A Large-field J = 1 – 0 Survey of CO and Its Isotopologues toward the Cassiopeia A Supernova Remnant

Abstract

We have conducted a large-field simultaneous survey of 12 CO, 13 CO, and C 18 O J  = 1 − 0 emission toward the Cassiopeia A (Cas A) supernova remnant (SNR), which covers a sky area of 3.°5 × 3.°1. The Cas giant molecular cloud (GMC) mainly consists of three individual clouds with masses on the order of 10 4 −10 5 M ☉ . The total mass derived from the 13 CO emission of the GMC is 2.1 × 10 5 M ☉ and is 9.5 × 10 5 M ☉ from the 12 CO emission. Two regions with broadened (6–7 km s −1 ) or asymmetric 12 CO line profiles are found in the vicinity (within a 10′ × 10′ region) of the Cas A SNR, indicating possible interactions between the SNR and the GMC. Using the GAUSSCLUMPS algorithm, 547 13 CO clumps are identified in the GMC, 54% of which are supercritical (i.e., α vir  < 2). The mass spectrum of the molecular clumps follows a power-law distribution with an exponent of −2.20. The pixel-by-pixel column density of the GMC can be fitted with a log-normal probability distribution function (N-PDF). The median column density of molecular hydrogen in the GMC is 1.6 × 10 21 cm −2 and half the mass of the GMC is contained in regions with H 2 column density lower than 3 × 10 21 cm −2 , which is well below the threshold of star formation. The distribution of the YSO candidates in the region shows no agglomeration.