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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.
|21 CM H1 Line Spectra of Galaxies in Nearby Clusters|
A compilation of HI line fluxes, systemic velocities and line widths ispresented for \Ndet detected galaxies, mostly in the vicinities of 30nearby rich clusters out to a redshift of z ~ .04, specifically for usein applications of the Tully-Fisher distance method. New 21 cm HI lineprofiles have been obtained for ~ 500 galaxies in 27 Abell clustersvisible from Arecibo. Upper limits are also presented for \Nnod galaxiesfor which HI emission was not detected. In order to provide ahomogeneous line width determination optimized for Tully-Fisher studies,these new data are supplemented by the reanalysis of previouslypublished spectra obtained both at Arecibo and Green Bank that areavailable in a digital archive. Corrections for instrumental broadening,smoothing, signal-to-noise and profile shape are applied, and anestimate of the error on the width is given. When corrected forturbulent broadening and viewing angle, the corrected velocity widthspresented here will provide the appropriate line width parameter neededto derive distances via the Tully-Fisher relation.
|A 2572 and HCG 94 - galaxy clusters but not as we know them: an X-ray case study of optical misclassifications|
We present the results of a spectral-imaging analysis of X-ray dataobtained with the Position Sensitive Proportional Counter aboard theROSAT Observatory in a 32-ks pointed observation of Hickson's CompactGroup (HCG) £94. Besides HCG 94, A2572, a richness class 0Abell cluster, is also contained in the central region of the field ofview. Both systems are at a redshift of z~0.04 and are falling towardeach other at a velocity of about 1000 km s^-1. Their three-dimensionalspatial separation is probably of the order of an Abell radius; however,as yet, no clear signs of dynamical interaction are discernible in theX-ray data. We find HCG 94's gas temperature and unabsorbed X-rayluminosity to be far too high for a galaxy group, thereby confirming theclaim of Ebeling, Voges & Bohringer that HCG 94 should be classifiedas a galaxy cluster. The opposite is true for the Abell cluster A2572,the optical richness of which has been overestimated due to theinclusion of HCG 94. In the X-ray, A2572 appears at first sight like atypical binary cluster with two equally massive and X-ray-brightsubclusters in the process of merging. However, the available X-ray,optical, and radio data strongly suggest that A2572 proper is, in fact,merely a loose group of galaxies, while the second component is a muchricher and more distant cluster seen in superposition. A deprojectionanalysis shows HCG 94 to host a moderate cooling flow; this picture issupported by a radial increase in the column density of absorbingmaterial and a decrease in the gas temperature toward the clustercentre. HCG 94's total gravitating mass is much higher than what couldbe anticipated from its appearance in the optical. Our findings henceunderline the need for X-ray-selected cluster samples. For all threeclusters studied in this paper we find the baryon fraction to rise withradius and reach values of 15 to 30 per cent at the outer edge of ourstudy regions. If any of these values is to be taken as representativeof the overall baryon fraction of the Universe, then this resultrequires the latter to be open with Omega_0<0.35 if a conflict withthe baryon density derived from nucleosynthesis calculations is to beavoided.
|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.
|A dynamical analysis of twelve clusters of galaxies|
Four-hundred-twenty-eight new redshift measurements for galaxies in thevicinity of 12 Abell clusters are presented. The data are supplementedby previously published data with 3 deg of each cluster center. Thecluster selection, the variety of telescopes and instrumentation used toobtain the galaxy redshifts, and the available X-ray observations arediscussed. Each cluster is exmained in some detail, with the emphasisplaced on the nature of the observed velocity distributions. Robust andresistant estimators of the velocity location and scale are applied inorder to quantify these distributions. The offset in velocity space ofthe dominant galaxy in each cluster or subcluster is considered withrespect to the central location in the velocity space of the cluster asa whole, and the physical implications of significant offsets found inseveral clusters are discussed. Dynamical estimates of the masses ofclusters and/or subclusters are obtained; for clearly bimodal systems,two-body models are employed to specify their likely dynamical state.
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