HSC-FIRST radio galaxy survey: Selection and initial results

Kodai Nobuhara

The radio galaxy is an important population of AGNs to study the evolution of massive galaxies, because the host galaxy of radio galaxies is generally characterized by a large stellar mass and old stellar population. The radio galaxy is interesting also for understanding the final phase of the AGN evolution, since radio galaxies are characterized by a relatively high mass of SMBHs and a low Eddington ratio. Especially, radio galaxies showing a very large radio loudness are interesting, since low-z radio galaxies showing a larger radio loudness tend to have a larger M_BH and a lower Eddington ratio. However the number of radio galaxies discovered so far is quite small at high-z. This naturally leads to our interests to study high-z radio galaxies with a very large R, for exploring the early completion of the galaxy-SMBH coevolution in the early Universe. Motivated by this, we focus on the FIRST radio survey because the 70% of FIRST sources are not detected in the SDSS due to too shallow optical images. Therefore, we started a new search for radio galaxies with HSC-FIRST matched catalog made by using the HSC-Wide data which is much more sensitive than SDSS. When we constructed the matched catalog, we adopted a simple positional matching where we set the search radius to 1 arcsecond to achieve high completeness and low contamination. As the results, we found a number of radio galaxies with the radio loudness (in observed frame; R_obs = F_radio / F_opt) higher than 4.5. In addition, there are some radio galaxies whose photometric redshifts are higher than 3. In this talk, we report the current status of our study.