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LQAC - Large Quasar Astrometric Catalog, 2nd Release

HEASARC
Archive

Overview

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 ICRF-2 (the second realization of the International Celestail Reference Frame) and with the maximum of information concerning their physical properties, e.g., redshifts, photometry, absolute magnitudes.

In the paper, tha authors first of all make 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 carry 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 perform cross identification with external catalogs 2MASS, B1.0 and GSC2.3 in order to complete photometric data for the objects. Moreover, they compute the absolute magnitude of their extragalactic objects by taking into account recent studies concerning Galactic absorption. In addition, substantial improvements are brought 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 which creates no ambiguity for identification. Secondly, 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, CDS Cat. I/313). Thirdly, the authors introduce a morphological classification for the objects which enables them in particular to define clearly if the object is point-like or extended.

The final catalog, 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, CDS Cat. J/A+A/494/799) and a little more than the number of quasars recorded in the up-dated version of the Veron Cetty and Veron (2010, CDS Cat. VII/258, 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 discuss the homogeneity of the data and carry out a statistical analysis concerning the spatial density and the distance to the nearest neighbour in their published paper. The authors adopt a cosmology with H0 = 72 km s-1 Mpc-1 and q0 = -0.58 in this study.


Catalog Bibcode

2012A&A...537A..99S

References

The second release of the Large Quasar Astrometric Catalogue (LQAC-2).
    Souchay J., Andrei A.H., Barache C., Bouquillon S., Suchet D., Taris F.,
    Peralta R.
    <Astron. Astrophys. 537, A99 (2012)>
    =2012A&A...537A..99S        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in January 2012 based on CDS Catalog J/A+A/537/A99 file lqac2.dat.

HEASARC Implementation

The positions in the original CDS version of this table were specified in decimal degrees (J2000.0 equatorial coordinates) to a precision of 10-9 degrees for the ra and dec parameters, and of 10-7 degrees for the lqrf2_ra and lqrf2_dec parameters. The authors note in the CDS ReadMe file that this is much greater than the actual precision of the positions. In this HEASARC representation, both sets of positions are specified to lower accuracy (0.001 seconds of time in RA, 0.01 arcseconds in Declination). The software that the HEASARC uses to precess coordinates to different equators, e.g., to B1950.0, does not aspire to be of astrometric accuracy and likely will reduce the effective precision by an order of magnitude, i.e., to no better than 0.01 seconds of time in RA or 0.1 arcseconds in Declination.

The original CDS table conatining this catalog had a parameter for the 3.6-cm (8.4-GHz) flux density of the quasars for which there were no non-zero values. The HEASARC has omitted this parameter in its version of this catalog. The HEASARC has converted the units for the other flux density parameters from the Janskies given in the original version into mJy, since the latter is the standard unit for radio catalogs in the HEASARC database system.


Parameters

Name
The LQAC-2 source designation based on the J2000.0 equatorial coordinates in decimal degrees, e.g., 'LQAC 243-025-001' is the first quasar that was identified in the range 243 < RA < 244 degrees and -26 < Dec < -25 degrees. This strategy has the advantage of providing a rather simple names encoding the sky position of the object which will not change in the case of future updates of the LQAC.

RA
The Right Ascension of the quasar in the selected equinox, as given in the original catalog from which it was selected by the LQAC authors, i.e., the catalog which is flagged first in alphabetic order in the catalog_flags parameter (q.v.). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-2. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

Dec
The Declination of the quasar in the selected equinox, as given in the original catalog from which it was selected by the LQAC authors, i.e., the catalog which is flagged first in alphabetic order in the catalog_flags parameter (q.v.). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-2. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

LII
The Galactic Longitude of the quasar.

BII
The Galactic Latitude of the quasar.

