A Comprehensive JWST/NIRSpec Census of Broad-line Active Galactic Nuclei: Faint, Low-mass Accretors and a Population of Little Red Dots

Abstract

We present a sample of 227 broad-line active galactic nuclei (BLAGNs), incorporating 148 newly identified sources, spanning a redshift interval from z = 0.8 to 7.2. We analyze spectroscopic data from the NIRSpec instrument on board the James Webb Space Telescope, using the G140H, G140M, G235H, G235M, G395H, and G395M gratings to survey N ~ 80,000 galaxies for BLAGNs. Through emission-line fitting, using a sum of Gaussian models for $H\alpha$, $H\beta$, [N II] $\lambda \lambda$6548, 6584, and [O III] $\lambda \lambda$4959, 5007, we separate active galactic nucleus (AGN) broad-line components from narrow-line emission. We find the detection rate of BLAGNs to be relatively consistent across our redshift range. Compared to typical low-z AGNs (z $\lesssim$ 1), high-z BLAGNs are systematically fainter and less massive, yet they accrete more efficiently, with most showing Eddington ratios between 0.1 and 1.0. This confirms rapid black hole growth during the early cosmic epochs. The detection of faint, low-mass BLAGNs at high redshift also helps bridge the observational gap between local supermassive black holes and remote luminous quasars, providing a more complete view of black hole-galaxy coevolution across cosmic time. We also identify 48 known little red dots (LRDs) in our BLAGN sample. For these LRDs, we find a systematic preference for exponential over Gaussian broad-line profiles, which are consistent with electron scattering rather than virial broadening. This implies that standard virial black hole masses for LRDs may be overestimated by up to 2 orders of magnitude.

Submitted to the Astrophysical Journal, 19 pages, 7 figures

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