Description
(Ultra) luminous infrared galaxies ((U)LIRGs) are nearby laboratories that allow us to study similar processes to those occurring in high redshift submillimeter galaxies. Understanding the heating and cooling mechanisms in these galaxies can give us insight into the driving mechanisms in their more distant counterparts. Molecular emission lines play a crucial role in cooling excited gas, and recently, with Herschel Space Observatory we have been able to observe the rich molecular spectrum. Carbon monoxide (CO) is the most abundant and one of the brightest molecules in the Herschel wavelength range. CO transitions from J=4-3 to 13-12 are observed with Herschel, and together, these lines trace the excitation of CO. We study Arp 299, a colliding galaxy group, with one component (A) harboring an active galactic nucleus and two more (B and C) undergoing intense star formation. For Arp 299 A, we present PACS spectrometer observations of high-J CO lines up to J=20-19 and JCMT observations of ^13^CO and HCN to discern between UV heating and alternative heating mechanisms.
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