LQAC-6: Sixth Release of the Large Quasar Astrometric Catalogue A compilation of 2 073 099 objects with 1 739 187 Gaia DR3 counterparts

Context. In addition to being objects of intense interest for cosmology and studies of the evolution of the universe, quasars are used to define quasi-inertial positions on the celestial sphere. Since its first publication in 2009, the purpose of the Large Quasar Astrometric Catalogue (LQAC) has been to provide the largest catalogue of bona fide quasars suitable for astrometry, with the high-precision positions from Gaia becoming available in the fourth release (LQAC-4). Aims. Following the same kind of procedure as in the previous releases of the LQAC, our aim is to compile the maximum number of recorded quasars, with optimised equatorial coordinates and fundamental information about their physical properties such as the redshift, the photometry, radio fluxes, morphological index. Methods. New quasars from the SDSS DR16Q release were cross-matched with the precedent LQAC-5 compilation with a 1 '' radius, which leads to 225 082 objects not present in the previous LQAC-5 release. Another cross-match was done with the Gaia Celestial Reference Frame 3 (GCRF3) catalogue, which is itself a compilation of a large number of quasars catalogues, accompanied with very accurate Gaia DR3 positions. Moreover, AGN's coming from 19 individual extragalactic surveys not considered in the previous LQAC compilations are added. Results. This new LQAC-6 release contains 2 073 099 objects, which is 3.5 times the number of objects recorded in the previous LQAC-5 release. Among them, 1 739 187 objects were found in common with the Gaia DR3, within a 1" search radius. A large part of new objects belong to the GCRF3 catalogue, which gathers a total number of 1 614 218 objects. Conclusions. The LQAC-6 delivers a nearly complete catalogue of quasars and AGN's to the astronomical community, with the aim of giving their best equatorial coordinates with respect to the recent ICRF3 and with exhaustive additional information. For as much as 83.9% of the sample, these coordinates are extracted from the very recent Gaia DR3.