James Webb Space Telescope Feed Post

CANUCS: An Updated Mass and Magnification Model of Abell 370 with JWST

Examples of Gold, Silver, and Bronze systems shown in an RGB image made of F200W, F150W, and F115W filters. Top: System 6 is a Gold system - it has 3 images with well-determined redshifts and the colors and morphology of the images make it clear that they are the same galaxy. Middle: System 23 is a Silver system; there are 2 knots visible in some images but not the others and the colors of the images appear slightly different. The Ly-alpha emission that determines its redshift is much stronger in the first image than the other two. This may be a true system, but because of these factors, we are not confident enough to include it in the Gold category. Bottom: System 32 is a Bronze system; while these images all show Ly-alpha emission at the same redshift in the MUSE data, the images are very faint and the colours appear somewhat different. The third image (right) is an example of a Quartz image - there is no source seen here in the NIRCAM data. This system is included in the catalogue for completeness but is classified as Bronze because we cannot confidently verify that it is a true system. We report an updated mass and magnification model of galaxy cluster Abell 370 using new NIRCam and NIRISS data from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). Using Lenstool and a combination of archival HST and MUSE data with new JWST data as constraints, we derive an improved gravitational lensing model and extract magnifications of background galaxies with uncertainties. Using our best fit model, we perform a search for new multiply imaged systems via predicted positions. We report no new multiply imaged systems with identifiable redshifts, likely due to already very deep HST and Spitzer data, but confirm a z~8 multiply imaged system by measuring its redshift with NIRISS and NIRSpec spectra. We find that the overall shape of the critical curve for a source at z=9.0 is similar to previous models of Abell 370, with small changes. We investigate the z~8 galaxy with two images observable with an apparent magnitude in the F125W band of 26.0±0.2 and 25.6±0.1. After correcting for the magnifications of the images, 7.2+0.2-1.2 and 8.7+0.4-0.4, we use SED fitting to find an intrinsic stellar mass of log(M*/M?) = 7.35+0.04-0.05, intrinsic SFR of 3.5+2.2-1.4 M?/yr, and MUV of -21.3+0.2-0.2, which is close to the knee of the luminosity function at that redshift. Our model, and corresponding magnification, shear, and convergence maps are available on request and will be made publicly available on MAST in a CANUCS data release.