(Proposal ID) S13B-019

(PI) Matsuoka, Kenta

(Proposal Title)
Chemical Enrichment in Radio-Quiet AGNs

(Abstract)
The chemical evolution is one of the most important issues in understanding the
 evolution of galaxies. The most straight-forward way to tackle this issue is 
to probe the systematic trends of 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 
(~10^1-4pc). Previous studies were limited to radio galaxy sample in studying 
metallicities at high redshift, showing no evolution of metallicities. Note, 
however, that high-z radio galaxies (HzRGs) are generally associated with very 
massive, e.g., log(M_*/M_sun) > 11.0, host galaxies. The so-called downsizing 
evolutionary scenario suggests the very early completion of the chemical 
evolution in such mas-sive systems, that possibly prevents us from identifying 
"immature" systems. We therefore focus on radio-quiet type-2 AGNs hosted by 
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 a sample of 12 radio-quiet type-2
 AGNs to infer their metallicity, which would show clear evolutionary trends 
at z~3.