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

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 $\hat{I}¼$m 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 H$\hat{I}\pm$ photons, bringing the galaxy $\sim$100 times above the empirical relation between infrared excess and UV continuum slope (IRX-${\hat{I}}_{\mathrm{UV}}^2$). The northern component is higher in dust attenuation and thus fainter in UV and H$\hat{I}\pm$ 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 $10^{10.8\pm 0.1}{\mathrm{M}}_{\odot }$ and star-formation rate of $10^{2.8\pm 0.2}{\mathrm{M}}_{\odot }{\mathrm{yr}}^{-1}$, 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 H$\hat{I}\pm$-emitting galaxies confirmed through NIRCam slitless spectroscopy at 3.9-5 $\hat{I}¼$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.

44 pages, 16 figures, 2 tables. Accepted for publication in ApJ