A search for candidate strongly-lensed dusty galaxies in the Planck satellite catalogues

Abstract

The shallow, all-sky Planck surveys at sub-millimeter wavelengths have detected the brightest strongly gravitationally lensed dusty galaxies in the sky. The combination of their extreme gravitational flux boosting and image stretching offers the unique possibility of measuring in extraordinary detail, via high-resolution imaging and spectroscopic follow-up, the galaxy structure and kinematics in early evolutionary phases, thus gaining otherwise unaccessible direct information on physical processes in action. However the extraction of candidate strongly lensed galaxies from Planck catalogues is hindered by the fact that they are generally detected with poor signal-to-noise ratio, except for the few brightest ones. Thus their photometric properties are strongly blurred so that they are very difficult to single out. We have devised a method capable of increasing by a factor of about three to four the number of identified Planck-detected strongly lensed galaxies, although with an unavoidably limited efficiency. Our approach exploits the fact that strongly lensed galaxies have sub-millimeter colours definitely colder than nearby dusty galaxies that constitute the overwhelming majority of extragalactic sources detected by Planck. The sub-mm colours of the 47 confirmed or very likely Planck-detected strongly lensed galaxies have been used to estimate the colour range spanned by objects of this kind. Moreover, most nearby galaxies and radio sources can be picked up by cross-matching with the IRAS and PCNT catalogues, respectively. We present samples of lensed candidates selected at 545, 857 and 353 GHz, comprising 177, 97 and 104 sources, respectively. The efficiency of our approach, tested exploiting data from the SPT survey covering 2, 500 deg 2 , is estimated to be in the range 30%-40%. We also discuss stricter selection criteria increasing the estimated efficiency to 50% at the cost of a somewhat lower completeness. Our analysis of SPT data has identified a dozen of galaxies that can be reliably considered previously unrecognized Planck-detected strongly lensed galaxies. Extrapolating the number of Planck-detected confirmed or very likely strongly lensed galaxies found within the SPT and H-ATLAS survey areas, we expect from 150 to 190 such sources over the full |b| > 20 • sky.

Detecting gravitational lenses using machine learning: exploring interpretability and sensitivity to rare lensing configurations

“…∼ 10 strong lenses per deg 2 with 𝑆 500 ≥ 10 mJy (e.g. Trombetti et al 2021). This implies ∼ 150 000 strong submm-wave lenses over the entire Euclid survey area, comparable to the total expected to be found with the Euclid VIS instrument (e.g.…”

PASSAGES: The Large Millimeter Telescope and ALMA Observations of Extremely Luminous High Redshift Galaxies Identified by the Planck

“…They are included in the entire Planck-WISE sample used to characterise the properties of the Planck-selected DSFG population as a whole later in § 5. While this paper is undergoing a referee review, Trombetti et al (2021) posted on the arXiv.org preprint server a paper reporting a search for candidate strongly lensed dusty galaxies in the Planck catalogues using a similar SED analysis method utilising more recent Planck photometry products, trained using a sample of known Planck selected DSFGs including most of the sources reported here. Their follow-up confirmation work has started, and a future comparison of the two methods should prove interesting.…”