Affiliation: GALSPEC, EPFL

Contribution: Oral

Title: Emission-line diagnostics for high-redshift populations of AGN

Abstract: Recent JWST observations have discovered a growing population of faint, low-mass AGN at early cosmic epochs, possibly extending out to z11. However, reliably identifying AGN, particularly type-2 AGN, and estimating their properties such as accretion rates, masses, BH to SF rate ratios, and ambient metallicities remains challenging. In this talk, we will explore how novel synthetic spectra featuring emission lines from both young star clusters and AGN in high-redshift, simulated galaxies can aid in interpreting JWST spectroscopic data of high-redshift AGN. Specifically, we have developed novel grids of AGN photo-ionization models that encompass the continuum and emission from both the broad-line region (BLR) and narrow-line region (NLR). These grids are self-consistently connected to simulated galaxies from our new, high-resolution, high-redshift cosmological zoom simulations (with advanced models for black hole (BH) accretion and winds), as well as from the SC SAM, IllustrisTNG, and GAEA SAM, by matching the free grid parameters to the BH properties predicted and making geometrical assumptions regarding the viewing angle to include a BLR and continuum component. Using this unique framework, we re-examine optical and UV emission-line diagnostics and selection criteria for AGN and introduce novel diagnostics for assessing BH accretion rates, BH accretion to SF rate ratios, and metallicities around AGN. We find that the [OIII]-, Hb-, HeII-, and CIV]-line luminosities are closely linked to BH accretion rates. Also, ratios such as [NII]/Ha, CIV]/HeII, and CIII/HeII offer reliable methods for estimating the BH accretion to SF rate ratios. Applying these diagnostics to public JWST-JADES data of galaxies with identified AGN, we find AGN luminosities between 10^41 and 10^45 erg/s and BH accretion to SFR ratios between 0.001 and 0.1. This suggests that BH growth relatively dominates over galaxy growth in these galaxies at early epochs. Finally, we discuss further prospects of future applications of this interpretative framework to upcoming JWST and EUCLID data.

This contribution can be found here (pdf).

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Contribution: Poster

Title: New-generation emission-line modelling for simulated galaxies: intermediate- and high-redshift predictions for Euclid and JWST

Abstract: We present a novel method of modelling spatially resolved nebular emission from individual HII regions for galaxies in cosmological simulations (e.g. IllustrisTNG, GAEA SAM), in which we self-consistently couple new-generation photoionization models to simulated galaxies. For that, we extract information for the unresolved HII regions in the cosmological simulations from the cutting-edge, high-resolution GRIFFIN simulations, which resolve individual stars in a multi-phase ISM, and can, thus, follow star cluster formation and evolution and their ambient gas properties. Resulting emission-line catalogues (also accounting for line emission due to AGN, post-AGB stars and shocks) are validated against observed emission-line properties of low-redshift galaxies (line luminosity functions, BPT diagrams, line-ratio metallicity relations etc). We further present a direct comparison of rest-frame optical and UV emission-line properties of high-redshift galaxies, observed with JWST out to z=10, as well as predictions for line-emitting galaxy populations between z = 0 and 2.5 in upcoming Euclid surveys. Specifically, compared to new JWST data, the optical emission-line properties of simulated galaxies reflect the observed evolution of the [OIII]λ5007 luminosity function from z=0 to z=6-8, the observed increase in [OIII]/Hβ at fixed [NII]/Hα, and the observed increase in [OIII]/[OII] at a given ([OIII]+[OII])/Hβ. This evolution of line ratios seems to be primarily driven by an increased ionisation parameter in higher-redshift galaxies, governed by both higher sSFRs and higher gas densities. Related to that, we also find that the vast majority of predicted line-ratio calibrations for metallicity estimates strongly evolve with redshift, consistent with first metallicity estimates derived via the direct-T method from NIRSpec spectra of z=2-8 galaxies. This motivated us to derive associated high-z metallicity calibrations — potentially useful for the interpretation of on-going and future spectroscopic surveys of intermediate- and high-redshift galaxies with Euclid and JWST.

This contribution can be found in the Poster Hall.