A Lack of Resolved Near-Infrared Polarization Across the Face of M51

TL;DR

This study used near-infrared observations to measure polarization across galaxy M51, finding no detectable polarization and constraining the mechanisms responsible for polarization in the galaxy.

Contribution

It provides the first upper limits on H-band polarization in M51, challenging existing models of polarization dependence on wavelength.

Findings

H-band polarization in M51 is less than 0.05%.

Results rule out Serkowski-like wavelength dependence.

Other polarization mechanisms cannot explain the low polarization ratio.

Abstract

The galaxy M51 was observed using the Mimir instrument on the Perkins telescope to constrain the resolved H-band (1.6 $\mu$m) 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 arcsecond 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 ($P_H/P{VRI} \lesssim 0.05$) across the face of M51.