2019ApJ...874..172K

The formaldehyde H₂CO(1₁₀-1₁₁) absorption line and H110α radio recombination line have been observed toward the Aquila Molecular Cloud using the Nanshan 25 m telescope operated by the Xinjiang Astronomical Observatory CAS. These first observations of the H₂CO (1₁₀-1₁₁) absorption line determine the extent of the molecular regions that are affected by the ongoing star formation in the Aquila molecular complex and show some of the dynamic properties. The distribution of the excitation temperature T_ex for H₂CO identifies the two known star formation regions W40 and Serpens South as well as a smaller new region Serpens 3. The intensity and velocity distributions of H₂CO and ¹³CO(1-0) do not agree well with each other, which confirms that the H₂CO absorption structure is mostly determined by the excitation of the molecules resulting from the star formation rather than by the availability of molecular material as represented by the distribution. Some velocity-coherent linear ¹³CO(1-0) structures have been identified in velocity channel maps of H₂CO and it is found that the three star formation regions lie on the intersect points of filaments. The H110α emission is found only at the location of the W40 H II region and spectral profile indicates a redshifted spherical outflow structure in the outskirts of the H II region. Sensitive mapping of H₂CO absorption of the Aquila Complex has correctly identified the locations of star formation activity in complex molecular clouds and the spectral profiles reveal the dominant velocity components and may identify the presence of outflows.