James Webb Space Telescope Feed Post

JADES: Resolving the Stellar Component and Filamentary Overdense Environment of HST-Dark Submillimeter Galaxy HDF850.1 at z=5.18

HST F814W/F105W/F160W and Spitzer/IRAC Channel 1/2 (3.6/4.5 µm) images at the location of HDF850.1. Image sizes are 3 ''×3'' (north up, east left). HDF850.1 is not detected in HST images and blended with two foreground galaxies in IRAC images. Abstract: HDF850.1 is the brightest submillimeter galaxy (SMG) in the Hubble Deep Field. It is known as a heavily dust-obscured star-forming galaxy embedded in an overdense environment at z=5.18. With nine-band NIRCam images at 0.8-5.0 µm obtained through the JWST Advanced Deep Extragalactic Survey (JADES), we detect and resolve the rest-frame UV-optical counterpart of HDF850.1, which splits into two components because of heavy dust obscuration in the center. The southern component leaks UV and Ha photons, bringing the galaxy ~100 times above the empirical relation between infrared excess and UV continuum slope (IRX-ßUV). The northern component is higher in dust attenuation and thus fainter in UV and Ha surface brightness. We construct a spatially resolved dust attenuation map from the NIRCam images, well matched with the dust continuum emission obtained through millimeter interferometry. The whole system hosts a stellar mass of 1011.0±0.1M? and star-formation rate of 103.0±0.2M?yr-1, placing the galaxy at the massive end of the star-forming main sequence at this epoch. We further confirm that HDF850.1 resides in a complex overdense environment at z=5.17-5.30, which hosts another luminous SMG at z=5.30 (GN10). The filamentary structures of the overdensity are characterized by 109 Ha-emitting galaxies confirmed through NIRCam slitless spectroscopy at 3.9-5 µm, of which only eight were known before the JWST observations. Given the existence of a similar galaxy overdensity in the GOODS-S field, our results suggest that 50±20% of the cosmic star formation at z=5.1-5.5 occur in protocluster environments.