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|Disk galaxies near the line of sight to 3C 273 and conjectures on Lyman-alpha absorption|
Using 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.
|Neutral hydrogen detection survey of dwarf galaxies. II - Faint Virgo dwarfs and a field sample|
Neutral hydrogen spectra are presented for 53 faint dwarf galaxies inVirgo, completing the Arecibo survey of all late-type dwarfs in theVirgo Cluster Catalog, and for 42 dwarf galaxies from the field sampleof Binggeli et al. (1989). For detected galaxies, heliocentricvelocities, profile widths, and single-beam fluxes are tabulated. Thefield sample has been used to investigate the field luminosity functionand the clustering of dwarf galaxies vis-a-vis bright galaxies.
|IRAS observations of galaxies in the Virgo cluster area|
IRAS data on 196 galaxies in the area of the Virgo Cluster arepresented. The data derive from combining all available surveyobservations for each object and therefore achieve greater sensitivitythan the IRAS Point Source Catalog (PSC). The enhanced sensitivityallows 78 galaxies to be detected at 12 microns, 82 at 25 microns, 139at 60 microns, and 135 at 100 microns, compared to 16, 23, 88, and 95detections listed in the PSC. From the blue compact dwarf galaxy sample,23 and 19 objects are detected at 60 and 100 microns, compared to threeand two detections listed in the PSC. The emission in three close pairsof galaxies which are reported as single sources in the PSC areseparated here. These statistics demonstrate the importance andpotential of a detailed examination of IRAS data, especially forpossibly resolved sources and, in particular, for galaxies out toredshifts of 0.008 or galaxies with D(25) of 3 arcmin or greater.
|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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