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LQAC - Large Quasar Astrometric Catalog, 3rd 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 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, CDS Cat. I/313). 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 H0 = 70 km s-1 Mpc-1, OmegaM = 0.3, OmegaLambda = 0.7, and q0 = -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, 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 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 H0 = 72 km s-1 Mpc-1 and q0 = -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.


Catalog Bibcode

2015A&A...583A..75S

References

The third release of the Large Quasar Astrometric Catalog (LQAC-3):
a compilation of 321 957 objects.
    Souchay J., Andrei A.H., Barache C., Kalewicz T., Gattano C., Coelho B.,
    Taris F., Bouquillon S., Becker O.
    <Astron. Astrophys. 583, A75 (2015)>
    =2015A&A...583A..75S        (SIMBAD/NED BibCode)

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)

The construction of the Large Quasar Astrometric Catalogue (LQAC).
    Souchay J., Andrei A.H., Barache C., Bouquillon S., Gontier A-M.,
    Lambert S.B., Le Poncin-Lafitte C., Taris F., Arias E.F., Suchet D.,
    Baudin M.
   <Astron. Astrophys. 494, 799 (2009)>
   =2009A&A...494..799S

Provenance

This table was created by the HEASARC in June 2016 based on CDS Catalog J/A+A/583/A75, file lqac3.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 10-10 degrees for the ra, dec, 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 HEASARC has converted the units for the other flux density parameters from the Jansky units 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-3 source designation based on the J2000.0 equatorial coordinates in decimal degrees. E.g., 'LQAC 243-027 001' is the first object that was identified in the range 243 < RA < 244 degrees and -28 < Dec < -27 degrees. Note that the HEASARC has removed '_' characters that were present in the names in the original input table, e.g., 'LQAC_243-027_001', so as to conform to the Dictionary of Nomenclature of Celestial Objects recommendation for LQAC names. For objects that were already present in the LQAC-2 release, the number remains unchanged. Moreover, some SDSS quasars that were present in the LQAC-2 compilation were no longer present in the LQAC-3 one. In that case, for the sake of coherence, their number has not been utilized again to name a new quasar in the same box.

Alt_Name
The original name of the object. For objects already present in the catalog of quasars and active nuclei by Veron-Cetty & Veron (2010), the authors use the same terminology. This parameter was not present in the LQAC and LQAC-2 catalogs.

Broad_Type
This parameter value indicates the attribution of the nature of the object: "QUASAR" for quasars fully recognized optically, "AGN" for AGNs, "BL LAC" for BL Lac objects, and "RADIO" for point-like objects concerned principally with radio VLBI emissions (catalogs A, B, C, D), which are those for which the authors have no optical counterpart in their compilation.

RA
The Right Ascension of the object 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-3. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

Dec
The Declination of the object 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-3. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

LII
The Galactic Longitude of the object.

BII
The Galactic Latitude of the object.

LQRF_RA
The Right Ascension of the object in the selected equinox, as given in the ICRF according to the astrometric algorithms described in Section 4 of the LQAC-3 paper. These coordinates are supposed to be more exact than the original ones except for the quasars present in the radio VLBI catalogs (flags A, B, C, D). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-3. See the discussion in the HEASARC_Implementation section above for more details of the precision of the positions.

LQRF_Dec
The Declination of the object in the selected equinox, as given in the ICRF according to the astrometric algorithms described in Section 4 of the LQAC-3 paper. These coordinates are supposed to be more exact than the original ones except for the quasars present in the radio VLBI catalogs (flags A, B, C, D). The position was given in J2000.0 equatorial coordinates in the original CDS version of the LQAC-3. 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 3 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 = VLBA (VCS Petrov et al., Cat. J/AJ/136/580, version 2013)
    C = VLA (Cat. J/ApJS/141/13, J/AJ/126/2562, J/AJ/129/1163, J/AJ/131/1872)
    D = JVAS (Patnaik et al., Cat. VIII/60)
    E = SDSS
    F = 2QZ (Croom et al., Cat. VII/241)
    G = 2df-SDSS (2df-SDSS LRG and QSO survey (2009));
         da Angela et al., 2008MNRAS.383..565D;
         LRG: Cannon et al., Cat. J/MNRAS/372/425;
         QOS: Croom et al., Cat. J/MNRAS/392/19
    H = FIRST (Becker et al., Cat. VIII/71)
    I = Hewitt and Burbridge, Cat. VII/158
    J = 2MASS (only for magnitude information) (Cutri et al., Cat. II/246)
    K = GSC2.3 (only for magnitude information) (Lasker et al., Cat. I/305)
    L = B1.0 (only for magnitude information) (Monet et al., Cat. I/284)
    M = Veron-Cetty and Veron (2010, Cat. VII/258)
    m = object is a SDSS quasar found only in Veron-Cetty and Veron (2010,
         Cat. VII/258) catalog, but no more in the new SDSS releases
  

Cross_Id_Flag
This parameter contains 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 arcseconds) and/or redshift discrepancies, coded as follows (notice that the HEASARC has changed the original mixture of symbols 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
  

Redshift
The redshift z of the object as determined from the original catalog (generally indicated by the value of the alt_name parameter).

