arXiv subjects

Paula Gherghinescu

Publications and source records attributed to Paula Gherghinescu.

4 recordsLinked to original sources

arXiv2026

Bar-halo interaction: the role of orbital anisotropy

We investigate the dynamical response of dispersion-dominated halo populations to a rotating galactic bar, focusing on how the underlying halo phase space distribution function (DF), and in particular the orbital anisotropy, shapes resonant structure formation. Using controlled test-particle simulations in a fixed Milky Way-like potential, we systematically vary the velocity anisotropy and net rotation of halo-like components while keeping the halo density profile, global potential, and bar properties fixed. We find that bar-induced resonances generate prominent substructure in energy-angular momentum space, but that the morphology, strength, and density contrast (i.e. overdensities versus underdensities) of these features depend sensitively on the halo orbital anisotropy and how resonant transport aligns with gradients of the DF in action space. For instance, radially biased halos tend to exhibit stronger responses and features across all main resonances. Our results also show that angular momentum exchange and the torque exerted on a halo are governed not only by its density profile but crucially by its orbital anisotropy structure. This highlights the importance of halo anisotropy when interpreting phase-space substructure in the stellar halo of the Milky Way with current and future surveys, while also having implications in further understanding the DM halo-bar coupling in disk galaxies.

astro-ph.GA↗

arXiv2026

Stirring Things Up: Bar-induced substructures in the stellar halo of a cosmological Milky Way analogue

The stellar halo of the Milky Way contains the remnants of past accretion events, which could be detectable as substructures in the classical integrals of motion space, such as energy and angular momentum (E-Lz). However, our galaxy also contains a non-axisymmetric stellar bar, which traps stars in resonant orbits, leading to substructures in phase-space. Using a high-resolution magneto-hydrodynamic cosmological zoom-in simulation of a Milky Way analogue, we explore the connection between the bar and the accreted stellar halo. We find that the bar induces prominent substructures, or "ridges", in E-Lz, caused by the resonances. The most pronounced of these is caused by the corotation and the retrograde 1:1 resonances, with weaker ridges visible due to the prograde 1:1 and outer Lindblad resonance. The ridges are present across much of the stellar halo, with variations in radius due to the morphology of different orbital families. We explore the scattering of orbits at the resonances, finding that stars trapped at the 1:1 retrograde resonance become more circularised and have more negative angular momentum. Additionally, stars can move between the corotation and retrograde 1:1 families, thus alternating between prograde and retrograde motion. Due to these scatterings and the pre-existing metallicity gradients in the accreted population, the bar-induced substructures have distinct metallicities compared to stars in the surrounding phase-space. Our results suggest the need for caution when searching the Milky Way stellar halo for accreted substructures in both integral of motions and chemical spaces, since these can be induced by internal perturbations.

astro-ph.GA↗

arXiv2025

How much can we learn from resolved stellar kinematics of galactic haloes using action-based dynamical models?

Dynamical models are used to study dark matter (DM) in galaxies, how galaxies assemble through mergers, and to test galaxy formation models. Despite its widespread use, there has been no systematic study quantifying how much information can be obtained from just two on-sky positions and line-of-sight velocities, which are typically available for nearby external galaxies. In this work, we introduce axisymmetric, action-based dynamical models that use the positions and velocities of stellar halo stars to jointly constrain the total mass distribution of galaxies and the underlying DM component, as well as the stellar halo phase-space distribution. We rigorously test the method using both idealised equilibrium galaxy mocks and cosmological hydrodynamical simulations from the Auriga suite, systematically assessing how its performance degrades as the available phase-space information is progressively reduced. We further examine the impact of galaxy inclination, modelling assumptions, and methodological systematics on the recovered mass profiles. A crucial development in this work is the improved marginalisation of the model likelihood over missing phase-space dimensions. Our models successfully recover the total and DM mass distributions, as well as the kinematic properties of the stellar tracers, within the derived confidence intervals. However, we find that with limited (3D or 4D) phase-space information, the flattening of the DM halo cannot be constrained with any degree of certainty. Nevertheless, the recovered mass profile is insensitive to the flattening. This finding is independently validated by Schwarzschild modelling tests.

astro-ph.GA↗

arXiv2023

Action-based dynamical models of M31-like galaxies

In this work, we present an action-based dynamical equilibrium model to constrain the phase-space distribution of stars in the stellar halo, present-day dark matter distribution, and the total mass distribution in M31-like galaxies. The model comprises a three-component gravitational potential (stellar bulge, stellar disk, and a dark matter halo), and a double-power law distribution function (DF), $f(\mathbf{J})$, which is a function of actions. A Bayesian model-fitting algorithm was implemented that enabled both parameters of the potential and DF to be explored. After testing the model-fitting algorithm on mock data drawn from the model itself, it was applied to a set of three M31-like haloes from the Auriga simulations (Auriga 21, Auriga 23, Auriga 24). Furthermore, we tested the equilibrium assumption and the ability of a double-power law distribution function to represent the stellar halo stars. The model incurs an error in the total enclosed mass of around 10 percent out to 100 kpc, thus justifying the equilibrium assumption. Furthermore, the double-power law DF used proves to be an appropriate description of the investigated M31-like halos. The anisotropy profiles of the halos were also investigated and discussed from a merger history point of view.

astro-ph.GA↗