Protostellar outflows: a window to the past

Abstract

During the early phases of low-mass star formation, episodic accretion causes the ejection of high-velocity outflow bullets, which carry a fossil record of the driving protostar’s accretion history. We present 44 SPH simulations of 1 M⊙ cores, covering a wide range of initial conditions, and follow the cores for five free-fall times. Individual protostars are represented by sink particles, and the sink particles launch episodic outflows using a subgrid model. The Optics algorithm is used to identify individual episodic bullets within the outflows. The parameters of the overall outflow and the individual bullets are then used to estimate the age and energetics of the outflow, and the accretion events that triggered it; and to evaluate how reliable these estimates are, if observational uncertainties and selection effects (like inclination) are neglected. Of the commonly used methods for estimating outflow ages, it appears that those based on the length and speed of advance of the lobe are the most reliable in the early phases of evolution, and those based on the width of the outflow cavity and the speed of advance are most reliable during the later phases. We describe a new method that is almost as accurate as these methods, and reliable throughout the evolution. In addition we show how the accretion history of the protostar can be accurately reconstructed from the dynamics of the bullets if each lobe contains at least two bullets. The outflows entrain about ten times more mass than originally ejected by the protostar.

The Evolution of Protostellar Outflow Cavities, Kinematics, and Angular Distribution of Momentum and Energy in Orion A: Evidence for Dynamical Cores

“…From Figure 9, it is clear that Class I protostars have the highest total molecular outflow mass rate. This is opposite to the recent simulations showing the decrease in outflow mass-loss rate from Class 0 to Class I protostars (Rohde et al 2022). The molecular outflow mass rate per lobe of Class I protostars is around 60% higher than that of Class 0 protostars and 6 times higher than flatspectrum sources.…”

“…However, this simple method is heavily dependent on observational parameters (see Section 5.1) and inaccurately assumes that all the gas in the molecular outflow is moving at a uniform (constant) velocity from the source position to the current position. One problem with this assumption is that the gas in a molecular outflow is mostly made of material that has been entrained by the underlying protostellar wind rather than material that was launched by the protostar-disk system (Offner & Chaban 2017;Rohde et al 2022).…”

HOPS 361-C’s Jet Decelerating and Precessing through NGC 2071 IR

“…This is consistent with local and rapid decay of the jet's kinetic energy except if the jet's ejection velocity increases with time. Prior studies have investigated protostellar outflowinduced feedback into molecular clouds (e.g., Matzner 2007;Carroll et al 2009;Raga et al 2009;Federrath et al 2014;Frank et al 2014;Nakamura & Li 2014;Rohde et al 2022). The short 0.2 pc dissipation length in HOPS 361-C's jet and total kinetic energy suggest that precessing binary systems could sustain and affect the distribution of length scales for outflow-induced turbulent energy injected into NGC 2071 IR.…”

Shedding Light on the Ejection History of Molecular Outflows: Multiple Velocity Modes and Precession

“…Jets and outflows develop as protostellar accretion occurs and they aid in the removal of angular momentum from the collapsing protostellar core. The morphology and kinematics of molecular outflows could thus provide fossil records of the accretion history of a protostar (Rohde et al 2022). Molecular outflows from young protostars extend up to a few ∼0.1 pc, with collimation angles of a few degrees only and velocities up to 100 km s −1 (see, e.g., the review by Bally 2016).…”