2012ApJ...761L..28P

The galaxy M51 was observed using the Mimir instrument on the Perkins Telescope to constrain the resolved H-band (1.6 µm) polarization across the galaxy. These observations place an upper limit of P_H< 0.05% on the H-band polarization across the face of M51, at 0.6 arcsec pixel sampling. Even with smoothing to coarser angular resolutions, to reduce polarization uncertainty, the H-band polarization remains undetected. The polarization upper limit at H band, when combined with previous resolved optical polarimetry, rules out a Serkowski-like polarization dependence on wavelength. Other polarization mechanisms cannot account for the observed polarization ratio (P_H/P_VRI ≲ 0.05) across the face of M51.