Presentation #333.03 in the session Molecular Clouds, HII Regions, and the ISM II.
Barnard’s Loop is a famous arc of H-alpha emission located in the Orion star forming region. We present new details of a possible formation mechanism for the Loop and compare our results with recent work suggesting a major feedback event occurred in the region around 6 Myr ago. In particular, we elaborate on the discovery of coherent, radial, 3D expansion of the OBP-Near/Briceno-1 (OBP-B1) cluster at the center of Barnard’s Loop from Swiggum et al. (2021). Simple estimates of gravitational effects from both stars and gas indicate that gravitational feedback from the gas may have strongly affected the kinematics of the stars in OBP-B1. We argue that a feedback event produced this cluster expansion and contributed to the formation of Barnard’s Loop and the Orion-Eridanus superbubble, though other feedback events were necessary to fully shape the region.
What can measures of feedback tell us about the larger Orion-Eridanus region? Through new modeling of Aluminum-26 emission from the COMPTEL satellite, a radioactive tracer of supernovae and Wolf-Rayet stars, we find on the order of 20 supernovae could produce the observed emission throughout the Orion-Eridanus region. Magnetic field polarization measurements show remarkable correspondence with the Aluminum-26, indicating both observables likely trace hot ejecta from these feedback events. Next, 3D dust mapping is used to characterize the topology of the entire region, which shows that Barnard’s Loop corresponds to a roughly spherical 3D cavity around the OPB-B1 cluster. We further report the discovery of a coherent dust ring that traces a subshell of gas in Orion-Eridanus and constrains the orientation of the Orion-Eridanus superbubble. Finally, we compare the entire region with simulations that form a structure remarkably similar to the observed properties of Barnard’s Loop and discuss their implications for understanding the history of the region.