arXiv subjects

P. Sánchez-Martín

Publications and source records attributed to P. Sánchez-Martín.

3 recordsLinked to original sources

arXiv2026

Arm morphology in off-centre barred galaxies

Many barred galaxies, including the Large Magellanic Cloud (LMC), display strong lopsidedness and off-centre bars. The dynamical connection between bar-disc misalignments, internal mass asymmetries, and arm morphology is not yet fully characterised. We investigate how internal mass imbalances within the bar and global offsets between the bar and the centre of mass of the system modify the equilibrium-point structure and the invariant manifolds that organise arms. We construct a barred galaxy model which includes an off-centred and asymmetric in shape bar. Using numerical continuation, we track the position, stability, and bifurcations of the Lagrangian equilibrium points as functions of the displacement of the asymmetric mass component along the bar and of the offset between the bar and the system's centre of mass. For representative configurations we compute the invariant manifolds of planar Lyapunov orbits around unstable points and analyse the resulting arm structures. Internal bar lopsidedness and modest bar-disc offsets that keep the centre of mass inside the bar preserve the classical configuration with five equilibrium points, but strongly distort the associated invariant manifolds, producing two arms with different densities and shapes. The bar-disc offset reaches a threshold at the point at which the galactic centre of mass exits the bar ellipsoid, in which a pitchfork bifurcation removes the collinear unstable points and the system transitions to a three-equilibrium-point configuration in which a single unstable point and its associated manifold supports one arm. This framework is compatible with the observed correlation between off-centre bars and photometric lopsidedness, and it provides a dynamical explanation for the strongly asymmetric arm morphology of galaxies such as the LMC.

astro-ph.GA↗

arXiv2025

Capturing the short-term characteristics of a barred galaxy from a single snapshot

Using a dataset of stars from a barred galaxy that provides instantaneous positions and velocities in the sky, we propose a method to identify its key structures, such as the central bar and spiral arms, and to determine the bar pattern speed in the short term. This is accomplished by applying combinatorial and topological data analysis techniques to the available star-state information set. To validate the methodology, we apply it to two scenarios: a test particle simulation and a N-body simulation, both evaluated when the bar is fully formed. In both cases, the results are robust and consistent. We then use these outcomes to calibrate a classical dynamical model and compute related structures, such as equilibrium points and invariant manifolds, which we verify align with the galaxy's spiral arms.

astro-ph.GA↗

arXiv2023

Formation of asymmetric arms in barred galaxies

We establish a dynamical mechanism to explain the origin of the asymmetry between the arms observed in some barred disk galaxies, where one of the two arms emanating from the bar ends is very well defined, while the second one displays a ragged structure, extending between its ridge and the bar. To this purpose, we study the invariant manifolds associated to the Lyapunov periodic orbits around the unstable equilibrium points at the ends of the bar. Matter from the galaxy center is transported along these manifolds to the periphery, forming this way the spiral arms that emanate from the bar ends. If the mass distribution in the galaxy center is not homogeneous, because of an asymmetric bar with one side stronger than the other, or because of a non-centered bulge, the dynamics about the two unstable Lagrange points at the ends of the bar will not be symmetric as well. One of their invariant manifolds becomes more extended than the other, enclosing a smaller section and the escaping orbits on it are fewer and dispersed in a wider region. The result is a weaker arm, and more ragged than the one at the other end of the bar.

astro-ph.GA↗