EDGE : predictable scatter in the stellar-mass–halo-mass relation of dwarf galaxies
(2026) In Monthly Notices of the Royal Astronomical Society 549(3).- 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... (More)
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.
(Less)
- author
- Kim, Stacy Y. ; Read, Justin I. ; Rey, Martin P. ; Orkney, Matthew D.A. ; Nigudkar, Sushanta ; Pontzen, Andrew ; Taylor, Ethan ; Agertz, Oscar LU and Das, Payel
- organization
- publishing date
- 2026-07
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- dark matter, galaxies: dwarf, galaxies: evolution, galaxies: haloes, galaxies: statistics, galaxies: stellar content
- in
- Monthly Notices of the Royal Astronomical Society
- volume
- 549
- issue
- 3
- article number
- stag825
- publisher
- Oxford University Press
- external identifiers
-
- scopus:105041371872
- ISSN
- 0035-8711
- DOI
- 10.1093/mnras/stag825
- language
- English
- LU publication?
- yes
- id
- b338b6aa-1b47-46a4-9d18-16e55d9ecbc9
- date added to LUP
- 2026-08-21 15:25:19
- date last changed
- 2026-08-21 15:26:22
@article{b338b6aa-1b47-46a4-9d18-16e55d9ecbc9,
abstract = {{<p>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<sup>–1</sup>, 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.</p>}},
author = {{Kim, Stacy Y. and Read, Justin I. and Rey, Martin P. and Orkney, Matthew D.A. and Nigudkar, Sushanta and Pontzen, Andrew and Taylor, Ethan and Agertz, Oscar and Das, Payel}},
issn = {{0035-8711}},
keywords = {{dark matter; galaxies: dwarf; galaxies: evolution; galaxies: haloes; galaxies: statistics; galaxies: stellar content}},
language = {{eng}},
number = {{3}},
publisher = {{Oxford University Press}},
series = {{Monthly Notices of the Royal Astronomical Society}},
title = {{EDGE : predictable scatter in the stellar-mass–halo-mass relation of dwarf galaxies}},
url = {{http://dx.doi.org/10.1093/mnras/stag825}},
doi = {{10.1093/mnras/stag825}},
volume = {{549}},
year = {{2026}},
}