Umag
The visual magnitude of the object in the u band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Bmag
The visual magnitude of the object in the b band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Vmag
The visual magnitude of the object in the v band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Gmag
The visual magnitude of the object in the g band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Rmag
The visual magnitude of the object in the r band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Imag
The visual magnitude of the object in the i band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Zmag
The visual magnitude of the object in the z band. The photometric system in which the magnitude has been measured is not homogeneous for each band. The priority is indicated by the first catalog_flags value starting from the first optical catalog, the SDSS, with flag E. For instance, the value of the r magnitude of a quasar observed both by the SDSS (flag E) and the 2QZ (flag F) is taken from the SDSS, whereas the value of the b magnitude, only present in the 2QZ, will be taken from this latter survey.

Jmag
The J infrared magnitude of the object for the 21,844 quasars for which the authors found a counterpart in the 2MASS survey.

Kmag
The H infrared magnitude of the object for the 21,844 quasars for which the authors found a counterpart in the 2MASS survey.

Flux_20_cm
The radio flux density of the object at 1.4 GHz (20 cm), in mJy, when available. These radio flux densities concern exclusively the quasars coming from the four first catalogs (flags A to D), those coming from VLBI sessions.

Flux_13_cm
The radio flux density of the object at 2.3 GHz (13 cm), in mJy, when available. These radio flux densities concern exclusively the quasars coming from the four first catalogs (flags A to D), those coming from VLBI sessions.

Flux_6_cm
The radio flux density of the object at 5.0 GHz (6 cm), in mJy, when available. These radio flux densities concern exclusively the quasars coming from the four first catalogs (flags A to D), those coming from VLBI sessions.

Flux_3p6_cm
The radio flux density of the object at 8.4 GHz (3.6 cm), in mJy, when available. These radio flux densities concern exclusively the quasars coming from the four first catalogs (flags A to D), those coming from VLBI sessions.

Flux_1p2_cm
The radio flux density of the object at 24 GHz (1.2 cm), in mJy, when available. These radio flux densities concern exclusively the quasars coming from the four first catalogs (flags A to D), those coming from VLBI sessions.

B_Band_Sharp_Index
The "sharp" morphology index of the PSF of the object in the b band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sharp indices characterizing the skewness of the PSF.

B_Band_Sround_Index
The "sround" morphology index of the PSF of the object in the b band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sround indices characterizing the roundness of the PSF.

B_Band_Ground_Index
The "ground" morphology index of the PSF of the object in the b band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The ground indices characterizing the normality of the PSF.

R_Band_Sharp_Index
The "sharp" morphology index of the PSF of the object in the r band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sharp indices characterizing the skewness of the PSF.

R_Band_Sround_Index
The "sround" morphology index of the PSF of the object in the r band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sround indices characterizing the roundness of the PSF.

R_Band_Ground_Index
The "ground" morphology index of the PSF of the object in the r band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The ground indices characterizing the normality of the PSF.

I_Band_Sharp_Index
The "sharp" morphology index of the PSF of the object in the i band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sharp indices characterizing the skewness of the PSF.

I_Band_Sround_Index
The "sround" morphology index of the PSF of the object in the i band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The sround indices characterizing the roundness of the PSF.

I_Band_Ground_Index
The "ground" morphology index of the PSF of the object in the i band, where the determination has been explained in full detail in Section 5.4 of the LQAC-3 reference paper. The ground indices characterizing the normality of the PSF.

Abs_Bmag
The absolute magnitude Mb of the quasar in the b band calculated according to equation (1) of the reference paper, viz.,

    Mb = mb + 5 -(5 * log DL) - Ab - Kb
  
where DL is the luminosity distance, Ab is the Galactic extinction in the b band and Kb (usually termed the K-correction) is the effect of the redshift on the part of the spectrum corresponding to the b band.

Abs_Imag
The absolute magnitude Mi of the quasar in the i band calculated according to equation (1) of the reference paper, viz.,

    Mi = mi + 5 -(5 * log DL) - Ai - Ki
  
where DL is the luminosity distance, Ai is the Galactic extinction in the i band and Ki (usually termed the K-correction) is the effect of the redshift on the part of the spectrum corresponding to the i band.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 23-Jun-2016