An Empirical Approach to Selecting the First Growing Black Hole Seeds with JWST/NIRCam

The James Webb Space Telescope (JWST) will have the sensitivity to detect early low-mass black holes (BHs) as they transition from “seeds” to supermassive BHs. Based on the JAGUAR mock catalog of galaxies, we present a clean color selection that takes advantage of the unique UV slope of accreting supermassive BHs with a relatively low mass and high accretion rates. We show that those galaxies hosting ∼10⁶ M _⊙ BHs radiating at >10% of their Eddington luminosity separate in color space from inactive systems for a range of host stellar masses. Here we propose a set of 3-band, 2-color selection boxes (with 90% completeness; 90% purity; balanced purity/completeness) with JWST/NIRCam to identify the most promising growing BH candidates at z ∼ 7-10.