THE NATURE OF Hα-SELECTED GALAXIES ATz> 2. II. CLUMPY GALAXIES AND COMPACT STAR-FORMING GALAXIES

Abstract

We present the morphological properties of 109 H\alpha-selected galaxies at z>2 in SXDF-UDS-CANDELS field. With high-resolution optical/near-infrared images obtained by Hubble Space Telescope, we identify giant clumps within the H\alpha emitters (HAEs). We find that at least 41% of our sample show clumpy structures in the underlying disks. The color gradient of clumps is commonly seen in the sense that the clumps near the galactic center tend to be redder than those in the outer regions. The mid-infrared detection in galaxies with red clumps and the spatial distribution of H\alpha emission suggest that dusty star-formation activity is probably occurring in the nuclear red clumps. A gas supply to a bulge component through the clump migration is one of the most potent physical processes to produce such dusty star-forming clumps and form massive bulges in local early-type galaxies. They would become large quiescent galaxies at later times just by consumption or blowout of remaining gas. Also, while most of the HAEs have extended disks, we observe two massive, compact HAEs, whose stellar surface densities are significantly higher. They are likely to be the direct progenitors of massive, compact quiescent galaxies at z=1.5-2.0. Two evolutionary paths to massive quiescent galaxies are devised to account for both the size growth of quiescent galaxies and their increased number density from z~2 to z=0.