The X-CLASS survey: A catalogue of 1646 X-ray-selected galaxy clusters up to z ∼ 1.5^⋆

¹ Institute for Astronomy & Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, 15236 Palaia Penteli, Greece
e-mail: ekoulouridis@noa.gr
² IRAP, Université de Toulouse, CNRS, CNES, UT3, Toulouse, France
³ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁴ Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
⁵ Ulugh Beg Astronomical Institute of Uzbekistan Academy of Sciences, 33 Astronomicheskaya Str., Tashkent 100052, Uzbekistan
⁶ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, Athens 15784, Greece
⁷ Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, Brno 611 37, Czech Republic
⁸ Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
⁹ Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
¹¹ LAM, OAMP, Université Aix-Marseille, CNRS, Pôle de l’Étoile, Site de Château Gombert, 38 Rue Frédéric Joliot-Curie, 13388 Marseille 13 Cedex, France
¹² European Space Astronomy Centre, ESA, Villanueva de la Cañada, 28691 Madrid, Spain
¹³ School of Physics, HH Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, UK
¹⁴ School of Physics & Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹⁵ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
¹⁶ National Research Institute of Astronomy and Geophysics (NRIAG), 11421 Helwan, Cairo, Egypt
¹⁷ Telespazio UK for ESA, European Space Astronomy Centre, Operations Department, 28691 Villanueva de la Cañada, Spain

Received: 15 February 2021
Accepted: 30 April 2021

Abstract

Context. Cosmological probes based on galaxy clusters rely on cluster number counts and large-scale structure information. X-ray cluster surveys are well suited for this purpose because they are far less affected by projection effects than optical surveys, and cluster properties can be predicted with good accuracy.

Aims. The XMM Cluster Archive Super Survey, X-CLASS, is a serendipitous search of X-ray-detected galaxy clusters in 4176 XMM-Newton archival observations until August 2015. All observations are clipped to exposure times of 10 and 20 ks to obtain uniformity, and they span ∼269 deg² across the high-Galactic latitude sky (|b| > 20°). The main goal of the survey is the compilation of a well-selected cluster sample suitable for cosmological analyses.

Methods. We describe the detection algorithm, the visual inspection, the verification process, and the redshift validation of the cluster sample, as well as the cluster selection function computed by simulations. We also present the various metadata that are released with the catalogue, along with two different count-rate measurements, an automatic one provided by the pipeline, and a more detailed and accurate interactive measurement. Furthermore, we provide the redshifts of 124 clusters obtained with a dedicated multi-object spectroscopic follow-up programme.

Results. With this publication, we release the new X-CLASS catalogue of 1646 well-selected X-ray-detected clusters over a wide sky area, along with their selection function. The sample spans a wide redshift range, from the local Universe up to z ∼ 1.5, with 982 spectroscopically confirmed clusters, and over 70 clusters above z = 0.8. The redshift distribution peaks at z ∼ 0.1, while if we remove the pointed observations it peaks at z ∼ 0.3. Because of its homogeneous selection and thorough verification, the cluster sample can be used for cosmological analyses, but also as a test-bed for the upcoming eROSITA observations and other current and future large-area cluster surveys. It is the first time that such a catalogue is made available to the community via an interactive database which gives access to a wealth of supplementary information, images, and data.