Spitzer IRAC Detection and Analysis of Shocked Molecular Hydrogen Emission

TL;DR

This paper investigates how shocked molecular hydrogen's IRAC colors relate to physical conditions, enabling identification and thermal mapping of shocked gas in astrophysical objects using Spitzer data.

Contribution

It introduces a method to distinguish shocked H_2 emission in IRAC color space and demonstrates its application to create temperature maps from archival data.

Findings

High excitation H_2 occupies a unique IRAC color space region.

IRAC data can be used to map the thermal structure of shocked gas.

Temperature maps from IRAC data agree with spectroscopic measurements.

Abstract

We use statistical equilibrium equations to investigate the IRAC color space of shocked molecular hydrogen. The location of shocked H_2 in [3.6]-[4.5] vs [4.5]-[5.8] color is determined by the gas temperature and density of neutral atomic hydrogen. We find that high excitation H_2 emission falls in a unique location in the color-color diagram and can unambiguously be distinguished from stellar sources. In addition to searching for outflows, we show that the IRAC data can be used to map the thermal structure of the shocked gas. We analyze archival Spitzer data of Herbig-Haro object HH 54 and create a temperature map, which is consistent with spectroscopically determined temperatures.