The Diagnostic Potential of JWST in Characterizing Elusive AGNs

Abstract

Abstract It is now clear that a significant population of accreting black holes are undetected by commonly employed optical, mid-infrared color, X-ray, and radio selection methods as a result of obscuration or contamination of the emission from the nuclear region caused by star formation in the host galaxy. These elusive active galactic nuclei (AGNs) are an important component of the AGN population. They are often found in mergers, where significant black hole growth likely takes place, and in the lowest-mass galaxies or galaxies that lack classical bulges, a demographic that places important constraints on models of supermassive black hole seed formation and merger-free models of AGN fueling. In this work, we demonstrate the power of the James Webb Space Telescope (JWST) in uncovering and characterizing these elusive AGNs. We present an integrated modeling approach in which both the line and emergent continuum are predicted from gas exposed to the ionizing radiation from a young starburst and an AGN, focusing specifically on the spectral diagnostics available through JWST, and provide predictions on the detectability of key diagnostic lines by the near- and mid-infrared spectrometers, assuming typical conditions for the gas. We demonstrate the crucial need for JWST in uncovering low-level accretion activity even in nearby galaxies and out to redshifts of ≈1–3, depending on the ionization parameter, and gas phase metallicity. We present a redshift-dependent selection strategy that can be used to identify promising elusive AGN candidates for future follow-up study. The full suite of simulations is available online, where users can select specific parameters and retrieve the predicted continuum and infrared line luminosities from our models.