A modified gravity (MOG) theory, that has been successfully fitted to galaxy rotational velocity data, cluster data, the Bullet Cluster 1E0657-56 and cosmological observations, is fitted to the motion of satellite galaxies around host galaxies at distances 50-400 kpc providing a new sensitive test for MOG. We show that observational data from the Sloan Digital Sky Survey are consistent with MOG...

We present a structural analysis of nearby galaxies in spiral-spiral pairs in opticalBV RI bands and compare with the structures of isolated spiral galaxies and galaxies in ongoing mergers. We use these comparisons to determine how galaxy structure changes during galaxy interactions and mergers. We analyze light concentration (C), asymmetry (A), and clumpiness (S) parameters, and use the projec...

Gravitational lenses are a unique new constraint on the structure of galaxies. We review the evidence that most lenses are early-type galaxies, the optical properties of the lens galaxies, the evidence against constant M/L models, recent work on the axis ratios of the mass distribution , and the role stellar dynamics plays in gravitational lensing.

We study the morphology of the central region of a sample of Active Galactic Nuclei (AGN) and a " control " sample of normal galaxies using archival observations of the WFPC2 instrument onboard the Hubble Space Telescope (HST). We use the ellipse fitting technique in order to get a good description of the inner " smooth " light distribution of the galaxy. We then divide the observed galaxy imag...

We present a structural and photometric analysis of 42 elliptical/lenticular galaxies in (E/S0 + S) pairs observed in the BV RI color bands. The aim of the analysis is to empirically determine the effects of interactions on their morphology, structure and stellar populations as seen from the light concentration (C), asymmetry (A), and clumpiness (S) parameters. We further compare these values t...

We present the rotation velocities V and velocity dispersions σ along the principal axes of seven elliptical galaxies less luminous than MB = −19.5. These kinematics extend beyond the half-light radii for all systems in this photometrically selected sample. At large radii the kinematics not only confirm that rotation and “diskiness” are important in faint ellipticals, as was previously known, b...

Recent analysis of the distribution of clusters of galaxies is reviewed. Clusters of galaxies located in rich superclusters form a quasiregular lattice. The power spectrum of clusters of galaxies has a sharp peak at wavelength λ0 = 120 h Mpc corresponding to the lattice step. The peak in the spectrum may be due to processes during the inflationary stage of the structure evolution.

In hierarchical structure formation, merging of galaxies is frequent and known to dramatically affect their properties. To comprehend these interactions high-resolution simulations are indispensable because of the nonlinear coupling between pc and Mpc scales. To this end, we present the first adaptive mesh refinement (AMR) simulation of two merging, low mass, initially gas-rich galaxies (1.8×10...

Gas-dynamical studies using the Hubble Space Telescope are an integral component for future progress in the search for massive black holes in galactic nuclei. Here we present an extensive set of gas rotation curves obtained with the Space Telescope Imaging Spectrograph for the central regions of 23 disk galaxies. We find that the bulges of randomly selected, nearby spiral and S0 galaxies genera...

We use numerical simulations to examine the structure of merger remnants resulting from collisions of gas-rich spiral galaxies. When the gas fraction of the progenitors is small, the remnants structurally and kinematically resemble elliptical galaxies, in agreement with earlier work. However, if the progenitor disks are gas-dominated, new types of outcomes are possible. In fact, we show that a ...