LQAC ivo://nasa.heasarc/lqac NASA/GSFC HEASARC Souchay et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source Since the release of the original Large Quasar Astrometric Catalog (LQAC: Souchay et al. 2009, A&A, 494, 815), a large number of quasars have been discovered through very dense observational surveys. Following the same procedure as in the first release of the LQAC, the authors aim is to compile all the quasars recorded up until the present date, with the best determination of their ICRS equatorial coordinates, i.e., with respect to the newly established ICRF2 (the second realization of the International Celestial Reference Frame) and with the maximum of information concerning their physical properties, e.g., redshifts, photometry, absolute magnitudes. In the second paper, the authors first of all made a substantial review of the definitions and properties of quasars and AGN (Active Galactic Nuclei), the differentiation of these objects being unclear in the literature and even for specialists. This served their purpose when deciding which kinds of objects would be taken into account in this compilation. Then, they carried out the cross-identification between the 9 catalogs 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), radio fluxes and redshifts. They also performed cross identification with external catalogs 2MASS, B1.0 and GSC2.3 in order to complete photometric data for the objects. Moreover, they computed the absolute magnitude of their extragalactic objects by taking into account recent studies concerning Galactic absorption. In addition, substantial improvements were brought with respect to the first release of the LQAC. First, an LQAC name was given for each object based on its equatorial coordinates with respect to the ICRS, following a procedure which creates no ambiguity for identification. Secondly, 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) (Andrei et al., 2009, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/I/313">CDS Cat. I/313</a>). Thirdly, the authors introduced a morphological classification for the objects which enabled them in particular to define clearly if the object is point-like or extended. The authors adopted a cosmology with H<sub>0</sub> = 70 km s<sup>-1</sup> Mpc<sup>-1</sup>, Omega<sub>M</sub> = 0.3, Omega<sub>Lambda</sub> = 0.7, and q<sub>0</sub> = -0.65 in LQAC-3 (which is slightly different from that adopted for LQAC-2, notice). The final catalog, called LQAC-2, contained 187,504 quasars. This was roughly 65% larger than the 113,666 quasars recorded in the first version of the LQAC (Souchay et al. 2009, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/494/799">CDS Cat. J/A+A/494/799</a>) and a little more than the number of quasars recorded in the up-dated version of the Veron-Cetty and Veron (2010, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/VII/258">CDS Cat. VII/258</a>, HEASARC VERONCAT table) catalog, which was the densest compilation of quasars up to the present one. In addition to the quantitative and qualitative improvements implemented in this compilation, the authors discussed the homogeneity of the data and carried out a statistical analysis concerning the spatial density and the distance to the nearest neighbor in their published paper. The authors adopted a cosmology with H<sub>0</sub> = 72 km s<sup>-1</sup> Mpc<sup>-1</sup> and q<sub>0</sub> = -0.58 in this study. From an astrometric point of view, quasars constitute quasi-ideal reference objects in the celestial sphere, with an a priori absence of proper motion. Since the second release of the LQAC, a large number of quasars have been discovered, in particular with the upcoming new release of the SDSS quasars catalog. Following the same procedure as in the two previous releases of the LQAC, The authors' aim for LQAC-3 was to compile all the quasars recorded until the present date, with accurate recomputation of their equatorial coordinates in the ICRS and with the maximum of information concerning their physical properties, such as the redshift, the photometry, and the absolute magnitudes. The authors carried out the cross-identification between the 9 catalogs of quasars chosen for their huge number of objects, including all the available data related to magnitudes, radio fluxes, and redshifts. This cross identification was particularly delicate because of a slight change in coordinates between the objects common to two successive releases of the SDSS and the elimination of some of them. Equatorial coordinates were recomputed more accurately according to the algorithms used for the elaboration of the Large Quasar Reference Frame (LQRF). Moreover, absolute