We construct a family of simple analytical models of galaxy clusters at the present epoch and compare its predictions with observational data. We explore two processes that break the self-similarity of galaxy clusters: systematic variation in the dark matter halo concentration and energy injection into the intracluster gas, through their effects on the observed properties of galaxy clusters. Th...

We investigate the GRB formation rate based on the relation between the spectral peak energy (E p) and the isotropic luminosity. The E p –luminosity relation covers the energy range of 50 – 2000 keV and the luminosity range of 10 50 –10 54 erg s −1 , respectively. We find that the relation is considerably tighter than similar relations suggested previously. Using E p –luminosity relation, we es...

The masses of central supermassive black holes in a soft X-ray selected sample of the narrow-line Seyfert 1 galaxies (NLS1s) are estimated by some different methods to test their theoretical models. Apart from the methods using the Hβ linewidth and the [O III] linewidth, soft X-ray excess as a prominent character of NLS1s is used to estimate the black hole masses. The virial mass derived from t...

From Press-Schechter formalism and the observed X-ray cluster L-T relation, we derive an X-ray cluster luminosity function that can be applied to the growing number of high-redshift, X-ray cluster luminosity catalogs to constrain cosmological parameters. In this paper, we apply this luminosity function to the Einstein Medium Sensitivity Survey (EMSS) to constrain Ω0. Our results favor high valu...

The presence of multiple luminous galaxies in clusters can be explained by the finite time over which a galaxy sinks to the center of the cluster and merges with the the central galaxy. The simplest measurable statistic to quantify the dynamical age of a system of galaxies is the luminosity (magnitude) gap, which is the difference in photometric magnitude between the two most luminous galaxies....

We fit the near-infrared to radio spectral energy distributions of a sample of 30 luminous and ultra-luminous infrared galaxies with models that include both starburst and AGN components. The aim of the work was to determine important physical parameters for this kind of objects such as the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and t...

Radio emission from early–type (E and S0) galaxies usually signals the presence of a central supermassive black hole. If radio luminosity and black–hole mass are correlated, then we can use the large sample of radio galaxies observed in the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the local (z < 0.1) black–hole mass function for early–type galaxies. Integrating over this mass function yi...