Formaldehyde and RRLs in Molecular Clouds

Formation and destruction of molecules heavily influence behaviour of star-forming clouds by altering gas thermodynamic behaviour and strength of gas coupling to magnetic fields. Few of the important chemical species are hydrogen and formaldehyde ($\text{H}_2\text{CO}$). Understanding their distribution and properties in molecualr clouds with massive star formation potentially provides insights into the star formation process.

Formaldehyde absorption lines in particular are useful due to its independence from the kinetic temperature of the gas, allowing them to be detected in cold molecular clouds. Hydrogen radio recombination lines (RRLs) on the other hand allow for determination of clouds’ temperature, density, and kinematics, specifically in regions with high ionization fractions.

We observe formaldehyde absorption lines and RRLs in selected molecular clouds in the Bolocam Galactic Plane Survey (Aguirre et al., 2010) using the Nanshan 25-m radio telescope in Xinjiang, China. 88 out of the 217 clouds was detected with formaldehyde absorption lines, and 11 clouds with RRLs. Majority of the sources also potrayed complex velocity structures in their spectra, indicating the presence of multiple velocity components in the clouds.