http://arxiv.org/abs/2201.07418
We present $\sim$0.”3 (114 pc) resolution maps of [CI] $^{3}P_{1}$-$^{3}P_{0}$ (hereafter [CI] (1-0)) and $^{12}$CO (1-0) obtained toward Arp 220 with the Atacama Large Millimeter/submillimeter Array. The overall distribution of the [CI] (1-0) emission is consistent with the CO (1-0). While the [CI] (1-0) and CO (1-0) luminosities of the system follow the empirical linear relation for the unresolved ULIRG sample, we find a sublinear relation between [CI] (1-0) and CO (1-0) using the spatially-resolved data. We measure the [CI] (1-0)/CO (1-0) luminosity ratio per pixel in star-forming environments of Arp 220 and investigate its dependence on the CO (3-2)/CO (1-0) ratio ($R_{\rm CO}$). On average, the [CI] (1-0)/CO (1-0) luminosity ratio is almost constant up to $R_{\rm CO} \simeq 1$ and then increases with $R_{\rm CO}$. According to the radiative transfer analysis, a high CI/CO abundance ratio is required in regions with high [CI] (1-0)/CO (1-0) luminosity ratios and $R_{\rm CO} > 1$, suggesting that the CI/CO abundance ratio varies at $\sim$100 pc scale in Arp 220. The [CI] (1-0)/CO (1-0) luminosity ratio depends on multiple factors and may not be straightforward to interpret. We also find the high-velocity components traced by [CI] (1-0) in the western nucleus, likely associated with the molecular outflow. The [CI] (1-0)/CO (1-0) luminosity ratio in the putative outflow is 0.87 $\pm$ 0.28, which is four times higher than the average ratio of Arp 220. While there is a possibility that the [CI] (1-0) and CO (1-0) emission traces different components, we suggest that the high line ratios are likely because of elevated CI/CO abundance ratios based on our radiative transfer analysis. A CI-rich and CO-poor gas phase in outflows could be caused by the irradiation of the cosmic rays, the shock heating, and the intense radiation field.
J. Ueda, T. Michiyama, D. Iono, et. al.
Thu, 20 Jan 22
26/77
Comments: 16 pages, 10 Figures, 2 tables, accepted for publication in PASJ
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