Systematic Search for Galaxies in the Early Universe and their Nature

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Large systematic surveys for galaxies at redshift around 5 (cosmic age of 〜1 Gyr) were made in two fields, and found about 600 candidates. This is the largest sample in the world. Using the sample, we found the followings : We derived UV luminosity function(LF) of the galaxies with the highest accuracy. The resulting UVLF show an almost no evolution in the bright part, but a slight evolution in the fainter part when we compare it with those at z=3,4 (i). The cosmic star-formation rate density at z〜5 was turned out to be smaller than those at z=3 and 4, but the star-formation activity is still high in the era. For the subsample, we obtained UV spectra. We could confirm not only the redshifts, but also we found strength of Lyα emission is generally weak. We also found that interstellar metallic absorption lines were relatively strong, suggesting the presence of chemical evolution to some degree even at the cosmic age of 〜1Gyr(ii). Further, equivalent widths of the emissions may depend on UV luminosities of them (iii). This suggests that Lyα emitters are a subclass of the faint Lyman break galaxies. We obtain rest-frame spectral energy distributions of a part of the sample, and made fitting with spectral evolution model ; ages and amounts of dust extinction of them were estimated. We also found a lack of blue luminous galaxies (iv). Analysis of clustering property of Lyman break galaxies showed its correlation length was t larger than that at lower redshifts, supporting a scenario that galaxies formed earlier in the denser region. At z〜5, luminous galaxies tend to show a larger correlation length (v). In addition, we cross-correlated our catalog with X-ray source catalog and found two to four new counterparts. We also made stacking analysis with X-ray imaging data, but no significant signal was detected. Our results shown above (i)-(v) suggest that more massive galaxies formed earlier in the denser region.