Narrow line AGN selection in CEERS: spectroscopic selection, physical properties, X-ray and radio analysis

TL;DR

This study spectroscopically identifies and analyzes narrow-line AGNs in the CEERS survey, revealing their physical properties, weak X-ray emission, and potential heavy obscuration, expanding understanding of high-redshift AGN populations.

Contribution

It introduces new spectroscopic diagnostics for high-redshift NLAGNs and provides a comprehensive multiwavelength analysis including X-ray and radio properties.

Findings

Identified 52 NLAGNs at 2<z<9 using new emission line diagnostics.

Most high-z NLAGNs are X-ray weak and heavily obscured.

High-z NLAGNs have bolometric luminosities ~1.5dex below previous surveys.

Abstract

In this work, we spectroscopically select narrow-line AGNs (NLAGNs) among the ~300 publicly available medium-resolution spectra of the Cosmic Evolution Early Release Science Survey (CEERS). Using both traditional and newly identified emission line NLAGN diagnostics diagrams, we identified 52 NLAGNs at 2<z<9, on which we performed a detailed multiwavelength analysis. We also identified four new z<2 broad-line AGNs (BLAGNs), in addition to the eight previously reported z>4.5 BLAGNs. We found that most of the high-z NLAGN were selected using the recently proposed AGN diagnostic diagrams based on the [Oiii] $\lambda$4363 auroral line or high-ionization emission lines. We compared the emission line velocity dispersion and the obscuration levels of the sample of NLAGNs with those of the parent sample without finding significant differences between the two distributions, suggesting a population of AGNs heavily buried and not significantly impacting the host galaxies physical properties, as was further confirmed by spectral energy distribution fitting. The bolometric luminosities of the high-z NLAGNs selected in this work are ~1.5dex below the ones sampled by surveys before JWST, potentially explaining the weak impact of these AGNs. Finally, we investigated the X-ray properties of the selected NLAGNs and of the sample of high-z BLAGNs. We found that all but four NLAGNs are undetected in the deep X-ray image of the field, as well as all the high-z BLAGNs. We did not obtain a detection even by stacking the undetected sources, resulting in an X-ray weakness of ~1-2 dex from what was expected based on their bolometric luminosities. To discriminate between a heavily obscured AGN scenario or an intrinsic X-ray weakness of these sources, we performed a radio (1.4GHz) stacking analysis, which did not reveal any detection and left open the questions about the origin of the X-ray weakness.