Are JWST/NIRCam Color Gradients in the Lensed z = 2.3 Dusty Star-forming Galaxy El Anzuelo Due to Central Dust Attenuation or Inside-out Galaxy Growth?
Grogin, Norman A.; Koekemoer, Anton M.; Pirzkal, Nor; Frye, Brenda L.; Conselice, Christopher J.; Yan, Haojing; Cheng, Cheng; Yun, Min S.; Willmer, Christopher N. A.; Coe, Dan; Ryan, Russell E.; Driver, Simon P.; Robotham, Aaron S. G.; Windhorst, Rogier A.; Nonino, Mario; Cohen, Seth H.; Furtak, Lukas J.; Jansen, Rolf A.; Marshall, Madeline A.; Tompkins, Scott; Carleton, Timothy; Diego, Jose M.; Foo, Nicholas; Petric, Andreea; Pascale, Massimo; Harrington, Kevin C.; Kamieneski, Patrick S.; Summers, Jake S.
United States, China, Chile, Spain, Israel, United Kingdom, Australia, Canada, Italy
Abstract
Gradients in the mass-to-light ratio of distant galaxies impede our ability to characterize their size and compactness. The long-wavelength filters of JWST's NIRCam offer a significant step forward. For galaxies at Cosmic Noon (z ~ 2), this regime corresponds to the rest-frame near-infrared, which is less biased toward young stars and captures emission from the bulk of a galaxy's stellar population. We present an initial analysis of an extraordinary lensed dusty star-forming galaxy at z = 2.3 behind the El Gordo cluster (z = 0.87), named El Anzuelo ("The Fishhook") after its partial Einstein-ring morphology. The far-UV to near-IR spectral energy distribution suggests an intrinsic star formation rate of ${81}_{-2}^{+7}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ and dust attenuation A V ≈ 1.6, in line with other DSFGs on the star-forming main sequence. We develop a parametric lens model to reconstruct the source-plane structure of dust imaged by the Atacama Large Millimeter/submillimeter Array, far-UV to optical light from Hubble, and near-IR imaging with 8 filters of JWST/NIRCam, as part of the Prime Extragalactic Areas for Reionization and Lensing Science program. The source-plane half-light radius is remarkably consistent from ~1 to 4.5 μm, despite a clear color gradient where the inferred galaxy center is redder than the outskirts. We interpret this to be the result of both a radially decreasing gradient in attenuation and substantial spatial offsets between UV- and IR-emitting components. A spatial decomposition of the SED reveals modestly suppressed star formation in the inner kiloparsec, which suggests that we are witnessing the early stages of inside-out quenching.