Description
Organisers: Paula Gherghinescu, Nicholas Walton; co organisers: Sioree Ansar, Giorgia Busso, Nigel Hambly, Jason Hunt, Sophia Lilleengen, Nicholas Rowell, George Seabroke, Mark Taylor
The ESA Gaia mission is creating a 3-D map of over two billion stars in our Milky Way. Gaia continues to provide new insights into our understanding of the Milky Way. In particular, the field of Galactic dynamics is an example of study that has been revolutionized with the availability of data from the Gaia mission.
It is now possible to directly map the structure and kinematics of all major Galactic components to unprecedented detail and precision. However, many traditional dynamical modelling methods use the Jeans theorem and start by assuming the galaxy is in dynamical equilibrium and axisymmetric.
While these models continue to be valuable in offering aโ big pictureโ view up to large scales, their underlying assumptions can describe our Milky Way to first order only. For example, prominent non-axisymmetric structures such as the bar and spiral arms influence the dynamics of stars far across the disc, while the phase spiral (first revealed in the Gaia DR2 data), the warp, and the perturbation induced by the LMC in the outer halo highlight departures from equilibrium both locally and on the largest scales.
Current models do not fully capture the complexity of the data. With the increase in quantity and quality expected from Gaia DR4 and DR5 (supplemented with data from Euclid, LSST, and more) improved modelling methods are required.
The session will begin with an update from the Gaia:UK project team describing the latest scientific and technical performance of Gaia, developments in Gaia data acess, and giving a look ahead to the rapidly approaching seminal release of Gaia DR4, the full release of the 5 year Gaia nominal mission.
It will then focus more specifically in bringing together researchers working on a variety of novel numerical and analytical tools, as well as expertise in Gaia and associates survey data, to address challenges in improving our modelling techniques. Half block sessions will cover on (a) features and dynamics in the disc, (b) the dynamics of the halo, and (c) the Milky Way in a cosmological context.
This presentation will provide a brief update on the ESA Gaia mission status, reflecting that whilst inflight operations ceased with the recent (27 March 2025) 'passivation', the mission continues with current activity focused on the generation of Gaia Data Release 4 (Gaia DR4) scheduled for later in 2026.
Gaia DR4 will see a significant number of new data products being made available to...
Various tools and methods (web GUIs, client applications such as TOPCAT, client-side programmatic APIs, and code-to-data platforms such as the UK Gaia Data Mining Platform and ESA DataLabs) currently available for science exploitation of Gaia data releases will be summarised. Illustrative examples employing Gaia DR3 will be shown. Facility developments will be described in the context of a...
Tracing the Milky Way disc structure as a function of stellar age is key to understanding its formation history. However, fitting density models to observational data is a major challenge due to selection biases.
To avoid modelling the complex selection function, we focus on fitting stellar kinematics, using the quasi-isothermal disc distribution function. We use the APOGEE DR17 giant stars,...
One of the most striking things that we have learned about the Milky Way from Gaia data is the extent to which its disc has been disturbed. The way we describe and characterise this disturbance seems to depend on how we are looking at it. We can at least agree that the Milky Wayโs disc is rippling up and down, and a prime suspect for this disturbance is the Sagittarius dwarf galaxy shaking the...
Radial migrationโa process that moves stars from their birthplaces to their present-day galactocentric radiiโhas been shown to play a crucial role in shaping the Milky Way disc, particularly based on age and metallicity measurements of stars in the solar neighbourhood. With Gaia DR3, we now have chrono-chemo-kinematic maps of the Milky Way that extend far beyond the solar neighbourhood,...
A common task in Galactic dynamics is the inference on the gravitational potential and mass distribution of resolved stellar systems, such as globular clusters, nearby dwarf spheroidal galaxies, or haloes of Andromeda-like galaxies in the local Universe.
In one approach, the tracer population is described by a distribution function (DF) in the space of integrals of motion (e.g. actions),...
