The role of radial migration in open cluster and field star populations with Gaia dr3

TL;DR

This study uses Gaia DR3 data to compare the dynamical evolution of open clusters and field stars, revealing that older clusters tend to have more eccentric orbits and higher survival probabilities, highlighting the impact of radial migration.

Contribution

It provides a comparative analysis of the kinematic evolution of open clusters and field stars, emphasizing the role of orbital eccentricity in cluster longevity.

Findings

Younger clusters (<2-3 Gyr) are more resistant to perturbations.

Older clusters (>3 Gyr) have more eccentric, inclined orbits.

Oldest clusters tend to be more massive with higher eccentricity orbits.

Abstract

The survival time of a star cluster depends on its total mass, density, and thus size, as well as on the environment in which it was born and in which lies. Its dynamical evolution is influenced by various factors such as gravitational effects of the Galactic bar, spiral structures, and molecular clouds. Overall, the factors that determine the longevity of a cluster are complex and not fully understood. This study aims to investigate if open clusters and field stars respond differently to the perturbations that cause radial migration. In particular, we aim at understanding the nature of the oldest surviving clusters. We compared the time evolution of the kinematic properties of two Gaia DR3 samples: the first sample is composed of $\sim$40 open clusters and the second one of $\sim$66,000 MSTO field stars. Both selected samples are composed of stars selected with the same quality criterion, belonging to the thin disc, in a similar metallicity range, located in the same Galactocentric region [7.5-9 kpc] and with ages >1 Gyr. We performed a statistical analysis comparing the properties of the samples of field stars and of open clusters. A qualitative comparison of kinematic and orbital properties reveals that clusters younger than 2-3 Gyr are more resistant to perturbations than field stars and they move along quasi-circular orbits. Conversely, clusters older than approximately 3 Gyr have more eccentric and inclined orbits than isolated stars in the same age range. Such orbits lead them to reach higher elevations on the Galactic plane, maximising their probability to survive several Gyr longer. A formal statistical analysis reveals that there are differences among the time evolution of most of the kinematic and orbital properties of field stars and open clusters. Our results suggest that oldest survived clusters are usually more massive and move on orbits with higher eccentricity.