The second release of the Large Quasar Astrometric Catalog (LQAC-2)

Context. Since the first release of the LQAC (Large Quasar Astrometric Catalogue) a large number of quasars have been discovered through very dense observational surveys. As these objects constitute the cornerstones of modern astrometry by indicating quasi inertial directions, their spatial density and their astrometric quality must be studied in detail.
Aims: Following the same procedure as in this first release of the LQAC, our aim is to compile all the quasars recorded until the present date, with the best determination of their equatorial coordinates in the ICRS, i.e. with respect to the newly established ICRF2 and with the maximum of information concerning their physical properties (redshift, photometry, absolute magnitudes).
Methods: First of all we made a substantial review of the definitions and properties of quasars and AGN (active galactic nuclei), because the differenciation of these objects is unclear in the literature, even for specialists. Then we carried out the cross-identification between the nine catalogs of quasars chosen for their accuracy and their huge number of objects, including all the available data related to magnitudes, radiofluxes, and redshifts. Moreover, we computed the absolute magnitude of our extragalactic objects by taking the recent studies concerning the galactic absorption into account. In addition, substantial improvements were made with respect to the first release of the LQAC. First, an LQAC name is given for each object based on its equatorial coordinates with respect to the ICRS, following a procedure that creates no ambiguity in the identification. Second the equatorial coordinates of the objects were recomputed more accurately according to the algorithms used for the elaboration of the Large Quasar Reference Frame (LQRF). Third we introduce a morphological classification for the objects that in particular clearly defines if the object is point-like or extended.
Results: Our final catalog, called LQAC-2, contains 187 504 quasars. This is roughly 65% more than the 113 666 quasars recorded in the first version of the LQAC and a little more than the number of quasars recorded in the updated version of the Véron-Cetty & Véron (2010, A&A, 518, A10) catalog, which was the densest compilation of quasars up to now. In addition to the quantitative and qualitative improvements brought by our compilation, we discuss the homogeneity of the data and carry out statistical analysis of the spatial density and the distance to the closest neighbor.
Conclusions: The LQAC-2 will be useful for the astronomical community since it gives the most complete information available about the whole set of already recorded quasars, insisting on the precision and accuracy of their coordinates with respect to the ICRF-2.

The catalog is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/537/A99