The mass-metallicity relation of high-z type-2 active galactic nuclei
Astronomy and Astrophysics
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Matsuoka, K., Nagao, T., Marconi, A., Maiolino, R., Mannucci, F., Cresci, G., Terao, K., & et al. (2018). The mass-metallicity relation of high-z type-2 active galactic nuclei. Astronomy and Astrophysics, 616 https://doi.org/10.1051/0004-6361/201833418
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., CIV1549, HeII1640, and CIII]1909, 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 CIV1549/HeII1640 and CIII]1909/CIV1549. 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.
ECH2020 EUROPEAN RESEARCH COUNCIL (ERC) (695671)
External DOI: https://doi.org/10.1051/0004-6361/201833418
This record's URL: https://www.repository.cam.ac.uk/handle/1810/284722