Measuring Turbulence with Young Stars in the Orion Complex

TL;DR

This study uses 6D stellar data from Gaia and APOGEE-2 to measure turbulence in the Orion Complex, revealing that young stars retain natal turbulence signatures, which vary with location and are influenced by supernovae.

Contribution

It introduces a novel method of probing interstellar turbulence through 6D stellar kinematics, providing a more complete 3D picture compared to gas-based studies.

Findings

Diffuse groups show turbulence consistent with Larson's relation.

Dense clusters like ONC have lost initial turbulent signatures.

Evidence of local energy injection from supernovae influences turbulence.

Abstract

Stars form in molecular clouds in the interstellar medium (ISM) with a turbulent kinematic state. Newborn stars therefore should retain the turbulent kinematics of their natal clouds. Gaia DR2 and APOGEE-2 surveys in combination provide three-dimensional (3D) positions and 3D velocities of young stars in the Orion Molecular Cloud Complex. Using the full 6D measurements, we compute the velocity structure functions (VSFs) of the stars in six different groups within the Orion Complex. We find that the motions of stars in all diffuse groups exhibit strong characteristics of turbulence. Their first-order VSFs have a power-law exponent ranging from $\sim0.2-0.5$ on scales of a few to a few tens of pc, generally consistent with Larson's relation. On the other hand, dense star clusters, such as the Orion Nebula Cluster (ONC), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. The VSFs of several individual groups and the whole Complex all show features supporting local energy injection from supernovae. The measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of the groups. Our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics of the ISM. Unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6D information of stars, presenting a more complete picture of the 3D interstellar turbulence.