We report results from the second stage of an optical follow-up study aimed at determining new redshifts for clusters of galaxies selected from the ROSAT All-Sky Survey. We review the optical properties of all the clusters obtained so far in this programme, which comprises 71 clusters up to a redshift of 0.3. The fraction of central galaxies exhibiting optical line emission and an excess blue continuum is 34%, consistent with smaller, previous, X-ray samples. There is no trend for this fraction to increase with redshift, although we find a clear tendency for the strongest line emitters to have the bluest continua. The probability of the presence of line emission and an excess blue continuum is increased for those galaxies with associated radio sources, although the strength of these features does not appear to be related to the power of the radio emission.
Using a redshift survey of 1323 galaxies (1092 new or remeasured) in a region of 95deg^2^ centered on the nearby galaxy cluster Abell 2199, we analyze the supercluster containing A2199, A2197, and an X-ray group.
In this paper we present the results of a spectroscopic survey of galaxies in an area between the two clusters of galaxies A548 and A3367, suspected to be a close and interacting pair. With the use of multifiber spectroscopy, we measured 180 new velocities of galaxies in the central part of A 3367 and in the external regions of A 548. The redshift histogram shows the presence of three velocity peaks, at v~12000km/s, v~30000km/s and v~40000km/s, respectively. For these we estimate the density excess, the mean velocity, and the velocity dispersion. The first clump corresponds to an elongation of A 548: in particular we found a correspondence between the features of this peak and the substructures of A 548. The second peak has a velocity dispersion which is typical of clusters and the distribution of its members on the plane of the sky corresponds to the highest density peak in A 3367. We therefore suggest that the name A 3367 has to be attributed to this clump. Our general conclusion is that, differently from expected, A 548 and A 3367 do not form a close pair of merging clusters, since the two structures are at significantly different redshifts. Moreover, we found that the complex dynamical structure of A 548 has large coherence, with a projected extension in the range of 1-3h^-1^Mpc.
Redshift Survey Compact Groups (RSCGs) are tight knots of N>=3 galaxies selected from the CfA2+SSRS2 redshift survey. The selection is based on physical extent and association in redshift space alone. We measured 300 new redshifts of fainter galaxies within 1h^-1^Mpc of 14 RSCGs to explore the relationship between RSCGs and their environments. Thirteen of 14 RSCGs are embedded in overdense regions of redshift space. The systems range from a loose group of five members to an Abell cluster. The remaining group, RSCG 64, appears isolated. RSCGs are isolated and distinct from their surroundings to varying degrees, as are the Hickson compact groups. Among the 13 embedded RSCGs, three are distinct from their general environments (RSCG 9, RSCG 11, and RSCG 85).
We present results of the HST Advanced Camera for Surveys spectroscopic ground-based redshift survey in the field of A1689. We measure 98 redshifts, increasing the number of spectroscopically confirmed objects sixfold. We present two spectra from this catalog of the Sextet Arcs, images that arise from a strongly lensed Lyman break galaxy (LBG) at a redshift of z=3.038. Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and produces six separate images with a total r-band magnitude of r_625_=21.7. The two spectra, each of which represents emission from different regions of the LBG, show HI and interstellar metal absorption lines at the systemic redshift.
We use a dense redshift survey in the foreground of the Subaru GTO2deg^2^ weak-lensing field (centered at 16:04:44+43:11'24 (2000) to assess the completeness and comment on the purity of massive halo identification in the weak-lensing map. The redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts measured with the Hectospec on the MMT. Among the weak-lensing peaks with a signal to noise greater than 4.25, 2/3 correspond to individual massive systems; this result is essentially identical to the Geller et al. (2010ApJ...709..832G) test of the Deep Lens Survey (DLS) field F2. The Subaru map, based on images in substantially better seeing than the DLS, enables detection of less massive halos at fixed redshift as expected. We demonstrate that the procedure adopted by Miyazaki et al. (2002ApJ...580L..97M) for removing some contaminated peaks from the weak-lensing map improves agreement between the lensing map and the redshift survey in the identification of candidate massive systems.
New MMT/Hectospec spectroscopy centered on the galaxy cluster A2626 and covering a ~1.8deg^2^ area out to z~0.46 more than doubles the number of galaxy redshifts in this region. The spectra confirm four clusters previously identified photometrically. A2625, which was previously thought to be a close neighbor of A2626, is in fact much more distant. The new data show six substructures associated with A2626 and five more associated with A2637. There is also a highly collimated collection of galaxies and galaxy groups between A2626 and A2637 having at least three and probably four substructures. At larger scales, the A2626-A2637 complex is not connected to the Pegasus-Perseus filament.
We present the results of a redshift survey of intercluster galaxies in the central region of the Shapley Concentration supercluster, aimed at determining the distribution of galaxies in between obvious overdensities. Our sample is formed by 442 new redshifts, mainly in the b_J_ magnitude range 17-18.8. Adding the data from our redshift surveys on the A3558 and A3528 complexes, which are close to the geometrical centre of this supercluster, we obtain a total sample of ~2000 radial velocities. The average velocity of the observed intercluster galaxies in the Shapley Concentration appears to be a function of their ({alpha}, {delta} position, and it can be fitted by a plane in the three dimensional space ({alpha}, {delta}, v): the distribution of the galaxy distances around the best-fitting plane is described by a Gaussian with dispersion 3.8h^-1^Mpc.
We constrain the mass profile and orbital structure of nearby groups and clusters of galaxies. Our method yields the joint probability distribution of the density slope n, the velocity anisotropy {beta}, and the turnover radius r_0_ for these systems. The measurement technique does not use results from N-body simulations as priors. We incorporate 2419 new redshifts (included here) in the fields of 41 systems of galaxies with z<0.04.