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

JWST/NIRCam cutout images. The last panel shows a false-color image produced using all NIRCam data. The southern component of HDF850.1 is detected in all nine NIRCam bands and the northern component is only detected with the LW filters (F277W–F444W). 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.