We present an analysis of Chandra observations of the galaxy clusters A2670 and A2107. Their cD galaxies have large peculiar velocities (> 200 km s) and thus the clusters appear to be undergoing mergers. In A2670, we find a comet-like structure around one of the brightest galaxies. At the leading edge of the structure, there is a cold front. The mass of the X-ray gas in the comet-like structure...

Using N-body and SPH modeling we perform 3D numerical simulations of head-on collisions between gas rich disk galaxies, including collisions between counter-rotating disks and off-center collisions. Pure stellar intruders do not produce gaseous plumes similar to those seen in the Cartwheel and VII Zw466 complexes of interacting galaxies; the presence of gas in an intruder galaxy and radiative c...

Analysis of the frequency and physical properties of galaxies with starformation and AGN activity in different environments in the local universe is a cornerstone for understanding structure formation and galaxy evolution. We have built a new multiwavelength catalog for galaxies in a complete redshift survey (the 15R Survey), gathering information on their Hα, R-band, radio, far-infrared, and X...

The fine-structure lines of singly ([Ne II] 12.8 μm) and doubly ([Ne III] 15.6 μm) ionized neon are among the most prominent features in the mid-infrared spectra of star-forming regions, and have the potential to be a powerful new indicator of the star formation rate in galaxies. Using a sample of star-forming galaxies with measurements of the fine-structure lines available from the literature,...

We study the luminosity functions of high-redshift galaxies in detailed hydrodynamic simulations of cosmic reionization, which are designed to reproduce the evolution of the Lyman-α forest between z ∼ 5 and z ∼ 6. We find that the luminosity functions and total stellar mass densities are in agreement with observations when plausible assumptions about reddenning at z ∼ 6 are made. Our simulation...

E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] nor Hα emission lines. The existence of strong Balmer absorption lines indicates that E+A galaxies have experienced starburst within recent one Gyr. However, the lack of [OII] and Hα emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are i...

We present images of the 7mm free-free emission from the radio “supernebula” in NGC 5253 made with the Very Large Array and the Pie Town link. The images reveal structure in the nebula, which has a≤ 1 pc (∼50 mas radius) core requiring the excitation of 1200 O7 stars. The nebula is elongated, with an arc of emission curving to the northeast and to the south. The total ionizing flux within the c...

We review current models of energetic particle acceleration and nonthermal emission from objects of very different scales from clusters of galaxies through massive galaxies to supernova remnants. The nonthermal phenomena in clusters and massive galaxies are considered in the context of the hierarchical model of cosmic structure formation by accretion and merging of the dark matter (DM) substruc...

We explore the evolution of the morphology density relation using the COSMOS-ACS survey and previous cluster studies. The Gini parameter measured in a Petrosian aperture is found to be an effective way of selecting early-type galaxies free from systematic effects with redshift. We find galaxies are transformed from late (spiral and irregular) to early (E+S0) type galaxies more rapidly in dense ...

Normal spiral galaxies have exponential disks and logarithmic arms (spirals). They must be interrelated and the relation is suggested to be iso-ratio. Assume you come off the disk center by such route that the ratio of the star density on your left side to the one on your right side is constant. The route (iso-ratio curve) turns out to be logarithmic spiral! Such distribution of iso-ratio densi...