IAUS379: Dynamical Masses of Local Group Galaxies

The study of resolved stellar populations in the nearest galaxies, or "near-field cosmology", provides key constraints on the physics underlying galaxy formation and evolution. In this talk, I will present an overview of how deep, wide-field surveys of nearby groups of galaxies allow us to characterize the past and ongoing accretion processes shaping the halos of Milky Way-mass galaxies. This...

Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in a wide range of environments. Studies of the internal dynamics and dark matter content of UDGs that would elucidate their formation and evolution have been hampered by their low surface brightnesses. We identified a sample of low-mass early-type...

In the coming decade, thousands of stellar streams will be observed in the halos of external galaxies with the Nancy Grace Roman Space Telescope, the Euclid Space Telescope, and the Vera C. Rubin Observatory. Stellar streams form when a dwarf galaxy or a cluster of stars is torn apart due to an underlying galactic potential, leaving behind a swath of thousands of stars that exhibit coherent,...

Understanding the mass assembly of galaxies is one of the big open questions in astronomy. A dynamical analysis of galaxies of the ATLAS3D survey provides new clues about the galaxy evolution process of galaxies as the sample comprises a good mix of fast and slow rotators with very different growing scenarios. Slow rotators are thought to accrete about 50 per cent of their stellar mass from...

Dwarf galaxies are regarded as the oldest and most numerous galaxy type in the Universe, responsible for the formation of the higher mass galaxies we see today. While we know a lot about the properties of dwarfs in the Local Group as well as selected nearby groups and clusters, our understanding of these galaxies beyond the Local Volume is comparatively poor. The properties probed by this...

It has long been speculated that Blue Compact Dwarf galaxies (BCDs) are formed through the interaction between low-mass gas-rich galaxies, but due to a lack of evidence, this possibility has rarely been explored. We study a sample of compact star-forming dwarf galaxies that are selected from a merging dwarf galaxy catalog. We present a detailed study of their spectroscopic and structural...

The number density of extragalactic 21-cm radio sources as a function of their spectral line-widths -- the HI width function (HI WF) -- is in principle a sensitive tracer of the dark matter halo mass function (HMF). The Λ cold dark matter model predicts that the HMF should be identical everywhere provided it is sampled in sufficiently large volumes, implying that the same should be true of the...

It is routinely assumed that galaxy rotation curves are equal to their circular velocity curves (modulo some corrections) such that they are good dynamical mass tracers. I will present the results of an unconventional, visualisation-driven analysis of 33 low-mass field galaxies from the APOSTLE suite of galaxy formation simulations exploring the limits of the validity of this assumption. Only...

Galaxy clusters are the largest gravitationally bound structures in the Universe. Numerical simulations provide detailed scenarios on how they assemble and evolve over the lifetime of the Universe, but observational evidences supporting these predictions are still elusive. Galaxy populations in nearby clusters are dominated by dwarf stellar systems, and the number of these galaxies continues...

In this talk I will review techniques and idiosyncrasies in building mass models of disk galaxies using cold gas dynamics. I will particularly focus on HI disks, which are generally more extended than stellar disks, so they allow tracing galaxy dynamics out to the most dark-matter-dominated regions. The combination of HI observations and near-infrared photometry, tracing the distribution of...

The gravitational interaction between dark matter (DM) and baryons has long been ignored when building galaxies semi-empirically and observationally. In this talk, I will show that the baryonic gravity leads to an adiabatic contraction of DM halos, ignoring which would result in the built galaxies that are not in a dynamic equilibrium and hence cannot exist in reality. We propose a new...

We present a method to measure the the oblateness parameter q of the dark matter halo of gas rich galaxies that have extended HI disks. We have applied our model to a sample of 20 nearby galaxies that are gas rich and close to face-on, of which 6 are large disk galaxies, 8 have moderate stellar masses and 6 are low surface brightness dwarf galaxies. We have used the stacked HI velocity...

One of the primary hurdles in pushing dark matter constraints to dwarf scales the uncertainty in the stellar-mass--halo-mass (SMHM) relation. Results from simulations differ by two orders of magnitude at halo masses < 10^10 solar masses, and none can match observations. Moreover, there is no consensus on the amount of scatter. To address these uncertainties, I used high-resolution...

Recent large photometric, astrometric, and spectroscopic surveys have enabled the first systematic observations of Milky Way stellar streams in 6D. At the same time, cutting edge cosmological simulations are now at resolutions that allow for the study of dwarf galaxy streams around Milky Way-like hosts. In this talk, I will present the discovery and characterization of a population of 6D...

The plane-of-satellites problem is one of the most severe small-scale challenges for the standard Λ cold dark matter (ΛCDM) cosmological model: Several dwarf galaxies around the Milky Way and Andromeda co-orbit in thin, planar structures. A similar case has been identified around the nearby elliptical galaxy Centaurus A (Cen A). We studied the satellite system of Cen A with line-of-sight...

The mass content of the Universe is dominated by non-baryonic dark matter, according to the Lambda Cold Dark Matter cosmology interpretation of observational evidence. However, not all observations agree with the theory and many predictions remain difficult to investigate. In particular, simulations predict that the shapes of the most massive dark matter haloes deviate from spherical symmetry....

Since the early 2000s satellite dwarf galaxies of the Local Group and more recently, the nearby Centaurus A/M83 group, have been known to show morphological characteristics and spatial distributions that do not match predictions from ΛCDM simulations. In particular, satellite dwarf galaxies inhabiting the Local Group and the Centaurus A/M83 group appear to be co-rotating in confined disks...

Cosmological simulations have been used to understand the formation of structure in the LCDM paradigm on small and large scales. Most simulations start with unconstrained Gaussian initial conditions, and therefore generically do not produce good analogues of the Local Group at present day. While constrained simulations exist, these have difficulty in precisely satisfying all our observational...

The satellite galaxy systems of the Milky Way (MW) and M31 both show a very thin kinematically coherent structure or satellite plane. It has previously been shown that each plane is in 3.55σ tension with ΛCDM expectations, which combined with the similar structure around Centaurus A falsifies the model at 5.3σ confidence. In this talk, I will present hydrodynamical simulations of the MW and...

The Fornax cluster provides an unparalleled opportunity to investigate the formation and evolution of early-type galaxies in a dense environment. Using the spectroscopic data from the Visible Multi-Object Spectrograph at Very Large Telescope (VLT/VIMOS) from the FVSS survey, we have kinematically characterised the photometrically detected globular cluster (GC) candidates in the core of the...