LQRF2_RA
The Right Ascension of the quasar in the selected equinox, as given by the LQRF-2 (see Section 5.3 of the reference paper for more details). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-2. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

LQRF2_Dec
The Declination of the quasar in the selected equinox, as given by the LQRF-2 (see Section 5.3 of the reference paper for more details). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-2. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

Catalog_Flags
This parameter contains flags from 'A' to 'M' which indicate the presence of the quasar in one of the 13 catalogs specified in Section 4.1 and Table 1 of the reference paper:

       A = ICRF2 (Ma et al., 2009, IERS, Technical Note No. 35;
                  Boboltz et al., 2010, Bull. of the Am. Astron. Soc. 42,512)
       B = VLBI (VCS Petrov et al., CDS Cat. J/AJ/136/580, version 2010c)
       C = VLA (CDS Cat. J/ApJS/141/13, J/AJ/126/2562, J/AJ/129/1163,
                  J/AJ/131/1872)
       D = JVAS (Patnaik et al., CDS Cat. VIII/60)
       E = SDSS DR8, http://www.sdss8.org
       F = 2QZ (Croom et al., CDS Cat. VII/241)
       G = 2df-SDSS (2df-SDSS LRG and QSO survey (2009))
                  da Angela et al., 2008MNRAS.383..565D,
                  LRG: Cannon et al., CDS Cat. J/MNRAS/372/425
                  QOS: Croom et al., CDS Cat. J/MNRAS/392/19
       H = FIRST (Becker et al., CDS Cat. VIII/71)
       I = Hewitt with corrected position (Hewitt and Burbridge, Cat. VII/158)
       J = 2MASS (just to complete magnitude) (Cutri et al., CDS Cat. II/246)
       K = GSC2.3 (just to complete magnitude) (Lasker et al., CDS Cat. I/305)
       L = B1.0 (just to complete magnitude) (Monet et al., CDS Cat. I/284)
       M = VV2010 - QSO SDSS DR1 a DR7 (Veron and Veron 2010, CDS Cat. VII/258)
  

Cross_Id_Flag
This parameter comntains a flag which indicates that there are possible cross-identification ambiguities for the quasar between the Veron Catalog (VV2010: catalog 'M') and the other catalogs, based on positional (the angular distance rho between the object and its VV2010 counterpart exceeds 2 arcsecs) and/or redshift discrepancies, coded as follows (notice that the HEASARC has changed the original mixture of symbola and letters with numerical values):

      Value       Original Value    Meaning

        0              -            No cross-identification ambiguity
        1              *            2" < rho < 5" and Delta-z < 0.1
        2              !            2" < rho < 5" and Delta-z > 0.1
        3              x            rho > 5" and Delta-z < 0.1
        4              ?            rho > 5" and Delta-z > 0.1
  

Orig_Bad_Pos_Flag
This parameter comntains a flag which is set to 1 when the quasar has a very bad position in the original catalog.

Umag
The photometric apparent magnitude of the quasar in the u band, mu. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Bmag
The photometric apparent magnitude of the quasar in the b band, mb. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Vmag
The photometric apparent magnitude of the quasar in the v band, mv. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Gmag
The photometric apparent magnitude of the quasar in the g band, mg. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Rmag
The photometric apparent magnitude of the quasar in the r band, mr. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Imag
The photometric apparent magnitude of the quasar in the i band, mi. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Zmag
The photometric apparent magnitude of the quasar in the z band, mz. The photometric systems in which the magnitudes have been measured are inhomogeneous. For instance, this is the case for the r band measures which are present in both the SDSS and the 2QZ catalogs. Therefore, when a magnitude is available in 2 or more catalogs, the authors have preferred the value which is given by the first catalog specified in the catalog_flags parameter value for the specified object.

Jmag
The infrared J photometric magnitude J of the quasar coming from the cross-identication with the 2MASS Catalog.

Kmag
The infrared K photometric magnitude K of the quasar coming from the cross-identication with the 2MASS Catalog.

Flux_20_cm
The 20-cm (1.4-GHz) radio flux density of the quasar as obtained from the radio catalogs A (ICRF), B (VLBA), C (VLA) or D (JVAS), in mJy.

