Molecular Outflows in Low- and High-Mass Star Forming Regions

TL;DR

This review synthesizes current knowledge on molecular outflows from young stars, comparing models with observations, and discusses their impact on star-forming environments and future research directions.

Contribution

It provides a comprehensive comparison of outflow models with observational data and proposes a new perspective on explaining diverse outflow properties.

Findings

Multiple outflow models are insufficient to explain observed properties.

Outflows significantly disrupt their surrounding environment.

Shock-induced chemistry can serve as a chemical clock for outflow evolution.

Abstract

We review the known properties of molecular outflows from low- and high-mass young stars. General trends among outflows are identified, and the most recent studies on the morphology, kinematics, energetics, and evolution of molecular outflows are discussed, focusing on results from high-resolution millimeter observations. We review the existing four broad classes of outflow models and compare numerical simulations with the observational data. A single class of models cannot explain the range of morphological and kinematic properties that are observed, and we propose a possible solution. The impact of outflows on their cloud is examined, and we review how outflows can disrupt their surrounding environment, through the clearing of gas and the injection of momentum and energy onto the gas at distances from their powering sources from about 0.01 to a few pc. We also discuss the effects of shock-induced chemical processes on the ambient medium, and how these processes may act as a chemical clock to date outflows. Lastly, future outflow research with existing and planned millimeter and submillimeter instruments is presented.