EPoS Contribution
EPoS Contribution
Helical Magnetic Fields in Molecular Clouds? A New Method to Determine the Line-of-Sight Magnetic Field Structure in Molecular Clouds

Mehrnoosh Tahani
U Calgary, Calgary, CA
We present a new method to find the line-of-sight strength and morphology of magnetic fields in star forming regions using Faraday rotation measurements. We applied this method to four relatively nearby regions of Orion A, Orion B, Perseus, and California. We used rotation measure data from the literature and adopted a simple approach, based on relative measurements, to estimate the amount of rotation measure induced by the molecular clouds versus that from the rest of the Galaxy. We then used a chemical evolution code, along with extinction maps of each cloud, to find the electron column density of the molecular cloud at the position of each rotation measure data point. Combining the rotation measures produced by the molecular clouds and the electron column density, we calculated the line-of-sight magnetic field strength and direction.
In the California nebula and Orion A, we found clear evidence that the magnetic fields at one side of these filamentary structures were pointing towards us and were pointing away from us at the other side. This behavior is consistent with a helical magnetic field morphology. In the vicinity of available Zeeman measurements in Orion A, Orion B, and Perseus, we found magnetic field values of -23 ± 38 μG, -129 ± 28 μG, and 32 ± 101 μG, respectively, which are in agreement with the Zeeman Measurements.
Caption: Line-of-sight magnetic fields in OMC-A. Blue (red) circles show magnetic fields toward us (away from us). The size of the circles indicate the magnitude of magnetic field. Black square shows the location of the available Zeeman measurements. Color image is the extinction map (AV). The magnetic fields are dominantly towards us at the eastern side of this filamentary structure and away from us at its western side.
Collaborators:
R. Plume, U Calgary, CA
J.C. Brown, U Calgary, CA
J. Kainulainen, Chalmers UT, SE
Suggested Session: Magnetic fields