Flux_13_cm
The 13-cm (2.3-GHz) radio flux density of the quasar as obtained from the radio catalogs A (ICRF), B (VLBA), C (VLA) or D (JVAS), in mJy.

Flux_6_cm
The 6-cm (5.0-GHz) radio flux density of the quasar as obtained from the radio catalogs A (ICRF), B (VLBA), C (VLA) or D (JVAS), in mJy.

Flux_1p2_cm
The 1.2-cm (24-GHz) radio flux density of the quasar as obtained from the radio catalogs A (ICRF), B (VLBA), C (VLA) or D (JVAS), in mJy.

Redshift
The redshift z of the quasar.

Ref_Redshift
This parameter contains a reference code for the source of the redshift value, identical to the scheme used in the VV2010 catalog. This reference code is a letter chosen from E to I if the value of z has been taken from one of 5 basic catalogs of the compilation where this item is present (see the catalog_flags parameter description above). Otherwise, when the value of z has been taken from VV2010, a number linked to the catalogue reference in VV2010 from 1 to 1392 (ordered by decreasing number of quasars) is given. The full references corresponding to these numerical codes can be found in the file http://cdsarc.u-strasbg.fr/ftp/cats/J/A+A/537/A99/refs.dat.gz.

Bolometric_Distance
The bolometric distance DL of the quasar, in Mpc, as defined in equation (4) of the reference paper.

Reddening
The E(B-V) Galactic reddening value, in magnitudes, based on the map of Schlegel et al. (1998, ApJ, 500, 525).

B_Band_K_Corr
The K-correction in the b band, Kb, in magnitudes. This corrects for the effect of the source's redshift on the portion of its spectrum corresponding to the filter through which the absolute magnitude is determined.

I_Band_K_Corr
The K-correction in the i band, Ki, in magnitudes. This corrects for the effect of the source's redshift on the portion of its spectrum corresponding to the filter through which the absolute magnitude is determined.

Abs_Bmag
The absolute magnitude Mb of the quasar in the b band calculated according to equation (3) of the reference paper, viz.,

  Mb = mb + 5 -(5 * log DL) - Ab - Kb
  
where Ab is the extinction in the b band.

Abs_Imag
The absolute magnitude Mi of the quasar in the i band calculated according to equation (3) of the reference paper, viz.,

  Mi = mi + 5 -(5 * log DL) - Ai - Ki
  
where Ai is the extinction in the i band.

B_Band_Skewness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SHARP, which probes the skewness of its image on the B plate. This is discussed in more detail in Section 5.4 of the reference paper.

B_Band_Roundness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SROUND, which probes the roundness of its image on the B plate. This is discussed in more detail in Section 5.4 of the reference paper.

B_Band_Normalness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, GROUND, which probes the 'normalness' of its image on the B plate. This is discussed in more detail in Section 5.4 of the reference paper.

R_Band_Skewness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SHARP, which probes the skewness of its image on the R plate. This is discussed in more detail in Section 5.4 of the reference paper.

R_Band_Roundness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SROUND, which probes the roundness of its image on the R plate. This is discussed in more detail in Section 5.4 of the reference paper.

R_Band_Normalness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, GROUND, which probes the 'normalness' of its image on the R plate. This is discussed in more detail in Section 5.4 of the reference paper.

I_Band_Skewness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SHARP, which probes the skewness of its image on the I plate. This is discussed in more detail in Section 5.4 of the reference paper.

I_Band_Roundness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, SROUND, which probes the roundness of its image on the I plate. This is discussed in more detail in Section 5.4 of the reference paper.

I_Band_Normalness
A morphological characterization of the quasar point spread function (PSF) as derived from the IRAF task DAOFIND, GROUND, which probes the 'normalness' of its image on the I plate. This is discussed in more detail in Section 5.4 of the reference paper.


Contact Person

Questions regarding the LQAC database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 31-Jan-2012