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The Dynamics of Poor Systems of Galaxies
We assemble and observe a sample of poor galaxy systems that is suitablefor testing N-body simulations of hierarchical clustering and otherdynamical halo models. We (1) determine the parameters of the densityprofile rho(r) and the velocity dispersion profile sigma_p(R), (2)separate emission-line galaxies from absorption-line galaxies, examiningthe model parameters and as a function of spectroscopic type, and (3)for the best-behaved subsample, constrain the velocity anisotropyparameter, beta, which determines the shapes of the galaxy orbits. Oursample consists of 20 systems, 12 of which have extended X-ray emissionin the ROSAT All-Sky Survey. We measure the 877 optical spectra ofgalaxies brighter than m_R~15.4 within 1.5 h^-1 Mpc of the systemcenters (we take H_0=100 h km s^-1 Mpc^-1). Thus, we sample the systemmembership to a radius typically three times larger than other recentoptical group surveys. The average system population is 30 galaxies, andthe average line-of-sight velocity dispersion is ~300 km s^-1. TheNavarro, Frenk, & White universal profile and the Hernquist modelboth provide good descriptions of the spatial data. In most cases anisothermal sphere is ruled out. Systems with declining sigma_p(R) arewell-matched by theoretical profiles in which the star-forming galaxieshave predominantly radial orbits (beta>0) many of these galaxies areprobably falling in for the first time. There is significant evidencefor spatial segregation of the spectroscopic classes regardless ofsigma_p(R).
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The kinematics of dense clusters of galaxies. I - The data
We have measured redshifts in the fields of the 31 R greater than 1Abell clusters with z of 0.02-0.05 and absolute b exp II above 30 deg.At least ten of the fields are severely contaminated by superimposedvelocity peaks. We derive the mean velocities and velocity dispersionsof the 25 dense peaks in the sample. The abundance of peaks, 6.6 x 10exp -6 h-cubed Mpc exp -3, is consistent with the mean number density ofR above 1 Abell clusters. The range of velocity dispersions is 304-1346km/s. The median dispersion is 718 km/s. The subset of eight systemswith cD galaxies has a median velocity dispersion of 792 km/s, close tothat of non-cD systems (626 km/s). When these data are combined with 16cD cluster velocity dispersions from our previous study (Zabludoff etal., 1990, or ZHG) and Dunn (1991), eight of 25 cD galaxies havepeculiar motions larger than half the cluster velocity dispersions.These findings further support the conclusions of Beers and Geller(1983), ZHG, and Dunn (1991), who argue that cD galaxies do not lie inthe global kinematic center, but in local potential minima. If so,systems with speeding cD's are probably a guide to substructure indynamically evolving systems.
| 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.
| 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.
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