Abstract
The stellar-mass–halo-mass (SMHM) relation is central to our understanding of galaxy formation and the nature of dark matter. However, its normalization, slope, and scatter are highly uncertain at dwarf galaxy scales. In this paper, we present DarkLight, a new semi-empirical dwarf galaxy formation model designed to robustly predict the SMHM relation for the smallest galaxies. DarkLight harnesses a correlation between the mean star formation rate (SFR) of dwarfs and their peak rotation speed – the (Formula presented) SFR(Formula presented) –(Formula presented) relation – that we derive from simulations and observations. Given the sparsity of data for isolated dwarfs with (Formula presented) km s–1, we fit the (Formula presented) SFR(Formula presented) –(Formula presented) relation to observational data for dwarfs above this velocity scale and to the high-resolution EDGE (Engineering Dwarfs at Galaxy formation’s Edge) cosmological simulations below. Reionization quenching is implemented via distinct (Formula presented) SFR(Formula presented) –(Formula presented) relations before and after reionization. We find that the scatter in the SMHM relation is small at reionization, (Formula presented) 0.2 dex, but rises to (Formula presented) 0.5 dex ((Formula presented) ) at a halo mass of (Formula presented) M(Formula presented) as star formation is quenched by reionization but dark matter halo masses continue to grow. While we do not find a significant break in the slope of the SMHM relation, one can be introduced if reionization occurs early ((Formula presented) ). Finally, we find that dwarfs can be star forming today down to a halo mass of (Formula presented) 2 (Formula presented) M(Formula presented). We predict that the lowest mass star-forming dwarf irregulars in the nearby universe are the tip of the iceberg of a much larger population of quiescent isolated dwarfs.
| Original language | English |
|---|---|
| Article number | stag825 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 549 |
| Issue number | 3 |
| Early online date | 30 Apr 2026 |
| DOIs | |
| Publication status | Published - 31 Jul 2026 |
Data Availability Statement
The data underlying this article will be shared on reasonable request to the corresponding author. The DarkLight code is publicly available at https://pypi.org/project/darklight-galaxies and https://github.com/stacykim/darklight.Funding
SYK thanks Annika Peter, Niusha Ahvazi, Andrew Benson, Ethan Nadler, Yao-Yuan Mao, and Marla Geha for helpful discussions that improved this manuscript. JIR would like to acknowledge support from Science and Technology Facilities Council (STFC) grants ST/Y002865/1 and ST/Y002857/1. MR is supported by the Beecroft Fellowship funded by Adrian Beecroft. MO acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 852839). ET acknowledges the UKRI Science and Technology Facilities Council (STFC) for support (grant ST/V50712X/1). OA acknowledges support from the Knut and Alice Wallenberg Foundation, the Swedish Research Council (grant 2019–04659), and the Swedish National Space Agency (SNSA Dnr 2023–00164). This work was performed using the DiRAC Data Intensive service at Leicester, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The authors acknowledge the use of the University of Surrey Eureka supercomputer.
Keywords
- dark matter
- galaxies: dwarf
- galaxies: evolution
- galaxies: haloes
- galaxies: statistics
- galaxies: stellar content
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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