Climbing the CO Ladder: An Automated CO Excitation Analysis Tool
Abstract
In order to determine the physical properties of the ISM in galactic nuclei, we fit the 12CO excitation ladder with a large grid of Photon-Dominated Region (PDR) and X-ray Dominated Region (XDR) models. Since the HerCULES open time key program is gathering many extragalactic SPIRE spectra with multiple 12CO transitions, we developed an automated process to analyze the excitation components in these galaxies. The program finds the chi-squared minimized fit of up to three PDR/XDR components, as well as graphically displaying the chi-squared values for the other models, in order to analyze the degeneracies of the best fit models. A test case to validate our method is the merger Arp 299, which is composed of three sources. Source A (IC 694) harbors a dust enshrouded AGN, Source B (NGC 3690) is a starburst nucleus, and Source C is a small compact galaxy to the northwest of the merging galaxies. We find that our method is successful at automatically fitting their CO ladders, as well as distinguishing between XDR and PDR excitation, especially for the highest J transitions. We also find that the analysis of the chi-squared distribution is essential to interpreting the best-fit models and determining their validity.
- Publication:
-
American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22123507R