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XMMLSSOID - XMM-Newton Large-Scale Structure Optical Identifications Catalog



This table contains optical spectroscopic identifications of X-ray sources in ~3 square degrees of the XMM-Large Scale Structure survey (XMM-LSS), also covered by the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), which were obtained with the AAOmega instrument at the 3.9-m Anglo-Australian Telescope during the nights of 2006 September 25-27 and 2007 September 11-13.

In a flux-limited sample of 829 point-like sources in the optical band with g' <= 22 magnitudes and the 0.5-2 keV flux (f_0.5-2keV) > 10-15 erg/cm2/s, the authors observed 693 objects and obtained reliable spectroscopic identification for 487 sources, approximately 59% of the overall sample. The authors therefore have increased the number of identifications in this field by a factor close to 5. Galactic stellar sources represent about 15% of the total (74/487). About 54% (265/487) are broad-line active galactic nuclei (AGN) spanning redshifts between 0.15 and 3.87 with a median value of 1.68. The optical-to-X-ray spectral index (alpha_ox) of the broad-line AGN is 1.47 +/- 0.03, typical of optically selected type I quasars, and is found to correlate with the rest-frame X-ray and optical monochromatic luminosities at 2 keV and 2500 Angstroms, respectively. Consistent with previous studies, the authors find that alpha_ox is not correlated with z. In addition, 32 and 116 X-ray sources are, respectively, absorption- and emission-line galaxies at z < 0.76. From a line ratio diagnostic diagram, it is found that in about 50% of these emission-line galaxies, the emission lines are powered significantly by the AGN. 30 of the XMM sources are detected at one or more radio frequencies (see Table 5 in the published paper). In addition, 24 sources (listed in table 4 of the published paper) have ambiguous identification: in eight cases, two XMM sources have a single optical source within 6 arcsec of each of them, whereas two and 14 XMM sources have, respectively, three and two possible optical sources within 6 arcsec of each of them. Spectra of multiple possible counterparts were obtained in such ambiguous cases.

This HEASARC table contains the 487 sources which were reliably spectroscopically identified.

Catalog Bibcode



Optical identification of XMM sources in the Canada-France-Hawaii telescope
legacy survey.
    Stalin C.S., Petitjean P., Srianand R., Fox A.J., Coppolani F., Schwope A.
   <Mon. Not. R. Astron. Soc., 401, 294-306 (2010)>
   =2010MNRAS.401..294S    (SIMBAD/NED BibCode)


This table was created by the HEASARC in July 2010 based on the CDS Catalog J/MNRAS/401/294 file table2.dat.


The preferred catalog X-ray source designation ('XLSS JHHMMSS.s+DDMMSS') using the XLSS prefix for XMM-Newton Large Scale Structure survey, and the J2000.0 position of the X-ray source.

The Right Ascension of the optical counterpart to the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.001 seconds of time 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 coordinates to a precision of 0.001 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 angular separation between the XMM source and the optical counterpart positions, in arcseconds.

The g-prime magnitude of the optical counterpart to the X-ray source found in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS).

The eedshift of the optical counterpart to the X-ray source.

The quality flag of the optical spectrum. For most of the sources with spectral lines in their spectroscopic sample, the authors were able to obtain a reliable estimate of the redshift, since, for these sources, they were able to identify two or more lines in their spectra. They assign a quality flag (indicative of the reliability of the redshift) of Q= 1 for those reliable sources. For sources with only one broad or narrow emission/absorption line in their optical spectra, the redshift estimate is not secure as it is degenerate with more than one possible redshifts. For such sources, they assign a quality flag Q= 2 . For some sources, the spectral classification is unambiguous, however the spectra is of poor quality. For these sources, they have assigned a quality flag Q= 3. (The 206 sources for which spectral classification was not possible due to the poor quality of their spectra are NOT included in this table). Of the 487 identified sources, 432, 7 and 48 sources have quality flags Q of 1, 2 and 3, respectively.

The broad-band spectral index alpha_ox of the source. This characterizes the UV to X-ray spectral energy distribution of the object by assuming that the rest-frame flux emitted at 2500 Angstroms can be connected to the one at 2 keV with a simple power law. This is a simple measurement of the amount of X-ray radiation emitted mostly by non-thermal processes with respect to the amount of UV radiation emitted mostly by thermal processes. The authors estimated alpha_ox for each of the spectroscopically identified broad-line active galactic nuclei (BLAGN) and emission-line galaxies (ELGs: some of the ELGs are powered by AGN) in their sample. See Section 5.1 of the reference paper for more details on how they calculated alpha_ox.

This is a broad-brush spectroscopic identification of the object where QSO is self-evident, ELG means emission-line galaxy, ALG means absorption-line galaxy, and STA means galactic star.

This flag is set to 'S' to indicate objects which were detected by in the infrared by Spitzer in the Spitzer Wide-area Infrared Extragalactic Legacy Survey (SWIRE). Notice that in the original published paper, this flag was set to the value of 'SWIRE' in such cases.

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

Contact Person

Questions regarding the XMMLSSOID database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 08-Jul-2015 16:55:28 EDT