A 3D View of Orion: I. Barnard's Loop

TL;DR

This paper presents a 3D model of the Orion region, suggesting that feedback from clusters OBP-B1 and Orion X contributed to the formation of Barnard's Loop through large-scale gas expansion and cavity formation.

Contribution

It introduces a detailed 3D model of Orion's structure, highlighting the combined feedback effects of OBP-B1 and Orion X in shaping Barnard's Loop.

Findings

OBP-B1 and Orion X feedback contributed to Orion's large-scale gas expansion.

Barnard's Loop corresponds with a dust cavity around OBP-B1.

Expansion likely influenced the morphology of Orion's molecular clouds.

Abstract

Barnard's Loop is a famous arc of H$\alpha$ emission located in the Orion star-forming region. Here, we provide evidence of a possible formation mechanism for Barnard's Loop and compare our results with recent work suggesting a major feedback event occurred in the region around 6 Myr ago. We present a 3D model of the large-scale Orion region, indicating coherent, radial, 3D expansion of the OBP-Near/Brice\~{n}o-1 (OBP-B1) cluster in the middle of a large dust cavity. The large-scale gas in the region also appears to be expanding from a central point, originally proposed to be Orion X. OBP-B1 appears to serve as another possible center, and we evaluate whether Orion X or OBP-B1 is more likely to be the cause of the expansion. We find that neither cluster served as the single expansion center, but rather a combination of feedback from both likely propelled the expansion. Recent 3D dust maps are used to characterize the 3D topology of the entire region, which shows Barnard's Loop's correspondence with a large dust cavity around the OPB-B1 cluster. The molecular clouds Orion A, Orion B, and Orion $\lambda$ reside on the shell of this cavity. Simple estimates of gravitational effects from both stars and gas indicate that the expansion of this asymmetric cavity likely induced anisotropy in the kinematics of OBP-B1. We conclude that feedback from OBP-B1 has affected the structure of the Orion A, Orion B, and Orion $\lambda$ molecular clouds and may have played a major role in the formation of Barnard's Loop.