Kavli Affiliate: Susan E. Clark
| First 5 Authors: George Halal, Susan E. Clark, Ari Cukierman, Dominic Beck, Chao-Lin Kuo
| Summary:
Filamentary structures in neutral hydrogen (HI) emission are well aligned
with the interstellar magnetic field, so HI emission morphology can be used to
construct templates that strongly correlate with measurements of polarized
thermal dust emission. We explore how the quantification of filament morphology
affects this correlation. We introduce a new implementation of the Rolling
Hough Transform (RHT) using spherical harmonic convolutions, which enables
efficient quantification of filamentary structure on the sphere. We use this
Spherical RHT algorithm along with a Hessian-based method to construct HI-based
polarization templates. We discuss improvements to each algorithm relative to
similar implementations in the literature and compare their outputs. By
exploring the parameter space of filament morphologies with the Spherical RHT,
we find that the most informative HI structures for modeling the magnetic field
structure are the thinnest resolved filaments. For this reason, we find a
$sim10%$ enhancement in the $B$-mode correlation with polarized dust emission
with higher-resolution HI observations. We demonstrate that certain
interstellar morphologies can produce parity-violating signatures, i.e.,
nonzero $TB$ and $EB$, even under the assumption that filaments are locally
aligned with the magnetic field. Finally, we demonstrate that $B$ modes from
interstellar dust filaments are mostly affected by the topology of the
filaments with respect to one another and their relative polarized intensities,
whereas $E$ modes are mostly sensitive to the shapes of individual filaments.
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