Near-infrared emission line diagnostics for AGN from the local Universe to redshift 3
Creators: name: Calabrò, Antonello
name: Pentericci, Laura
name: Feltre, Anna
name: Haro, Pablo Arrabal
name: Radovich, Mario
name: Seillé, Lise Marie
name: Oliva, Ernesto
name: Daddi, Emanuele
name: Amorín, Ricardo
name: Bagley, Micaela B.
name: Bisigello, Laura
name: Buat, Véronique
name: Castellano, Marco
name: Cleri, Nikko
name: Dickinson, Mark
name: Fernández, Vital
name: Finkelstein, Steven
name: Giavalisco, Mauro
name: Grazian, Andrea
name: Hathi, Nimish
name: Hirschmann, Michaela
name: Juneau, Stéphanie
name: Kartaltepe, Jeyhan S.
name: Koekemoer, Anton
name: Lucas, Ray A.
name: Papovich, Casey
name: Pérez-González, Pablo
name: Pirzkal, Nor
name: Santini, Paola
name: Trump, Jonathan
name: de la Vega, Alexander
name: Wilkins, Stephen
name: Yung, L. Y. Aaron
name: Cassata, Paolo
name: Gobat, Raphael
name: Mascia, Sara
name: Napolitano, Lorenzo
name: Vulcani, Benedetta
Publisher: name: arXiv
Year: 2023
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Optical rest-frame spectroscopic diagnostics are usually employed to distinguish between star formation and AGN-powered emission. However, this method is biased against dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate this effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies. AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGNs and star-forming galaxies, especially at redshifts higher than 0.5. Using Cloudy photoionization models, we identify new AGN - star formation diagnostics based on the ratio of bright near-infrared emission lines, namely [SIII] 9530 Angstrom, [CI] 9850 Angstrom, [PII] 1.188 $μm$, [FeII] $1.257 μm$, and [FeII] $1.64 μm$ to Paschen lines (either Pa$γ$ or Pa$β$), providing simple, analytical classification criteria. We apply these diagnostics to a sample of 64 star-forming galaxies and AGNs at 0 &lt; z &lt; 1, and 65 sources at 1 &lt; z &lt; 3 recently observed with JWST-NIRSpec in CEERS. We find that the classification inferred from the near-infrared is broadly consistent with the optical one based on the BPT and the [SII]/H$α$ ratio. However, in the near-infrared, we find $\sim 60 \%$ more AGNs than in the optical (13 instead of 8), with 5 sources classified as 'hidden' AGNs, showing a larger AGN contribution at longer wavelengths, possibly due to the presence of optically thick dust. The diagnostics we present provide a promising tool to find and characterize AGNs from z=0 to z=3 with low and medium-resolution near-IR spectrographs in future surveys.
description: Paper accepted for publication in A&amp;A on 05/09/2023. Three public Github repositories include: (1) a table with emission line measurements for the paper sample : https://github.com/Anthony96/Line_measurements_nearIR , Cloudy emission line predictions for star-forming galaxies and AGN models : https://github.com/Anthony96/star-forming_models , https://github.com/Anthony96/AGN_models