Conveners
SESSION 2 : Sizes, Masses, and Formation histories of the Milky Way and of Andromeda
- Tony Sohn ()
SESSION 2 : Sizes, Masses, and Formation histories of the Milky Way and of Andromeda
- Alan McConnachie ()
SESSION 2 : Sizes, Masses, and Formation histories of the Milky Way and of Andromeda
- Alan McConnachie ()
SESSION 2 : Sizes, Masses, and Formation histories of the Milky Way and of Andromeda
- Philipp Richter ()
Our Galaxy, the Milky Way, provides us with a unique opportunity to measure the 3D shape of its dark-matter halo, thus testing the properties of the dark sector and the fundamental cosmological model. Until recently, however, these efforts have been thwarted by the scarcity of observational data, especially in the outer halo, as well as reliance on the assumption of a dynamical equilibrium,...
The Dark Energy Spectroscopic Instrument (DESI) is currently one of the most powerful instruments for wide-field multi-object spectroscopy. The synergy of DESI with current (e.g. ESA’s Gaia satellite) and future observing facilities including the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), and the Nancy Grace Roman Space Telescope’s High Latitude Survey (HLS) will yield...
The oldest, most metal-poor stars in the Milky Way are unique probes of early star formation and the assembly of the Milky Way. The Galactic bulge region has typically been avoided in the search for metal-poor stars, because of the extremely high density of mostly metal-rich stars and the high dust extinction. The bulk of the Galactic bulge is thought to originate from the (early) Galactic...
Under the current standard scenario, galaxies such as the Milky Way (MW) are thought to have formed through repeated mergers and accretions of small galaxies due to gravitational interactions. Since the relaxation timescale of these traces in phase space is as long as more than 10 billion years, it has been theoretically suggested that they may still exist in the halo. Advances in large-scale...
The mass of the Milky Way (MW) is important to the formation and evolution of galaxy. After decades of study, the mass of dark matter halo is still open. Most studies have used dynamical tracers in the inner regions of the halo, relying on extrapolations to estimate the mass of the MW. In our study, we determine the Milky Way mass distribution from fitting dynamical models to the...
We measure the enclosed Milky Way mass profile to Galactocentric distances of $\sim70$ and $\sim50$ kpc using the smooth, diffuse stellar halo samples of Bird et al. The samples are LAMOST and SDSS/SEGUE K giants (KG) and SDSS/SEGUE blue horizontal branch (BHB) stars with accurate metallicities. The 3D kinematics are available through LAMOST and SDSS/SEGUE distances and radial velocities and...
Classical Cepheids are excellent tracers to estimate the rotation velocity of the galaxies because they provide better distance accuracy with less uncertainty. With stringent radial velocity from the recent Gaia DR3 and proper motion, we estimate the rotation velocity of the Milky Way galaxy for 909 Classical Cepheids. We have used a more accurate distance estimated based on the...
In this talk, I will discuss the predictions of the $\Lambda$CDM model on the make-up of stellar and dark matter haloes of Milky Way-mass galaxies. I will show that the stellar haloes are made up largely of stars from massive mergers, like Gaia-Enceladus/Sausage in the Milky Way, while the same mergers also make up nearly half of the dark matter halo. Past mergers leave imprints in the...
Stellar streams are created when globular clusters or dwarf galaxies tidally disrupt in the gravitational potential of their host galaxy. These streams therefore offer a great probe to this galactic potential. Current observations show a multitude of Milky Way stellar streams to have substructure in the form of 'spurs', 'gaps' and even multiple components. These can originate from interactions...
Understanding the origin of the stellar streams around the Milky Way can be of great relevance to learn about the history of the Milky Way and the formation of its substructures. A previous study on the Milky Way streams (Pawlowski et al. 2012) showed that many of these (7 out of 14) present a similar orientation to that of the disk of satellite galaxies (DoS) and the young globular clusters...
