NIKA2

NIKA2
Name	NIKA2
Caption	NIKA2 camera on the IRAM 30m telescope
Organization	Institut de Radioastronomie Millimétrique
Location	Pico Veleta, Sierra Nevada, Spain
Wavelength	millimetre (1.15 mm, 2.0 mm)
Operation begin	2017
Telescope	IRAM 30-meter telescope

NIKA2 NIKA2 is a large-format millimetre-wave continuum camera installed at the IRAM 30-meter telescope on Pico Veleta in the Sierra Nevada designed for wide-field imaging and polarimetry. It was developed by a consortium led by the Institut de Radioastronomie Millimétrique in collaboration with institutions including the CNRS, CEA, Université Grenoble Alpes, and several European and North American laboratories. The instrument exploits kinetic inductance detectors pioneered in projects such as NIKA and advanced through technologies connected to work at Caltech, CEA Saclay, and Oxford University.

Overview

NIKA2 provides simultaneous dual-band imaging at approximately 1.15 mm and 2.0 mm with polarization sensitivity in the shorter band, operating at the focal plane of the IRAM 30-meter telescope. The project links scientific goals from programs like the Legacy Survey concept to targeted observations of objects such as galaxy clusters, molecular clouds, and high-redshift galaxies. Development drew on detector physics from groups associated with European Southern Observatory, cryogenic engineering related to CNRS facilities, and readout electronics influenced by work at NIST and MPA Garching.

Instrument Design and Technology

The focal plane uses arrays of lumped-element kinetic inductance detectors (LEKIDs) whose design builds on experiments at CEA, Université Grenoble Alpes, and IPAG. Cryogenics employ dilution refrigerators similar to systems used at IRAM, Max Planck Institute for Radio Astronomy, and ESO testbeds to reach temperatures below 100 mK. Optical coupling integrates refractive optics and corrugated feed horns informed by designs used on the Planck mission and the Herschel Space Observatory, while polarization modulation incorporates a rotating half-wave plate concept related to instruments like PolKa and SCUBA-2. Frequency multiplexed microwave readout electronics were developed in coordination with teams at CEA-LETI, INRIA, and University College London.

Observational Capabilities and Modes

NIKA2 supports wide-field mapping, pointed photometry, and polarization imaging, enabling studies comparable to surveys performed with instruments such as AzTEC, MAMBO, and LABOCA. Its dual-band simultaneous operation facilitates spectral index estimation similar to multi-band methods used by SPT and ACT, while its polarization mode enables magnetic field studies akin to work with POL-2 on the James Clerk Maxwell Telescope. Observing modes include raster scans, on-the-fly maps, and deep integrations coordinated with facilities like NOEMA, ALMA, and VLA for multi-wavelength follow-up.

Calibration and Data Processing

Flux calibration relies on primary calibrators such as Mars, Uranus, and secondary calibrators used by the IRAM 30m program, aligning methods with calibration pipelines from Herschel and Planck. Beam characterization and pointing models follow procedures established at IRAM and cross-checked against catalogs from Sloan Digital Sky Survey and Two Micron All Sky Survey. The data reduction pipeline integrates map-making algorithms developed alongside software from CASA-related communities, time-domain filtering techniques inspired by Bolocam and component-separation strategies used in Planck analyses. Polarization calibration employs observations of polarized standards and instrumental polarization models comparable to those used by WMAP and Planck teams.

Scientific Results and Surveys

NIKA2 has been used for large programs targeting the Sunyaev–Zel'dovich effect in galaxy clusters, dusty star-forming galaxies at high redshift, and magnetic field structure in nearby star-forming regions, complementing work from Planck, SPT, ACT, and ALMA. Key survey outcomes include constraints on pressure profiles in clusters akin to analyses by the Planck Collaboration and mass-observable scaling relations related to studies by the South Pole Telescope Collaboration. In star formation, NIKA2 observations have probed filamentary structure and column density similar to results from Herschel and JCMT programs, and millimetre photometry of high-redshift sources has supplemented source catalogs from SCUBA-2 and AzTEC surveys. Results feed into multi-wavelength campaigns with observatories such as Chandra X-ray Observatory, Spitzer Space Telescope, and Hubble Space Telescope.

Collaboration and Operations

The NIKA2 consortium comprises institutions across France, Spain, Italy, Germany, and Canada, coordinated through management structures comparable to those of the IRAM partnership and national agencies like CNRS and CNES. Observing time allocation follows procedures similar to those at IRAM 30m, with large programs and PI projects scheduled in coordination with international partners including ESO and university consortia. Operational support integrates technical teams experienced with receivers at IRAM, cryogenics groups from CEA, and software engineers familiar with pipelines used at ALMA and NOEMA.

Category:Millimetre astronomy instruments Category:Astronomical instrumentation