Broad Balmer-line Absorption in SDSS J172341.10+555340.5
  I present the discovery of Balmer-line absorption from H alpha to H9 in 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 +/- 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. I detect relatively
strong (EW_rest=20A) [O III] emission lines which are similar to those found in
other broad absorption line quasars with Balmer-line absorption. I derived a
column density of neutral hydrogen of 5.2x10^{17} cm^{-2} by using the curve of
growth and taking account of Ly alpha trapping. I searched for UV absorption
lines which have the same redshift with Balmer-line absorption. I found Al II}
and Fe III absorption lines at z=2.053 which correspond to previously
unidentified absorption lines, and the presence of other blended troughs that
were difficult to identify.
