The HST-Hyperion Survey: X-ray AGN Enhancement in the Hyperion Proto-supercluster
Abstract
Dense environments can influence both galaxy evolution and supermassive black hole growth, but whether they enhance or suppress (or both) active galactic nuclei (AGN) activity at high redshift (z≳2) remains uncertain. As one of the most massive structures identified in the early universe, the Hyperion proto-supercluster at z≈2.5 provides a unique opportunity to investigate this connection during an epoch near the peak of both cosmic star formation rate and AGN activity density. To examine the impact of galaxy environment on AGN activity, we measure the fraction of X-ray-selected AGN in Hyperion as a whole, its highly overdense peaks, and its outskirts, comparing these measurements to a coeval field sample. We identify X-ray AGN using the deep Chandra COSMOS-Legacy Survey and combine optical/near-infrared (NIR) photometry and photometric redshift information from COSMOS2020 with extensive ground-based spectroscopy and HST-grism observations. Redshift information is incorporated statistically using a Monte Carlo framework. We find a higher X-ray AGN fraction in Hyperion (7.4+3.2−1.8%) than in the coeval field (3.2+0.6−0.5%), corresponding to a ∼2.3σ difference. Strikingly, this enhancement is concentrated in the overdense peaks, where the X-ray AGN fraction reaches 12.3+5.5−3.4% (15.0+6.9−4.4% in the most massive peaks versus 6.2+11.9−2.1% in the less massive peaks), while the lower-density Hyperion outskirts (2.1+3.6−1.1%) show no evidence of enhancement relative to the field. These results add to the limited but growing evidence for enhanced AGN activity in high-redshift protostructures, suggesting that the dense environments at these epochs may preferentially trigger AGN during the early stages of cluster assembly.
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BibTeX
@misc{coburn2026hsthyperion,
title = {{The HST-Hyperion Survey: X-ray AGN Enhancement in the Hyperion Proto-supercluster}},
author = {Ashlen Coburn and Finn Giddings and Derek Sikorski and Roy Gal and Brian C. Lemaux and Ben Forrest and Emmet Golden-Marx and Lu Shen and Devontae C. Baxter and Olga Cucciati and Joel Diamond and Denise Hung and Lori Lubin and Ekta Shah and Sandro Bardelli and Monica Natalia Isla Llave and Hyewon Suh and Laurence Tresse and Fabio Vito and Giovanni Zamorani and Elena Zucca},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07047},
eprint = {2611.07047},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07047},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The HST-Hyperion Survey: X-ray AGN Enhancement in the Hyperion Proto-supercluster
AU - Ashlen Coburn
AU - Finn Giddings
AU - Derek Sikorski
AU - Roy Gal
AU - Brian C. Lemaux
AU - Ben Forrest
AU - Emmet Golden-Marx
AU - Lu Shen
AU - Devontae C. Baxter
AU - Olga Cucciati
AU - Joel Diamond
AU - Denise Hung
AU - Lori Lubin
AU - Ekta Shah
AU - Sandro Bardelli
AU - Monica Natalia Isla Llave
AU - Hyewon Suh
AU - Laurence Tresse
AU - Fabio Vito
AU - Giovanni Zamorani
AU - Elena Zucca
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.07047
UR - https://arxiv.org/abs/2611.07047
AB - Dense environments can influence both galaxy evolution and supermassive black hole growth, but whether they enhance or suppress (or both) active galactic nuclei (AGN) activity at high redshift (z≳2) remains uncertain. As one of the most massive structures identified in the early universe, the Hyperion proto-supercluster at z≈2.5 provides a unique opportunity to investigate this connection during an epoch near the peak of both cosmic star formation rate and AGN activity density. To examine the impact of galaxy environment on AGN activity, we measure the fraction of X-ray-selected AGN in Hyperion as a whole, its highly overdense peaks, and its outskirts, comparing these measurements to a coeval field sample. We identify X-ray AGN using the deep Chandra COSMOS-Legacy Survey and combine optical/near-infrared (NIR) photometry and photometric redshift information from COSMOS2020 with extensive ground-based spectroscopy and HST-grism observations. Redshift information is incorporated statistically using a Monte Carlo framework. We find a higher X-ray AGN fraction in Hyperion (7.4^+3.2_−1.8%) than in the coeval field (3.2^+0.6_−0.5%), corresponding to a ∼2.3σ difference. Strikingly, this enhancement is concentrated in the overdense peaks, where the X-ray AGN fraction reaches 12.3^+5.5_−3.4% (15.0^+6.9_−4.4% in the most massive peaks versus 6.2^+11.9_−2.1% in the less massive peaks), while the lower-density Hyperion outskirts (2.1^+3.6_−1.1%) show no evidence of enhancement relative to the field. These results add to the limited but growing evidence for enhanced AGN activity in high-redshift protostructures, suggesting that the dense environments at these epochs may preferentially trigger AGN during the early stages of cluster assembly.
ER -