The internal kinematics of local young stellar associations. Identifying correlations among age, expansion, rotation, and shear

TL;DR

This study investigates the internal motions of local young stellar associations, identifying key correlations influenced by the Galactic potential, which sheds light on star formation processes in our neighborhood.

Contribution

It provides the first robust statistical analysis linking internal kinematics of young stellar groups with Galactic influences, highlighting the role of the Galactic disk's gravitational potential.

Findings

Four correlations related to radial motions in the Galactic Z direction.

Galactic potential likely influences the observed internal motions.

Internal kinematics offer insights beyond current star-formation theories.

Abstract

Context. The local (<200 pc away) young (<50 Myr old) stellar associations (LYSA) provide fundamental evidence for the study of the star formation process in the local neighbourhood. Aims. We aim at exploring robust statistical correlations in the internal kinematics of LYSAs and of these with age. Methods. We analyse a public data set containing the linear velocity field parameters and expansion ages of 18 LYSAs. We identify the most robust correlations using frequentist and Bayesian methods. Results. Among the 45 correlations, we identify only four that passed both frequentist and Bayesian criteria, with these four related to radial motions in the Galactic Z direction. We hypothesise several origins for these four correlations and identify the gravitational potential of the Galactic disk as the most likely driving element. It imprinted the observed motions in the parent molecular clouds, and once the stars were formed, it also damped these motions on a timescale shorter than the LYSAs' ages. Conclusions. The internal kinematics of local young stellar associations contain fundamental information about the star-formation process that is not fully addressed by star-formation theories, in particular, rotation and shear. Although the Galactic potential appears to be the driving force of these correlations, we urge the theoretical community to provide predictions about the internal motions of expansion, rotation, and shear of stellar associations.