With the goal of investigating the role of the Galaxyโs large-scale dynamics on star formation, we use the hydrodynamical AREPO moving-mesh code to perform simulations of the Milky Way. Our models include a live stellar disc and bulge, a live dark matter halo, and a gaseous discโevolved self-consistently with no fixed potentials and under isothermal equations of state.
We compare our...
The Sagittarius dwarf galaxy is without a doubt getting tidally disrupted by the Milky Way. Recent results from Gaia show that the Milky Way disc is far from equilibrium. Various works have shown that the interaction with Sagittarius can have a significant effect on unsettling the Galactic disc, resulting in many observed features like the Galactic warp, disc corrugation, spiral structure,...
The infall of the LMC into the Milky Way (MW) has caused significant disequilibrium throughout the MW. In particular, it has moved the MW's centre of mass and deformed its dark matter halo. There are only a handful of tailored MWโLMC simulations that can capture all aspects of this dynamical disequilibrium.
I will show how we can utilise much simpler rigid MWโLMC models to still constrain...
The Gaia spacecraft has brought our Milky Way into focus in an unprecedented way. The synergy with ground-based spectroscopic surveys has provided us with photometry, 6-D phase-space coordinates, and spectra for millions of stars. This rich data has highlighted the presence of departures from dynamical equilibrium, such as the phase-space spiral.
Despite these departures, equilibrium...
Co-moving groups of stars (streams) are well known in the velocity space of the disc near the Sun. Many are thought to arise from resonances with the Galactic bar or spiral arms. In this work, we search for similar moving groups in the velocity space of the halo, at low angular momentum. From the asymmetry of the radial velocity distribution $v_R$, we identify two inward-moving streams with...
The fundamental nature of dark matter so far eludes direct detection experiments, but it has left its imprint in the population of low-mass sub-halos in the Milky Way (MW). Measurements of the MW phase space from observatories like Gaia will probe the lightest dark halos ever detectable (< 10^7 M_Sol) through their gravitational perturbations with thin tidal streams of stars. It is thus...
We use Gaia DR3 data and the HDBSCAN clustering algorithm to investigate the multidimensional kinematics of the Scorpius OB2 association, also known as the ScorpiusโCentaurus (Sco-Cen) association.
Previous studies, de Zeeuw (1999) using Hipparcos data, and Rizzuto et.al., (2013) using the Sydney University Stellar Interferometer indicate a large, coherent stellar structure with...
Recent observations have shown globular clusters to be systems of greater kinematic and morphological complexity than can be described using spherical non-rotating dynamical models. A new family of self-consistent models for quasi-relaxed stellar systems are presented, treating for the first time the case of asynchronous rotation within an external tidal field. Constructed as a double...
High-mass X-ray binaries (HMXBs) are systems in which a neutron star or black hole accretes material from a massive companion. HMXBs are expected to have experienced a supernova in their evolution. The impulsive kick associated with this event should affect the space velocity of the system in a way that depends on the nature and state of the progenitor binary. Here, we test whether the...
Data from ESAโs Gaia mission has revolutionised Galactic astronomy, providing an unprecedented view of the Solar neighbourhood and beyond. However, while it provides us a great opportunity to transform our understanding of the Milky Way, it has also highlighted how far from equilibrium our Galaxy is. The spiral pattern in vertical position vs. velocity is a signature of our Galaxyโs past...
The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing them to move significantly with respect to the outer halo. In this talk, I will present measurements of this interaction using the first two years of DESI spectroscopic survey observations. We probe this interaction by constructing a sample of...
Historic merger events are expected to leave imprints of their collisions in the stellar haloโs phase space and chemodynamics. However, interpreting such imprints is complicated by the complex hierarchical history expected in LCDM (Rey M. P.et al. , 2023, MNRAS, 521, 995 10.1093/mnras/stad513). Here, we explore the impact of merging within the PARADIGM simulations (Joshi G. D. et al ,...
