Stellar photometry of nearby irregular galaxies of the Local Group is used to identify and study the young and old stellar populations of these galaxies. An analysis of the spatial distributions of stars of different ages in face-on galaxies shows that the young stellar populations in irregular galaxies are concentrated toward the center, and form local inhomogeneities in star-forming regions, ...

Star formation history shows a gradual decline since the last 8-9 Gyr (z=1). The bulk of present-day stellar mass and metal content was formed at red-shifts lower than 2-3, which is consistent with a hierarchical scenario of galaxy formation. Observations of galaxy evolution during the last 2/3 of the Universe age could be done in great details, and provide numerous insights on the origin of th...

Using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) with an adaptive halo-based group finder, we investigate the luminosity and stellar mass functions for different populations of galaxies (central versus satellite; red versus blue; and galaxies in groups of different masses) and for groups themselves. The conditional stellar mass functio...

Rest-frame far-ultraviolet (FUV) luminosities form the ‘backbone’ of our understanding of star formation at all cosmic epochs. These luminosities are typically corrected for dust by assuming that the tight relationship between the UV spectral slopes (β) and the FUV attenuations (AFUV) of starburst galaxies applies for all starforming galaxies. Data from seven independent UV experiments demonstr...

We present the correlation dimension of resolved young stars in four actively star-forming dwarf galaxies that are sufficiently resolved and transparent to be modeled as projections of three-dimensional point distributions. We use data in the Hubble Space Telescope archive; photometry for one of them, UGCA 292, is presented here for the first time. We find that there are statistically distingui...

We study the evolution of the stellar mass density for the separate families of bulge–dominated and disk– dominated galaxies over the redshift range 0.25 ≤ z ≤ 1.15. We derive quantitative morphology for a statistically significant galaxy sample of 1645 objects selected from the FORS Deep and the GOODS–S Fields. We find that the morphological mix evolves monotonically with time: the higher the ...

We have analyzed Chandra observations of 18 low-luminosity early-type galaxies with LB ∼ 3×10L⊙B. Thermal emission from hot gas with temperatures between 0.2 and 0.8 keV comprises 5-70% of the total 0.5-2.0 keV emission from these galaxies. We find that the total X-ray luminosity from LMXBs (resolved plus the power-law component of the unresolved emission) scales roughly linearly with the K-ban...

We present the time evolution of the stellar metallicity for SDSS galaxies, a sample that spans five orders of magnitude in stellar mass (10 − 10 M⊙). Assuming the Bruzual & Charlot (2003) stellar population models, we find that more massive galaxies are more metal-rich than less massive ones at all redshifts; the mass-metallicity relation is imprinted in galaxies from the epoch of formation. F...

It is a longstanding and remarkable problem when and how red S0 galaxies were formed in clusters of galaxies. We here propose that the major mechanism for the S0 creation is galaxy merging between two spirals with unequal mass. Our numerical simulations demonstrate that galaxy merging exhausts a large amount of interstellar medium of two gas-rich spirals owing to the moderately enhanced star fo...

Deep, near–infrared imaging surveys have been motivated by the desire to study the rest–frame optical properties and stellar content of galaxies at high redshift. Here we briefly review their history, and illustrate one application, using HST NICMOS imaging of the Hubble Deep Field North to examine the rest–frame optical luminosities and colors of galaxies at 2 < z < 3, and to constrain their s...