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

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.

accepted in A&A, 10 pages, 9 figures

References in corpus (12)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Not all stars form in clusters - measuring the kinematics of OB associations with $Gaia$
• Significance Mode Analysis (SigMA) for hierarchical structures. An application to the Sco-Cen OB association
• Rotation in young massive star clusters
• Chamaeleon DANCe. Revisiting the stellar populations of Chamaeleon I and Chamaeleon II with Gaia-DR2 data
• Rotation of molecular clouds in M~51
• Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2
• Dynamical age of the Tucana-Horologium young stellar association
• The spin, expansion and contraction of open star clusters
• Evolution of star clusters with initial bulk rotation via N-body simulations
• Bayesian ages of local young stellar associations I. Through the expansion rate method