Volume 616, August 2018
|Number of page(s)||7|
|Section||Letters to the Editor|
|Published online||14 August 2018|
Letter to the Editor
The mass-metallicity relation of high-z type-2 active galactic nuclei
Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy
2 INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
3 Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
4 Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
5 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
6 Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
7 National Astronomical Observatory of Japan (NAOJ), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
Accepted: 14 July 2018
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., 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.
Key words: galaxies: evolution / galaxies: active / galaxies: nuclei / quasars: emission lines / quasars: general
© ESO 2018
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.