Title: Metallicity in the high-redshift Universe traced by radio galaxies
Author(s): Kenta Matsuoka
Abstract: Metallicity of galaxies is one of the most important aspects to understand the formation and evolution of galaxies, since it is closely related with the past star formation history of galaxies. Especially, to investigate metallicity of galaxies in high-z universe is very important to understand the formation and evolution of galaxies in the early universe. An approach to study the metallicity of galaxies in high-z universe is to focus on active galactic nuclei (AGNs). AGNs generally show various emission lines in rest-frame ultraviolet to infrared wavelengths, in contrast to star-forming galaxies. Here we focus on the rest-frame ultraviolet lines, since we can easily measure the emission-line fluxes of high-z AGNs by means of optical spectroscopic observations. Now we focus on the narrow-line region (NLR) of high-z radio galaxies (HzRGs) which is a good tracer of chemical properties in the spatial scale of their host galaxies. We present the new deep optical spectrum of the most distant radio galaxy at z=5.19 obtained with FOCAS on Subaru. Combining this result with previous observations, we discuss the NLR metallicity in HzRGs. Specifically we focus on the CIV/HeII and CIII]/CIV flux ratios that are sensitive to gas metallicity and ionization parameter. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations, we estimate the metallicity evolution for clouds of NLRs. In this conference we discuss about the chemical evolution and the luminosity-metallicity relation for 58 HzRGs at 1.2