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XMMLSSCLAS - XMM-Newton Large-Scale Structure Optical Counterparts and Redshifts



The XMM-Large Scale Structure (XMM-LSS) survey, covering an area of 11.1 square degrees, contains more than 6,000 X-ray point-like sources detected with the XMM-Newton Observatory to a flux of 3 x 10-15 erg/s/cm2 in the 0.5-2.0 keV band. The vast majority of these sources have optical (CFHTLS: Canada France Hawaii Telescope Legacy Survey), infrared (SWIRE: Spitzer Wide-area InfraRed Extragalactic legacy survey) InfraRed Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS), near-infrared (UKIDSS: UKIRT Infrared Deep Sky Survey) and/or ultraviolet (GALEX: Galaxy Evolution Explorer) counterparts.

The authors wished to investigate the environmental properties of the different types of the XMM-LSS X-ray sources by defining their environment using the i'-band CFHTLS W1 catalog of optical galaxies to a magnitude limit of 23.5 magnitudes. They have classified 4,435 X-ray selected sources on the basis of their spectra, spectral energy distributions (SEDs), and X-ray luminosities, and estimated their photometric redshifts, which have a 4-11 band photometry with an accuracy of sigma[Deltaz/(1+zsp)] = 0.076, with 22.6% outliers for i' < 26 mag. The authors estimated the local overdensities of 777 X-ray sources that have spectro-z or photo-z calculated by using more than seven bands (accuracy of sigma[(Deltaz/(1+zsp)] = 0.061, with 13.8% outliers) within the volume-limited region defined by 0.1 <= z <= 0.85 and -23.5 < M_i'_ < -20.

Although X-ray sources may be found in variety of environments, a high fraction (~55-60%), as verified by comparing with the random expectations, reside in overdense regions. The galaxy overdensities within which X-ray sources reside show a positive recent redshift evolution (at least for the range studied; z <~ 0.85). The authors also find that X-ray selected galaxies, when compared to AGN, inhabit significantly higher galaxy overdensities, although their spatial extent appear to be smaller than that of AGN. Hard AGN (harness ratios HR >= -0.2) are located in more overdense regions than soft AGN (HR < -0.2), which is clearly seen in both redshift ranges, although it appears to be stronger in the higher redshift range (0.55 < z < 0.85). Furthermore, the galaxy overdensities (with delta > 1.5, where delta is defined in equation (3) of the reference paper) within which soft AGN are embedded appear to evolve more rapidly compared to the corresponding overdensities around hard AGN.

This table contains the spectroscopic and/or photometric redshifts for 4,206 X-ray selected sources in the XMM-LSS field which have optical counterparts and have been classified by the authors.

Catalog Bibcode



Classification and environmental properties of X-ray selected point-like sources
in the XMM-LSS field.
    Melnyk O., Plionis M., Elyiv A., Salvato M., Chiappetti L., Clerc N.,
    Gandhi P., Pierre M., Sadibekova T., Pospieszalska-Surdej A., Surdej J.
    <Astron. Astrophys. 557, A81 (2013)>
    =2013A&A...557A..81M        (SIMBAD/NED BibCode)
The XMM-Large Scale Structure catalogue.
II. X-ray sources and associated multiwavelength data.
    Chiappetti L., Clerc N., Pacaud F., Pierre M., Gueguen A., Paioro L.,
    Polletta M., Melnyk O., Elyiv A., Surde J., Faccioli L.
    <Mon. Not. R. Astron. Soc. 429, 1652 (2013)>
    =2013MNRAS.429.1652C        (SIMBAD/NED BibCode)


This table was created by the HEASARC in September 2013 based on CDS Catalog J/A+A/557/A81 file table2.dat


The XMM-LSS source designation, viz. '2XLSSd JHHMMSS.s+DDMMSSc', from Chiappetti et al. (2013, MNRAS, 429, 1652). This uses the 2XLSSd prefix, the 'official', i.e., best-band, J2000.0 position of the X-ray source deduced after the rigid astrometric correction, and (in a very few cases) an a/b suffix. The letter suffix is used when the band merging is ambiguous and one 0.5-2keV band source may have two different hard band counterparts, or vice versa. The naming procedures used for the 2XLSSd X-ray sources are extensively discussed in Section 3.5 of Chiappetti et al. (2013).