Since the chemical abundances of stars are the fossil records of the physical conditions in galaxies, they provide the key information for recovering the assembly history of galaxies. In this work, we explore the chemo-chrono-kinematics of accreted and survived dwarf galaxies by analyzing six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local...
Andromeda (M31) is the nearest giant spiral galaxy to the Milky Way and the most massive member of the Local Group. It has long been recognized that M31's mass measurement is essential to understand the formation and evolution of the Local Group. I will review the different observational and modelling techniques that have developed over time to measure the mass of M31. I will discuss the the...
Proper motions (PMs) from HST and Gaia have revolutionized the field of Galactic archaeology in the Milky Way (MW). However, PM studies in and around our neighbor spiral galaxy M31 are still in their early stages with measurements being available for only a few satellites and M31 itself at the moment. Gaia can only detect some of the brightest stars in star forming regions at the distance of...
High-precision astrometric data from the Hubble Space Telescope (HST) and Gaia are revolutionizing our ability to study the Local Group. Currently, 6D phase space measurements (3-dimensional position and velocity) are available for a majority of the Milky Way’s known satellite galaxies and for four (11%) of M31’s satellite galaxies. As satellites trace the dark matter halos of their hosts,...
We present DESI observations of the stellar halo of M31 which reveal the kinematics of a recent merger in exquisite detail. Using data from less than four hours of observations by DESI survey we measure radial velocities of more than 7000 sources in M31. These observations show an intricate coherent kinematic structure in position and velocity space in M31 stellar halo. While hints of coherent...
Recent observations around the M31 have revealed many traces of past interactions with satellite galaxies. In particular, the Andromeda Giant Southern Stream (AGSS) in the halo and the double ring structure in the disc have been drawing attention. The AGSS is a giant structure extending more than 100 kpc from the center of M31 and is thought to have been formed in a collision with a satellite...
The rather intuitive concept of 'galaxy mass' is an ill-defined quantity in cosmology. First, because in an expanding, close-to-homogeneous Universe collapsed structures do not show well-defined boundaries, and second because the availability of dynamical tracers becomes very scarce in the outskirts of dark matter haloes. In this talk I will provide an overview of the timing argument, which...
The study of the dynamical mass of the Local Group requires a detailed knowledge of the velocity of its elements, in particular of the Milky Way (MW) and the Andromeda galaxy (M31). Nevertheless, a discrepancy between the proper motion of the disk of M31 and the global motion of its satellites has been identified. Moreover, recent results showing the influence of the Magellanic complex on the...
The large uncertainties on the measurement of the mass of galaxies is an important issue in modern astrophysics. For both the MW and M31, thanks to the gas rotation curve, the mass of the inner part of the haloes is well constrained. For the outer part of the haloes, we must turn to satellites galaxies as tracers. But, to use dwarf galaxies as such, it is absolutely crucial to determine the...
We estimate that the mass of the Milky Way (MW) is in the range of 2 to 15 $\times 10^{11} M_\odot$. It results from an analysis of the rotation curve (RC) from Gaia DR2 and using different profiles for baryon and dark matter (DM, including NFW & Einasto profile). The lower limit 2 $\times 10^{11} M_\odot$ corresponds to the Keplerian slope of RC at large radii. There were no major mergers in...
The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence for the existence of a rotating bar in M31. Using the position–velocity diagram of [O III] and H I, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km/s...
Triangulum (M33), a satellite of the Andromeda (M31) galaxy, is the only dwarf Spiral in the Local Group. With a mass ten times lower than M31’s and a star formation rate 10 times higher, M33 is the best local analog for high z galaxies. The Triangulum Extended Survey (TREX) is a large resolved stellar spectroscopic survey of M33 and its extended structures. With contiguous spectroscopic...
We review estimates of the total mass of the Local Group. High-accuracy proper motions (PMs) of M31 and other Local Group (LG) satellites have now been provided by the Gaia satellite. We revisit the timing argument to compute the total mass of the LG from the orbit of the Milky Way and M31. We discuss a number of systematic effects. The first is caused by the presence of the Large Magellanic...
