@article{21063,
  abstract     = {We report the detection of a 13σ Hα emission line from HDF850.1 at z = 5.188 ± 0.001 using the FRESCO (First Reionization Era SpectroscopicallyComplete Observations) NIRCam F444W grism observations. Detection of Hα in HDF850.1 is noteworthy, given its high far-infrared (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 [C II] from the Plateau de Bure Interferometer. Modelling the spectral energy distribution 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 Hα emission appears to arise entirely from the less-obscured southern component and shows a similar v∼ + 130 km s −1 velocity offset to that seen for [C II] relative to the source systemic redshift. Leveraging Hα-derived redshiftsfrom FRESCO observations, we find that HDF850.1 isforming in one of the richest environments identified to date at z > 5, with 100 z = 5.17–5.20 galaxies distributed across 13 smaller structures and a ∼(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 > 1014M cluster by z ∼ 0. 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 Hα 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.},
  author       = {Herard-Demanche, Thomas and Bouwens, Rychard J and Oesch, Pascal A and Naidu, Rohan P and Decarli, Roberto and Nelson, Erica J and Brammer, Gabriel and Weibel, Andrea and Xiao, Mengyuan and Stefanon, Mauro and Walter, Fabian and Matthee, Jorryt J and Meyer, Romain A and Wuyts, Stijn and Reddy, Naveen and Rowland, Lucie and van Leeuwen, Ivana and Haro, Pablo Arrabal and Dannerbauer, Helmut and Shapley, Alice E and Chisholm, John and van Dokkum, Pieter and Labbe, Ivo and Illingworth, Garth and Schaerer, Daniel and Shivaei, Irene},
  issn         = {1365-2966},
  journal      = {Monthly Notices of the Royal Astronomical Society},
  number       = {2},
  pages        = {788--808},
  publisher    = {Oxford University Press},
  title        = {{Mapping dusty galaxy growth at z > 5 with FRESCO: Detection of Hα in submm galaxy HDF850.1 and the surrounding overdense structures}},
  doi          = {10.1093/mnras/staf030},
  volume       = {537},
  year         = {2025},
}