# Ejection History of the IRAS 04166+2706 Molecular Jet

## TL;DR

This paper investigates the velocity structure of the IRAS 04166+2706 molecular jet, revealing a saw-tooth pattern explained by a spherically expanding wind model and supported by numerical simulations, shedding light on its ejection history.

## Contribution

It introduces a geometric model of a spherically expanding wind to explain the jet's velocity pattern, supported by numerical simulations, providing new insights into the jet's ejection history.

## Key findings

- The velocity pattern can be explained by a spherically expanding wind model.
- The inclination angle of 52° explains the observed velocity features.
- Numerical simulations support the geometric interpretation.

## Abstract

The high-velocity molecular jet driven by Class 0 protostar IRAS 04166+2706 exhibits a unique saw-tooth velocity pattern. It consists of a series of well-aligned symmetric knots with similar averaged speeds, whose speeds at peaks of emission decreases roughly linearly away from the origin. Recent ALMA observations of knots R6 and B6 reveal kinematic behavior with expansion velocity increasing linearly from the axis to the edge. This pattern can be formed by a spherically expanding wind with axial density concentration. In this picture, the diverging velocity profile naturally possesses an increasing expansion velocity away from the axis, resulting in a tooth-like feature on the position-velocity diagram through projection. Such geometric picture predicts a correspondence between the slopes of the teeth and the outflow inclination angles, and the same inclination angle of 52$^\circ$ of the IRAS 04166+2706 can generally explain the whole pattern. Aided by numerical simulations in the framework of unified wind model by Shang et al. (2006), the observed velocity pattern can indeed be generated. A proper geometrical distribution of the jet and wind material is essential to the reconstruction the ejection history of the system.