Tuesday, 8/6/13

Just one paper today – and on [CI]! Shimajiri et al. have mapped the Orion-A molecular clouds in [CI] using the ASTE 10m telescope down in Chile. They find that the [CI] has a similar distribution to 12CO(1-0), but even more similar to 13CO(1-0) and C18O(1-0), which doesn’t fit well if the main route to C^0 is through photodissociation of CO. (Instead, C^0 must persist deep within molecular clouds. An option is perhaps some charge exchange reaction with sulphur…

Title: Extensive [CI] Mapping toward the Orion-A Molecular Cloud
Authors: Shimajiri, Yoshito; Sakai, Takeshi; Tsukagoshi, Takashi; Kitamura, Yoshimi; Momose, Munetake; Saito, Masao; Oshima, Tai; Kohno, Kotaro; Kawabe, Ryohei
Publication: eprint arXiv:1308.1036
Publication Date: 08/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: 14 pages, 4 figures, 1 table, ApJL accepted for publication
Bibliographic Code: 2013arXiv1308.1036S


We have carried out wide-field (0.17 degree^2) and high-angular resolution (21.3 arcsec ~ 0.04 pc) observations in [CI] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in the On-The-Fly (OTF) mode. Overall features of the [CI] emission are similar to those of the CO (1–0) emission in Shimajiri et al. 2011; the total intensity ratio of the [CI] to CO emission ranges from 0.05 to 0.2. The optical depth of the [CI] emission is found to be 0.1 — 0.75, suggesting optically thin emission. The column density of the [CI] emission is estimated to be (1.0 — 19) x 10^17 cm^-2. These results are consistent with the results of the previous [CI] observations with a low-angular resolution of 2.2 arcmin (e.g. Ikeda et al. 1999). In the nearly edge-on PDRs and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [CI] emission coincide with those of the CO emission, inconsistent with the prediction by the plane-parallel PDR model (Hollenbach & Tielens 1999). In addition, the [CI] distribution in the Orion A cloud is found to be more similar to those of the ^{13}CO (1–0), C^{18}O (1–0), and H^{13}CO^+ (1–0) lines than that of the CO (1–0) line, suggesting that the [CI] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud.

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