Astronomy and Astrophysics, volume 616, L4-4 (2018/8-1)
The mass-metallicity relation of high-z type-2 active galactic nuclei.
MATSUOKA K., NAGAO T., MARCONI A., MAIOLINO R., MANNUCCI F., CRESCI G., TERAO K. and IKEDA H.
Abstract (from CDS):
The 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., CIVλ1549, HeIIλ1640, and CIIIλ1909, 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 CIVλ1549/HeIIλ1640 and CIIIλ1909/CIVλ1549. 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.
© ESO 2018
galaxies: evolution - galaxies: active - galaxies: nuclei - quasars: emission lines - quasars: general
Table A.1 WN J1338+3532 is WN B1336.0+3547 in SIMBAD.
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