Description
Organisers: Jason Hunt, Sophia Lilleengen, Michael Petersen, Eugene Vasiliev
Half a century after their introduction, basis function expansions are seeing a renaissance in galactic dynamics and evolution owing to (1) the ability of basis function expansions to model disequilibria, critical given modern observations in the Milky Way and nearby galaxies, (2) the need for compression and analysis efficiency with the sheer size and scope of modern simulations, and (3) the accessibility of modern software frameworks (agama, EXP, gala). Work over the past decade, often led in the UK, has generated a wealth of technical improvements, enabling wider and more creative applications to analytical, numerical, and observational galactic dynamics.
Some of the earliest uses of basis function expansions in galactic dynamics described systems in analytic terms, capturing complex dynamical mechanisms such as the evolution of spiral arms. Through modern software packages, basis function expansions power rapid N-body integration of idealised systems and detailed dynamical experiments, e.g. the Milky Way-LMC interaction. More recently, basis function expansions enable detailed-yet-computationally-inexpensive representations of galaxy components in cosmological simulations, describing the shape of cosmological halos and their evolution. Further, basis function expansions can also describe images, velocity moments, and chemical fields. These additional uses of basis function expansions are still in their infancy but show significant promise for coupling theoretical and observational dynamics in the large survey era.
The session will bring together developers, practitioners, and learners for a highlight tour of recent results in galactic dynamics and evolution to set the future of basis function expansion usage and development in the UK.
The DaRk mattEr and Astrophysics with Machine learning and Simulations (DREAMS) project will produce thousands of Milky Way-mass, cosmological hydrodynamic zoom-in simulations that simultaneously vary both the baryonic and dark matter physics. The large scale of this dataset presents a unique opportunity to investigate the role of both the light and dark sectors in the formation and...
Despite being well studied in N-body simulations, many challenges remain for understanding the role of chaos in the orbital evolution of isolated disc galaxies. Common methods used to identify chaos in simulations (e.g., surface of section, frequency drift, Lyapunov exponents) require long-duration sampling (on the order of a Hubble time) and/or static potentials. This poses a challenge in...
I review a recent mathematical development (arxiv:2302.06944) in the theory of biorthogonal basis sets, with particular attention given to practical numerical implementation. This work introduces an algorithm, the output of which is a traditional (Clutton-Brock-style) basis set, starting from any reasonable smooth function describing the zeroth-order spherical or disc-like mass density of...
The Kalnajs matrix method is an important example of the application
of basis functions in galactic dynamics. It has been used to
determine the global response of a stellar system to perturbations in
frequency space, particularly in understanding the modes and
instabilities of stellar discs. There are, however, two shortcomings
of the method. First, it relies on the use of action-angle...
Recent basis function expansion models of perturbations to the Milky Way's outer halo offer new avenues to constrain the mass distribution. A key observable in this context is the reflex motion of the Milky Way disc with respect to its dark matter halo, induced by the LMCโs infall. In this work, we investigate the sensitivity of the reflex motion signal to different outer-halo profiles of the...
The recent infall of the LMC into the Milky Way (MW) has dynamical implications throughout the MW's dark matter halo, leaving an imprint on the MW stellar streams. One way to study the impact of this merger is to use the statistical properties of populations of simulated stellar streams. Using time-evolving MW-LMC simulations described by basis function expansions, I analyse how perturbations...
The LMC has been shown to significantly affect many structures in the Milky Way, including streams and dwarfs. Recently, it has been demonstrated that the Tucana IV dwarf had a close passage (~4 kpc) with the LMC ~130 Myr ago. In this talk, I will present the results of N-body simulations of this encounter and how the LMC has distorted Tucana IV. I will show the results of N-body simulations...
The ongoing merger of the Milky Way (MW) and the LMC provides a unique opportunity to study galaxy interactions and develop new methods of probing dark matter theories. Basis function expansions (BFEs) give a functional description of these evolving and deforming systems with the ability to robustly simulate the interactions and resulting deformations of multiple components. I will present a...
I describe the approach for modelling the evolution of stellar systems with particle-based models using basis-set and multipole potential expansions. Several variants of this approach span the range between the self-consistent field method of Hernquist&Ostriker and the Lagrange point stripping method for stream generation, with different tradeoffs in complexity and realism. I discuss practical...
Studying the nature of the spiral arms is essential for understanding the intricate structure of the Milky Way disc. In recent years, The Gaia has provided groundbreaking observational data, revealing the detailed kinematical features of stars in the Milky Way. However, so far, the nature of spiral arms remains unresolved.
In this talk I will present the stellar kinematics traced by the...
The Gaia dataset has revealed many intricate Milky Way substructures in exquisite detail, including moving groups and the phase spiral. Precise characterisation of these features and detailed comparisons to theoretical models require engaging with Gaiaโs heteroscedastic noise model, particularly in more distant parts of the Galactic disc and halo. We propose a general, novel machine-learning...
The application of basis function expansions to imaging is still in early stages, but shows significant promise for quantifying galaxy morphology at even the highest redshifts. We will present a novel technique using Fourier series and Laguerre polynomial EXpansions (FLEX) to represent high-redshift disc galaxy images from JWST and HST. As a first application, we studied the evolution of disc...
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, necessitating the development of simulation and analysis codes which can model and interpret...
