NIKA2 Cosmological Legacy Survey

Blind detection of galaxy clusters in the COSMOS field via the Sunyaev-Zel’dovich effect

¹ Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53, avenue des Martyrs, 38000 Grenoble, France
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁴ School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK
⁵ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, F-91191 Gif-sur-Yvette, France
⁶ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, E-18012 Granada, Spain
⁷ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205 La Laguna, Tenerife, Spain
⁸ Universidad de La Laguna, Departamento de Astrofísica, E-38206 La Laguna, Tenerife, Spain
⁹ Aix Marseille Univ, CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
¹⁰ Institut Néel, CNRS, Université Grenoble Alpes, France
¹¹ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38400 Saint-Martin-d’Hères, France
¹² Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
¹³ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH, UK
¹⁴ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy
¹⁵ Institute for Research in Fundamental Sciences (IPM), School of Astronomy, Tehran, Iran
¹⁶ Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, 28850 Madrid, Spain
¹⁷ National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou, GR-15236 Athens, Greece
¹⁸ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, GR-15784 Zografos, Athens, Greece
¹⁹ High Energy Physics Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
²⁰ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC, 75014 Paris, France
²¹ Institute of Space Sciences (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona, Spain
²² ICREA, Pg. Lluís Companys 23, Barcelona, Spain
²³ Université Paris-Saclay, CEA, Département de Physique des Particules, 91191 Gif-sur-Yvette, France
²⁴ IRAP, CNRS, Université de Toulouse, CNES, UT3-UPS (Toulouse), France
²⁵ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, I-00133 Roma, Italy
²⁶ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁷ Institut d’Astrophysique de Paris, CNRS (UMR7095), 98 bis boulevard Arago, 75014 Paris, France
²⁸ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I, 69622 Villeurbanne, France

^⋆ Corresponding author: cherouvrier@lpsc.in2p3.fr

Received: 10 March 2025
Accepted: 2 June 2025

Abstract

Clusters of galaxies, formed in the latest stages of structure formation, are unique cosmological probes. With the advent of large CMB surveys like those from the Planck satellite, the ACT and SPT telescopes, we now have access to a large number of galaxy clusters detected at millimeter wavelengths via the thermal Sunyaev-Zel’dovich (tSZ) effect. Nevertheless, it is interesting to complement them with high-angular-resolution (tens of arcseconds) observations to target the lowest-mass and highest-redshift clusters. This is the case of observations with the NIKA2 camera, which is installed on the IRAM 30-m telescope in Pico Veleta, Spain. We used the existing 150 GHz (2 mm) data from the NIKA2 Cosmological Legacy Survey (N2CLS) Large Program to blindly search for galaxy clusters in the well-known COSMOS field, across a 877 arcmin² region centered on (RA, Dec)_J2000 = (10h00m28.81s, +02d17m30.44s). We first developed a dedicated data reduction pipeline to construct NIKA2 maps at 2 mm. We then used a matched-filter algorithm to extract cluster candidates assuming a universal pressure profile to model the expected cluster tSZ signal. We computed the purity and completeness of the sample by applying the previous algorithm to simulated maps of the sky signal in the COSMOS field, including tSZ contribution, point sources and instrumental noise. We find a total of 16 cluster candidates at S/N > 4, from which eight have either an optical or X-ray cluster (or group of galaxies) counterpart. This is the first blind detection of clusters of galaxies at mm wavelengths at 18″ angular resolution. For candidates with available redshift estimates, we derived their mass by modeling the cluster tSZ signal with a universal pressure profile via a MCMC analysis. From this analysis, we confirm that NIKA2 and the IRAM 30-m telescope should be sensitive to low-mass clusters at intermediate and high redshift, complementing current and planned large tSZ-based cluster surveys.