An Observational Study of Galaxy Properties in the Early Universe

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How galaxies formed and evolved is one of the fundamental issues in modern astronomy. To address this, issue, it is essential to observe very distant galaxies (i.e., galaxies in very early universes). The purpose of this research is to detect a large number of galaxies at redshift >5 using the 8.2m Subaru Telescope and study the statistical properties (such as luminosity function and spatial clustering) of very distant galaxies. The age of the universe at z=5 is 1.2 Giga years old, which is less than 10% of the current age, 14 Giga years.We made deep imaging observations in a blank field called ‘'Subaru Deep Field' in a number of bandpasses with a wide-field prime-focus camera on the Subaru Telescope, to select about 2000 galaxies over a redshift range of z=4-6. We found that the number density of bright galaxies increases by an order of magnitude from z=6 to z=4. This implies that we have located the era of the intense formation of massive galaxies. We infer that these bright galaxies are progenitors of galaxies seen in present-day galaxy groups and clusters. We also found in our sample that galaxies are distributed quite inhomogeneously in space, forming large-scale structures. This discovery is important in discussing the formation history of large-scale structure commonly seen in the present-day universe. Finally, we studied the photometric properties of red galaxies at redshift 1-2 using optical and infrared data and discussed their evolution in number density and color.