English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

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$$^{13}$CO toward a large sample ofGalactic molecular clouds, through the Shanghai Tianma 65-m radio telescope(TMRT). Our sample with 112 sources includes strong H$_2$CO sources from theTMRT molecular line survey at C-band and other known H$_2$CO sources. All threelines are detected toward 38 objects (43 radial velocity components) yielding adetection rate of 34\%. Complementary observations of their continuum emissionat both C- and Ku-bands were performed. Combining spectral line parameters andcontinuum data, we calculate the column densities, the optical depths and theisotope ratio H$_2$$^{12}$CO/H$_2$$^{13}$CO for each source. To evaluate photontrapping caused by sometimes significant opacities in the main isotopologue'srotational mm-wave lines connecting our measured K-doublets, and to obtain$^{12}$C/$^{13}$C abundance ratios, we used the RADEX non-LTE model accountingfor radiative transfer effects. This implied the use of the new collision ratesfrom \citet{Wiesenfeld2013}. Also implementing distance values fromtrigonometric parallax measurements for our sources, we obtain a linear fit of$^{12}$C/$^{13}$C = (5.08$\pm$1.10)D$_{GC}$ + (11.86$\pm$6.60), with acorrelation coefficient of 0.58. D$_{GC}$ refers to Galactocentric distances.Our $^{12}$C/$^{13}$C ratios agree very well with the ones deduced from CN andC$^{18}$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 ondust grain mantles and not in the gas phase.

A systematic TMRT observational study of Galactic $^{12}$C/$^{13}$C ratios from Formaldehyde