# $\rm H_2CO$ and $\rm H110\alpha$ Observations toward the Aquila Molecular Cloud

## TL;DR

This study used the Nanshan 25 m telescope to observe formaldehyde and radio recombination lines in the Aquila Molecular Cloud, revealing star formation regions, molecular excitation conditions, filament intersections, and outflows.

## Contribution

First observations of H2CO and H110α lines in Aquila, mapping star formation activity and molecular excitation, and identifying filament intersections and outflows.

## Key findings

- Identified star formation regions W40, Serpens South, and Serpens 3.
- H110α emission only at W40, indicating localized H II region activity.
- Detected velocity-coherent filaments and outflow structures.

## Abstract

The formaldehyde $\rm H_2CO(1_{10} - 1_{11})$ absorption line and H$110\alpha$ radio recombination line (RRL) 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 $\rm H_2CO$ $(1_{10} - 1_{11})$ 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 $\rm H_2CO$ 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 $\rm H_2CO$ and $\rm ^{13}CO(1-0)$ do not agree well with each other, which confirms that the $\rm H_2CO$ 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 $\rm ^{13}CO(1-0)$ structures have been identified in velocity channel maps of $\rm H_2CO$ and it is found that the three star formation regions lie on the intersect points of filaments. The $\rm H110\alpha$ 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 $\rm H_2CO$ 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.