Spitzer IRAC Color Diagnostics for Extended Emission in Star Forming Regions

TL;DR

This paper develops IRAC color diagnostics to analyze extended emission in star-forming regions, enabling differentiation between UV fluorescent and shock-excited molecular hydrogen emissions using Spitzer data.

Contribution

It introduces new IRAC color diagnostics based on Cloudy simulations to distinguish emission mechanisms in PDRs, validated with observations of NGC 2316.

Findings

Consistent PDR structure analysis with previous studies

Identification of shock-excited gas in NGC 2316

Diagnostic method applicable to other star-forming regions

Abstract

The infrared data from the Spitzer Space Telescope has provided an invaluable tool for identifying physical processes in star formation. In this study we calculate the IRAC color space of UV fluorescent molecular hydrogen (H$_2$) and Polycyclic Aromatic Hydrocarbon (PAH) emission in photodissociation regions (PDRs) using the Cloudy code with PAH opacities from Draine & Li 2007. We create a set of color diagnostics that can be applied to study the structure of PDRs and to distinguish between FUV excited and shock excited H$_2$ emission. To test this method we apply these diagnostics to Spitzer IRAC data of NGC 2316. Our analysis of the structure of the PDR is consistent with previous studies of the region. In addition to UV excited emission, we identify shocked gas that may be part of an outflow originating from the cluster.