Tracing the Magnetic Field of IRDC G028.23$-$00.19 Using NIR Polarimetry
  The importance of the magnetic (B) field in the formation of infrared dark
clouds (IRDCs) and massive stars is an ongoing topic of investigation. We
studied the plane-of-sky B field for one IRDC, G028.23-00.19, to understand the
interaction between the field and the cloud. We used near-IR background
starlight polarimetry to probe the B field and performed several observational
tests to assess the field importance. The polarimetric data, taken with the
Mimir instrument, consisted of H-band and K-band observations, totaling 17,160
stellar measurements. We traced the plane-of-sky B-field morphology with
respect to the sky-projected cloud elongation. We also found the relationship
between the estimated B-field strength and gas volume density, and we computed
estimates of the normalized mass-to-magnetic flux ratio. The B-field
orientation with respect to the cloud did not show a preferred alignment, but
it did exhibit a large-scale pattern. The plane-of-sky B-field strengths ranged
from 10 to 165 {\mu}G, and the B-field strength dependence on density followed
a power law with an index consistent with 2/3. The mass-to-magnetic flux ratio
also increased as a function of density. The relative orientations and
relationship between the B field and density imply that the B field was not
dynamically important in the formation of the IRDC. The increase in
mass-to-flux ratio as a function of density, though, indicates a dynamically
important B field. Therefore, it is unclear whether the B field influenced the
formation of G28.23. However, it is likely that the presence of the IRDC
changed the local B-field morphology.
