Jow, D. L.; Hill, Ryley; Scott, Douglas; Soler, J. D.; Martin, P. G.; Devlin, M. J.; Fissel, L. M.; Poidevin, F.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 474, Issue 1, p.1018-1027
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2
2018
Citations
54
Refereed citations
50
Description
We present the projected Rayleigh statistic (PRS), a modification of the
classic Rayleigh statistic, as a test for non-uniform relative
orientation between two pseudo-vector fields. In the application here,
this gives an effective way of investigating whether polarization
pseudo-vectors (spin-2 quantities) are preferentially parallel or
perpendicular to filaments in the interstellar medium. For example,
there are other potential applications in astrophysics, e.g. when
comparing small-scale orientations with larger scale shear patterns. We
compare the efficiency of the PRS against histogram binning methods that
have previously been used for characterizing the relative orientations
of gas column density structures with the magnetic field projected on
the plane of the sky. We examine data for the Vela C molecular cloud,
where the column density is inferred from Herschel submillimetre
observations, and the magnetic field from observations by the
Balloon-borne Large-Aperture Submillimetre Telescope in the 250-, 350-
and 500-μm wavelength bands. We find that the PRS has greater
statistical power than approaches that bin the relative orientation
angles, as it makes more efficient use of the information contained in
the data. In particular, the use of the PRS to test for preferential
alignment results in a higher statistical significance, in each of the
four Vela C regions, with the greatest increase being by a factor 1.3 in
the South-Nest region in the 250 - μ m band.