We search for ultra-luminous QSOs at high redshift using photometry from the SkyMapper Southern Survey DR3, in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 119 newly discovered Southern QSOs, of which 97 with -29 < M_145 < -27 and 4 < z < 5.5 are found an effective search area of 14,120 deg^2. In combination with already known QSOs, we construct a sample that is >90% complete for M_145 < -27.5 at z=4.4 and for M_145 < -28 at z=5.4. This Southern sample has a surface density that is over 3 times higher than in previous searches in the Northern hemisphere, which is only partly due to a more inclusive selection. We derive the bright end of the QSO luminosity function at restframe 145nm and measure its slope as $beta approx -3.84$ at z~5. We also present the first z~5 QSO luminosity function at restframe 300nm.
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