Polarimetry toward the Musca dark cloud. I. The catalog

We have used CCD imaging polarimetry to obtain linear polarization measurements of background stars toward the filamentary Musca dark cloud. We present a catalog of 2497 objects with polarization signal-to-noise ratio larger than 5. This allows us to build polarization maps to infer the detailed geometry of the local magnetic field. We show composite polarization maps along the cloud and explore general correlations of the polarimetric data with the morphology of the region. We find the overall field to be strikingly aligned with the projected small axis of the filamentary cloud. We detect a lower limit for the polarization across the cloud of similar to2%, with an enhanced polarization of 6%-7% in the central region. We find evidence that the polarization pattern is altered in the inner regions, those associated with higher extinction.