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|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|H I observations of lenticular and early type galaxies|
High sensitivity H I observations of 56 galaxies, mostly S0's (47objects), carried out with the Arecibo radio telescope are presented.Twelve S0's and four S0/a spirals have been detected, among which 12 forthe first time, and nine of them have been mapped. In addition,absorption lines have been found in two S0's. A detailed discussion ofthe results of the mapping has made it possible to solve several casesof confusion and to find out two possible cases of H I ring structuresor flat rotation curves in S0's. Finally for six mapped galaxies, asimple deconvolution procedure has led to the derivation of the total HI fluxes and of the H I diameters; on the average, the ratio of the H Idiameter to the optical one is found to be 30 percent higher for theS0's than for the spirals.
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