JADES: Resolving the Stellar Component and Filamentary Overdense Environment of Hubble Space Telescope (HST)-dark Submillimeter Galaxy HDF850.1 at z = 5.18

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 $0.8-5.0\ \mu\mathrm{m}$ obtained through the JWST Advanced Deep Extragalactic Survey, 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 $\mathrm{H}\alpha$ photons, bringing the galaxy $\sim 100$ times above the empirical relation between infrared excess and UV continuum slope ($\mathrm{IRX}-\beta_{\mathrm{UV}}$ ). The northern component is higher in dust attenuation and thus fainter in UV and $\mathrm{H}\alpha$ 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 $10^{10.8 \pm 0.1}\ M_{\odot}$ and star formation rate (SFR) of $10^{2.8 \pm 0.2}\ M_{\odot}/\mathrm{yr}$ , 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 $109$ $\mathrm{H}\alpha$ -emitting galaxies confirmed through NIRCam slitless spectroscopy at $3.9-5.0\ \mu\mathrm{m}$ , 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 $50\% \pm 20\%$ of the cosmic star formation at $z = 5.1-5.5$ occur in protocluster environments.

The Astrophysical Journal, Volume 961, Issue 1, id.69, 24 pages