Alignment of Magnetic Fields and Gas Structures in the Orion A Cloud

We present new H-band polarization measurements of stars in and behind the southern region of the Orion A Cloud, L1641N, taken with the WIRC+Pol spectropolarimeter at the Palomar Observatory, in order to study the structure of the magnetic field in this nearby star-forming region. We concentrate our observations on stars that lie, in projection, on the outskirts of cores. As such, our observations probe the magnetic field orientation in the medium to low-density regions of the cloud. We use the 12CO(1-0) and 13CO(1-0) molecular line maps from the CARMA-NRO Orion survey to determine the gas structure and kinematics and to compare the field structure orientation with the morphology of the diffused gas in the south-central region of Orion A. We find that structures in the 12CO and 13CO maps are, on average, more aligned with the magnetic field compared to C18O maps, hinting at decreased magnetic field influence towards denser regions in the cloud. Through closer examination, we see 12CO and 13CO gas with V_lsr (local standard of rest) around 9 km/s tend to be more aligned than gases of other velocities, while C18O gas shows average misalignment across all velocities. In addition, we find that the magnetic field of the central region of Orion A tends to have a more East-West orientation, agreeing with observations made by Planck using dust emission. Finally, given the lower dispersion of B-field orientations in the region, we estimate the overall field strength in the region to be relatively high.