A Molecular Line Investigation of the Interaction between Mid-infrared Bubbles and the Interstellar Medium

TL;DR

This study used the Green Bank Telescope to analyze molecular lines in mid-infrared bubbles, revealing complex gas kinematics and interactions with surrounding clouds, but found no clear evidence of bubble-IRDC interactions or infall.

Contribution

First detailed molecular line investigation of MIR bubbles examining gas dynamics and interactions with IRDCs and YSOs.

Findings

Detected CS (1-0) emission in all sources.

No evidence of infall in the observed gas.

Complex non-Gaussian line shapes indicating multiple clouds.

Abstract

We used the Green Bank Telescope to detect molecular lines observed toward Mid-Infrared (MIR) bubbles N62, N65, N90, and N117. The bubbles were selected from Watson et al. (2016) who detected non-Gaussian CS (1-0) emission lines toward the bubbles. Two of the bubbles are adjacent to infrared dark clouds (IRDCs); we examined these sources for evidence of interaction between the bubble rim and IRDC. The other two bubbles contain YSOs interior to the bubble rim; in these sources we observed the gas near the YSOs. We detect CS (1-0) emission toward all of the sources, and in several pointings the CS emission shows non-Gaussian line shapes. HC$_3$N (5-4), C$^{34}$S (1-0), CH$_3$OH (1-0), and SiO (v=0) (1-0) were also detected in some pointings. We calculate column densities and abundances for the detected molecules. We compare the velocity of optically-thick CS emission with the velocity of the other, optically thin lines to look for evidence of infall. We find that even in pointings with non-Gaussian CS emission, our detections do not support an infall model. We interpret the kinematics of the gas in N62, N65, and N117 as likely evidence of multiple clouds along the line of sight moving at slightly offset velocities. We do not detect evidence of bubble rims interacting with IRDCs in N62 or N90. The gas interior to bubbles appears more disrupted than the gas in the IRDCs. N65 shows significantly stronger emission lines than the other sources, as well as the most complicated non-Gaussian line shapes.