IAUS379: Dynamical Masses of Local Group Galaxies

I will briefly summarise the key methods for the determination of the dynamical mass and mass profiles of dwarf galaxies. I will then discuss in detail the observational challenges associated with making the necessary measurements and obtaining the necessary data, with a focus on the systematic, technical, and physical limitations of the measurement. I will review the implications of these...

The Milky Way satellite dwarf galaxy Antlia II is one of the lowest surface brightness galaxies known. It has a size comparable to the Large Magellanic Cloud, but only 10^6 solar masses of stars. We present kinematic and chemical measurements from the Southern Stellar Stream Spectroscopic Survey using the AAT/2dF, which clearly demonstrate that Antlia II is tidally disrupting. The orbit and...

Andromeda (And) XIX is a unique dwarf galaxy in the M31 system. Its large half-light radius (in excess of 3 kpc) and low surface brightness (29.3 magnitudes per square arcsecond) make it one of the most diffuse galaxies in the known Universe. In addition to its extreme structural properties, its dynamics also suggest that it sits in a low density dark matter halo that may have been shaped by...

Analysing the stellar kinematic properties of a dwarf galaxy makes it possible to investigate which internal mechanisms have shaped its evolution. Isolated dwarf galaxies with an extended star formation history, in particular, offer the opportunity to study not only star formation processes at low-mass and low-metallicity scales, but also to understand how internal kinematic properties evolve...

One particularly promising way to understand the nature of dark matter is to study the so-called core-cusp problem. Many solutions have been investigated to solve it and one possibility is that the nature of the dark matter itself is different from the successful $\Lambda$-Cold Dark Matter model. To reduce the impact of baryonic physics which obscures our ability to constrain dark matter, we...

We present kinematics and detailed chemical abundances of stars in the outskirts (out to ~8 half-light radii) of the Tucana II ultra-faint dwarf galaxy (< 10^5 Lsun; UFD) from high-resolution Magellan/MIKE spectroscopy. The Milky Way’s UFDs are “relic” galaxies (~13 Gyr old) from the early universe, making their stars unique probes of the first stages of galactic evolution. Previous...

Previous studies of Ultra-Faint Dwarfs (UFDs) show that their dynamical mass-to–light ratios are the highest values measured in any type of galaxy, implying relatively pure dark-matter halos with minimal baryonic content. Furthermore, UFDs have the lowest metallicities, oldest ages, smallest sizes, and simplest assembly histories of all galaxies. Understanding the nature of these galaxies...

Gaia has revolutionized our understanding of the Milky Way (MW) and its satellite system. However, the proper motions (PMs) of dwarf galaxies outside the MW system remain out of reach by Gaia and will remain so even with future data releases. This is problematic, as it means that our understanding of systems outside the MW will be limited and we may be basing much of our cosmological modeling...

Leo P is a poorly studied near-primordial isolated dwarf irregular galaxy at a distance of ∼ 1.6 Mpc, with an extremely low mass of ∼ 105M⊙.
From Hubble Space Telescope and Arecibo Legacy Fast observations, its characteristics show the same behaviour as expected in a low-luminosity dSph Milky Way satellite. It was defined as the “quintessential system to test theories of how the smallest...

To investigate the dynamical nature of the kinematic asymmetry in the isolated gas-rich dwarf irregular galaxy W LM in the Local Group, we first examine whether an m = 1 perturbation in the halo potential could be a mechanism creating such kinematical asymmetry.
By fitting a theoretical rotational velocity associated with an m = 1 perturbation in the halo potential model to the observed...

The chemical abundance patterns exhibited by stars in Ultra-Faint Dwarf (UFD) galaxies can provide a wealth of information about the evolutionary history of UFDs, including what dynamical history the stars in a UFD may have experienced. Of particular interest are stars in the outer regions of UFDs because they may hold evidence of tidal stripping, mergers, or other mechanisms; and because of...

In the hierarchical clustering scenario based on the $\Lambda$ cold dark matter ($\Lambda$CDM) model, sub-galactic dark matter halos (subhalos) are of crucial importance in building up the larger structures via merging processes. Moreover, dwarf galaxies around the Milky Way (MW) are ideal sites for studying the nature of dark matter since they are dark-matter-dominated systems.

