paper gives a catalogue of the groups and associations obtained by means of a revised hierarchical algorithm applied to a sample of 4143 galaxies with diameters D25 larger than 100 arcsec and redshifts smaller than 6000 km s-1 (the method and the groups properties are detailed in Paper I). In the present paper, the 264 groups of galaxies obtained in this way (and which contain at least 3 sample galaxies) are listed, with the loose associations surrounding them and the individual members of each aggregate as well; moreover, the location of every entity among 13 regions corresponding roughly to superclusters, is specified. Finally, 1729 galaxies belong to the groups, and 466 to the associations, i.e. the total fraction of galaxies within the various aggregates amounts to 53%.