Direct Proof for the Formation of Proto-Elliptical Galaxies and Their Origin

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We have developed an effective way to cull the candidates for star forming elliptical galaxies at high redshift, and have successfully discovered numerous candidates (sBzK and pBzK galaxies at 1.4<z<2.5) by using the Subaru/Suprime-Camera. sBzK galaxies are currently under intense star forming activity, and their stellar masses, spatial densities, and clustering properties are comparable to those of nearby massive ellipticals. pBzK galaxies are post starburst galaxies with comparable stellar masses to sBzKs and their clustering and spatial densities are as large as giant ellipticals in clusters of galaxies of the local universe. These results suggest that BzK galaxies are elliptical galaxies in their major formation epoch; sBzKs evolve to pBzKs, then to EROs at z~1, and finally to passive elliptical galaxies at z-0. To confirm high SFRs inferred from SED of sBzK galaxies, we measured 1.2mm flux of 2 sBzKs to find very high SFRs as 500~1500 solar mass per year, supporting our previous f … More indings of active star forming nature of sBzK galaxies. These galaxies are more luminous in K-band than Scuba sources at z~2, from which one can learn that sBzKs had a short-period evolutionary stage of very active star formation with dense dust clouds. We have also observed one sBzK galaxy, BzK-15504 with near infrared 3D spectrograph SINFONI on VLT for the first time of this kind of observation of high redshift galaxies. Surprisingly, this galaxy has a rapidly rotating disk of comparable mass and rotational velocity to those of the Milky Way disk, and is now in the stage of bulge formation with gas infall of considerable amount into a central massive black hole. It is not clear is if this massive gas disk is stable, or the galaxy will eventually merge with other galaxies to form a single massive elliptical galaxy.This study strongly suggests the following scenario for the formation and evolution of massive elliptical galaxies: The formation of massive ellipticals occur at z~2 universe, before which mass assembly has not yet completed and galaxies have relatively smaller SFRs (due to a lack of sufficient gas available). Once formed at z~2, galaxies are detected as sBzK galaxies, which then evolve into pBzK galaxies, ERO galaxies, and finally giant elliptical galaxies on the Hubble sequence. The timescale of this process would depend on the galaxy environment in the sense that galaxies evolve much quicker in dense environment and more massive galaxies evolve more rapidly. Thus, our finding of the formation epoch of massive ellipticals at z~2 should correspond to the general field and the formation epoch could be much earlier in the cluster environments. Thus there is a possibility to discover clustering of star forming dusty galaxies at much higher redshift. Identifying such proto-clusters of galaxies would tell a lot about elliptical galaxies in their infant ages. Less