Has JWST Seen Everything? Hunting for "NIRCam-dark" Dusty Star-Forming Galaxies at $z \simeq 6 - 9$ with ALMA2040

Fengwu Sun; Belén Alcalde Pampliega; Hiddo Algera; Manuel Aravena; Tom Bakx; Karina I. Caputi; Pierre Cox; Elisabete da Cunha; Andreas Faisst; Yoshinobu Fudamoto; Carlotta Gruppioni; Mahmoud Hamed; Jacqueline Hodge; Patrick S. Kamieneski; Adarsh Kumar; Ivanna Langan; Andrea Lapi; Umberto Maio; Chiara Mazzucchelli; Dieu D. Nguyen; Mamta Pandey-Pommier; Dominik A. Riechers; Irene Shivaei; Sabine Thater

arXiv · 2610.20727

Has JWST Seen Everything? Hunting for "NIRCam-dark" Dusty Star-Forming Galaxies at $z \simeq 6 - 9$ with ALMA2040

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Abstract

JWST/NIRCam has recovered the stellar counterparts of many ALMA-detected, formerly HST-dark galaxies, yet ALMA has started identifying dusty star-forming galaxies (DSFGs) at $z>6$ that remain extremely faint or undetected even with NIRCam. These "NIRCam-dark" DSFGs may trace a missing rapid-growth phase connecting UV-luminous galaxies at $z>10$ to massive quiescent galaxies at $z\gtrsim4$. So far, the small, heterogeneously selected NIRCam-dark sample is insufficient to determine their abundance or role in the evolution of massive galaxies. We show that a blind 1.3-mm continuum survey with ALMA2040 can provide the first high-significance census of this elusive NIRCam-dark DSFG population across $z\simeq 6 - 9$. We conduct sensitivity and survey-speed calculations requiring a $10σ$ detection of a NIRCam-dark DSFG with a dust-obscured star-formation rate of $60\,M_\odot\,{\rm yr}^{-1}$ at $z = 8$. At a like-for-like 7.5-GHz normalization, ALMA2040 will reach the required 1.3-mm RMS of $21\,μ$Jy beam$^{-1}$ about 90 times faster than current ALMA. With 100 hr on-source, ALMA2040 can cover an area of $\sim0.5$ deg$^2$ and detect $\langle N \rangle\sim16$ NIRCam-dark DSFGs over $7.5 10$ and the rapid emergence of massive quiescent systems at $z\gtrsim 4$.

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Fengwu Sun, Belén Alcalde Pampliega, Hiddo Algera, Manuel Aravena, Tom Bakx, Karina I. Caputi, Pierre Cox, Elisabete da Cunha, Andreas Faisst, Yoshinobu Fudamoto, Carlotta Gruppioni, Mahmoud Hamed, Jacqueline Hodge, Patrick S. Kamieneski, Adarsh Kumar, Ivanna Langan, Andrea Lapi, Umberto Maio, Chiara Mazzucchelli, Dieu D. Nguyen, Mamta Pandey-Pommier, Dominik A. Riechers, Irene Shivaei, Sabine Thater. 2026-10-14. Has JWST Seen Everything? Hunting for "NIRCam-dark" Dusty Star-Forming Galaxies at $z \simeq 6 - 9$ with ALMA2040. https://arxiv.org/abs/2610.20727

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