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|Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample|
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In 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.
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|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).
|HI observations of galaxies in nearby Zwicky clusters|
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.
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