James Webb Space Telescope Feed Post

Hidden Giants in JWST's PEARLS: An Ultramassive z = 4.26 Submillimeter Galaxy that Is Invisible to HST

Three-color images of 9' × 9' regions around (a) 850.1 and (b) 850.2 constructed from JWST NIRCam imaging, with F090W+F150W as blue, F200W+F277W as green, and F356W+F444W as red. Panels (c) and (e) show $5^{\prime\prime} \times $ 5' regions using F277W, F356W, and F444W as blue, green, and red and the same filter combination is used in panels (d) and (f), which show views of 850.1 and 850.2 "de-sheared" to correct for the lensing magnification (the scale bar indicates 1 kpc). Panels (a) and (b) also show the SMA 880 µm contours (starting from 2s in 7s increments), these unambiguously identify the two submillimeter sources. Note that 850.1 corresponds to an extremely red, highly structured source lying close to a bright, foreground disk galaxy with several fainter sources in close proximity. In contrast, 850.2 is more isolated and appears to be a bluer, disk-like system. The various sources and features discussed in the text are identified on each panel: distinct sources have labels starting with "A," "B" for potential subcomponents, and "C" for likely emission-line features. The colors and photometric redshifts suggest that "knot" B1 near 850.1 is likely to lie at z < 4.26, while B2 is probably a close/interacting companion seen in projection to 850.1 or a less-obscured component within the galaxy. The photometric-redshift analysis also suggests that A1, A4, and A5 are likely to be cluster members at z ~ 0.35, while A2 and A3 are probably behind the cluster, but foreground to 850.1 and 850.2. Abstract: We present a multiwavelength analysis using the Submillimeter Array (SMA), James Clerk Maxwell Telescope, NOEA, JWST, the Hubble Space Telescope (HST), and the Spitzer Space Telescope of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A 1489. These SMA-located sources both lie at z = 4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at ? 2 µm, even with deep JWST/NIRCam observations. We investigate their stellar, interstellar medium, and dynamical properties, including a pixel-level spectral energy distribution analysis to derive subkiloparsec-resolution stellar-mass and AV maps. We find that 850.1 is one of the most massive and highly obscured, AV ~ 5, galaxies known at z > 4 with M* ~1011.8M? (likely forming at z > 6), and 850.2 is one of the least massive and least obscured, AV ~ 1, members of the z > 4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z ? 3–4 based on imaging at ? 2 µm, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar-mass distribution, ${R}_{{\rm{e}}}^{\mathrm{mass}}$ ~1 kpc, but its expected evolution means that it matches both the properties of massive, quiescent galaxies at z ~ 1.5 and ultramassive early-type galaxies at z ~ 0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature that we link to the active dynamical environment it resides within.