Calibration and Performance of the NIKA2 camera at the IRAM 30-meter Telescope

Abstract

NIKA2 is a dual-band millimetric continuum camera of 2900 Kinetic Inductance Detectors (KID), operating at $150$ and $260\mathrm{GHz}$, installed at the IRAM 30-meter telescope. We present the performance assessment of NIKA2 after one year of observation using a dedicated point-source calibration method, referred to as the \emph{baseline} method. Using a large data set acquired between January 2017 and February 2018 that span the whole range of observing elevations and atmospheric conditions encountered at the IRAM 30-m telescope, we test the stability of the performance parameters. We report an instantaneous field of view (FOV) of 6.5' in diameter, filled with an average fraction of $84\%$ and $90\%$ of valid detectors at $150$ and $260\mathrm{GHz}$, respectively. The beam pattern is characterized by a FWHM of $17.6^{\prime \prime }\pm 0.1^{\prime \prime }$ and $11.1^{\prime \prime }\pm 0.2^{\prime \prime }$, and a beam efficiency of $77\%\pm 2\%$ and $55\%\pm 3\%$ at $150$ and $260\mathrm{GHz}$, respectively. The rms calibration uncertainties are about $3\%$ at $150\mathrm{GHz}$ and $6\%$ at $260\mathrm{GHz}$. The absolute calibration uncertainties are of $5\%$ and the systematic calibration uncertainties evaluated at the IRAM 30-m reference Winter observing conditions are below $1\%$ in both channels. The noise equivalent flux density (NEFD) at $150$ and $260\mathrm{GHz}$ are of $9\pm 1\mathrm{mJy}\cdot {\mathrm{s}}^{1/2}$ and $30\pm 3\mathrm{mJy}\cdot {\mathrm{s}}^{1/2}$. This state-of-the-art performance confers NIKA2 with mapping speeds of $1388\pm 174$ and $111\pm 11{\mathrm{arcmin}}^2\cdot {\mathrm{mJy}}^{-2}\cdot {\mathrm{h}}^{-1}$ at $150$ and $260\mathrm{GHz}$. With these unique capabilities of fast dual-band mapping at high (better that 18'') angular resolution, NIKA2 is providing an unprecedented view of the millimetre Universe.

37 pages, accepted for publication in A&A