Seven broad absorption line quasars with excess broad band absorption
  near 2250 \AA
  We report the discovery of excess broad band absorption near 2250 A (EBBA) in
the spectra of seven broad absorption line (BAL) quasars. By comparing with the
statistical results from the control quasar sample, the significance for the
detections are all above the > 4{\sigma} level, with five above > 5{\sigma}.
The detections have also been verified by several other independent methods.
The EBBAs present broader and weaker bumps at smaller wavenumbers than the
Milky Way, and similar to the Large Magellanic Cloud. The EBBA bump may be
related to the 2175 A bump seen in the Local Group and may be a counterpart of
the 2175 A bump under different conditions in the early Universe. Furthermore,
five objects in this sample show low-ionization broad absorption lines
(LoBALs), such as Mg II and Al III, in addition to the high-ionization broad
absorption lines (HiBALs) of C IV and Si IV. The fraction of LoBALs in our
sample, ~70%, is surprisingly high compared to that of general BAL quasars,
~10%. Although the origin of the bump is still not clear, the coexistence of
both BALs and bumps and the significantly high fraction of LoBALs may indicate
the bump carriers is closely related to the early evolution phase of quasars.