We...

The unusually low velocity dispersion and large sizes of `feeble giant' galaxies, such as Crater II or Antlia II, pose a challenge to our understanding of dwarf galaxies in the Lambda Cold Dark Matter (LCDM) cosmogony. Their low velocity dispersions suggest either a dark halo mass much lower than the minimum expected from hydrogen cooling limit arguments, or one that is in the late stages of...

Dwarf galaxies play a key role in probing the dynamics of the Milky Way, the history of star formation in the Local Group, and the accretion and retention of gas in dark matter halos at the smallest scales of galaxy formation. In this work, we use the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), the deepest, widest photometric survey ever carried out in the northern hemisphere,...

The dwarf spheroidal galaxies (dSphs) in the Local Group are excellent test beds for probing the properties of dark matter and its role in galaxy formation.
These galaxies are sufficiently close that it is possible to measure line-of-sight velocities for large samples of resolved stars. This kinematic information enables us to study the structural properties of their dark matter...

Dwarf galaxies are valuable laboratories for dynamical studies related to dark matter and galaxy evolution, yet it is currently unknown just how extended their stellar components are. Each satellite orbiting within the Milky Way’s (MW’s) gravitational potential may undergo tidal stripping by the host galaxy, or alternatively, may themselves have accreted yet smaller systems whose debris...

Gaia EDR3 has provided proper motions of Milky Way (MW) dwarf galaxies with an unprecedented accuracy, which allows us to investigate their orbital properties. We found that the total energy and angular momentum of MW dwarfs are much larger than that of MW K-giant stars, Sagittarius stream stars and globular clusters. It suggests that many MW dwarfs have recently infall into the Milky Way...

Dwarf satellite galaxies around Andromeda (M31) and the Milky Way form thin, coherently rotating planes argued to be in tension with expectations from the cold-dark-matter (CDM) model of cosmology. For M31, this disagreement is compounded by a prominent asymmetry in its satellite distribution; over 80% of its dwarfs lie in the hemisphere facing the Milky Way. To a degree, lopsided dwarf galaxy...

The discussion "dark matter vs. modified gravity" has not been resolved yet. It was proposed that dynamical friction could be used to discriminate between the two alternatives. Analytic calculations indicate that, with modified gravity, globular clusters (GCs) of low-mass galaxies experience much stronger dynamical friction than in the equivalent system with Newtonian gravity and dark matter....

In this talk I will present our results on environmental secular evolution processes that affect satellite galaxies as they enter their hosts.
Our approaches consist of global statistical analysis of satellites, and the modelling of detailed observations. For the latter approach we study distant gas rich dwarf satellites like Leo T and Phoenix, which are entering the Milky Way. Both...

Low-mass or dwarf galaxies are particularly compelling laboratories for star formation quenching because they are highly susceptible to quenching effects from both internal stellar feedback and external environment. We explore the role of ram pressure in the environmental regulation of gas content and quenching of low-mass galaxies in zoom-in hydrodynamic simulations of Milky Way (MW) mass...

Ultra-faint dwarf galaxies (UFDs) are often found in large numbers in close proximity to the Milky Way and other massive spiral galaxies. As such, their projected stellar ellipticity and extended light distributions are often thought to owe to tidal forces. I discuss the projected stellar ellipticities and faint stellar outskirts of isolated ultra-faints, drawn from the `Engineering Dwarfs at...

Numerous observations in recent years have shown that the satellite galaxies orbiting our local galaxies tend to align their orbits in one or two thin planes around the host galaxy. This has been observed in local galaxies, Andromeda and Centaurus A, and our own Milky Way. Numerical simulations in a cosmological context find these planes to be rare or short-lived leading to tension between...

Prolate rotation in galaxies (rotation around the major axis) is a rare phenomenon in the Universe. The effect has been exclusively attributed to past major mergers and thus studies of prolate-rotating systems can help us better understand the hierarchical process of galaxy evolution. Dynamical studies of such galaxies is important to find their gravitational potential profile, total mass, and...