Satellite Group Infall into the Milky Way: Exploring the Crater-Leo Case with New HST Proper Motions
Author ORCID Identifier
Document Type
Article
Publication Date
7-15-2024
Abstract
Context. Within Λ cold dark matter (ΛCDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3–5 members rather than individually, and this has been suggested as a possible mechanism driving the formation of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and to also have identical orbital planes and directions. Aims. Looking at observatio ns of Milky Way satellites, the dwarf galaxies Leo II, IV, V, and Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested ‘Crater-Leo group’ shows a coherent distance gradient and all these objects align along a great circle on the sky. We used proper motion data to investigate whether the phase-space distribution of the members of the proposed group are indeed consistent with group infall. Methods. To further investigate this possibility, we used Gaia Data Release 3 (DR3) and new Hubble Space Telescope (HST) proper motions – namely, (µα∗, µδ) = (−0.1921 ± 0.0514, −0.0686 ± 0.0523) mas yr−1 for Leo IV and (µα∗, µδ) = (0.1186 ± 0.1943, −0.1183 ± 0.1704) mas yr−1 for Leo V – to derive accurate orbital properties for the proposed group objects. In addition, we explored other possible members of this putative association. Results. Leo II, Leo IV, and Crater 1 show orbital properties consistent with those we predict from assuming group infall. However, our results suggest that Crater II was not accreted with the rest of the objects. If confirmed with increasingly accurate proper motions in the future, the Crater-Leo objects would appear to constitute the first identified case of a cosmologically expected, typical group infall event, as opposed to the highly hierarchical Magellanic Cloud system.
Keywords
galaxies: dwarf, galaxies: kinematics and dynamics, Galaxy: kinematics and dynamics, globular clusters: individual: Crater 1, Local Group
Publication Title
Astronomy and Astrophysics
Grant
2020
Rights
© The Authors 2024. This is an Open Access work distributed under the terms of the Creative Commons Attribution Licence (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Satellite group infall into the Milky Way: Exploring the Crater-Leo case with new HST proper motions Mariana P. Júlio, Marcel S. Pawlowski, Sangmo Tony Sohn, Salvatore Taibi, Roeland P. van der Marel and Stacy S. McGaugh A&A, 687 (2024) A212 DOI: https://doi.org/10.1051/0004-6361/202449985
Manuscript Version
Final Publisher Version