We have completed a spectroscopic survey of X-ray point sources in eight low-redshift clusters of galaxies (0.05 < z < 0.31) and have identified 40 cluster members with broad-band (0.3–8 keV) X-ray luminosities between LX = 8×1040 and 4×1043 erg s−1. There are between two and ten X-ray sources per cluster. We use visible-wavelength emission lines, X-ray spectral shapes, and multiwavelength flux...

The energy fed by active galactic nuclei to the surrounding diffuse baryons changes their amount, temperature, and distribution; so in groups and in member galaxies it affects the X-ray luminosity and also the Sunyaev-Zel’dovich effect. Here we compute how the latter is enhanced by the transient blastwave driven by an active quasar, and is depressed when the equilibrium is recovered with a depl...

We study the enviromental dependence and the morphological composition of the galaxy colormagnitude diagram at z ∼ 0.7, using a pilot sub-sample of the COSMOS survey. The sample includes ∼ 2000 galaxies with IAB < 24 and photometric redshift within 0.61 < z < 0.85, covering an area of 270 square-arcmin. Galaxy morphologies are estimated via a non-parametric automatic technique. The (V − z) vs. ...

We present observational evidence for a galaxy ‘Type’ dependence to the location of a spiral galaxy’s disk parameters in the μ0–log h plane. With a sample of ∼40 Low Surface Brightness galaxies (both bulgeand disk-dominated) and ∼80 High Surface Brightness galaxies, the early-type disk galaxies (≤Sc) tend to define a bright envelope in the μ0–logh plane, while the late-type (≥Scd) spiral galaxi...

One of the central features of the last 8 to 10 billion years of cosmic history has been the emergence of a wellpopulated red sequence of non-star-forming galaxies. A number of models of galaxy formation and evolution have been devised to attempt to explain this behavior. Most current models require feedback from supermassive black holes (AGN feedback) to quench star formation in galaxies in th...

We study the internal structural properties of 37 long duration gamma-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope. Our goal is to gain insights in the type of galaxies that gives rise to GRBs, and the relationship of GRB hosts to high-redshift galaxies selected through more traditional photometric methods. We measure structural properties of our sample from Hubble Space...

One of the possible origins of short gamma-ray bursts (SGRBs) is merging of compact binaries, and the effect of large kick velocity is a signature that can be used as an observational test for this hypothesis. Intracluster SGRBs that escaped from a host galaxy in a galaxy cluster are interesting in this context, since they would escape more easily by cluster tidal force, and would have brighter...

We propose two new methods for measuring tangential peculiar velocities of rich clusters of galaxies. Our first method is based on weak gravitational lensing and takes advantage of the differing images of background galaxies caused by moving and stationary gravitational potentials. Our second method is based on measuring relative frequency shifts between multiple images of a single strongly len...

Arcsec-resolution VLA observations – newly obtained as well as published – of 40 nearby galaxies are discussed, completing a study of the radio properties of a magnitude-limited sample of nearby galaxies of the composite LINER/H ii type. Our results reveal an overall detection rate of at least 25% AGN candidates among these composite sources. The general properties of these AGN candidates, as c...

We present results of broad band BVRI observations of a sample of galaxies with a low surface brightness (LSB) disk and a bulge. These galaxies are well described as exponential disks and exponential bulges with no preferred value for either scale length or central surface brightness. The median B band disk scale length is 12.6 kpc (H0 = 75 km s−1 Mpc−1) which is much larger than scale lengths ...