SEVEN BROAD ABSORPTION LINE QUASARS WITH EXCESS BROADBAND ABSORPTION NEAR 2250 Å

We report the discovery of excess broadband absorption (EBBA) near 2250 angstrom 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 greater than or similar to 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 angstrom bump seen in the Local Group and may be a counterpart of the 2175 angstrom bump under different conditions in the early universe. Furthermore, five objects in this sample show low-ionization BAL (LoBALs), such as Mg II and Al III, in addition to the high-ionization BAL of C IV and Si IV. The fraction of LoBALs in our sample, similar to 70%, is surprisingly high compared to that of general BAL quasars, similar to 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 that the bump carriers are closely related to the early evolution phase of quasars.