The Right Ascension of the optical counterpart to the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table.

The Declination of the optical counterpart to the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table.

The Galactic Longitude of the optical counterpart to the X-ray source.

The Galactic Latitude of the optical counterpart to the X-ray source.

The spectroscopic redshift of the source, when available.

The rank or quality of the spectroscopic redshift. The spectroscopic redshift quality codes are as follows:

             1 = good quality (two or more lines in the spectrum)
             2 = acceptable redshift (one clear line in the spectrum)
             3 = dubious redshift
             9 = unknown or does not exist

The reference code(s) for the sources of the spectroscopic redshifts:

  Code Bibcode             Authors              CDS Version

   1 = 2005A&A...439..845L Le Fevre et al.      Cat. III/250
   2 = 2007A&A...474..473G Garcet et al.        Cat. J/A+A/474/473
   3 = 2007AJ....133..186L Lacy et al.          Cat. J/AJ/133/186
   4 = 2010MNRAS.401..294S Stalin et al.        Cat. J/MNRAS/401/294
   5 = ................... Lidman et al.        2012, accepted, PASA
   6 = ................... NED                  NASA/IPAC Extragalactic Database
   7 = 2006MNRAS.372..741S Simpson et al.       Cat. J/MNRAS/372/741
  and  2012MNRAS.421.3060S Simpson et al.       Cat. J/MNRAS/421/3060
   8 = 2007MNRAS.381.1369G Geach et al.         Cat. J/MNRAS/381/1369
   9 = 2008ApJS..176..301O Ouchi et al.         Cat. J/ApJS/176/301
  10 = 2008MNRAS.389..407S Smail et al.
  11 = 2007MNRAS.382..971V van Breukelen et al. and 2009MNRAS.395...11V
  12 = 2010MNRAS.403.2063F Finoguenov et al.    Cat. J/MNRAS/403/2063
  13 = ................... Akiyama et al.       2013, in prep
  14 = ................... Croom et al.         2013, in prep
  15 = ................... SDSS DR9 data The authors did
                                                not use the SDSS redshifts in the
                                                calculations; they were added to
                                                the table later.
The compilation of redshifts from sources 7-14 can be found at

The spectral classification of the source.

The photometric redshift of the source, when available.

The classification of the source according to its SED, as follows:

         GAL = normal galaxy templates of Ilbert et al. (2009ApJ...690.1236I)
               or templates #1-6 of Salvato et. al (2009ApJ...690.1250S)
     AGN/QSO = hybrid and AGN/QSO templates (#7-30) of Salvato et al.

The rank or quality of the photometric redshift, coded as follows (where PDZ is the redshift probability distribution as given by the LePhare photometric analysis for redshift estimation software:

           1 = good quality photometric redshift: 7 or more bands, PDZ = 100
               (when PDZ = 100, the solution is unique);
           2 = medium quality photometric redshift: 7 or more bands, PDZ < 100;
           3 = dubious photometric redshift, 4-6 bands;
           4 = no redshift because of lack of photometry;
           5 = no redshift because the objects are invisible (very faint) or
               wrong associations (probably misclassified).

The hardness ratio of the XMM-LSS X-ray source, HR = (H - S)/(H + S), where S and H denote the count rate (ct/s) in the soft (0.5-2.0 keV) and the hard (2-10 keV) bands, respectively. Considering the average errors of the count rates measurements, the authors estimate a typical uncertainty for HR of 0.1.

The X-ray luminosity of the XMM-LSS X-ray source in the soft (0.5-2.0 keV) band, in erg/s.

The X-ray luminosity of the XMM-LSS X-ray source in the hard (2-10 keV) band, in erg/s.

The final classification of the XMM-LSS source: AGN, GAL (galaxy), QSO or STAR. The criteria for these classifications are discussed in Sections 3 and 4 of the reference paper.

This Boolean flag parameter is set to '1' if the authors have flagged the source as a 'DOG' (dust-obscured galaxy), else is 0. The criteria for this classification are discussed in Section 4.3 of the reference paper.

The HEASARC Browse object classification based on the value of the final_class parameter.

Contact Person

Questions regarding the XMMLSSCLAS database table can be addressed to the HEASARC Help Desk.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 23-Nov-2022 19:38:11 EST