Evidence for Radial Expansion at the Core of the Orion Complex with Gaia EDR3

TL;DR

This study uses Gaia data to analyze the core of the Orion complex, revealing radial expansion in two stellar groups possibly driven by stellar feedback, contrasting with more complex motions in other groups.

Contribution

It provides new evidence of radial expansion in specific Orion groups and links their motions to dust structures, highlighting feedback effects on star formation.

Findings

Radial expansion observed in Briceño-1 and OBP-near groups

Expansion confined to these groups, others show complex motions

Stars are located at the center of a dust shell

Abstract

We present a phase-space study of two stellar groups located at the core of the Orion complex: Brice\~no-1 and Orion Belt Population-near (OBP-near). We identify the groups with the unsupervised clustering algorithm, Shared Nearest Neighbor (SNN), which previously identified twelve new stellar substructures in the Orion complex. For each of the two groups, we derive the 3D space motions of individual stars using Gaia EDR3 proper motions supplemented by radial velocities from Gaia DR2, APOGEE-2, and GALAH DR3. We present evidence for radial expansion of the two groups from a common center. Unlike previous work, our study suggests that evidence of stellar group expansion is confined only to OBP-near and Brice\~no-1 whereas the rest of the groups in the complex show more complicated motions. Interestingly, the stars in the two groups lie at the center of a dust shell, as revealed via an extant 3D dust map. The exact mechanism that produces such coherent motions remains unclear, while the observed radial expansion and dust shell suggest that massive stellar feedback could have influenced the star formation history of these groups.