The NIKA2 large-field-of-view millimetre continuum camera for the 30 m IRAM telescope

¹ Laboratoire Lagrange, Université et Observatoire de la Côte d’Azur, CNRS, Bd de l’Observatoire, 06304 Nice, France
² University of Sciences and Technology Houari Boumediene (U.S.T.H.B.), BP 32 El Alia, 16111 Bab Ezzouar, Algiers, Algeria
³ Astronomy Instrumentation Group, University of Cardiff, The Parade, CF24 3AA, UK
⁴ Laboratoire AIM, CEA/IRFU, CNRS/INSU, Université Paris Diderot, CEA-Saclay, 91191 Gif-Sur-Yvette, France
⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁶ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), 13388 Marseille, France
⁷ Institut Néel, CNRS and Université Grenoble Alpes (UGA), 25 Av. des Martyrs, 38042 Grenoble, France
e-mail: alessandro.monfardini@neel.cnrs.fr
⁸ Institut de RadioAstronomie Millimétrique (IRAM), 18012 Granada, Spain
⁹ Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS, 53 av. des Martyrs, 38000 Grenoble, France
¹⁰ Institut de RadioAstronomie Millimétrique (IRAM), 38000 Grenoble, France
¹¹ Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹² LERMA, CNRS, Observatoire de Paris, 61 avenue de l’Observatoire, 75014 Paris, France
¹³ School of Earth and Space Exploration and Department of Physics, Arizona State University, Tempe, AZ 85287, USA
¹⁴ Institut d’Astrophysique de Paris, CNRS (UMR 7095), 98bis boulevard Arago, 75014 Paris, France

Received: 3 July 2017
Accepted: 13 September 2017

Abstract

Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. cosmic microwave background and high-redshift galaxies). General purpose, large-field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-of-view of 6.5 arcmin in diameter, and configurable to map the linear polarisation at 260 GHz.

Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors, and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an adhoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-m IRAM telescope at Pico Veleta, near Granada (Spain).

Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper.

Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum angular resolutions of around 11 and 17.5 arcsec at respectively 260 and 150 GHz. The noise equivalent flux densities are, at these two respective frequencies, 33±2 and 8±1 mJy s^1/2. A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years.