High-Sensitivity Observations of Molecular Lines with the Arecibo Telescope

Histogram of the number of sources with 6.7 GHz methanol absorption at different flux density bins. Colours and line type (solid, dashed, dotted) in the upper panel identify the radio continuum flux density based on interferometric images. Colours and line type in the lower panel identify ranges in FWHM of the absorption lines. (∗) NGC 1333 is a low-mass star forming region and the absorption is against the CMB (Pandian et al. 2008). The absorption line detected toward NGC 2264 is also likely against the CMB (Pandian et al. 2008). (∗∗) Extragalactic absorption has been reported toward NGC 3079, Arp 220 and Mrk 348.

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.

W. S. Tan, E. D. Araya, L. E. Lee, P. Hofner, S. Kurtz, H. Linz, L. Olmi
Comments: 19 pages, 8 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2006.11817 [astro-ph.GA] (or arXiv:2006.11817v1 [astro-ph.GA] for this version)
Submission history
From: Esteban Araya Ph.D.
[v1] Sun, 21 Jun 2020 14:54:23 UTC (695 KB)
Astrobiology, Astrochemistry

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