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Following up on our initial observation of a large polarization of the thermal far-infrared emission from warm dust in the molecular cloud underlying the "Arched Filaments" in the Galactic center radio Arc, we have again used the University of Chicago Array Polarimeter on the Kuiper Airborne Observatory to increase the number of sampled points to over 100. The large percentage polarization initially reported at 14 independent positions (up to 6%, Morris et al. 1992, ApJ 399 L3) is confirmed, and is found to extend over at least half of the 5' x 7' region containing the arched filaments. The following conclusions can be drawn from the preliminary data: 1) At every location towards the Arched Filaments where the signal-to-noise ratio is sufficiently large to assess its direction unambiguously, the E-vectors of the polarized far-IR emission are approximately perpendicular to those filaments. The implication is that the emitting dust grains are aligned by a magnetic field whose projection onto the plane of the sky is oriented parallel to the radio filaments, and which follows the curvature of those filaments; 2) The polarization is unusually large over much of the region; 3) The orientation of the polarization vectors changes slowly and smoothly across the region, with little change in the polarization angle from one point to the next. It therefore appears that the alignment agent, apparently a strong magnetic field, is ordered and uniform on scales of a parsec or greater. 4) The polarization of the emission arising to the south of the radio filaments remains high, and the projected field direction there merges smoothly with that in the filaments, and perhaps (across a 5-arcminute gap) with the magnetic field in the dust ring of Sgr A (Hildebrand et al. 1990, ApJ, 362, 114).
This research is supported by NASA.
