Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper
  The most luminous quasars at high redshift harbour the fastest-growing and
most massive black holes in the early Universe. They are exceedingly rare and
hard to find. Here, we present our search for the most luminous quasars in the
redshift range from $z=4.5$ to $5$ using data from SkyMapper, Gaia and WISE. We
use colours to select likely high-redshift quasars and reduce the stellar
contamination of the candidate set with parallax and proper motion data. In
$\sim$12,500~deg$^2$ of Southern sky, we find 92 candidates brighter than
$R_p=18.2$. Spectroscopic follow-up has revealed 21 quasars at $z\ge 4$ (16 of
which are within $z=[4.5,5]$), as well as several red quasars, BAL quasars and
objects with unusual spectra, which we tentatively label OFeLoBALQSOs at
redshifts of $z\approx 1$ to $2$. This work lifts the number of known bright
$z\ge 4.5$ quasars in the Southern hemisphere from 10 to 26 and brings the
total number of quasars known at $R_p<18.2$ and $z\ge 4.5$ to 42.
