LQAC-4: Fourth release of the Large Quasar Astrometric Catalogue

Abstract

Context. From an astrometric point of view, quasars constitute the best and almost ideal reference objects in the celestial sphere, with a priori no significant proper motion. Since the third release of the Large Quasar Astrometric Catalogue (LQAC-3), a large number of quasars have been discovered, in particular those coming from the DR12Q release of the SDSS. Moreover, for cross-matched objects, we have taken advantage of the very accurate determinations of the quasars identified within the recent Gaia DR1 catalogue. Aims. Following the same procedure as in the three previous releases of the LQAC, our aim is to compile the large majority of all the quasars recorded so far. Our goal is to record their best coordinates and substantial information concerning their physical properties such as the redshift as well as multi-bands apparent and absolute magnitudes. Emphasis is given to the results of the cross-matches with the Gaia DR1 catalogue. Methods. New quasars coming from the DR12Q release were cross-matched with the precedent LQAC-3 compilation with a 1 search radius, in order to add the objects without counterpart to the LQAC-4 compilation. A similar cross-match was done with Gaia DR1 to identify the known quasars detected by Gaia. This enables one to improve significantly the positioning of these objects, and in parallel to study the astrometric performance of the individual catalogues of the LQAC-4 compilation. Finally, a new method was used to determine absolute magnitudes. Results. Our final catalogue, called LQAC-4, contains 443 725 objects. This is roughly 37.82% more than the number of objects recorded in the LQAC-3. Among them, 249 071 were found in common with the Gaia DR1, with a 1 search radius. That corresponds to 56.13% of the whole population in the compilation. Conclusions. The LQAC-4 delivers to the astronomical community a nearly complete catalogue of spectroscopically confirmed quasars (including a small proportion of compact AGNs), with the aim of giving their best equatorial coordinates with respect to the ICRF2 and with exhaustive additional information. For more than 50% of the sample, these coordinates come from the very recent Gaia DR1.

VVV-WIT-04: an extragalactic variable source caught by the VVV Survey

“…VVV-WIT-04 is a point source located ∼ 0.20 arcsec apart from the position of PMN J1515-5559. Catalogued as the quasar LQAC 228-055 001 (Souchay et al 2015;Gattano et al 2018), the archive radio data of PMN J1515-5559 are consistent with non-thermal radiation from a compact radio source as expected for an AGN. As discussed in Section 3 (see also Figures 2 and 3) the colour of VVV-WIT-04 is not a typical star colour, but rather it is in agreement with a very reddened quasar (e.g., Mateos et al 2012;Ivanov et al 2016;Maitra et al 2019), leading us to suggest that VVV-WIT-04 has an extragalactic origin as the near-IR counterpart of PMN J1515-5559.…”

“…VVV-WIT-04 is located at coordinates RA, DEC (J2000)=15:15:12.69, −55:59:32.78, corresponding to l, b=−37.869,1.432 deg. The position coincides within ∼ 0.2 arcsec with the radio source PMN J1515−5559 (= LQAC 228-055 001, Wright et al 1994;Souchay et al 2015;Gattano et al 2018). Precise coordinates for J1515−5559 from the Very-Long-Baseline Interferometry (VLBI) Source Position Catalogue 1 are RA,DEC (J2000)…”

A New Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources

“…By no means is the OCARS catalog intended to replace large general catalogs of extragalactic objects, such as LQAC (Gattano et al 2018) or Milliquas (Flesch 2015), which are essential for many studies. The application of the OCARS catalog has a much narrower sphere than that of such comprehensive databases.…”

LQAC-5: The fifth release of the Large Quasar Astrometric Catalogue

“…The resulting Large Quasar Astrometric Catalogues (LQAC) were updated on a regular basis, in particular by including at each release a large amount of newly discovered quasars that came from successive SDSS releases. A decade ago, the fist version of the LQAC (Souchay et al 2009) contained 113 666 objects, whereas the last version -the LQAC-4 (Gattano et al 2018) -includes 443 725 objects.…”

“…With respect to the LQAC-4 (Gattano et al 2018), the updated version LQAC-5 presented in this paper constitutes a real progress in a quantitative and qualitative point of view. First, it contains a significant number of new quasars, due to the introduction of the last release of the SDSS quasar survey DR14Q (Pâris et al 2018).…”