The Shock Dynamics of Heterogeneous YSO Jets: 3-D Simulations Meet Multi-Epoch Observations

TL;DR

This paper uses 3-D simulations and HST observations to study how small-scale clumps in YSO jets interact, creating complex morphologies and kinematic patterns observed in emission lines, highlighting the importance of heterogeneity.

Contribution

The study introduces a new non-equilibrium cooling method in 3-D simulations to accurately model the dynamics and emission features of heterogeneous YSO jets, aligning well with observations.

Findings

Simulations reproduce observed knot and shock structures in YSO jets.

Interactions of clumps produce bright knots and frothy emission patterns.

Results support heterogeneity as a key factor in jet evolution.

Abstract

High resolution observations of Young Stellar Object (YSO) jets show them to be composed of many small-scale knots or clumps. In this paper we report results of 3-D numerical simulations designed to study how such clumps interact and create morphologies and kinematic patterns seen in emission line observations. Our simulations focus on clump scale dynamics by imposing velocity differences between spherical, over-dense regions which then lead to the formation of bow shocks as faster clumps overtake slower material. We show that much of the spatial structure apparent in emission line images of jets arises from the dynamics and interactions of these bow shocks. Our simulations show a variety of time-dependent features, including bright knots associated with Mach stems where the shocks intersect, a "frothy" emission structure that arises from the presence of the Non-linear Thin Shell Instability (NTSI) along the surfaces of the bow shocks, and the merging and fragmentation of clumps. Our simulations use a new non-equilibrium cooling method to produce synthetic emission maps in H$\alpha$ and [S II]. These are directly compared with multi-epoch Hubble Space Telescope (HST) observations of Herbig-Haro (HH) jets. We find excellent agreement between features seen in the simulations and the observations in terms of both proper motion and morphologies. Thus we conclude that YSO jets may be dominated by heterogeneous structures and that interactions between these structures and the shocks they produce can account for many details of YSO jet evolution.