High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS

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We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGN) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs).

• Using Herschel-PACS, we have detected transitions in the J$_{upp}$ = 14 - 20 range ($\lambda \sim$ 130 - 185 $\mu$m, $\nu \sim$ 1612 - 2300 GHz) with upper limits on (and in two cases, detections of) CO line fluxes up to J$_{upp}$ = 30.
• The PACS CO data obtained here provide the first well-sampled FIR extragalactic CO SLEDs for this range, and will be an essential reference for future high redshift studies.
• We find a large range in the overall SLED shape, even amongst galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize the excitation source of a galaxy.