Letter to the Editor

NIKA2 unveils and pinpoints the Planck compact sources

¹ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38400 Saint-Martin-d’Hères, France
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, E-18012 Granada, Spain
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁵ School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK
⁶ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM, F-91191 Gif-sur-Yvette, France
⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa-OAL, Tapada da Ajuda, PT1349-018 Lisboa, Portugal
⁸ Departamento de Física, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, PT1749-016 Lisboa, Portugal
⁹ Aix Marseille Univ, CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
¹⁰ Institut Néel, CNRS, Université Grenoble Alpes, France
¹¹ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
¹² Univ. Grenoble Alpes, CNRS, LPSC-IN2P3, 53, av. des Martyrs, 38000 Grenoble, France
¹³ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy
¹⁴ Institute for Research in Fundamental Sciences (IPM), School of Astronomy, Tehran, Iran
¹⁵ Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, 28850, Madrid, Spain
¹⁶ Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
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, GR-15784 Athens, Greece
¹⁹ High Energy Physics Division, Argonne National Laboratory, 9700 South Cass Av., Lemont, IL 60439, USA
²⁰ LUX, 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 IRAP, CNRS, Université de Toulouse, CNES, UT3-UPS, (Toulouse), France
²⁴ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, I-00133 Roma, Italy
²⁵ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁶ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS (UMR7095), Paris, France
²⁷ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I, 69622 Villeurbanne, France

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Received: 11 February 2026
Accepted: 15 March 2026

Abstract

Context. The Planck Catalogue of Compact Sources (PCCS2) is an unbiased census of the millimetre sky at sub-Jansky levels, and thus a valuable resource for studies of galaxy evolution. Nevertheless, its application to extra-galactic studies is hindered by its limited angular resolution of a few arcminutes.

Aims. In order to open the PCCS2 for an in-depth exploitation, understanding whether they are active galactic nuclei, dusty star forming galaxies, proto-clusters, or chance alignments is paramount. Improving the positional information and angular resolution will also be beneficial in this quest. Here we aim to unveil the PCCS2 sources in the northern hemisphere.

Methods. We observed the bright end of the 143 and 217 GHz PCCS2 at Dec ≥ −41.2 degrees with the New IRAM KID Arrays 2 camera (NIKA2) at 1.2 mm (260 GHz) and 2.0 mm (150 GHz). The sample includes 487 targets. Map making and source extraction were carried out with the latest version of the NIKA2 data reduction software.

Results. NIKA2 detected 54% and 77% of the targets at 1.2 and 2.0 mm. More than 95% are point-like sources, five are resolved in two components, and only 4% are extended at the resolution of NIKA2. By cross-matching the NIKA2 catalogue to the NASA Extragalactic Database, the redshift of ∼86% of the sources was found, covering the range from z ∼ 0 to 3.4, with a median z = 0.77.

Conclusions. The number density of the 143 GHz PCCS2 is 0.029 deg⁻², in good agreement with model predictions. Roughly 80% of these sources are QSOs or AGN, with a median NIKA2 spectral index α = −1.15, typical of non-thermal synchrotron emission. With a positional accuracy smaller than 3.0 arcsec, and an angular resolution of 11.6 and 18.0 arcsec at 1.2 and 2.0 mm, respectively, the NIKA2 PCCS2 catalogue is hereby released to the community.