High-Sensitivity Observations of Molecular Lines with the Arecibo Telescope

TL;DR

This high-sensitivity survey of molecular lines with the Arecibo Telescope revealed new spectral features in star-forming regions, including excited OH and CH3OH absorption, providing insights into molecular environments and dynamics.

Contribution

The study presents the most sensitive molecular line survey in the 6.0-7.4 GHz range, detecting previously unseen spectral features in high-mass star-forming regions.

Findings

Detection of excited OH and 6.7 GHz CH3OH absorption lines.

Association between CH3OH absorption and radio continuum sources.

Broad 6.035 GHz OH absorption indicating expansion or outflow.

Abstract

We report on one of the highest sensitivity surveys for molecular lines in the frequency range 6.0 to 7.4 GHz conducted to date. The observations were done with the 305m Arecibo Telescope toward a sample of twelve intermediate/high-mass star forming regions. We searched for a large number of transitions of different molecules, including CH3OH and OH. The low RMS noise of our data (~5 mJy for most sources and transitions) allowed detection of spectral features that have not been seen in previous lower sensitivity observations of the sources, such as detection of excited OH and 6.7 GHz CH3OH absorption. A review of 6.7 GHz CH3OH detections indicates an association between absorption and radio continuum sources in high-mass star forming regions, although selection biases in targeted projects and low sensitivity of blind surveys imply incompleteness. Absorption of excited OH transitions was also detected toward three sources. In particular, we confirm a broad 6.035 GHz OH absorption feature in G34.26+0.15 characterized by an asymmetric blue-shifted wing indicative of expansion, perhaps a large scale outflow in this HII region.