Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies near M101
- 1The Dalton School
Abstract
I report the discovery of three faint, semiresolved, quiescent candidate dwarf galaxies, which are potential backsplash galaxies associated with the nearby spiral M101 ( D ∼ 6.7 Mpc). The galaxies are cataloged as Shapiro DG-I/MAGE1412+5650, Shapiro DG-II, and Shapiro DG-III. Sha DG-I is concurrently discovered in ID-MAGE. The backsplash candidates lie in a magnitude range M V ∼ −7.3 to −8.1, and half-light radii r h ∼ 110−140 pc. Hydrodynamical simulations suggest a population of backsplash galaxies that have been environmentally stripped by interactions with a host and ejected from the system, though they have not yet been definitively observed in the local Universe. Initial distance estimates are determined using surface-brightness fluctuations in Sérsic model-subtracted CFHTLS and Hyper Suprime-Cam archival images. The galaxies are not detected in the Galaxy Evolution Explorer, or H α for Sha DG-I/MAGE1412+5650, providing upper limits on their star formation rate history. The provisional distances and quiescences of the dwarf candidates are consistent with a potential backsplash nature, though Hubble Space Telescope/JWST follow-up are necessary for stronger constraints, and to probabilistically distinguish from cosmic web stripping. Sha DG-II is alternatively a possible satellite of NGC 5585. Abundance models of satellites based on halo masses, which can be extended to model backsplash galaxies, will enable important consistency tests of ΛCDM with upcoming surveys, e.g., LSST. This is briefly explored in the context of the M101 group.
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BibTeX
@article{shapiro2026discovery,
title = {{Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies near M101}},
author = {Julian Shapiro},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/ae99cb},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae99cb},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies near M101
AU - Julian Shapiro
PY - 2026
DA - 2026/10/06
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae99cb
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae99cb
AB - I report the discovery of three faint, semiresolved, quiescent candidate dwarf galaxies, which are potential backsplash galaxies associated with the nearby spiral M101 ( D ∼ 6.7 Mpc). The galaxies are cataloged as Shapiro DG-I/MAGE1412+5650, Shapiro DG-II, and Shapiro DG-III. Sha DG-I is concurrently discovered in ID-MAGE. The backsplash candidates lie in a magnitude range M V ∼ −7.3 to −8.1, and half-light radii r h ∼ 110−140 pc. Hydrodynamical simulations suggest a population of backsplash galaxies that have been environmentally stripped by interactions with a host and ejected from the system, though they have not yet been definitively observed in the local Universe. Initial distance estimates are determined using surface-brightness fluctuations in Sérsic model-subtracted CFHTLS and Hyper Suprime-Cam archival images. The galaxies are not detected in the Galaxy Evolution Explorer, or H α for Sha DG-I/MAGE1412+5650, providing upper limits on their star formation rate history. The provisional distances and quiescences of the dwarf candidates are consistent with a potential backsplash nature, though Hubble Space Telescope/JWST follow-up are necessary for stronger constraints, and to probabilistically distinguish from cosmic web stripping. Sha DG-II is alternatively a possible satellite of NGC 5585. Abundance models of satellites based on halo masses, which can be extended to model backsplash galaxies, will enable important consistency tests of ΛCDM with upcoming surveys, e.g., LSST. This is briefly explored in the context of the M101 group.
SN - 0004-637X
SN - 1538-4357
ER -