This project will continue the operation of the Submillimeter Polarimeter for Antarctic Remote Observations (SPARO) at the South Pole for the next three winter seasons. The SPARO instrument is operated on the Viper 2-meter telescope, and has recently been upgraded following its first year of observations. In the exceptionally transmissive and stable winter-time skies over the Antarctic plateau, SPARO provides a powerful probe of magnetic fields in interstellar regions. Measurements at submillimeter wavelengths provide a method for mapping magnetic fields in the denser interstellar regions of the galaxy by measuring the linear polarization of thermal emission from magnetically aligned interstellar dust grains. Interstellar magnetic fields are generally difficult to observe, but they can contribute to our understanding of two general problems in which interstellar gas (and thus probably also magnetic fields) play important roles: the study of the galactic center, and star formation. The galactic center is a highly radiationally active region. In some centers, known as "active galactic nuclei" (AGN), the nucleus or central core produces more radiation than the entire rest of the galaxy. The size of an AGN can be smaller than the size of our solar system, and current theory suggests that there is a supermassive black hole at the center of an AGN. Observations proposed here are aimed at (a) confirming SPARO's recent discovery of a large-scale toroidal magnetic field at the galactic center, (b) testing a magnetic outflow model for the "Galactic Center Lobe" - a radio structure possibly tracing gas that has been ejected from the galactic nucleus, and (c) mapping large-scale magnetic fields in a sample of star forming clouds in order to study the relationship between the elongated shapes of these clouds and their magnetic fields.
