Galactic orbital motions of star clusters: static versus semicosmological time-dependent Galactic potentials

Abstract

In order to understand the orbital history of Galactic halo objects, such as globular clusters, authors usually assume a static potential for our Galaxy with parameters that appear at the present-day. According to the standard paradigm of galaxy formation, galaxies grow through a continuous accretion of fresh gas and a hierarchical merging with smaller galaxies from high redshift to the present day. This implies that the mass and size of disc, bulge, and halo change with time. We investigate the effect of assuming a live Galactic potential on the orbital history of halo objects and its consequences on their internal evolution. We numerically integrate backwards the equations of motion of different test objects located in different Galactocentric distances in both static and time-dependent Galactic potentials in order to see if it is possible to discriminate between them. We show that in a live potential, the birth of the objects, 13 Gyr ago, would have occurred at significantly larger Galactocentric distances, compared to the objects orbiting in a static potential. Based on the direct N-body calculations of star clusters carried out with collisional N-body code, NBODY6, we also discuss the consequences of the time-dependence of a Galactic potential on the early- and long-term evolution of star clusters in a simple way, by comparing the evolution of two star clusters embedded in galactic models, which represent the galaxy at present and 12 Gyr ago, respectively. We show that assuming a static potential over a Hubble time for our Galaxy as it is often done, leads to an enhancement of mass-loss, an overestimation of the dissolution rates of globular clusters, an underestimation of the final size of star clusters, and a shallower stellar mass function.

12 pages, 11 figures, 4 tables, accepted for publication in MNRAS

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• Enlightening the dynamical evolution of Galactic open clusters: an approach using Gaia DR3 and analytical descriptions
• The orbital evolution of UFDs and GCs in an evolving Galactic potential
• Identifying the possible ex-situ origin of the globular clusters of the Milky Way: A kinematic study
• Study of the Influence of an Evolving Galactic Potential on the Orbital Properties of 152 Globular clusters with Data from the Gaia EDR3 Catalogue
• The Escape of Globular Clusters from the Satellite Dwarf Galaxies of the Milky Way