Igniting Galaxy Formation in the Postreionization Universe
Creators
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1.
Pomona College
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2.
Carnegie Observatories
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3.
California State Polytechnic University
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4.
California Institute of Technology
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California State University, Long Beach
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6.
The University of Texas at Austin
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7.
Yale University
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8.
University of Zurich
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9.
University of California, Berkeley
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10.
University of Southern California
Abstract
It is widely believed that the ultraviolet background produced during the epoch of reionization conspires against the formation of low-mass galaxies. Indeed, this mechanism is often invoked as part of the solution to the so-called "missing satellites problem." In this paper we employ FIREbox , a large-volume cosmological simulation based on the Feedback In Realistic Environments physics model, to characterize the mechanisms governing galaxy ignition in the postreionization era. By carefully matching recently ignited halos (with stellar ages below 100 Myr at the time of selection) to halos that failed to form any stars, we conclude that the presence of cold dense gas and halo concentration helps incite the process of galaxy formation. Concretely, we find that 100% of recently ignited halos experience cold dense gas enhancements relative to their matched failed counterparts. Likewise, approximately 83% display enhancements in both cold dense gas and Navarro–Frenk–White concentration ( c NFW ), while the remaining ∼17% exhibit enhanced cold dense gas content and suppressed c NFW values. Lastly, our simulation suggests that galaxy ignition can occur as late as z = 2, potentially allowing us to observationally catch this process "in the act" in the foreseeable future.
Copyright and License
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
J.M. dedicates this paper to his beloved late father, Juan Moreno Pérez (RIP), on his journey to the stars. J.M. is funded by a Pomona College Large Research Grant and thanks the Carnegie Observatories for their hospitality. C.W. acknowledges the CPP Provost’s Teacher-Scholar Program. F.J.M. is funded by the National Science Foundation (NSF) Math and Physical Sciences (MPS) Award AST-2316748. M.K.R.W. acknowledges support from NSF MPS Ascending Faculty Catalyst Award AST-2444751. J.S. and M.B.K. acknowledge support for program JWST-AR-06278 by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. E.C. and R.F. acknowledge financial support from the Swiss National Science Foundation (grant No. 200021-188552). M.B.K. also acknowledges support from NSF grants AST-1910346, AST-2108962, and AST-2408247; NASA grant 80NSSC22K0827; HST-GO-16686, HST-AR-17028, HST-AR-17043, and JWST-GO-03788 from STScI; and from the Samuel T. and Fern Yanagisawa Regents Professorship in Astronomy at UT Austin. A.W. received support from NSF, via CAREER award AST-2045928 and grant AST-2107772. Support for P.F.H. was provided by a Simons Investigator Award. The authors wish to thank Alejandro Benítez-Llambay, Martin Rey, and Ethan Nadler for thoughtful suggestions on an earlier draft, and the anonymous reviewer for their insightful comments. The authors also acknowledge the labor by the cleaning and the clerical staff, the food service workers, the technical support personnel, and many others that make the astronomy research enterprise possible. This work was conducted on Tongva–Gabrielino land.
Contributions
J.M. wrote the entire manuscript and led every aspect of the project. C.W., F.J.M., and M.K.R.W. made significant contributions to the original design of the paper. M.K.R.W. also provided unique observational insight. J.S. and P.J.G. provided special support regarding connections to the early Universe, while E.C. and R.F. created the simulations and A.H.F. catalogs. M.B.K., A.W., J.B.S., and P.F.H. provided additional support on the big-picture context of the project and the creation of our physics model. All authors contributed substantially to the final polishing of this manuscript.
Software References
yt (M. J. Turk et al. 2011), Amiga Halo Finder (S. R. Knollmann & A. Knebe 2009).
Files
Moreno_2026_ApJ_997_181.pdf
Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2511.03785 (arXiv)
Funding
- National Science Foundation
- 2316748
- National Science Foundation
- 2444751
- National Aeronautics and Space Administration
- JWST-AR-06278
- National Aeronautics and Space Administration
- 5-03127
- Swiss National Science Foundation
- 20021-188552
- National Science Foundation
- 1910346
- National Science Foundation
- 2108962
- National Science Foundation
- 2408247
- National Aeronautics and Space Administration
- 80NSSC22K0827
- National Aeronautics and Space Administration
- 16686
- National Aeronautics and Space Administration
- 17028
- National Aeronautics and Space Administration
- 17043
- National Aeronautics and Space Administration
- 03788
- National Science Foundation
- 2045928
- National Science Foundation
- 2107772
- Simons Foundation
Dates
- Submitted
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2025-11-06
- Accepted
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2025-12-05
- Available
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2026-01-22Published
Caltech Custom Metadata
- Caltech groups
- Astronomy Department , TAPIR , Walter Burke Institute for Theoretical Physics , Division of Physics, Mathematics and Astronomy (PMA) , Physics Department
- Publication Status
- Published