EROSE: An algorithm searching for resolved Local Group satellites
- 1Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
- 2Kapteyn Astronomical Institute, University of Groningen
- 3Max-Planck-Institut für Astronomie
Abstract
Systematic searches for ultra-faint Milky Way satellite galaxies essentially consist of local density estimators coupled with colour–magnitude cuts following stellar isochrone tracks. These selections are typically performed in 2D colour–magnitude spaces and have rarely, if ever, been extended to higher-dimensional spaces. Moreover, these studies typically only consider g -, r -, and i -band photometry, disregarding the use of the shallower but metal-sensitive u band. Entering a new era of wide-field surveys, we focused our study on LSST, which will provide exceptional depth and uniform coverage in all ugri bands. We conducted our analysis using simulated data from the LSST Data Challenge 2 (DC2), which covers a 300deg ² high-galactic-latitude region of the sky and reaches the expected survey depth after five years of observations. After generating and injecting simulated dwarf galaxies of various properties into the DC2 footprint, we attempted to retrieve them using EROSE , a new fast multi-band searching algorithm designed for easy use in any survey and any combination of input photometric bands. Exploring different combinations of photometric bands, we find that a multi-colour-magnitude space combining all three gri photometric bands slightly outperforms, on average, the more commonly used colour–magnitude spaces combining only gr or ri . However, the highest recovery fraction is achieved using a colour–magnitude space combining the u and g bands, recovering on average 64.1 −6.0 +6.3 % of the injected satellites, a value slightly higher than that obtained when combining gri . This improvement is particularly evident for the most extended systems, for which the additional colour information provided by the u band improves our ability to isolate metal-poor member stars from contaminating foreground populations. We estimate that the LSST will discover ∼50 new Milky Way dwarf galaxies, more than doubling the currently known number of satellites within its footprint. Combining the LSST photometric bands with a space-based star–galaxy separation could further improve these results, enabling discoveries of satellites populating the low-mass end of the Milky Way’s satellite galaxy luminosity function and providing valuable constraints on dark matter models.
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BibTeX
@article{rusterucci2026erose,
title = {{EROSE: An algorithm searching for resolved Local Group satellites}},
author = {Samuel Rusterucci and Nicolas F. Martin and Else Starkenburg},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202660053},
url = {https://www.aanda.org/10.1051/0004-6361/202660053},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - EROSE: An algorithm searching for resolved Local Group satellites
AU - Samuel Rusterucci
AU - Nicolas F. Martin
AU - Else Starkenburg
PY - 2026
DA - 2026/10/16
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202660053
UR - https://www.aanda.org/10.1051/0004-6361/202660053
AB - Systematic searches for ultra-faint Milky Way satellite galaxies essentially consist of local density estimators coupled with colour–magnitude cuts following stellar isochrone tracks. These selections are typically performed in 2D colour–magnitude spaces and have rarely, if ever, been extended to higher-dimensional spaces. Moreover, these studies typically only consider g -, r -, and i -band photometry, disregarding the use of the shallower but metal-sensitive u band. Entering a new era of wide-field surveys, we focused our study on LSST, which will provide exceptional depth and uniform coverage in all ugri bands. We conducted our analysis using simulated data from the LSST Data Challenge 2 (DC2), which covers a 300deg ² high-galactic-latitude region of the sky and reaches the expected survey depth after five years of observations. After generating and injecting simulated dwarf galaxies of various properties into the DC2 footprint, we attempted to retrieve them using EROSE , a new fast multi-band searching algorithm designed for easy use in any survey and any combination of input photometric bands. Exploring different combinations of photometric bands, we find that a multi-colour-magnitude space combining all three gri photometric bands slightly outperforms, on average, the more commonly used colour–magnitude spaces combining only gr or ri . However, the highest recovery fraction is achieved using a colour–magnitude space combining the u and g bands, recovering on average 64.1 −6.0 +6.3 % of the injected satellites, a value slightly higher than that obtained when combining gri . This improvement is particularly evident for the most extended systems, for which the additional colour information provided by the u band improves our ability to isolate metal-poor member stars from contaminating foreground populations. We estimate that the LSST will discover ∼50 new Milky Way dwarf galaxies, more than doubling the currently known number of satellites within its footprint. Combining the LSST photometric bands with a space-based star–galaxy separation could further improve these results, enabling discoveries of satellites populating the low-mass end of the Milky Way’s satellite galaxy luminosity function and providing valuable constraints on dark matter models.
SN - 0004-6361
SN - 1432-0746
ER -