Identification confusion and blending concealment in the SDSS-DR16 Quasar catalogues -- 40 new quasars and 82 false quasars identified

Abstract: The SDSS-DR16 Quasar Superset and pipeline catalogues are searched for undeclared quasars which were concealed by or confused with other objects, usually due to incomplete deblending. Forty such quasars with redshifts are found and herewith presented. Also, 82 entries in the SDSS-DR16Q main quasar catalogue are shown to be non-quasars, some also due to incomplete deblending, especially "line poachers". Other non-quasars are shown to be star spikes or moving stars or other types, and 7 new quasars are identified from analysis of "unplugged" spectra. These numbers are tiny compared with the millions of DR16 spectra, but highlight some heretofore overlooked systematics. The deblending issue is discussed throughout.