IAUS379: Dynamical Masses of Local Group Galaxies

When interpreted within the framework of Newtonian dynamics, the internal kinematic properties of Local Group dwarf galaxies indicate that most of these systems are completely dominated by their dark matter halos. These dwarf galaxies are therefore among the best test-benches for dark matter theories. In this review talk, I will first provide an overview of our current understanding of the...

Stellar streams are one of the most powerful tracers to determine the mass of the Milky Way and other nearby galaxies. Full 6D phase space data is necessary for us to get there. In this talk, I will discuss two ongoing spectroscopic programs to study the stellar streams in our Milky Way and highlight a few latest scientific results from these two programs. The Southern Stellar Stream...

Like any other galaxy in the universe, evidence shows that the assembly of the Milky Way is irrefutably hierarchical. The Galactic halo in particular has a nonlinear structure with a vast number of cold stellar streams with complex morphologies that prove to be a powerful test for the nature and distribution of dark matter in the halo.

In this work, we select halo main sequence stars using...

Stellar streams are sensitive probes of the Galactic potential. The likelihood of a model given stream data can only be assessed using simulations. However, comparison to simulation is challenging in a noisy 6D phase space in which even the stream paths are hard to quantify. Here we present a novel application of Self-Organizing Maps and first-order Kalman Filters to reconstruct the stream...

Providing a detailed picture of the complexity of the Sagittarius stream is an important aspect of investigating the outer Galactic halo and constraining the Milky Way potential. Several attempts have been made to model the complex structure of the Sagittarius stream. However, no model has yet been able to match all the intricate features observed for the stream, including for instance a...

The position, velocity, and chemical composition of each star provide clues to the evolutionary history of galaxies. While the Gaia mission has offered invaluable information about the Milky Way, to understand the growth of disk galaxies in the Universe we must look beyond our galaxy.

The Andromeda Galaxy (M31) is ideal for this task thanks to its proximity (making it possible for...

We use oxygen and argon abundances for planetary nebulae (PNe) with low internal extinction (progenitor ages of (>4.5 Gyr) and high extinction (progenitor ages <2.5 Gyr), as well as those of the H II regions, to constrain the chemical enrichment and star formation efficiency in the thin and thicker discs of M31. The argon element is produced in larger fraction by Type Ia supernovae (SNe) than...

Recent observational efforts such as Gaia are leading us toward a new era of data abundance which offers us an incredible opportunity for discovering new physics. Thanks to recent advances in the field of machine learning, it is possible to extract valuable information from the colossal amount of data now available.
In particular, auto-differentiation allows us to get a better grasp of...

Based on Gaia Early Data Release 3 (EDR3), we estimate the proper motions for 46 dwarf galaxies of the Milky Way. The uncertainties in proper motions, determined by combining both statistical and systematic errors, are smaller by a factor 2.5, when compared with Gaia Data Release 2. We have derived orbits in four Milky Way potential models that are consistent with the MW rotation curve. ...

The ongoing merger of the Milky Way and the Large Magellanic Cloud (LMC) is deforming the dark matter haloes of both galaxies, effectively making these galaxies a local dark matter collider. Within this collider, stellar streams act as useful detectors as they are very sensitive to the gravitational potential, and span large parts of the Milky Way halo.
The Orphan-Chenab (OC) stream is...

The Large Magellanic Cloud (LMC) has a complex dynamics driven by both internal and external processes. The external forces are due to tidal interactions with the Small Magellanic Cloud (SMC) and the Milky Way, while internally its dynamics mainly depends on the stellar, gas, and dark matter mass distributions. Despite the overall complexity of the system, very often simple physical models can...

We combine Gaia EDR3 astrometry with accurate photometry and utilize a probabilistic mixture model to measure the systemic proper motion of 52 dwarf spheroidal (dSph) satellite galaxies of the Milky Way (MW). For the 46 dSphs with literature line-of-sight velocities we compute orbits in both a MW and a combined MW + Large Magellanic Cloud (LMC) potential and identify Car II, Car III, Hor I,...

The baryonic Tully-Fisher relation is a correlation between the quantity of stars and gas in a galaxy and its flat rotation speed. The relation found in external galaxies appears to hold for rotationally supported Local Group galaxies. It may also hold for some if not all of the pressure supported dwarfs. The flat rotation speed depends on dynamical mass, providing a constraint on total mass...

Determination of the mass density profiles of dwarf galaxies (and specifically whether there is a central core or cusp) provides a critical test of both the properties of dark matter (DM) and the physics of cosmological structure formation. The nearby classical dwarf spheroidal galaxies (dSphs) of the Milky Way yield some of the best dynamical constraints. While large line-of-sight velocity...

The mass-anisotropy degeneracy is still one of the main issues in estimating the dark matter distribution in dwarf spheroidal galaxies, especially for the commonly used second-order Jeans analysis. We study the extension of spherical Jeans modeling by incorporating the fourth-order velocity moments under the assumption of dynamical equilibrium and a constant velocity anisotropy. The inclusion...

An accurate and unambiguous determination of the inner distribution of dark matter in dwarf spheroidal (dSph) galaxies has proven to be a challenge for a few decades now. Some of the complications include the degeneracies inherent to the dynamics of stellar systems, but also the limits of the available data (e.g., just one component of the 3D space velocities of the tracers), and the need for...

According to our currently favored cosmological framework, the Lambda- Cold Dark Matter model, galaxies like the Milky Way were built through the accretion and merger of smaller systems. In this scenario, the extended halo of the Milky Way must retain information about this process. Key to unveiling this information is our ability to trace the outermost regions of the halo by detecting and...

The ESA's astrometric mission Gaia has added an invaluable wealth of astrometric and photometric data for more than a billion stars in our Galaxy (Gaia Collaboration et al. 2018). The synergy between Gaia's third data release, EDR3, and large scale-spectroscopic surveys give us comprehensive information about individual stars in the Milky Way. To complement these data sets, we deliver new...

The combination of astrometric and chemical information from Galactic stars has revealed great detail about the structure, dynamics and history of our own Galaxy. In external galaxies, it is impossible to map the distribution of individual stars, but high signal-to-noise integral field spectroscopy data at various wavelengths, together with sophisticated dynamical models, give us the...

The wide-field spectrographs 4MOST and MOONS will enter operations in 2024 at the ESO Paranal Observatory. These upcoming survey facilities will play an important role in various fields over the next decade. In particular, both will host surveys aimed at observing nearby Local Group galaxies. Here, we provide an overview of all the planned 4MOST and MOONS surveys that focus on Local Group...

Very wide stellar binaries, with semi-major axes of hundreds of AU and larger, constitute sensitive probes of the underlying gravitational potential in which they live, having provided some of the first experimental constraints on the nature of dark matter in the Milky Way halo.  As such, the detection and characterization of populations of wide binaries in nearby old dwarf galaxies could...