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Local Group Galaxies from an External Perspective

Published online by Cambridge University Press:  30 October 2025

S. S. McGaugh Open the ORCID record for S. S. McGaugh [Opens in a new window]
S. S. McGaugh*
Affiliation:
Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH, USA
*
email: stacy.mcgaugh@case.edu
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Abstract

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I discuss Local Group galaxies from the perspective of external galaxies that define benchmark scaling relations. Making use of this information leads to a model for the Milky Way that includes bumps and wiggles due to spiral arms. This model reconciles the terminal velocities observed in the interstellar medium with the rotation curve derived from stars, correctly predicts the gradual decline of the outer rotation curve, and extrapolates well out to 50 kpc. Rotationally supported Local Group galaxies are in excellent agreement with the baryonic Tully-Fisher relation. Pressure supported dwarfs that are the most likely to be in dynamical equilibrium also align with this relation. Local Group galaxies thus appear to be normal members of the low redshift galaxy population. There is, however, a serious tension between the dynamical masses of the Milky Way and M31 and those expected from the stellar masshalo mass relation of abundance matching.

Keywords

Local Group (929)Milky Way Galaxy (1054)Dwarf galaxies (416)Galaxy masses (607)

Information

Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 19 , Symposium S379: Dynamical Masses of Local Group Galaxies , December 2023 , pp. 32 - 37
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Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of International Astronomical Union

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