Kunihiko Tanaka, Tomoharu Oka, Shinji Matsumura, Makoto Nagai, Kazuhisa Kamegai
This letter presents a Nyquist-sampled, high-resolution [CI] 3P1-3P0 map of
the -0.2 deg < l < 1.2 deg x -0.1 deg < b < 0 deg region in the Central
Molecular Zone (CMZ) taken with the Atacama Submillimeter Telescope Experiment
(ASTE) 10 m telescope. We have found that molecular clouds in the CMZ can be
classified into two groups according to their [CI]/13CO intensity ratios: a
bulk component consisting with clouds with a low, uniform [CI]/13CO ratio
(0.45) and another component consisting of clouds with high [CI]/13CO ratios (>
0.8). The [CI]-enhanced regions appear in M-0.02-0.07, the circumnuclear disk,
the 180-pc ring and the high velocity compact cloud CO+0.02-0.02. We have
carried out a large velocity gradient (LVG) analysis and have derived the
C^0/CO column density ratio for M-0.02-0.07 as 0.47, which is approximately
twice that of the bulk component of the CMZ (0.26). We propose several
hypotheses on the origin of high C^0 abundance in M-0.02-0.07, including
cosmic-ray/X-ray dissociation and mechanical dissociation of CO in the
pre-existing molecular clouds. We also suggest the possibility that M-0.02-0.07
is a cloud at an early stage of chemical evolution from diffuse gas, which was
possibly formed by the bar-induced mass inflow in the Galactic Center region.
View original:
http://arxiv.org/abs/1111.4029
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