Measuring the Mass-to-Flux Ratio in Molecular Clouds

Kristen Thompson

Abstract: 

What is the role of magnetic fields in star formation? Although the answer is not yet known, one model places responsibility for the progression of star formation on the shoulders of magnetic fields. If the fields are strong enough, and strict coupling between the gas and the field is maintained, they can delay, or even prevent, the gravitational collapse of a molecular cloud and the subsequent formation of stars. The support of a cloud by a magnetic field can prevent gravitational collapse if the magnetic energy of the cloud is approximately equal to the gravitational energy. The ratio of gravitational to magnetic energy can be determined observationally and is called the mass-to-flux ratio. Much work has been focused on determining the mass-to-flux ratio in molecular cloud cores, where only a small fraction of the mass resides. We are engaged in the first systematic survey aimed to determine this ratio in molecular clouds as a whole. We determine mass-to-flux ratios via the Zeeman effect in 18 cm OH absorption lines toward extragalactic continuum sources distributed at random through the sky using the Arecibo radio telescope. In this talk, I will present our some of our current results of this ongoing project and discuss what they might imply about the role of magnetic fields in the star formation process.