Mapping dusty galaxy growth at $z>5$ with FRESCO: Detection of H$α$ in submm galaxy HDF850.1 and the surrounding overdense structures

• DOI: 10.48550/arxiv.2309.04525
• Publication Date: 2023-01-01
• Authors: Herard-Demanche, ...; Bouwens, Rychard J.; Oesch, Pascal A.; Naidu, Rohan P.; Decarli, Roberto; Nelson, Erica J.; Brammer, Gabriel; Weibel, Andrea; Xiao, Mengyuan; Stefanon, Mauro; Walter, Fabian; Matthee, Jorryt; Meyer, Romain A.; Wuyts, Stijn; Reddy, Naveen; Haro, Pablo Arrabal; Dannerbauer, Helmut; Shapley, Alice E.; Chisholm, John; van Dokkum, Pieter; Labbe, Ivo; Illingworth, Garth; Schaerer, Daniel; Shivaei, Irene
• Keywords: Astrophysics of Galaxies (astro-ph.GA); FOS: Physical sciences

Submitted to MNRAS. 20 pages, 10 figures and 8 tables (including appendices)<br/>We report the detection of a 13$σ$ H$α$ emission line from HDF850.1 at $z=5.188\pm0.001$ using the FRESCO NIRCam F444W grism observations. Detection of H$α$ in HDF850.1 is noteworthy, given its high far-IR luminosity, substantial dust obscuration, and the historical challenges in deriving its redshift. HDF850.1 shows a clear detection in the F444W imaging data, distributed between a northern and southern component, mirroring that seen in [CII] from the Plateau de Bure Interferometer. Modeling the SED of each component separately, we find that the northern component has a higher mass, star formation rate (SFR), and dust extinction than the southern component. The observed H$α$ emission appears to arise entirely from the less-obscured southern component and shows a similar $Δ$v$\sim$+130 km/s velocity offset to that seen for [CII] relative to the source systemic redshift. Leveraging H$α$-derived redshifts from FRESCO observations, we find that HDF850.1 is forming in one of the richest environments identified to date at $z>5$, with 100 $z=5.17-5.20$ galaxies distributed across 10 structures and a $\sim$(15 cMpc)$^3$ volume. Based on the evolution of analogous structures in cosmological simulations, the $z=5.17-5.20$ structures seem likely to collapse into a single $>$10$^{14}$ $M_{\odot}$ cluster by $z\sim0$. Comparing galaxy properties forming within this overdensity with those outside, we find the masses, SFRs, and $UV$ luminosities inside the overdensity to be clearly higher. The prominence of H$α$ line emission from HDF850.1 and other known highly-obscured $z>5$ galaxies illustrates the potential of NIRCam-grism programs to map both the early build-up of IR-luminous galaxies and overdense structures.<br/>