Testing Galactic Magnetic Field Models using Near-Infrared Polarimetry

TL;DR

This study uses near-infrared polarimetry data of starlight to test and constrain models of the Galactic magnetic field, effectively ruling out several theoretical configurations and refining the spiral pitch angle estimate.

Contribution

It combines new NIR polarimetric observations with simulations to evaluate and constrain dynamo models of the Galactic magnetic field, providing empirical rejection of certain magnetic geometries.

Findings

Rejection of A0-type magnetic field models.

Rejection of S0 and disk-even halo-odd geometries at lower significance.

Estimated spiral magnetic field pitch angle of -6° ± 2°.

Abstract

This work combines new observations of NIR starlight linear polarimetry with previously simulated observations in order to constrain dynamo models of the Galactic magnetic field. Polarimetric observations were obtained with the Mimir instrument on the Perkins Telescope in Flagstaff, AZ, along a line of constant Galactic longitude (\ell = 150\circ) with 17 pointings of the 10' \times 10' field of view between -75\circ < b < 10\circ, with more frequent pointings towards the Galactic midplane. A total of 10,962 stars were photometrically measured and 1,116 had usable polarizations. The observed distribution of polarization position angles with Galactic latitude and the cumulative distribution function of the measured polarizations are compared to predicted values. While the predictions lack the effects of turbulence and are therefore idealized, this comparison allows significant rejection of A0-type magnetic field models. S0 and disk-even halo-odd magnetic field geometries are also rejected by the observations, but at lower significance. New predictions of spiral-type, axisymmetric magnetic fields, when combined with these new NIR observations, constrain the Galactic magnetic field spiral pitch angle to -6\circ \pm 2\circ.