| How galaxies such as our own Milky Way formed and evolved remains a mystery. There are two general approaches in galaxy formation and evolution studies. One is to infer formation histories via archaeological investigations of galaxies at low redshift, in the local Universe. The other is to study galaxy formation and evolution in action by observing faint distant galaxies, the ancestors of local galaxies, in the more distant and younger Universe, at higher redshift.;I employ the first approach to study the formation of elliptical galaxies, the most massive galaxies in the Universe. I investigate the stellar content of 1923 elliptical galaxies, the largest high-fidelity sample in the local Universe, as a function of stellar mass and environment. I infer their star formation histories, finding that isolated low-mass elliptical galaxies formed their stars slightly later than their counterparts in galaxy clusters.;I measure the cosmic star formation rate (SFR) density at redshift z ∼ 1, when the Universe was eight billion years younger. The cosmic SFR density measures how many stars are being formed per unit volume of the Universe. I show that galaxies were more actively forming stars eight billion years ago than they are at present, by roughly an order of magnitude. The reason why galaxies are so much less active at present remains unknown, partly due to the small sample size of distant galaxies observed previously.;To improve the sample size, we have completed a new galaxy survey, the Prism Multi-object Survey (PRIMUS). We have observed ∼ 120, 000 galaxies spanning distances from the local Universe to redshift z ∼ 1. We specifically targeted fields with existing multi-wavelength data in the X-ray, ultraviolet, optical, and infrared. The large sample and multi-wavelength data allow precise statistical studies of galaxy evolution since z ∼1. As a preliminary result from PRIMUS, I show that 15% of galaxies that appear to lack star formation in the optical actually show star formation when observed in the infrared. The overall contribution of these obscured star-forming galaxies to the cosmic SFR density is not negligible (about 10%). |
