Discovery of two broad absorption line quasars at redshift about 4.75
  using the Lijiang 2.4m telescope
  The ultraviolet broad absorption lines have been seen in the spectra of
quasars at high redshift, and are generally considered to be caused by outflows
with velocities from thousands kilometers per second to one tenth of the speed
of light. They provide crucial implications for the cosmological structures and
physical evolutions related to the feedback of active galactic nuclei (AGNs).
Recently, through a dedicated program of optically spectroscopic
identifications of selected quasar candidates at redshift 5 by using the
Lijiang 2.4 m telescope, we discovered two luminous broad absorption line
quasars (BALQSOs) at redshift about 4.75. One of them may even have the
potentially highest absorption Balnicity Index (BI) ever found to date, which
is remarkably characterized by its deep, broad absorption lines and
sub-relativistic outflows. Further physical properties, including the metal
abundances, variabilities, evolutions of the supermassive black holes (SMBH)
and accretion disks associated with the feedback process, can be investigated
with multi-wavelength follow-up observations in the future.
