3D Integral Field H₂ Spectroscopy in Outflows

Summary

We describe the new capability provided by integral field spectroscopy for simultaneously mapping a wide range of shocked emission lines across outflows at high spatial resolution. We have used the MPE-3D near-IR integral field spectrometer on the AAT to carry out a detailed observational study of the physics of shocked H₂ and [Fe II] excitation within individual bow shocks. Simultaneous measurement of line ratio variations with position across and along bow shocks will strongly constrain shock models in a number of outflow sources. In Orion, where broad H₂ line widths had previously implied magnetically moderated C shocks, our higher resolution echelle observations of the H₂ velocity profiles in two of the bullets (Tedds et al. 1999) contradict any steady-state molecular bow shock models. This suggests that instabilities or supersonic turbulence may be important in this case. 3D measurements of the corresponding H₂ level populations will address this.

Introduction

The nature of molecular shocks, which play an important role in the processes of momentum and energy transfer within star forming molecular clouds (McKee 1989), is still uncertain (Draine & McKee 1993). In this paper we describe how new developments in integral field spectroscopy provide us with the opportunity to self-consistently distinguish between competing shock models. The Orion molecular cloud is the brightest known source of shocked H₂ emission and as such has been the primary test bed for theoretical models.