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A VLA 20 CM survey of poor groups of galaxies
The paper reports on VLA 20 cm observations of an extensive sample ofgalaxies in 139 poor groups. These groups, composed of galaxies down tothe limit of the Zwicky et al. (CGCG) catalog, were chosen using apercolation algorithm set at a high surface-density threshold.Approximately 50 percent of the groups have measured redshifts. Thesegroups were surveyed using a 'snapshot' mode of the VLA with aresolution of about 13 arcsec. Analysis of the resulting radio andoptical properties reveals that the presence of a nearby companiongalaxy has an important role in generating radio emission in a galaxy.CCD observations of two radio-loud, disturbed galaxies with companionsare presented and are used to discuss models of radio-source production.Nine tailed radio galaxies are found in the poor groups, which is muchmore than had been expected from previous work on rich clusters and fromtheoretical models. The paper discusses previous statistical biases andproposes a method for bending head-tail sources in poor groups. From theconfinement of extended radio features associated with tailed sources,the presence of a substantial intracluster medium that should radiatesignificantly at soft-X-ray energies is predicted.
| Gravitational amplification of brightest cluster galaxies by foreground clusters
It is suggested that the Hubble diagram of brightest cluster galaxies(BCG) is strongly affected by gravitational amplifications due toforeground clusters of galaxies. Galaxies from Kristian et al.'s (1978)sample are placed with respect to foreground Zwicky clusters and theirdeviations from the mean magnitude-redshift relation are compared to thepredictions of Ricci gravitational amplification formula. It is foundthat the gravitational brightness increase reaches some tenth ofmagnitudes for these BCGs and that it has induced a strong selectioneffect artificially increasing the deceleration parameter q0.Once these effects are accounted for the Hubble diagram value ofq0 might agree with the low values obtained for the densityparameter sigma0 (0.1-0.2) without any need for rapidevolution.
| Radio and optical observations of 9 nearby Abell clusters - A262, A347, A569, A576, A779, A1213, A1228, A2162, A2666
A survey is made of 61 Abell clusters included in the HEAO-2 satelliteobserving program at 1.4 GHz. Data are presented on the nine clusters ofdistance class 1 and 2. With a view to establishing galaxy morphologiesand extending the sample of the galaxies with known velocities, platesand spectra are obtained with a 152-cm telescope. The bivariate radioluminosity function of the cluster galaxies is determined for the threemorphological types, E, SO, and S plus Irr, dividing these into threedifferent classes of absolute optical magnitude. The radio luminosityfunctions of E and SO galaxies in present clusters do not differ fromthose of E and SO galaxies in clusters having higher richness. Someevidence exists that spiral galaxies in clusters have a lowerprobability of being radio sources than field ones. Also included is abrief discussion of the sizes of cluster radio sources and thecorrelation between radio emission and the presence of emission linesfrom a galaxy.
| The use of the Kitt Peak IDS in determining galaxy redshifts - Results for five clusters
The redshifts of 71 galaxies in five clusters determined using the KittPeak Image Dissector Scanner (IDS) are presented and the accuracy ofvelocities determined with the IDS system is discussed. Data wereobtained from observations of absorption or emission lines in the range3600-5400 A using the IDS on a 2.1-m telescope and effective aperturesof 3.8 x 10.3 arcsec from galaxies belonging to the AWM 7 = NGC 1129, A1213, A 1795, A 2589 and A 2666 clusters. Wavelength errors due tomechanical flexure, off-center guiding and spectrum noise are estimatedto provide an uncertainty of + or - 1.21 A or 92 km/sec in measurementsof a given spectrum, and comparison of the velocities determined by theKitt Peak IDS with those determined by the Lick IDS supports the errorvalue. Implications of the mean heliocentric redshifts andrelativistically correct velocity dispersions obtained for the structureand membership of the AWM 7 cluster are discussed.
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