Broad Balmer-Line Absorption in SDSS J172341.10+555340.5

Abstract

Abstract We present the discovery of Balmer-line absorption from H$\alpha$ to H9 in an iron low-ionizaton broad absorption line (FeLoBAL) quasar, SDSS J172341.10$+$555340.5, by near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera for OHS (CISCO) attached to the Subaru Telescope. The redshift of the Balmer-line absorption troughs is 2.0530$\ \pm\ $0.0003, and it is blueshifted by 5370 km s$^{-1}$ from the Balmer emission lines. It is more than 4000 km s$^{-1}$ blueshifted from the previously known UV absorption lines. We detected relatively strong (EW$_{\rm rest} =$ 20 Å) [O III] emission lines that are similar to those found in other broad absorption line quasars with Balmer-line absorption. We also derived the column density of neutral hydrogen of 5.2 $\times$ 10$^{17}\ $cm$^{-2}$ by using the curve of growth and taking account of Ly$\alpha$ trapping. We searched for UV absorption lines that had the same redshift with Balmer-line absorption, and found Al III and Fe III absorption lines at $z =$ 2.053 that correspond to previously unidentified absorption lines, and the presence of other blended troughs that were difficult to identify.