A Comprehensive JWST/NIRSpec Census of Broad-Line Active Galactic Nuclei: Faint, Tiny, but Highly Accreting Sources in the Remote Universe

Caroline Baccus, Xinfeng Xu

First listed 2025-12-02 | Last updated 2025-12-02

Abstract

We present a sample of 252 broad-line Active Galactic Nuclei (BLAGNs), incorporating 171 newly identified sources, spanning a redshift interval from $z$ = 0.8 to 7.2. We have analyzed spectroscopic data from the NIRSpec instrument aboard the James Webb Space Telescope, using the G140H, G140M, G235H, G235M, G395H, and G395M gratings to survey N $\sim$ 80,000 galaxies for BLAGNs. Through emission-line fitting, using a sum of Gaussian models for {H$α$}, {H$β$}, [N II] $λ\lambda6548, 6584$, and [O III] $ λ\lambda4959, 5007$, we separate AGN broad-line components from narrow-line emission. We find the detection rate of BLAGNs to be relatively consistent across our redshift range. Compared to typical low-$z$ AGNs ($z$ $\lesssim$ 1), the 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 the 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.

Short digest

Mining the DJA v4 NIRSpec database (~80,000 galaxies) with the G140/235/395 H/M gratings, the authors fit Hα/Hβ+[O III],[N II] with multi-Gaussian models and an F-test to isolate bona fide broad components (FWHM > 1000 km s−1, S/N > 5; forbidden lines narrow). They assemble 252 BLAGNs (171 new) spanning z = 0.8–7.2 and find an almost uniform detection rate with redshift. High‑z BLAGNs are systematically fainter and less massive yet accrete efficiently, with Eddington ratios 0.1–1.0. This census bridges local SMBHs and remote luminous quasars, sharpening constraints on rapid early black‑hole growth.

Key figures to inspect

• Figure 1: Inspect the decomposition for VALENTINO-3567-51909 (z = 4.626) to verify broad Hβ/Hα wings and that [O III]/[N II] remain narrow—this shows the selection logic (broad vs. narrow widths) in a concrete spectrum.
• Figure 2: Check the redshift histogram and BLAGN fraction versus z; confirm the near‑uniform detection rate and note the high‑z tail reaching z ≈ 7.2.
• Figure 3: Read the M_BH–L_bol plane with Eddington‑ratio tracks; locate this sample relative to SDSS DR16 contours and literature points to see that many high‑z objects sit at high λ_Edd at lower M_BH.
• Figure 4: Use the second scaling comparison (overlaid with literature and low‑z contours) to see how the sample populates high‑λ_Edd/low‑M_BH space across redshift, reinforcing the “faint, tiny, highly accreting” picture.