Obscured AGN at 1.5 <z< 3.0 from the zCOSMOS-deep Survey

Abstract

Context. The physics and demographics of high-redshift obscured active galactic nuclei (AGN) is still scarcely investigated. New samples of such objects, selected with different techniques, can provide useful insights into their physical properties. Aims. With the goal to determine the properties of the gas in the emitting region of type 2 AGN, in particular, the gas metal content, we exploit predictions from photoionization models, including new parameterizations for the distance of gas distribution from the central source and internal microturbulence in the emitting clouds, to interpret rest-frame UV spectral data. Methods. We selected a sample of 90 obscured (type 2) AGN with 1.45 ≤ z ≤ 3.05 from the zCOSMOS-deep galaxy sample by 5σ detection of the high-ionization C IV λ1549 narrow emission line. This feature in a galaxy spectrum is often associated with nuclear activity, and the selection effectiveness has also been confirmed by diagnostic diagrams based on utraviolet (UV) emission-line ratios. We applied the same selection technique and collected a sample of 102 unobscured (type 1) AGN. Taking advantage of the large amount of multiband data available in the COSMOS field, we investigated the properties of the C IV-selected type 2 AGN, focusing on their host galaxies, X-ray emission, and UV emission lines. Finally, we investigated the physical properties of the ionized gas in the narrow-line region (NLR) of this type 2 AGN sample by combining the analysis of strong UV emission lines with predictions from photoionization models. Results. We find that in order to successfully reproduce the relative intensity of UV emission lines of the selected high-z type 2 AGN, two new ingredients in the photoionization models are fundamental: small inner radii of the NLR (≈90 pc for LAGN = 1045 erg s−1), and the internal dissipative microturbulence of the gas-emitting clouds (with vmicr ≈ 100 km s−1). With these modified models, we compute the gas-phase metallicity of the NLR, and our measurements indicate a statistically significant evolution of the metal content with redshift. Finally, we do not observe a strong relationship between the NLR gas metallicity and the stellar mass of the host galaxy in our C IV-selected type 2 AGN sample.

Chemical abundances of Seyfert 2 AGNs – II. N2 metallicity calibration based on SDSS

“…0, 8.40, 8,56, 8.69, 8.86, 9.00, respectively, Metallicity values in this range has been found for AGNs with redshifts varying from ∼ 0 to ∼ 7 (e.g. Nagao et al 2006a;Feltre, Charlot & Gutkin 2016;Matsuoka et al 2018;Thomas et al 2019;Mignoli et al 2019;Pérez-Montero et al 2019;Dors et al 2014Dors et al , 2015Dors et al , 2018. We found that photoionization models assuming (Z/Z⊙) > 2.0 produce similar intensities of N 2, therefore, only (Z/Z⊙) < = 2.0 were assumed in our analysis.…”

Chemical abundances in Seyfert galaxies – V. The discovery of shocked emission outside the AGN ionization axis

“…Storchi-Bergmann et al 1998;Feltre et al 2016;Castro et al 2017) and at high redshifts (e.g. Dors et al 2018;Mignoli et al 2019;Guo et al 2020).…”

Connection between galactic downsizing and the most fundamental galactic scaling relations

“…On the other hand, by imposing the same scaling relations at higher redshift, we computed a forward evolution of the galaxies at lower redshifts and towardsthe present time. In this framework, we also study the evolution of the galaxies that at redshift z = 2.2 follow the flat MZR as derived by Mignoli et al (2019).…”

“…We also analyze the temporal evolution and the fate of the galaxies with stellar masses, metallicities, and SFRs constrained by the high-redshift MZRs and MSRs. In particular, we discuss the implications of the newly observed flat MZR at redshift z = 2.2 by Mignoli et al (2019), who analyzed the metal content of 88 C iv-selected galaxies containing type 2 AGN with reliable measurements at high redshift.…”