James Webb Space Telescope Feed Post

A large population of strongly lensed faint submillimetre galaxies in future dark energy surveys inferred from JWST imaging

JWST MIRI F1800W imaging of the strong gravitational lens from PRIMER as 4.5 × 4.5 arcsec cutouts centred on the visible foreground lens. The lensed background source lies just to its upper right, clearly visible as an arc in the left image. ALMA imaging is presented as overlaid contours on the right image, depicting the lensed background source as a bright image and fainter counterimage, with no foreground lens visible. Abstract: Bright galaxies at sub-millimetre wavelengths from Herschel are now well known to be predominantly strongly gravitationally lensed. The same models that successfully predicted this strongly lensed population also predict about one percent of faint 450µm-selected galaxies from deep JCMT surveys will also be strongly lensed. Follow-up ALMA campaigns have so far found one potential lens candidate, but without clear compelling evidence e.g. from lensing arcs. Here we report the discovery of a compelling gravitational lens system confirming the lensing population predictions, with a zs=3.4±0.4 submm source lensed by a zspec=0.360 foreground galaxy within the COSMOS field, identified through public JWST imaging of a 450µm source in the SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES) catalogue. These systems will typically be well within the detectable range of future wide-field surveys such as Euclid and Roman, and since sub-millimetre galaxies are predominantly very red at optical/near-infrared wavelengths, they will tend to appear in near-infrared channels only. Extrapolating to the Euclid-Wide survey, we predict tens of thousands of strongly lensed near-infrared galaxies. This will be transformative for the study of dusty star-forming galaxies at cosmic noon, but will be a contaminant population in searches for strongly lensed ultra-high-redshift galaxies in Euclid and Roman.