The edge-on galaxy NGC 891 was probed using near-infrared ( NIR ) imaging polarimetry in the H -band ( 1.6 \mu m ) with the Mimir instrument on the 1.8 m Perkins Telescope .
Polarization was detected with signal-to-noise ratio greater than three out to a surface brightness of 18.8 mag arcsec ^ { -2 } .
The unweighted average and dispersion in polarization percentage ( P ) across the full disk were 0.7 % and 0.3 % , respectively , and the same quantities for polarization position angle ( P.A . )
were 12° and 19° , respectively .
At least one polarization null point , where P falls nearly to zero , was detected in the NE disk but not the SW disk .
Several other asymmetries in P between the northern and southern disk were found and may be related to spiral structure .
Profiles of P and P.A .
along the minor axis of NGC 891 suggest a transition from magnetic ( B ) field tracing dichroic polarization near the disk mid-plane to scattering dominated polarization off the disk mid-plane .
A comparison between NIR P.A .
and radio ( 3.6 cm ) synchrotron polarization P.A .
values revealed similar B-field orientations in the central-northeast region , which suggests that the hot plasma and cold , star-forming interstellar medium may share a common B-field .
Disk-perpendicular polarizations previously seen at optical wavelengths are likely caused by scattered light from the bright galaxy center and are unlikely to be tracing poloidal B-fields in the outer disk .