Spider-Webb: enhanced star formation in low-mass galaxies within the Spiderweb protocluster revealed by JWST Pa$β$ narrow-band imaging

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Main Authors: Daikuhara, Kazuki, Kodama, Tadayuki, Koyama, Yusei, Shimakawa, Rhythm, Dannerbauer, Helmut, Pérez-Martínez, Jose Manuel, Pérez-González, Pablo G., Kubo, Mariko, Ibar, Eduardo, Best, Philip N., Naufal, Abdurrahman, Zhang, Yuheng, Laishram, Ronaldo
Format: Preprint
Published: 2026
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author Daikuhara, Kazuki
Kodama, Tadayuki
Koyama, Yusei
Shimakawa, Rhythm
Dannerbauer, Helmut
Pérez-Martínez, Jose Manuel
Pérez-González, Pablo G.
Kubo, Mariko
Ibar, Eduardo
Best, Philip N.
Naufal, Abdurrahman
Zhang, Yuheng
Laishram, Ronaldo
author_facet Daikuhara, Kazuki
Kodama, Tadayuki
Koyama, Yusei
Shimakawa, Rhythm
Dannerbauer, Helmut
Pérez-Martínez, Jose Manuel
Pérez-González, Pablo G.
Kubo, Mariko
Ibar, Eduardo
Best, Philip N.
Naufal, Abdurrahman
Zhang, Yuheng
Laishram, Ronaldo
contents Understanding the role of the environment in galaxy evolution is key to revealing the physical processes that regulate galaxy growth. We study the star formation activity of \pab\ emitters (PBEs) in the Spiderweb protocluster at $z=2.16$ using \textit{James Webb Space Telescope}/NIRCam narrow-band imaging. To investigate the environmental dependence of star formation, we derive star formation rates (SFRs) from the \pab\ emission line and compare SFRs in the Spiderweb protocluster with those in the field. Our main finding is that low-mass PBEs ($M_\star < 10^9\,M_\odot$) in the Spiderweb protocluster exhibit an enhancement in star formation compared to their field counterparts. This excess persists even without applying dust-attenuation corrections, indicating that enhanced star formation in the protocluster is robust regardless of whether a dust correction is applied. In contrast, intermediate- and high-mass PBEs ($M_\star > 10^9\,M_\odot$) show no significant deviation from the field, revealing a strong mass dependence in the environmental effects on star formation. No clear spatial concentration toward the cluster core of starbursting low-mass galaxies within the protocluster is seen, suggesting that their enhancement is not restricted to the cluster core. We suggest that starbursts in low-mass galaxies are facilitated by environmental processes such as galaxy mergers/interactions, and/or efficient gas supply. While the enhancement at the low-mass end is consistent with trends reported for other protoclusters at similar redshifts, the behaviour of star formation at intermediate masses ($10^{9} < M_\star/M_\odot < 10^{10}$) is not uniform across protoclusters. Our \pab-based results in the Spiderweb protocluster indicate that star-formation enhancement at cosmic noon depends on both mass and the dynamical state of the protocluster.
format Preprint
id arxiv_https___arxiv_org_abs_2605_20590
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Spider-Webb: enhanced star formation in low-mass galaxies within the Spiderweb protocluster revealed by JWST Pa$β$ narrow-band imaging
Daikuhara, Kazuki
Kodama, Tadayuki
Koyama, Yusei
Shimakawa, Rhythm
Dannerbauer, Helmut
Pérez-Martínez, Jose Manuel
Pérez-González, Pablo G.
Kubo, Mariko
Ibar, Eduardo
Best, Philip N.
Naufal, Abdurrahman
Zhang, Yuheng
Laishram, Ronaldo
Astrophysics of Galaxies
Understanding the role of the environment in galaxy evolution is key to revealing the physical processes that regulate galaxy growth. We study the star formation activity of \pab\ emitters (PBEs) in the Spiderweb protocluster at $z=2.16$ using \textit{James Webb Space Telescope}/NIRCam narrow-band imaging. To investigate the environmental dependence of star formation, we derive star formation rates (SFRs) from the \pab\ emission line and compare SFRs in the Spiderweb protocluster with those in the field. Our main finding is that low-mass PBEs ($M_\star < 10^9\,M_\odot$) in the Spiderweb protocluster exhibit an enhancement in star formation compared to their field counterparts. This excess persists even without applying dust-attenuation corrections, indicating that enhanced star formation in the protocluster is robust regardless of whether a dust correction is applied. In contrast, intermediate- and high-mass PBEs ($M_\star > 10^9\,M_\odot$) show no significant deviation from the field, revealing a strong mass dependence in the environmental effects on star formation. No clear spatial concentration toward the cluster core of starbursting low-mass galaxies within the protocluster is seen, suggesting that their enhancement is not restricted to the cluster core. We suggest that starbursts in low-mass galaxies are facilitated by environmental processes such as galaxy mergers/interactions, and/or efficient gas supply. While the enhancement at the low-mass end is consistent with trends reported for other protoclusters at similar redshifts, the behaviour of star formation at intermediate masses ($10^{9} < M_\star/M_\odot < 10^{10}$) is not uniform across protoclusters. Our \pab-based results in the Spiderweb protocluster indicate that star-formation enhancement at cosmic noon depends on both mass and the dynamical state of the protocluster.
title Spider-Webb: enhanced star formation in low-mass galaxies within the Spiderweb protocluster revealed by JWST Pa$β$ narrow-band imaging
topic Astrophysics of Galaxies
url https://arxiv.org/abs/2605.20590