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|The UZC-SSRS2 Group Catalog|
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
|An Imaging and Spectroscopic Survey of Galaxies within Prominent Nearby Voids. II. Morphologies, Star Formation, and Faint Companions|
We analyze the optical properties of ~300 galaxies within and aroundthree prominent voids of the Center for Astrophysics Redshift Survey. Wedetermine CCD morphologies and Hα equivalent widths from ourimaging and spectroscopic survey. We also describe a redshift survey of250 neighboring galaxies in the imaging survey fields. We assess themorphology-density relation, EW(Hα)-density relation, and theeffects of nearby companions for galaxies in low-density environmentsselected with a smoothed large-scale (5 h-1 Mpc) galaxynumber density n. Both the morphological mix and the Hα line widthdistribution of galaxies at modest underdensities, 0.5R=16.13, demonstrates that the incidence ofa close companion in redshift space is insensitive to global densityover the range we investigate (0.163 σ) fromΔcz>~200 km s-1 at 0.5-1 at n<=0.5n. In the lowest densityenvironments, galaxies with companions clearly (~4 σ) havestronger star formation than comparable galaxies at larger globaldensity (0.5-1 kpc and 1000 km s-1) varies little over theentire density range. These results, combined with the luminosity- andcolor-density relations of this sample (Paper I), suggest that theformation and evolution of field galaxies are insensitive to large-scaleunderdensity down to a threshold of roughly half the mean density. Thedifferences in galaxy properties at the lowest global densities we canexplore (n<=0.5n) may be explained by (1) a relative scarcity of thesmall-scale primordial density enhancements needed to form massiveearly-type/absorption-line galaxies and (2) present-day galaxyencounters that are relatively more effective because of the lowervelocity dispersion on small scales (<~200 h-1 kpc) weobserve in these regions. In the voids, where the luminous galaxiespresumably formed more recently, there should be more gas and dustpresent for active star formation triggered by nearby companions.
|An Imaging and Spectroscopic Survey of Galaxies within Prominent Nearby Voids. I. The Sample and Luminosity Distribution|
We study the optical properties of a large sample of galaxies inlow-density regions of the nearby universe. We make a 5 h-1Mpc smoothed map of the galaxy density throughout the Center forAstrophysics Redshift Survey (CfA2) to identify galaxies within threeprominent nearby ``voids'' with diameter >~30 h-1 Mpc. Weaugment the CfA2 void galaxy sample with fainter galaxies found in thesame regions from the more recent and deeper Century and Redshiftsurveys . We obtain B and R CCD images and high signal-to-noiselong-slit spectra for the resulting sample of 149 void galaxies, as wellas for an additional 131 galaxies on the periphery of these voids. Herewe describe the photometry for the sample, including B isophotalmagnitudes and B-R colors. For the 149 galaxies that lie in regionsbelow the mean survey density, the luminosity functions in B and R arewell fit by Schechter functions with respective parameters(αB=-0.5+/-0.3, B*=-18.9+/-0.2) and(αR=-0.9+/-0.3, R*=-20.4+/-0.3). The Bluminosity function (LF) is consistent with typical survey LFs (e.g.,the Southern Sky Redshift Survey), and the R LF is consistent with theCentury Survey. The B and R LFs of 131 galaxies in the ``voidperiphery''-regions between the mean density and twice the mean-havesimilar Schechter parameters. The CfA2 LF is inconsistent with bothsamples at the 3.5 σ level. When we narrow our analysis to the 46galaxies in regions below half the mean density, the LF is significantlysteeper: α~-1.4+/-0.5. The typical survey LFs are inconsistentwith this subsample at the ~2 σ level. The B-R color distributionof galaxies in the lowest density regions is also shifted significantly(~3 σ) blueward of the higher density samples. The most luminousred galaxies (R<~-21) are absent from the lowest density regions at the2.5 σ level.
|Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies|
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
|A survey of the Pisces-Perseus supercluster. VI - The declination zone +15.5 deg to 21.5 deg|
New results are presented of Arecibo observations in the 21 cm line of765 galaxies with declinations between 15.5 deg and 21.5 deg, in thePisces-Perseus supercluster zone. If considered independently on theneighboring parts of sky, this region, to the South of the superclusterridge, shows significantly less evidence of structure on large scales inexcess of 30 Mpc, contrasting substantially with the characteristics ofthe declination zones immediately to the North.
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