James Webb Space Telescope Feed Post

Hidden giants in JWST's PEARLS: An ultra-massive z = 4.26 sub-millimeter galaxy that is invisible to HST

6"x 6" thumbnails of 850.1 and 850.2. From left to right the panels show the HST ACS F435W, F606W, and F814W imaging and JWST NIRCam F090W, F150W, F200W, F277W, F356W, and F444W images. The striking red colors of 850.1 are clear as the bulk of the emission from the galaxy, apart from the knots B1 and B2 (the former of which we suggest is foreground), is undetectable shortward of 2 um (the F200W band). In contrast the bright central regions of 850.2 are detectable down to F606W (corresponding to ~ 1100 A in the restframe at z = 4.26), but are undetected in F435W (restframe ~ 830 A) showing the presence of a strong Lyman break. Fitted ellipses at three isophotelevels are overlaid on the F356W image of 850.1, illustrating the "bar"-like feature seen in the central regions of the galaxy. At z = 4.26 the 912~ A Lyman break falls at the extreme red end of the F435W filter transmission, while the Lyalpha emission line falls in F606W, Halpha in F356W (strong emission from which likely explains the point-like feature C1 in 850.2, which probably corresponds to a giant [HII] region with an intrinsic size of ~ 50–100 pc), and the nebular emission lines [OIII] 4959/5007 are in F277W and [OII] 3727 lies in F200W. The various sources and features discussed in the text are identified on the F090W thumbnails.