Oral Presentation
Variation in grain alignment within the Ophiuchus Molecular Cloud
Presenter: Kate Pattle (National Tsing Hua University)
If we wish to use submillimeter continuum polarization measurements as a tracer of magnetic fields in molecular clouds, it is essential that we understand the physical conditions under which dust grains are aligned with their local magnetic field direction. Dust polarization fraction is typically observed to decrease toward dense regions, suggestive of grain misalignment at high extinction, and/or variation of the magnetic field on small scales at high densities. We present polarization observations of three dense clumps in the L1688 region of the Ophiuchus molecular cloud taken as part of the JCMT BISTRO (B-Fields in Star-forming Region Observations) Large Program. We find that efficient grain alignment persists to significantly higher column densities in Oph A, which is located between two massive stars and so has a significantly elevated flux of high-energy photons, than in the otherwise comparable Oph B and C regions, but also find significant variation in grain alignment efficiency with environment across the Oph A region. We discuss our results in the context of the radiative alignment torque (RAT) theory of grain alignment.
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