Matsuoka, K.K.MatsuokaNagao, T.T.NagaoMarconi, AlessandroAlessandroMarconiMaiolino, R.R.MaiolinoMANNUCCI, FILIPPOFILIPPOMANNUCCICRESCI, GIOVANNIGIOVANNICRESCITerao, K.K.TeraoIkeda, H.H.Ikeda2021-03-152021-03-1520180004-6361http://hdl.handle.net/20.500.12386/30703The mass-metallicity relation (MZR) of type-2 active galactic nuclei (AGNs) at 1.2 < z < 4.0 is investigated by using high-z radio galaxies (HzRGs) and X-ray selected radio-quiet AGNs. We combine new rest-frame ultraviolet (UV) spectra of two radio-quiet type-2 AGNs obtained with FOCAS on the Subaru Telescope with existing rest-frame UV emission lines, i.e., C IVλ1549, He IIλ1640, and C IIIλ1909, of a sample of 16 HzRGs and 6 additional X-ray selected type-2 AGNs, whose host stellar masses have been estimated in literature. We divided our sample in three stellar mass bins and calculated averaged emission-line flux ratios of C IVλ1549/He IIλ1640 and C IIIλ1909/C IVλ1549. Comparing observed emission-line flux ratios with photoionization model predictions, we estimated narrow line region (NLR) metallicities for each mass bin. We found that there is a positive correlation between NLR metallicities and stellar masses of type-2 AGNs at z 3. This is the first indication that AGN metallicities are related to their hosts, i.e., stellar mass. Since NLR metallicities and stellar masses follow a similar relation as the MZR in star-forming galaxies at similar redshifts, our results indicate that NLR metallicities are related to those of the host galaxies. This study highlights the importance of considering lower-mass X-ray selected AGNs in addition to radio galaxies to explore the metallicity properties of NLRs at high redshift.STAMPAenArticle10.1051/0004-6361/2018334182-s2.0-85051962912000441816900003https://www.aanda.org/articles/aa/full_html/2018/08/aa33418-18/aa33418-18.html2018A&A...616L...4MFIS/05 - ASTRONOMIA E ASTROFISICA