Kinematic study of the Orion Complex: Analysing the young stellar clusters from big and small structures

TL;DR

This study uses Gaia DR3 data and clustering algorithms to analyze the spatial and kinematic properties of young stellar clusters in the Orion Complex, revealing expansion patterns and sub-structures.

Contribution

It introduces a hierarchical clustering approach to classify Orion's stellar groups into big and small structures, identifying new clusters and analyzing their dynamics.

Findings

Evidence of expansion in Orion OB1 association.

Detection of sub-structures within larger clusters.

Identification of new small stellar groups.

Abstract

In this work, we analysed young stellar clusters with spatial and kinematic coherence in the Orion star-forming complex. For this study, we selected a sample of pre-main sequence candidates using parallaxes, proper motions and positions on the colour-magnitude diagram. After applying a hierarchical clustering algorithm in the 5D parameter space provided by Gaia DR3, we divided the recovered clusters into two regimes: Big Structures and Small Structures, defined by the number of detected stars per cluster. In the first regime, we found 13 stellar groups distributed along the declination axis in the regions where there is a high density of stars. In the second regime, we recovered 34 clusters classified into two types: 14 as small groups completely independent from the larger structures, including four candidates of new clusters, and 12 classified as sub-structures embedded within five larger clusters. Additionally, radial velocity data from APOGEE-2 and GALAH DR3 was included to study the phase space in some regions of the Orion complex. From the Big Structure regime, we found evidence of a general expansion in the Orion OB1 association over a common centre, giving a clue about the dynamical effects the region is undergoing. Likewise, in the Small Structure regime, the projected kinematics shows the ballistic expansion in the $\lambda$ Orionis association and the detection of likely events of clusters' close encounters in the OB1 association.