magnitudes and morphological indexes of the new objects were given, following the same method as in the LQAC-2. The final catalog, called LQAC-3, contains 321,957 objects including a small proportion of AGNs (14,128) and BL Lac objects (1,183). This is roughly 70% more than the number of objects recorded in the LQAC-2. The LQAC-3 will be useful for the astronomical community since it gives the most complete information available about the whole set of already recorded quasars, with emphasis on the precision and accuracy of their coordinates with respect to the ICRF2. This table was created by the HEASARC in June 2016 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/583/A75">CDS Catalog J/A+A/583/A75</a>, file lqac3.dat. This is a service provided by NASA HEASARC . 2015A&A...583A..75S https://heasarc.gsfc.nasa.gov/W3Browse/all/lqac.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=lqac& GET text/xml 180 99999 true 208.263431533 -87.852264369 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=lqac GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_lqac&Action=More+Options&Action=Parameter+Search&ConeAdd=1 GALAXY CATALOG 0.0166666666666667 Infrared Optical Radio public lqac Large Quasar Astrometric Catalog, 3rd Release name Object Designation Based on the Equatorial Coordinates of Each Object meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable vmag Photometric Magnitude in Optical V Band Between 500 and 600 nm mag phot.mag;em.opt.V double nullable rmag Photometric Magnitude in Optical R Band Between 600 and 750 nm mag phot.mag;em.opt.R double nullable kmag Photometric Magnitude in Infrared K Band Between 2000 and 3000 nm mag phot.mag;em.IR.K double nullable flux_20_cm Radio Flux Density Between 750 and 1500 MHz (20 cm) mJy phot.flux.density;em.radio.750-1500MHz double nullable redshift Redshift src.redshift double nullable abs_imag Absolute Magnitude in Band I mag phys.magAbs;em.opt.I double nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable flux_6_cm Radio Flux Density Between 3 and 6 GHz (6 cm) mJy phot.flux.density;em.radio.3-6GHz double nullable broad_type Nature of the Object: AGN, BL LAC, QUASAR, RADIO, or RADIO+ src.class char nullable alt_name Alternative Designation from the Original Catalog meta.id char nullable abs_bmag Absolute Magnitude in Band B mag phys.magAbs;em.opt.B double nullable cross_id_flag Flag [01234] Indicates Cross-Id Ambiguity of Quasar meta.code;src short nullable b_band_sharp_index Sharp Morphology Index in Band B meta.code;src.morph;em.opt.B double nullable b_band_sround_index Sround Morphology Index in Band B meta.code;src.morph;em.opt.B double nullable gmag Photometric Magnitude in Optical G Band Between 400 and 500 nm mag phot.mag;em.opt.B double nullable flux_13_cm Radio Flux Density Between 1500 and 3000 MHz (13 cm) mJy phot.flux.density;em.radio.1500-3000MHz double nullable i_band_sround_index Sround Morphology Index in Band I meta.code;src.morph;em.opt.I double nullable lqrf_ra Right Ascension Given by LQRF degree pos.eq.ra double nullable jmag Photometric Magnitude in Infrared Band Between 1000 and 1500 nm mag phot.mag;em.IR.J double nullable catalog_flags Flags [A-Mm] Indicate Presence of Quasar in the 13 Catalogs in the Compilation meta.code char nullable bmag Photometric Magnitude in Optical B Band Between 400 and 500 nm mag phot.mag;em.opt.B double nullable flux_3p6_cm Radio Flux Density Between 6 and 12 GHz (3.6 cm) mJy phot.flux.density;em.radio.6-12GHz double nullable i_band_sharp_index Sharp Morphology Index in Band I meta.code;src.morph;em.opt.I double nullable i_band_ground_index Ground Morphology Index in Band I meta.code;src.morph;em.opt.I double nullable zmag Photometric Magnitude in Optical Z Band mag phot.mag;em.opt.I double nullable flux_1p2_cm Radio Flux Density Between 12 and 30 GHz (1.2 cm) mJy phot.flux.density;em.radio.12-30GHz double nullable lii Galactic Longitude degree pos.galactic.lon double nullable imag Photometric Magnitude in Optical I Band Between 750 and 1000 nm mag phot.mag;em.opt.I double nullable bii Galactic Latitude degree pos.galactic.lat double nullable b_band_ground_index Ground Morphology Index in Band B meta.code;src.morph;em.opt.B double nullable umag Photometric Magnitude in Optical U Band Between 300 and 400 nm mag phot.mag;em.opt.U double nullable r_band_ground_index Ground Morphology Index in Band R meta.code;src.morph;em.opt.R double nullable lqrf_dec Declination Given by LQRF degree pos.eq.dec double nullable r_band_sround_index Sround Morphology Index in Band R meta.code;src.morph;em.opt.R double nullable r_band_sharp_index Sharp Morphology Index in Band R meta.code;src.morph;em.opt.R double nullable