Spitzer spectral line mapping of protostellar outflows: I. Basic data and outflow energetics

TL;DR

This study uses Spitzer spectral mapping to analyze protostellar outflows, revealing detailed molecular hydrogen emission and energetics, and contrasting non-dissociative and dissociative shock contributions in star-forming regions.

Contribution

First detailed spectral maps of protostellar outflows covering key molecular and atomic lines, providing new insights into outflow energetics and shock processes.

Findings

H2 luminosities range from 0.02 to 0.75 L_solar.

Molecular hydrogen lines dominate cooling in warm gas.

[FeII] emission traces faster, dissociative shocks.

Abstract

We report the results of spectroscopic mapping observations carried out toward protostellar outflows in the BHR71, L1157, L1448, NGC 2071, and VLA 1623 molecular regions using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations, covering the 5.2 - 37 micron spectral region, provide detailed maps of the 8 lowest pure rotational lines of molecular hydrogen and of the [SI] 25.25 micron and [FeII] 26.0 micron fine structure lines. The molecular hydrogen lines, believed to account for a large fraction of the radiative cooling from warm molecular gas that has been heated by a non-dissociative shock, allow the energetics of the outflows to be elucidated. Within the regions mapped towards these 5 outflow sources, total H2 luminosities ranging from 0.02 to 0.75 L(solar) were inferred for the sum of the 8 lowest pure rotational transitions. By contrast, the much weaker [FeII] 26.0 micron fine structure transition traces faster, dissociative shocks; here, only a small fraction of the fast shock luminosity emerges as line radiation that can be detected with Spitzer/IRS.