The comparison of H2CO （110-111）, C^18O （1-0） and the continuum towards molecular clouds

We present large scale observations of C^18O （1-0） towards four massive star forming regions： MON R2, S156, DR17/L906 and M17/M18. The transitions of H2CO （110-111）, C^18O （1-0） and the 6cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non-LTE...

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Published in天文和天体物理学研究：英文版 no. 8; pp. 959 - 970
Main Author Xin-Di Tang Jarken Esimbek Jian-Jun Zhou Gang Wu Daniel Okoh
Format Journal Article
LanguageEnglish
Published 2014
Subjects
CO吸附
TE模型
亮度温度
分子云
吸收线
恒星形成区
温度范围
连续辐射
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Summary:We present large scale observations of C^18O （1-0） towards four massive star forming regions： MON R2, S156, DR17/L906 and M17/M18. The transitions of H2CO （110-111）, C^18O （1-0） and the 6cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non-LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 - 8 K. The excitation of the H2CO absorption line is affected by strong background continuum emission. From a comparison of H2CO and C^18O maps, we found that the extent of H2CO absorption is broader than that of C^18O emission in the four regions. Except for the DR17 region, the maximum in H2CO absorption is located at the same position as the C^18O peak. A good correlation between intensities and widths of H2CO absorption and C^18O emission lines indicates that the H2CO absorption line can trace the dense, warm regions of a molecular cloud. We find that N（H2CO） is well correlated with N（ C^18O） in the four regions and that the average ratio of column densities is （N（H2CO）/N（ClSO）） ～0.03.
Bibliography:ISM; clouds -- molecules -- stars; formation
We present large scale observations of C^18O （1-0） towards four massive star forming regions： MON R2, S156, DR17/L906 and M17/M18. The transitions of H2CO （110-111）, C^18O （1-0） and the 6cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non-LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 - 8 K. The excitation of the H2CO absorption line is affected by strong background continuum emission. From a comparison of H2CO and C^18O maps, we found that the extent of H2CO absorption is broader than that of C^18O emission in the four regions. Except for the DR17 region, the maximum in H2CO absorption is located at the same position as the C^18O peak. A good correlation between intensities and widths of H2CO absorption and C^18O emission lines indicates that the H2CO absorption line can trace the dense, warm regions of a molecular cloud. We find that N（H2CO） is well correlated with N（ C^18O） in the four regions and that the average ratio of column densities is （N（H2CO）/N（ClSO）） ～0.03.
11-5721/P
ISSN:1674-4527
2397-6209