Other
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008acasn..49..144z&link_type=abstract
Acta Astronomica Sinica, vol. 49, no. 2, p. 144-158
Other
1
Stars: Formation, Ism: Lines, Stars: Emission Line, Ism: Molecules
Scientific paper
With the 13.7m millimeter wave telescope of Purple Mountain Observatory at the Qinghai Station,simultaneous observations of 12CO, 13CO and C18O line emission were carried out towards 24 Galactic high-mass star forming cores which were associated with water masers and surveyed by the Spitzer. All ofthem were detected in C18O lines with the average map size of about 8'×&8'. In our sample 11 cores were mapped within the regions where C18O integrated intensity reaches the half maximum,while the rest were not observed with so large scale of mapping because of the low SNR or the intrinsically extended morphology of the cores. HCN and CS molecules are widely used as tracers of dense gas due to their high critical density. However HCN and CS are always optically thick, while 13CO is mostly optically thin and C18O is absolutely optically thin, which make us able to detect innermost to the core of molecular cloud. On the other hand, there has been few big-scale survey of C18O recently, therefore we just execute mapping comparison, especially mapping of optically-thin molecule C18O to study inside characteristics of molecular cloud, which supplies useful reference for subsequent observation and research to the molecule C18O with telescope of higher sensitivity. We discussed the characteristics and the integrated intensity ratios of 12CO to 13CO (R12/13), 13CO to C18O (R13/18) and 12CO to C18O (R12/18) statistically towards the 11 fully mapped dense cores in our sample. We concluded that as a tracer of of high column density of the dense gas, C18O is absolutely optically thin and can detect the detailed structure of the cores. In general, these three ratios gradually increase from the innermost to the outer part of the cores. We found that the integrated intensity ratio R12/13 ranges from 2 to 6; R13/18 4 to 20 with a small fluctuation of 6---12 in the inner part of the cores; R12/18 13---90, and typically 13---50 in the denser regions of the cores. Our later work is going to statistically compare diverse gas tracers13CO, HCN, CS et al.) and different ratios(HCN/13CO, HCN/C18O et al.) with star formation rate (indicated with Spitzer 8, 24, 70, 160 microns et al.) according to those data above, the observing result of HCN, CS, HNC, HCO+ and Spitzer mid/far infrared data. Then the best detectors of both dense gas and star-forming rate can be confirmed. The local correlation between high-density molecular gas and star-forming rate is deduced.
Gao Yanfang
Zhang Yue-Lian
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