In most interstellar clouds, the interstellar dust grains that are mixed in with the gas somehow acquire a net alignment with respect to the ambient Galactic magnetic field. This causes the thermal emission from these grains to be linearly polarized, and because the grains are very cold this emission has relatively long wavelength - lying in the submillimeter band. Thus, submillimeter polarimetry provides a method for mapping interstellar magnetic fields.

The image at right shows an example of a magnetic field map made with our previous polarimeter, Hertz. The contours show emission from the cloud, and the vectors show the polarimetry data. The curved lines are a fit to these vectors, showing the hourglass magnetic field line configuration that is predicted by models for gravitational collapse in star forming clouds.

The image at right shows a map of submillimeter thermal emission from dust in the Orion giant molecular cloud, obtained using the SHARC-II camera. With SHARP, we plan to obtain magnetic field maps of this cloud and other giant molecular clouds. Such maps will have about 1000 individual polarization measurements, more than for any previous submillimeter polarization map. The dashed line shows the area in Orion that we plan to observe, and the 12 x 12 pixel footprint of SHARP (enlarged) is also shown. These maps will provide information on the importance of magnetic fields for the dynamics of these turbulent clouds and for star formation.

SHARP will also be used to study magnetic fields in a variety of other targets, including isolated low-mass protostars, protoplanetary disks, external galaxies, and the black hole Sgr A*. Preliminary results will be posted to SHARP's main home page as they become available.

We are working with the theory group of Alex Lazarian (U. of Wisconsin), to coordinate observations and theoretical simulations.