Probing global star and galaxy formation using deep multi-wavelength surveys

We present a deep survey covering 0.84 square degrees over four widely separated areas of sky to RAB ≃ 26.5 over the wavelength range 0.35mum to 2.2mum. This broad wavelength coverage allows probing the rest-frame ultraviolet (UV) and optical light of galaxies from the present epoch to z = 6.5, while the spatially discrete sampling avoids problems of cosmic variance. These panchromatic data also allow highly accurate estimates of photometric redshifts. It is shown that photometric redshifts work very well for the majority of galaxies, making this a useful tool for galaxy surveys. However, the application of both observational and theoretical galaxy templates is found to be dominated by systematic errors in photometry. A method to obtain correct photometry using spectroscopic redshifts is developed. Furthermore, a template library known to be valid for 0 < z < 3 is calculated, along with corrections, using the 2148 spectra available in the wide field Hawaii-Hubble-Deep Field North (H-HDF-N) area. When these templates are used with our method for correcting zero-points a typical RMS error of dz/(1 + z) < 0.04 is obtainable for the normal galaxy population. It is further shown that these templates provide accurate photometric redshifts at z < 5.; These extensive data place significant constraints on the evolution and demographics of the galaxy population. It is shown that the number of z > 5 galaxies is significantly overestimated by pure color selection. The panchromatic luminosity function is then calculated for optically bright galaxies. The faint end slope of the star-forming galaxy luminosity function is shown to be flattening with time. This indicates a drop in the relative number of faint galaxies as the universe ages. However, the average luminosity of a galaxy also decreases as a power law of index 3.3 from z = 5 to the present, indicating that cosmic downsizing with time is a fundamental phenomenon. The ultraviolet luminosity density and star formation rate is found to be decreasing as a power law with an index of 2.0 for z < 2, but is unchanged for z > 2. It is shown that the shape of the luminosity evolution is explained by a drop in the average galaxy luminosity combined with an increase in the galaxy number density with time.