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# PGC 40951

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 Completing H I observations of galaxies in the Virgo clusterHigh sensitivity (rms noise  0.5 mJy) 21-cm H I line observationswere made of 33 galaxies in the Virgo cluster, using the refurbishedArecibo telescope, which resulted in the detection of 12 objects. Thesedata, combined with the measurements available from the literature,provide the first set of H I data that is complete for all 355 late-type(Sa-Im-BCD) galaxies in the Virgo cluster with mp ≤ 18.0mag. The Virgo cluster H I mass function (HIMF) that was derived forthis optically selected galaxy sample is in agreement with the HIMFderived for the Virgo cluster from the blind HIJASS H I survey and isinconsistent with the Field HIMF. This indicates that both in this richcluster and in the general field, neutral hydrogen is primarilyassociated with late-type galaxies, with marginal contributions fromearly-type galaxies and isolated H I clouds. The inconsistency betweenthe cluster and the field HIMF derives primarily from the difference inthe optical luminosity function of late-type galaxies in the twoenvironments, combined with the HI deficiency that is known to occur ingalaxies in rich clusters.Tables \ref{t1, \ref{sample_dat} and Appendix A are only available inelectronic form at http://www.edpsciences.org Nearby Optical Galaxies: Selection of the Sample and Identification of GroupsIn this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales. Total magnitude, radius, colour indices, colour gradients and photometric type of galaxiesWe present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory. New aperture photometry for 217 galaxies in the Virgo and Fornax clusters.We present photo electric multi-aperture photometry in UBVRI of 171 and46 galaxies in the Virgo and Fornax clusters, respectively. Many of thegalaxies have not been observed in at least one of these passbandsbefore. We discuss the reduction and transformation into the Cousinsphotometric system as well as the extinction coefficients obtainedbetween 1990 and 1993. Disk galaxies near the line of sight to 3C 273 and conjectures on Lyman-alpha absorptionUsing data from the preceding paper (Hoffman, Lewis & Salpeter 1995)and recent literature, we augment compilations by Salzer (1992) and byMorris et al. (1993) to select (by projected distance) 22 disk galaxiesnear the line of sight to the quasar 3C 273. These galaxies arecorrelated with the seven Lyman-alpha absorption lines (from HubbleSpace Telescope (HST) observations) below 10,000 km/s on velocity scalestypical of galaxy groups (a few hundred km/s). For three of the sevenlines an individual galaxy is close enough in position and velocity thatit may provide the absorption. This includes the galaxy MGC 0-32-16,which has a projected separation of 204 kpc and a velocity difference of93 km/s from the lowest velocity absorption line. For a fourth of theseven lines, there is a small group of galaxies fairly close by. For theremaining three of the seven absorption lines, however, no ordinarygalaxies are nearby. Thus, while some of the absorption lines are likelyto arise in extensions of ordinary galaxy disks, the majority must becaused by otherwise invisible objects. Whatever the physical nature ofthese objects, many of them are likely to reside in 'clouds orfilaments' in void-like regions which also contain some ordinarygalaxies or galaxy groups. As an alternative to 'minihalos' for theinvisible objects, we postulate an 'almost invisible' class of galaxies('Vanishing Cheshire Cats') which are born with central column densitiesalready about 10 times smaller than for ordinary disk galaxies and whichthen suffer further mass loss from the inner disk. Recent observationsthat show a larger fraction of Lyman-limit systems with H I columndensity below 1017.7/cm for z less than 1 than for z greaterthan 2 provide further motivation for this model. General study of group membership. II - Determination of nearby groupsWe 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. The Virgo cluster as a test for quantization of extragalactic redshiftsTifft's (1972, 1977) hypothesis that redshifts are partially quantizedwith a periodicity in the range 70-75 km/s is tested for samples ofbright spiral and dwarf irregular galaxies with accurate H I redshiftsin the region of the Virgo cluster. The heliocentric redshifts arecorrected for solar motion, first by adopting an estimate of the sun'smotion with respect to the centroid of the Local Group, and then byallowing the solar velocity vector to vary in direction over the wholesky. Power spectrum analyses of the corrected redshifts are used tosearch for a significant periodicity in the prescribed range 70-75 km/s.No such periodicity is found for the dwarf irregulars, but there is apossible periodicity of about 71.1 km/s for the bright spirals. In afurther exploratory study, the sample of 112 spirals is divided upaccording to environment. The spirals in high-density regions of thecluster show no quantization, whereas those in low-density regionsappear to be partially quantized in intervals of about 71.0 km/s. H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster areaNew single-beam Arecibo H I observations of 298 late-type galaxies inthe Virgo Cluster drawn mostly from the new catalog of Binggeli,Sandage, and Tammann (1985) are presented. Two hundred seventeen ofthese constitute a magnitude-limited 'complete sample' of such galaxies,types Sdm through Im and BCD. Sixty-one percent of this 'completesample' was detected, greatly enhancing the store of redshifts and H Imasses for such galaxies in the Virgo Cluster. For detected galaxies,heliocentric velocities, 50 percent profile widths, and single-beamfluxes are presented. For those that escaped detection, upper limits arecomputed to the flux appropriate to the redshift range (-600 to +3000km/s). Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
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