Presentation #241.04 in the session Evolution of Galaxies — iPoster Session.
The first massive galaxies to form after the Big Bang demonstrate the unique evolution and early properties of our universe. The search for massive high-redshift galaxies at z > 3.5 (less than 2 billion years post-Big Bang) has thus far been limited by a lack of adequate coverage and depth in long-wavelength imaging. The H20 survey covers two 10 deg2 contiguous fields and combines Subaru Hyper Suprime-Cam grizy optical imaging with Spitzer [3.6 micron] + [4.5 micron] deep-IR imaging. This survey provides some of the first robust characterizations of populations of massive galaxies at these redshifts. In our analysis, we use the ultra-deep H20 survey to identify a sample of ~1500 galaxies at 3.5 < z < 5.8 with masses > 1010.5 M☉, which have well-defined physical properties. With these sources, we extend previous work investigating the size-mass relation. We find that sizes quantified by effective radii generally increase with mass out to z ~ 4.5-4.7. We also identify candidate quiescent, star-forming, and post-starburst galaxies, and find that the fractions of post-starburst and quenched galaxies rapidly decrease above z = 3.8 and z = 4.1 respectively. Through preliminary visual classification, which distinguishes isolated and disturbed sources, we estimate a major-merger fraction of ~40% at 3.5 < z < 3.8, which agrees with predictions from recent cosmological simulations.