We study the effect of surface brightness on the mass–metallicity relation using nearby galaxies whose gas content and metallicity profiles are available. Previous studies using fiber spectra indicated that lower surface brightness galaxies have systematically lower metallicities for their stellar mass, but the results were uncertain because of aperture effects. With stellar masses and surface ...

The integrated galaxial initial mass function (IGIMF) is the relevant distribution function containing the information on the distribution of stellar remnants, the number of supernovae and the chemical enrichment history of a galaxy. Since most stars form in embedded star clusters with different masses the IGIMF becomes an integral of the assumed (universal or invariant) stellar IMF over the em...

We study the nature of faint, red-selected galaxies at z ∼ 2 − 3 using the Hubble Ultra Deep Field (HUDF) and Spitzer Infrared Array Camera (IRAC) photometry. Given the magnitude limit of the HST data, we detect candidate galaxies to HAB < 26 mag, probing lower-luminosity (lower mass) galaxies at these redshifts. We identify 32 galaxies satisfying the (J110 − H160)AB > 1.0 mag color selection, ...

We present deep JHK images of I Zw 18, the most metal-deficient Blue Compact Dwarf (BCD) galaxy known, and analyze them in conjunction with archival HST/WFPC2 optical images. To investigate the stellar populations, we have divided the main body of I Zw18 into eight regions, and fit the optical, near-infrared (NIR), and hybrid optical-NIR colors of these and the C component with evolutionary syn...

Using samples drawn from the Sloan Digital Sky Survey, we study the relationship between local galaxy density and the properties of galaxies on the red sequence. After removing the mean dependence of average overdensity (or “environment”) on color and luminosity, we find that there remains a strong residual trend between luminosity–weighted mean stellar age and environment, such that galaxies w...

ABSTRACT The CMDs/TRGB (Color-Magnitude Diagrams/Tip of the Red Giant Branch) section of the Extragalactic Distance Database contains a compilation of observations of nearby galaxies from the Hubble Space Telescope. Approximately 250 (and increasing) galaxies in the Local Volume have CMDs and the stellar photometry tables used to produce them available through the web. Various stellar populatio...

We study the spectroscopic properties of a sample of 10 void galaxies identified in the Sloan Digital Sky Survey (SDSS) and compare these with the properties of galaxies in higher density regions (wall galaxies). This sample of void galaxies covers the range of absolute magnitude from Mr 1⁄4 13:5 to Mr 1⁄4 22:5 in regions with density contrast / < 0:6. We compare the equivalent widths of H , [O...

We present first results from three-dimensional hydrodynamic simulations of the high redshift formation of dwarf galaxies. The simulations use an Eulerian adaptive mesh refinement technique to follow the non–equilibrium chemistry of hydrogen and helium with cosmological initial conditions drawn from a popular Λ-dominated cold dark matter model. We include the effects of reionization using a uni...

We describe the spectral energy distributions (SEDs) of Lyman Break Galaxies (LBGs) at z∼3 using deep mid-infrared and optical observations of the Extended Groth Strip, obtained with IRAC and MIPS on board Spitzer and from the ground, respectively. We focus on LBGs with detections at all four IRAC bands, in particular the 26 galaxies with IRAC 8 μm band (rest–frame K-band) detections. We use st...

We explore mechanisms for the regulation of star formation in dwarf galaxies. We concentrate primarily on a sample in the Virgo cluster, which has HI and blue total photometry, for which we collected Hα data at the Wise Observatory. We find that dwarf galaxies do not show the tight correlation of the surface brightness of Hα (a star formation indicator) with the HI surface density, or with the ...