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 $3.5^{\circ }\times 3.1^{\circ }$. The Cas giant molecular cloud (GMC) mainly consists of three individual clouds with masses on the order of $10^4-10^5{M}_{\odot }$. The total mass derived from the ${}^{13}\mathrm{CO}$ emission of the GMC is 2.1$\times 10^5{M}_{\odot }$ and is 9.5$\times 10^5{M}_{\odot }$ from the ${}^{12}\mathrm{CO}$ emission. Two regions with broadened (6$-$7 km s${}^{-1}$) or asymmetric ${}^{12}$CO line profiles are found in the vicinity (within a 10${}^{\prime }\times 10^{\prime }$ 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. $\hat{I}{\pm }_{\mathrm{vir}}<2$). 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 $1.6\times 10^{21}$ cm${}^{-2}$ and half the mass of the GMC is contained in regions with H${}_2$ column density lower than $3\times 10^{21}$ cm${}^{-2}$, which is well below the threshold of star formation. The distribution of the YSO candidates in the region shows no agglomeration.

24 pages, 18 figures