A pilot sample of Planck-selected strongly lensed sub-millimetre galaxies: NOEMA observations and physical characterisation

Abstract

The extreme brightness of high-z strongly lensed galaxies detected by Planck surveys, thanks to their exceptionally large gravitational magnifications, offers a unique opportunity to investigate their structure and kinematics during their active star formation phase in extraordinary detail. As a step in this direction, we present our analysis of NOEMA imaging and spectroscopic data for four lensed high-z galaxy candidates. We performed continuum and line imaging of the sources at 2 and 3 mm bands down to 1''.2 spatial resolution and 40 rm km ̊m s ^ -1 spectral resolution, reconstructed and fitted the line profiles, and produced moment maps of the line emission to investigate the spatial distribution and kinematics of the molecular gas. We also carried out the gravitational lens modelling for one of the sources. The continuum images showed multiple components for at least two of the sources, strongly supporting the strong lensing scenario. We detected two CO lines with high S/N values for all sources, at CO(3--2), CO(4--3), and CO(5--4) transitions; for one source, we also detected the CI (1--0) line. We derived accurate spectroscopic redshifts 2.3 łesssim z łesssim 3.3, with 1σ uncertainties δ z ≈ 10^ -4 ̊m km , ̊m s ^ -1 ) double-peaked line profiles and substantial velocity gradients, while the fourth shows relatively narrow single-peaked lines and no detectable velocity gradients, possibly indicating a nearly face-on geometry or intrinsically simple kinematics.