An (in)complete NIRSpec census of Balmer absorption in Type 1 AGN – radiation-driven outflows in little red dots, quasars and variable stars
Abstract A notable achievement of the first generation of JWST surveys was the discovery of an abundance of faint high-redshift (z > 4) broad-line active galactic nuclei (AGN) in the Lbol < 1045 erg s−1 regime, previously only accessible at z < 1. The high prevalence of absorption features in their broad hydrogen lines is one of the peculiarities of a significant fraction of this new population. In this paper, we conduct a broad census of Balmer absorption in a sample of 47 Type-1 AGN spanning 2 < z < 7. Accounting for incompleteness of JWST spectroscopic data, we estimate that $44_{-6}^{+21}$ % of Little Red Dots (LRDs) have absorption in Hα while the incidence rate is <25 % (at 2σ) in Little Blue Dots (LBDs). Additionally, R1000 JWST/NIRSpec data is strongly resolution limited, implying an inability to disentangle Doppler broadening in the absorption from optical depth effects. This is alleviated with R2700 observations, although some degeneracies remain. We find a significant correlation between the velocity of the Balmer absorption and the [OIII]5007 narrow line luminosity, suggesting a common driving mechanism. We do not find any other significant correlations (and do not confirm previously claimed correlations) between Balmer absorption and other spectral properties of LRDs (except for the expected correlation between Hα and Hβ absorption velocities). Comparing LRDs, quasars and stellar Hα absorbers, we establish that absorption in both LRDs and broad absorption line quasars is consistent with radiatively driven outflows, echoing the physics of variable stars yet occurring at vastly different scales.
Authors
- G. Cresci (ORCID: https://orcid.org/0000-0002-5281-1417)
- E. Bertola (ORCID: https://orcid.org/0000-0001-5487-2830)
- R. Maiolino (ORCID: https://orcid.org/0000-0002-4985-3819)
- Stefano Carniani (ORCID: https://orcid.org/0000-0002-6719-380X)
- Ignas Juodžbalis (ORCID: https://orcid.org/0009-0003-7423-8660)
- ALESSANDRO MARCONI (ORCID: https://orcid.org/0000-0002-9889-4238)
- Jan Scholtz (ORCID: https://orcid.org/0000-0001-6010-6809)
- Emma Curtis-Lake (ORCID: https://orcid.org/0000-0002-9551-0534)
- Andrew J. Bunker (ORCID: https://orcid.org/0000-0002-8651-9879)
- C. Marconcini (ORCID: https://orcid.org/0000-0002-3194-5416)
- Brant E. Robertson (ORCID: https://orcid.org/0000-0002-4271-0364)
- Giacomo Venturi (ORCID: https://orcid.org/0000-0001-8349-3055)
- Eleonora Parlanti (ORCID: https://orcid.org/0000-0002-7392-7814)
- Junyu Zhang (ORCID: https://orcid.org/0000-0002-1574-2045)
- Xihan Ji (ORCID: https://orcid.org/0000-0002-1660-9502)
- Francesco D'Eugenio (ORCID: https://orcid.org/0000-0003-2388-8172)
- Hannah Übler (ORCID: https://orcid.org/0000-0003-4891-0794)
- P Rinaldi
- Amanda Stoffers (ORCID: https://orcid.org/0009-0009-5464-3558)
- Zheng Ma
Institutions
- Space Telescope Science Institute (US)
- University of Arizona (US)
- University of Hertfordshire (GB)
- Scuola Normale Superiore (IT)
- University of California, Santa Cruz (US)
- University of Cambridge (GB)
- Arcetri Astrophysical Observatory (IT)
- University of Oxford (GB)
- Max Planck Institute for Extraterrestrial Physics (DE)
- University of Florence (IT)
- University College London (GB)
- National Institute for Astrophysics (IT)
Publication Details
- Journal
- Monthly Notices of the Royal Astronomical Society
- Published
- 2026-11-06
- DOI
- https://doi.org/10.1093/mnras/stag2131
- Citations
- 15
- Primary Topic
- Galaxies: Formation, Evolution, Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 12.48
Funders
- National Aeronautics and Space Administration
- Space Telescope Science Institute
- UK Research and Innovation
- European Commission
- Max-Planck-Gesellschaft
- Istituto Nazionale di Astrofisica
- Science and Technology Facilities Council