Letters of Intent received in 2021

LoI 2023-2140
Dynamical Masses of Local Group Galaxies

Topics

Dynamics of galaxies;
Astrometry and 3D velocities;
Large surveys of resolved stars;
The Galaxy and its halo;
Rotation curves of galaxies ;
Dwarf spheroidal and ultra-faint dwarfs;
Dwarf irregular galaxies;
Magellanic System;
Andromeda System;
Near field cosmology;
Dark matter;
Galaxy formation

Rationale

The Local Group is an ideal place for studying the dynamics of galaxies, thanks to their proximity. In particular, the early studies of the flat rotation curve of M31 have played a key role in establishing the dark-matter paradigm, first based on its ionized gas disk investigated by Vera Rubin, and then based on the more extended neutral gas studied by Albert Bosma. Since that time, HST and Gaia have provided considerable advances in establishing 3D-velocities in the Local Group. Combined with a very large number of ground-based surveys of the Milky Way and nearby galaxies (APOGEE, 2MASS, WISE, SDSS, DESI, PAndAs, PHAT, ...), our knowledge of the Galaxy and its neighborhood has reached a level of maturity not attainable at larger distances. As a result, e.g. the Milky Way now has the most precise rotation curve amongst other giant spiral galaxies.

However, there are still debates about the dynamical or total mass for most galaxies of the Local Group. This has a considerable impact, as it limits all studies aiming at understanding the past and future of these galaxies. For example, the total mass inferred for the Milky Way depends on the a priori choice of dynamical tracers in the halo, and may still vary by factors larger than two. There is also some recent evidence that the Large Magellanic Cloud could be far much more massive than initially thought, which could modify the dynamical status of many galaxies in the Local Group, including our own. Yet, here the current uncertainty reaches a factor close to 10! The wealth of observational data has also revealed the importance of non-equilibrium dynamics for interpreting local galaxies, which again can be best studied in the Local Group where full 6D phase-space information can be accessed. Furthermore, the status of several dwarf galaxies is still uncertain, and some of the smallest ones could be confused with globular clusters, resulting in very uncertain total masses.

The range of galaxy masses studied in the Local Group is huge, from the several hundred of billion solar masses for the Milky Way or M31, down to ultra-faint galaxies like Segue 1 that have only a few hundreds of stars. Uncertainties in mass determination reach factors from two to thousands, from the more to the least massive galaxies respectively. This has substantial implications, including in the area of (near-field) cosmology, and in studies of dark matter and its alternatives. The goal of this meeting is to gather specialists of the many galaxies of the Local Group and slightly beyond, including observers and theorists, in order to discuss the status of their dynamical mass estimates, to present novel approaches to observations, modeling and theory, as well as to establish common strategies for future advances. Comparison with mass estimates made at larger distances will be discussed in a session at the end of the Symposium. Large time will be allocated for discussions, which is essential for getting the opinions of all participants.