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| EPoS Contribution |
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Prelude to Star Formation - The Mass-to-Flux Ratio in Galactic GMCs
Thomas H. Troland University of Kentucky, Lexington, USA | |
| The very earliest phase of star formation occurs in Giant Molecular Clouds. What is the role of the magnetic field at this very early stage? In the evolutionary sequence, GMCs lie between diffuse HI gas, from which GMCs presumably form, and molecular cores, which develop after GMC formation. Existing Zeeman effect data establish that the densest diffuse HI gas, the Cold Neutral Medium, is magnetically subcritical. Zeeman data also establish that molecular cloud cores are mildly supercritical. Yet we know very little about the mass-to-flux ratio of GMCs as a whole. Therefore, we know little about the role of the magnetic field in guiding GMC evolution from cloud formation through fragmentation to star formation. A typical GMC has N(H) of about 1.5 x 10^2/cm^2. If the cloud is magnetically critical, then the total field strength is about 60 microgauss. Fields of this strength are detectable via the Zeeman effect in 18 cm OH absorption lines toward extragalactic radio continuum sources. We are currently undertaking such a study using the Arecibo telescope. We have chosen extragalactic sources lying behind galactic GMCs. The lines of sight to these sources sample the general environments of GMCs, not the cores preferentially. Preliminary indications from data obtained at Arecibo suggest that GMCs are mildly magnetically supercritical. Analysis of the full data set will be complete by the time of the Ringberg meeting. I will report the results of this analysis and the implications of these results for magnetic effects in the earliest stages of star formation. | |
| Collaborators: K. Thompson, U of Kentucky, USA C. Heiles, U of California, Berleley, USA |
Key publication
Suggested Session: Magnetic Fields, Molecular Clouds |