Second release of LQAC: LQAC2
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Since the first release of the Large Quasar astrometric Catalogue (LQAC) by Souchay et al. (2009), a large number of quasars have been discovered through very dense observational surveys. As these objects represent the cornerstones of modern astrometry by representing quasi inertial directions, their spatial density and their astrometric quality must be emphasized and studied in detail.

Following the same procedure as in this first release of the LQAC (Souchay et al. 2009) 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 (Ma et al. 2009; Boboltz et al. 2010) and the maximum of information concerning their physical properties (redshift, photometry, absolute magnitudes).

First of all we make a substantial review of the definitions and properties of quasars and AGN (Active Galactic Nuclei), the differenciation of these objects being unclear in the literature and even for specialists. This will serve our purpose when deciding which kinds of objects will be taken into account in our compilation. Then we carry out the cross-identification between the 9 catalogues of quasars chosen for their accuracy and their huge number of objects, using a flag for each of them, and including all the available data related to magnitudes (infrared and optical), radiofluxes and redshifts. We also perform cross identification with external catalogues 2MASS, B1.0 and GSC2.3 in order to complete photometric data of the objects. Moreover we compute the absolute magnitude of our extragalactic objects by taking into account the recent studies concerning the galactic absorption. In addition substantial improvements are brought with respect to the first release of the LQAC (Souchay et al. 2009). At first a LQAC name is given for each object based on its equatorial coordinates with respect to the ICRS, following a procedure which creates no ambiguity for identification. At second the equatorial coordinates of the objects are recomputed more accurately according to the algorithms used for the elaboration of the Large Quasar Reference Frame (LQRF) (Andrei et al. 2009). At third we introduce a morphological classification for the objects which enables in particular to define clearly if the object is point-like or extended.

Our final catalogue, called LQAC-2, contains 187,504 quasars. This is roughly 65% larger than the 113,666 quasars recorded in the first version of the LQAC (Souchay et al. 2009) and a little more than the number of quasars recorded in the up-dated version of the Veron Cetty and Veron (2010) catalogue, 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 concerning the spatial density and the distance to the closest neighbour.