CO rotational line emission from a dense knot in Cas A Evidence for active post-reverse-shock chemistry

Abstract

We report a Herschel detection of high-J rotational CO lines from a dense knot in the supernova remnant Cas A. Based on a combined analysis of these rotational lines, and previously observed ro-vibrational CO lines, we find the gas to be warm (two components at 400 and 2000 K) and dense (1e6-7 cm-3), with a CO column density of 5e17 cm-2. This, along with the broad line widths (400 kms-1), suggests that the CO emission originates in the post-shock region of the reverse shock. As the passage of the reverse shock dissociates any existing molecules, the CO has most likely reformed in the last few years, in the post-shock gas. The CO cooling time is comparable to the CO formation time, so possible heating sources (UV photons from the shock front, X-rays, electron conduction) to maintain the large column density of warm CO are discussed.

Accepted to A&A Letters, 4 pages, 4 figures

References in corpus (7)

• SN 2005cs in M51 II. Complete Evolution in the Optical and the Near-Infrared
• Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope
• Dust and the type II-plateau supernova 2004et
• Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af
• Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A
• Carbon Monoxide in the Cold Debris of Supernova 1987A
• Carbon Monoxide in the Cassiopeia A Supernova Remnant

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