(Proposal ID) S14B-003

(PI) Matsuoka Kenta

(Proposal Title)
 Chemical Enrichment in Radio-Quiet AGNs

(Abstract)
The chemical evolution is one of the most key issues to understand the 
evolution of galaxies. The most straightforward way to tackle this issue is 
exploring the systematic trends in the metallicity as a function of redshift. 
At high redshift, active galactic nuclei (AGNs) are useful to investigate gas 
metallicities. In particular, type-2 AGNs provide a powerful tool to 
investigate the metallicity at the spatial scale of their host galaxies 
(~ 10^{1-4}pc). In the previous studies, high-z radio galaxies (HzRGs) are 
only targets as type-2 AGNs at high redshift, and they do not show the 
metallicity evolution. Note, however, that HzRGs are generally associated 
with very massive, e.g., log(M_star/M_sun) > 11.0, host galaxies. The so-
called downsizing evolutionary scenario suggests the very early completion 
of the chemical evolution in such massive systems, that possibly prevents us 
from identifying "immature'' systems. We therefore focus on radio-quiet type-2 
AGNs hosted in less-massive galaxies. Moreover, the proposed observation 
allows us to examine the metallicity without the shock excitation whereas 
HzRGs may be affected. We propose to obtain rest-frame UV spectra of radio-
quiet type-2 AGNs to infer their metallicity, which would show clear 
evolutionary trends at z ~ 3.