Exploring Grain Alignment Mechanisms in Giant Molecular Clouds using GPIPS

Details Exploring Grain Alignment Mechanisms in Giant Molecular Clouds using GPIPS Exploring Grain Alignment Mechanisms in Giant Molecular Clouds using GPIPS

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21348606j&link_type=abstract

American Astronomical Society, AAS Meeting #213, #486.06; Bulletin of the American Astronomical Society, Vol. 41, p.459

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The linear polarization of starlight along a line of sight arises from the alignment of anisotropic dust grains with the local magnetic field direction. The exact process which aligns the dust grains with the local magnetic field is still unknown. However, an understanding of the alignment mechanism is necessary to be able to interpret polarization maps as tracers of the galactic magnetic field. Recent arguments suggest that radiative aligned torques (RATs) dominate alignment in giant molecular clouds (GMCs), including the infrared dark cloud cores (IRDCs) within them. To test RAT theory, a nearby GMC at l = 53, b = 0 was chosen to be observed this past June as part of the Galactic Plane Infrared Polarization Survey (GPIPS). The cloud covers a 1 x 2 degree region of the galactic plane ( 200 GPIPS field-of-views), and displays regions of varying extinction, morphology, and radiation environments as seen using the GLIMPSE, MIPS, and GRS 13CO data. With an average sampling of 100 stars per GPIPS field-of-view (10’ x 10'), we expect 20,000 stars will show detectable polarizations -a factor of 600 greater than in previous polarimetric studies. A plot of degree of NIR polarization P(%) vs. I/Imax, found using GRS 13CO data, is ideal for comparison to the models of Cho & Lazarian (2005). Approximate Av values are found using the 2MASS color excesses, EH-K. This aids in the generation of a plot of P(%)/Av vs. Av in dark clouds, to compare to the results of Arce et al. (1998) to test the notion that grains are aligned only for a few skin-depths.
This work is partially supported by NSF grant AST-0607500.

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