README

Status of the X-CLASS Database

(last update 12th February 2021)

The construction of the X-CLASS catalogue from the XMM-Newton Science Archive and the C1 cluster selection are described in detail by Clerc et al. (2012b) and Koulouridis et al. (2021). We summarize below, the content of the current online catalogue.

• 4176 XMM-Newton archival observations until August 2015 (window mode observations were not processed as well as observations for which one focal plane is missing)
• All observations are clipped to exposure times of 10 and 20 ks to obtain uniformity and span∼269 deg2 across the high-Galactic latitude (|b|>20°) sky.
• 1646 cluster candidates are retained after data screening.
• 1559 well-selected clusters are available online for the public.
• 87 sources were dubious and were classified as "provisional". Although they are kept in the main public catalogue, they are not published online. Nevertheless, they are included in appendix D of Koulouridis et al. (2021), especially since this list may contain high-redshift cluster candidates.
• For each cluster, the information on X-ray detection as well as the X-ray and optical images overlaid by X-ray contours are available.
• The catalogue provides the cluster count-rates measured within an aperture in full exposure and in six energy bands [0.5 - 2], [2 - 10], [0.5 - 0.9], [1.3 - 2], [2 - 5] and [5 - 7] keV.
• The sample spans a wide redshift range, from the local Universe up to z∼1.5. 982 spectroscopically confirmed clusters, and over 70 clusters above z=0.8.
• Redshifts were obtained from the public astronomical resources (NED, CDS, SDSS skyserver etc.) and from the literature and dedicated follow-up, especially by:
  • Mehrtens et al 2012, pertaining to the XCS catalogue (comparison between the X-CLASS and XCS catalogues can be found in Clerc et al., 2012b)
  • Sadibekova et al., 2014, the X-CLASS - redMaPPer sample
  • Clerc et al., 2016, pertaining to the SPIDERS survey
  • Ridl et al., 2017, the GROND observations of the X-CLASS clusters
• A dedicated NED page displays a sky field (through Aladin Sky Atlas tool) with the coincidences within a radius of 3 arcmin around the X-ray centroid. Only extragalactic objects with a known redshift are listed.

The first X-CLASS catalogue & Cosmology

• The first catalogue release (Clerc et al., 2012b) comprised 845 clusters.
• 347 clusters were used for the cosmological analysis with the following selection criteria:
• 0 < off-axis <10’
• 40 < Ext_LH < 5000
• 0.009 < CR < 0.5

Notes

• We are seeking the missing redshifts and would be grateful to the X-CLASS database users for any information in this respect (the origin of the communicated redshifts will be duly acknowledged in the database).

Related publications

• Koulouridis et al., 2021, submitted to A&A: The X-CLASS survey: A catalogue of 1646 X-ray-selected galaxy clusters up to z<1.5
• The full list of X-CLASS related publications is accessible from this page.

Please carefully read the user guides below before using our cluster catalogue.
• the general documentation on the database,
• the description of the catalogue columns.
If you detect inexact information or for any questions concerning database content, please contact the database manager.


Acknowledgments

This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.
We gratefully acknowledge support from the CNRS/IN2P3 Computing Center (Lyon - France) for providing computing and data-processing resources needed for this work.
This research has made use of "Aladin sky atlas" developed at CDS, Strasbourg Observatory, France.