The 2175 \AA~ Bump Features in FeLoBAL Quasars: One Indicator of MW-like
  Dust in the Nuclear Region of Quasar
  To investigate the properties of dust in the nuclear region of quasars, we
explored the extinction curves of the iron low-ionization broad absorption line
(FeLoBAL) quasar SDSS J163004.29+311957.6 and its two analogues. The
parameterized extinction curves indicated the Milky Way-like 2175 \AA~ bump
features in underlying extinction, which are similar to those seen in the Local
Group and a subset of high-redshift star-forming galaxies. Compared to the bump
features in the Large Magellanic Clouds (LMC), the detections in this work are
much closer to those in the Milky Way (MW). These bump features, as well as
those in the high- and low-ionization broad absorption line (BAL) quasars of
Zhang et al., are probably the counterpart of the 2175 \AA~ bump features in
the quasar environment. This type of dust grain is generally small, easily
disrupted by high-energy photons and has difficulty surviving in the radiation
field of the active galactic nucleus (AGN). However, due to the presence of
absorption-line outflows, the 2175 \AA~ bump feature in quasars, which should
be rare, is seen many times in BAL quasars. The shielding effect of outflow
clouds allows the MW-like dust grains to be assembled or extends the survival
period in the quasar nuclear region. The process, and physical and chemical
conditions deserve further observational study and investigation.
