Properties of distant galaxies and QSO absortion line systems: A deep multicolor imaging survey of the early universe

I present a study on statistical properties of faint galaxy population identified in the Hubble Deep Fields (HDFs). The broad-band imaging observations of the HDFs present the deepest images of the universe ever obtained. Based on the available optical and near-infrared space- and ground-based imaging data of the HDFs, I conducted photometry and photometric redshift measurements of all the objects detected in the HDFs.; First, I developed and improved three kinds of techniques that allowed to optimally determine the photometry and redshift of faint galaxies identified in the HDFs. They are (1) optimal photometry technique, (2) non-negative least-squares image reconstruction technique, and (3) photometric redshift technique. Using these techniques, I constructed a catalog of 5,318 galaxies and 47 stars across ∼12 arcmin2 of the total survey area of the HDFs. The redshift range of the galaxies spans 0 < z < 10 and beyond.; Next, based on the HDF observations, I studied a history of cosmic star formation toward high redshifts (0 < z < 10). The study was motivated by previous measurements of the ultraviolet (UV) luminosity density by other groups. Previous conclusions were that the UV luminosity density increases with increasing redshift up to z ∼ 1--2 and then decreases or remains constant (e.g., Madau et al. 1996, 1998). On the other hand, previous work neglected the effect of cosmological surface brightness dimming, that could dominate the measurements at high redshifts. I revisited this problem by considering the distribution of star formation rate intensity (calculated from the rest-frame 1500 A luminosity of galaxies) and thereby making explicit the surface brightness threshold of the HDF observations. The results of the analysis include (1) by neglecting cosmological surface brightness dimming effects, previous measurements have missed a dominant fraction of the UV luminosity density at z ≳ 2, (2) the UV luminosity density plausibly increases monotonically with redshift toward the highest redshifts z ≈ 10, and (3) the distribution of star formation rate intensities matches the distribution of neutral hydrogen column densities traced by damped Lyman-alpha absorption systems at redshifts z ≈ 2--5.