تقرير
A systematic TMRT observational study of Galactic $^{12}$C/$^{13}$C ratios from Formaldehyde
| العنوان: | A systematic TMRT observational study of Galactic $^{12}$C/$^{13}$C ratios from Formaldehyde |
|---|---|
| المؤلفون: | Yan, Y. T., Zhang, J. S., Henkel, C., Mufakharov, T., Jia, L. W., Tang, X. D., Wu, Y. J., Li, J., Zeng, Z. A., Wang, Y. X., Li, Y. Q., Huang, J., Jian, J. M. |
| سنة النشر: | 2019 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - Astrophysics of Galaxies |
| الوصف: | We present observations of the C-band $1_{10}-1_{11}$ (4.8 GHz) and Ku-band $2_{11}-2_{12}$ (14.5 GHz) K-doublet lines of H$_2$CO and the C-band $1_{10}-1_{11}$ (4.6 GHz) line of H$_2$$^{13}$CO toward a large sample of Galactic molecular clouds, through the Shanghai Tianma 65-m radio telescope (TMRT). Our sample with 112 sources includes strong H$_2$CO sources from the TMRT molecular line survey at C-band and other known H$_2$CO sources. All three lines are detected toward 38 objects (43 radial velocity components) yielding a detection rate of 34\%. Complementary observations of their continuum emission at both C- and Ku-bands were performed. Combining spectral line parameters and continuum data, we calculate the column densities, the optical depths and the isotope ratio H$_2$$^{12}$CO/H$_2$$^{13}$CO for each source. To evaluate photon trapping caused by sometimes significant opacities in the main isotopologue's rotational mm-wave lines connecting our measured K-doublets, and to obtain $^{12}$C/$^{13}$C abundance ratios, we used the RADEX non-LTE model accounting for radiative transfer effects. This implied the use of the new collision rates from \citet{Wiesenfeld2013}. Also implementing distance values from trigonometric parallax measurements for our sources, we obtain a linear fit of $^{12}$C/$^{13}$C = (5.08$\pm$1.10)D$_{GC}$ + (11.86$\pm$6.60), with a correlation coefficient of 0.58. D$_{GC}$ refers to Galactocentric distances. Our $^{12}$C/$^{13}$C ratios agree very well with the ones deduced from CN and C$^{18}$O but are lower than those previously reported on the basis of H$_2$CO, tending to suggest that the bulk of the H$_2$CO in our sources was formed on dust grain mantles and not in the gas phase. Comment: 27 pages, 8 figures, 7 tables. Accepted for publication in The Astrophysical Journal |
| نوع الوثيقة: | Working Paper |
| DOI: | 10.3847/1538-4357/ab17d6 |
| URL الوصول: | http://arxiv.org/abs/1904.04108 |
| رقم الأكسشن: | edsarx.1904.04108 |
| قاعدة البيانات: | arXiv |
| DOI: | 10.3847/1538-4357/ab17d6 |
|---|