Polarimetry at millimetre wavelengths with the NIKA and NIKA2 camera
Résumé
The role played by magnetic fields in the star formation process is an outstanding
question of modern astrophysics. Herschel satellite observations have unveiled
filamentary structures as the preferential sites of star formation. Complementary low
resolution observations of dust polarisation by the Planck satellite have demonstrated
that these filamentary structures are associated to well organised magnetic fields, which
should play a major role in this process. A better understanding of this process requires
detailed observations of galactic dust polarisation on scales of 0.01 pc to 0.1 pc. Such
high resolution polarisation observations can be carried out at the IRAM 30 meter
telescope using the recently installed NIKA2 camera, which features two frequency
bands at 260 (polarised) and 150 (non polarised) GHz for a total of 3300 detectors, 12
and 18 arcsec FWHM resolution and Field of View (FoV) of 6.5 arcminutes diameter.
The NIKA camera, which consists of two arrays of 132 and 224 LEKIDs (Lumped
Element Kinetic Inductance Detectors) covering a FoV of ∼ 1.8 arcminutes at 1.25 (260)
and 2.05 (150) mm (GHz), was installed at the IRAM 30 telescope from 2012 to 2015.
NIKA was equipped of a room temperature polarisation system (a multi-layer half wave
plate and a grid polariser facing the NIKA cryostat window), which permitted the
simultaneous reconstruction of the three Stokes parameters, I, Q and U at 150 and 260
GHz. The purpose of this contribution is to discuss the polarisation performance of the
NIKA camera. We present results on compact and extended sources obtained dur ing
the February 2015 observational campaign. Furthermore, a first polarised light of NIKA2
instrument will be presented.