The construction of the large quasar astrometric catalogue (LQAC)

Context. The very large and increasing number of quasars reckoned from various sky surveys leads to a large quantity of data which brings various and inhomogeneous information in the fields of astrometry, photometry, radioastronomy and spectroscopy. Aims. In this paper, we describe our work that aims to make available a general compilation of the largest number of recorded quasars obtained from all the available catalogues, with their best position estimates, and providing physical information at both optical and radio wavelengths. Thus, we construct a catalogue compilation designated Large Quasar Astrometric Catalogue (LQAC) giving coordinates, multiband photometry, radio fluxes, redshift, luminosity distances and absolute magnitudes. Methods. We gather the 12 largest quasar catalogues (4 from radio interferometry programs, 8 from optical surveys), and we carry out systematic cross-identifications of the objects. Information concerning u, b, v, g, r, i, z, J, K photometry as well as redshift and radio fluxes at 1.4 GHz, 2.3 GHz, 5.0 GHz, 8.4 GHz and 24 GH are given when available. A small proportion of remaining objects, not present in the 12 catalogues and included in the Véron-Cetty & Véron quasar catalogues, are added to the compilation. Results. The LQAC contains 113 666 quasars. We discuss the external homogeneity of the data by comparing the coordinates, the redshifts and the magnitudes of objects belonging to different catalogues. We use up-to-date cosmological parameters as well as recent models for galactic extinction and K-correction in order to evaluate the absolute magnitudes of the objects.