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

TL;DR

This study uses JWST NIRCam imaging to resolve the stellar components and environment of the heavily dust-obscured submillimeter galaxy HDF850.1 at z=5.18, revealing its complex structure and overdense environment with filamentary structures and numerous Hα emitters.

Contribution

First detailed resolution of HDF850.1's stellar components and environment at high redshift using JWST, highlighting its complex structure and overdense protocluster environment.

Findings

HDF850.1 splits into two components with different dust and UV properties.

The galaxy resides in a filamentary overdensity with 109 Hα emitters.

Approximately 50% of cosmic star formation at z=5.1-5.5 occurs in protoclusters.

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 $\mu$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$\alpha$ photons, bringing the galaxy $\sim$100 times above the empirical relation between infrared excess and UV continuum slope (IRX-$\beta_\mathrm{UV}$). The northern component is higher in dust attenuation and thus fainter in UV and H$\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 $10^{10.8\pm0.1}\,\mathrm{M}_\odot$ and star-formation rate of $10^{2.8\pm0.2}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$, 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$\alpha$-emitting galaxies confirmed through NIRCam slitless spectroscopy at 3.9-5 $\mu$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 $50\pm20$% of the cosmic star formation at $z=5.1-5.5$ occur in protocluster environments.