A Gravitational Lens Survey with the Planck Surveyor

The Planck Surveyor cosmic microwave background (CMB) imaging mission will make very sensitive maps of the whole sky at microwave, millimetre (mm) and sub-mm wavelengths. The steep source counts expected in the highest frequency Planck bands are likely to be associated with a strong magnification bias, and so the fraction of galaxies magnified by a factor of two or more could be greater than 10%. In this paper, previous predictions of the significance of the Planck survey for studies of lensing statistics are updated, to reflect our expanded knowledge of the properties of high-redshift dusty galaxies, obtained from far-infrared and sub-mm surveys. A catalogue of probably about 10 galaxies, but perhaps as many as 10 or as few as 10, is expected to be generated from the final Planck all-sky maps. Of order 1000 galaxies, a better determined number, might reasonably be expected to be strongly lensed. Coordinated sub-mm and far-infrared follow-up observations made using the SPIRE and PACS instruments aboard the ESA cornerstone mission FIRST – Planck’s travelling companion to its L2 orbit – and the ground-based ALMA interferometer array will provide accurate positions and very valuable information about the spectral energy distributions (SEDs), redshifts and astrophysical properties of the galaxies in the Planck catalogue. ALMA and radio images will also reveal their morphology, and the characteristic arc and multiple image structures produced by gravitational lensing. Studies of these bright sub-mm-selected galaxies will allow new insight into the process of galaxy formation and evolution.