The HST-Hyperion Survey: Environmental Imprints on the Stellar-Mass Function at z~2.5
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| Format: | Preprint |
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2025
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| author | Sikorski, Derek Forrest, Ben Lemaux, Brian C. Shen, Lu Giddings, Finn Gal, Roy Cucciati, Olga Golden-Marx, Emmet Hu, Weida Hung, Denise Lubin, Lori Ronayne, Kaila Shah, Ekta Bardelli, Sandro Baxter, Devontae C. Gururajan, Gayathri Tresse, Laurence Zamorani, Giovanni Diamond, Joel Guaita, Lucia Hathi, Nimish Zucca, Elena |
| author_facet | Sikorski, Derek Forrest, Ben Lemaux, Brian C. Shen, Lu Giddings, Finn Gal, Roy Cucciati, Olga Golden-Marx, Emmet Hu, Weida Hung, Denise Lubin, Lori Ronayne, Kaila Shah, Ekta Bardelli, Sandro Baxter, Devontae C. Gururajan, Gayathri Tresse, Laurence Zamorani, Giovanni Diamond, Joel Guaita, Lucia Hathi, Nimish Zucca, Elena |
| contents | Not all galaxies at Cosmic Noon evolve in the same way. It remains unclear how the local environment -- especially the extreme overdensities of protoclusters -- affects stellar mass assembly at high redshift. The stellar mass function (SMF) encodes these processes; comparing SMFs across environments reveals differences in evolutionary history. We present the SMF of the Hyperion proto-supercluster at $z\sim2.5$, one of the largest and most massive protostructures known. This dataset provides the most statistically robust SMF of a single protostructure at $z>2$. By comparing the SMF of overdense peaks within Hyperion to the coeval field, we ask: how early, and how strongly, does a dense environment favor massive galaxies? Using COSMOS2020 photometry with ground-based and new HST grism spectroscopy, we construct a 3D overdensity map that assigns galaxies to peaks, outskirts, or the field. We perform 100 Monte Carlo realizations to propagate redshift and mass uncertainties, and derive SMFs normalized to the field. The peaks show a clear excess of massive galaxies: number densities at $\log(M_*/M_\odot)\sim 11$ are ~10x higher than the field, while those at $\log(M_*/M_\odot)\sim 9.5$ are enhanced by only ~3.5x. By contrast, the outskirts and Hyperion as a whole mirror the field. Environmental effects on stellar mass growth are thus evident by $z\sim 2.5$. The densest regions already host galaxies with accelerated growth, while the global SMF masks this signal. Protostructures therefore begin shaping the high-mass end of the SMF well before cluster quenching, and may drive the elevated star formation at Cosmic Noon. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_02714 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The HST-Hyperion Survey: Environmental Imprints on the Stellar-Mass Function at z~2.5 Sikorski, Derek Forrest, Ben Lemaux, Brian C. Shen, Lu Giddings, Finn Gal, Roy Cucciati, Olga Golden-Marx, Emmet Hu, Weida Hung, Denise Lubin, Lori Ronayne, Kaila Shah, Ekta Bardelli, Sandro Baxter, Devontae C. Gururajan, Gayathri Tresse, Laurence Zamorani, Giovanni Diamond, Joel Guaita, Lucia Hathi, Nimish Zucca, Elena Astrophysics of Galaxies Not all galaxies at Cosmic Noon evolve in the same way. It remains unclear how the local environment -- especially the extreme overdensities of protoclusters -- affects stellar mass assembly at high redshift. The stellar mass function (SMF) encodes these processes; comparing SMFs across environments reveals differences in evolutionary history. We present the SMF of the Hyperion proto-supercluster at $z\sim2.5$, one of the largest and most massive protostructures known. This dataset provides the most statistically robust SMF of a single protostructure at $z>2$. By comparing the SMF of overdense peaks within Hyperion to the coeval field, we ask: how early, and how strongly, does a dense environment favor massive galaxies? Using COSMOS2020 photometry with ground-based and new HST grism spectroscopy, we construct a 3D overdensity map that assigns galaxies to peaks, outskirts, or the field. We perform 100 Monte Carlo realizations to propagate redshift and mass uncertainties, and derive SMFs normalized to the field. The peaks show a clear excess of massive galaxies: number densities at $\log(M_*/M_\odot)\sim 11$ are ~10x higher than the field, while those at $\log(M_*/M_\odot)\sim 9.5$ are enhanced by only ~3.5x. By contrast, the outskirts and Hyperion as a whole mirror the field. Environmental effects on stellar mass growth are thus evident by $z\sim 2.5$. The densest regions already host galaxies with accelerated growth, while the global SMF masks this signal. Protostructures therefore begin shaping the high-mass end of the SMF well before cluster quenching, and may drive the elevated star formation at Cosmic Noon. |
| title | The HST-Hyperion Survey: Environmental Imprints on the Stellar-Mass Function at z~2.5 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.02714 |