Discovery of Extremely Broad Balmer Absorption Lines in SDSS J152350.42+391405.2

TL;DR

This paper reports the discovery of extremely broad Balmer absorption lines in a quasar, revealing unique properties of the absorbing gas and its location, and providing insights into quasar outflows and their physical conditions.

Contribution

The study presents the first detailed analysis of broad Balmer absorption lines in a quasar, including spectroscopic measurements and physical modeling, expanding understanding of quasar absorption phenomena.

Findings

Balmer absorption lines are at z=0.6039 and blueshifted by 10,353 km/s.

Absorption profiles have widths of approximately 12,000 km/s.

Absorbers are located about 0.2 parsecs from the central source.

Abstract

We present the discovery of Balmer line absorption from H$\alpha$ to H$\gamma$ in an iron low-ionization broad absorption line (FeLoBAL) quasar SDSS J152350.42+391405.2 (hereafter J1523), by the quasi-simultaneous optical and near-infrared spectroscopy. The Balmer line absorption is at $z_{absor}$ = 0.6039 +/-0.0021 and blueshifted by v=10,353 km/s with respect to the Balmer emission lines. All Balmer BALs have uniform absorption profile with the widths of $\Delta$ v ~12,000 km/s. We also found the absorption trough in He 1* $\lambda$10830 with the same velocity and width in the H-band TripleSpec spectrum of J1523. This object is only the tenth active galactic nucleus known to exhibit non-stellar Balmer absorption, and also the case with the highest velocity and broadest Balmer absorption lines which have ever been found. A CLOUDY analysis shows that the absorbers require an gas density of $log_{10} n_ e (cm^{-3})=9$ and an ionization parameter of $log_{10} U=-1.0$. They locate at a distance of ~0.2 pc from the central ionizing source which is slightly farther than that of BELRs. Furthermore, J1523 is one of the brightest Balmer-BAL quasar ever reported, with unique iron absorption variations, making it as the most promising candidate for follow up high-resolution spectroscopy, multi-band observations, and long-term monitoring.