The LX-sigma Relation for Galaxies and Clusters of Galaxies

We demonstrate that individual elliptical galaxies and clusters of galaxies form a continuous X-ray luminosity---velocity dispersion (LX-sigma) relation. Our samples of 280 clusters and 57 galaxies have LX ~ sigma^4.4 and LX ~ sigma^10, respectively. This unified LX - sigma relation spans 8 orders of magnitude in LX and is fully consistent with the observed and theoretical luminosity---temperature scaling laws. Our results support the notion that galaxies and clusters of galaxies are the luminous tracers of similar dark matter halos.Comment: 11 pages, including 2 tables and 2 figures. Accepted for publication in The Astrophysical Journal Letters; the Letters version excludes Table 1, which is available in ASCII format at http://tdc-www.harvard.edu/lxsigm

The Rotation Velocity - Density Relation

We have assembled 21-cm linewidths for 376 of the 732 galaxies in a magnitude-limited redshift survey of the the Perseus-Pisces region. We analyze a distance limited subset of 271 galaxies (131 widths) to examine the relationship between linewidth and local density. The sample indicates that galaxies with linewidths $\gtrsim 480$ km/s are absent from regions where the galaxy density is $\lesssim 0.03$ galaxies Mpc$^{-3}$ ($M_{B(0)}< -18.3$). This effect is in the direction predicted by standard CDM models. Galaxies with linewidths $\lesssim$ 480 km/s appear throughout the sample. The observational constraints could be substantially improved with a larger sample, IR photometry, and more uniform 21-cm data.Comment: 11 pages, 9 postscript figures; to appear in July 1996 A

The dynamics and evolution of clusters of galaxies

Research was undertaken to produce a coherent picture of the formation and evolution of large-scale structures in the universe. The program is divided into projects which examine four areas: the relationship between individual galaxies and their environment; the structure and evolution of individual rich clusters of galaxies; the nature of superclusters; and the large-scale distribution of individual galaxies. A brief review of results in each area is provided

A Morphology--Cosmology Connection for X--Ray Clusters

We employ N--body/$3D$ gas dynamic simulations of the formation of galaxy clusters to determine whether cluster X--ray morphologies can be used as cosmological constraints. Confirming the analytic expectations of Richstone, Loeb, \& Turner, we demonstrate that cluster evolution is sensitive to the cosmological model in which the clusters form. We further show that evolutionary differences are echoed in the gross morphological features of the cluster X--ray emission. We examine current--epoch X--ray images of models originating from the same initial density fields evolved in three different cosmologies: (i) an unbiased, low density universe with \Omega_o \se 0.2; (ii) an unbiased universe dominated by vacuum energy with \Omega_o \se 0.2 and \lambda_o \se 0.8 and (iii) a biased Einstein--deSitter model (\Omega \se 1, $\sigma_8=0.59$). Using measures of X--ray morphology such as the axial ratio and centroid shifting, we demonstrate that clusters evolved in the two low $\Omega_o$ models are much more regular, spherically symmetric, and centrally condensed than clusters evolved in the Einstein--deSitter model. This morphology--cosmology connection, along with the availability of a large body of cluster X--ray observations, makes cluster X--ray morphology both a powerful and a practical cosmological discriminant.Comment: (uuencoded, compressed postscript, 9 pages including figures), CFA-370