# A Survey of Magnetic Field Strengths in the Envelopes of Molecular Clouds via the 18 cm OH Zeeman Effect

## TL;DR

This survey used 18 cm OH Zeeman observations to measure magnetic fields in molecular cloud regions, providing insights into their role in cloud evolution and collapse.

## Contribution

It offers the first extensive magnetic field measurements in inter-core regions of molecular clouds using the Zeeman effect.

## Key findings

- Magnetic field strengths are approximately 15 microgauss.
- Detected Zeeman signals at 3 sigma in 9 clouds.
- Provided upper limits for non-detections.

## Abstract

We present the results of an extensive Arecibo observational survey of magnetic field strengths in the inter-core regions of molecular clouds to determine their role in the evolution and collapse of molecular clouds as a whole. Sensitive 18 cm OH Zeeman observations of absorption lines from Galactic molecular gas in the direction of extragalactic continuum sources yielded 38 independent measurements of magnetic field strengths. Zeeman detections were achieved at the three sigma level toward 9 clouds, while the others revealed sensitive upper limits to the magnetic field strength. Our results suggest that total field strengths in the inter-core regions of GMCs are about 15 microgauss.