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Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars
Journal article   Open access   Peer reviewed

Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars

Karen M Leighly, Sarah C Gallagher, Hyunseop Choi, Donald M Terndrup, Julianna R Voelker, Gordon T Richards and Leah K Morabito
The Astrophysical journal, v 993(1), 129
01 Nov 2025
DOI: https://doi.org/10.3847/1538-4357/ae04df
url
https://doi.org/10.3847/1538-4357/ae04dfView
Published, Version of Record (VoR) Open

Abstract

Correlation Density Dust emission Emission Ionization Line shape Line spectra Luminosity Optical analysis Optical thickness Outflow Quasars Red shift Spectra Absorption Iron
While C iv is the most common absorption line in broad absorption line quasar spectra, Balmer absorption lines (BALs) are among the rarest. We present analysis of Balmer absorption in a sample of 14 iron low-ionization BAL quasars (FeLoBALQs); eight are new identifications. We measured velocity offset, width, and apparent optical depth. The partial covering that is ubiquitous in BAL quasar spectra alters the measured Balmer optical depth ratios; accounting for this, we estimated the true H(n = 2) column density. We found the anticipated correlation between Eddington ratio and outflow speed, but it is weak in this sample because nearly all of the objects have the low outflow speeds characterizing loitering outflow FeLoBAL quasars, objects that are also found to have low accretion rates. Measurements of dN/dv, the differential column density with respect to the outflow speed, are anticorrelated with the luminosity and Eddington ratio: the strongest absorption is observed at the lowest speeds in the lowest-luminosity objects. The absorption line width is correlated with αoi, the Fλ point-to-point slope between 5100 Å and 3 μm. This parameter is strongly correlated with the Eddington ratio among low-redshift quasars. BALs have been recently found in the spectra of little red dots (LRDs), a class of high-redshift objects discovered by JWST. We note suggestive similarities between LRDs and FeLoBAL quasars in the emission-line shape, the presence of steep reddening and a scattered blue continuum, the lack of hot dust emission, and X-ray weakness.

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Astronomy & Astrophysics
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