| Type |
Journal Article |
| Names |
Blakesley Burkhart, A. Lazarian, B. M. Gaensler |
| Publication |
The Astrophysical Journal |
| Volume |
749 |
| Issue |
2 |
| Pages |
145 |
| Date |
April 1, 2012 |
| URL |
http://adsabs.harvard.edu/abs/2012ApJ...749..145B |
| Library Catalog |
NASA ADS |
| Abstract |
Faraday rotation of linearly polarized radio signals provides a very
sensitive probe of fluctuations in the interstellar magnetic field and
ionized gas density resulting from magnetohydrodynamic (MHD) turbulence.
We used a set of statistical tools to analyze images of the spatial
gradient of linearly polarized radio emission (|∇P|) for both
observational data from a test image of the Southern Galactic Plane
Survey (SGPS) and isothermal three-dimensional simulations of MHD
turbulence. Visually, in both observations and simulations, a complex
network of filamentary structures is seen. Our analysis shows that the
filaments in |∇P| can be produced both by interacting shocks and
random fluctuations characterizing the non-differentiable field of MHD
turbulence. The latter dominates for subsonic turbulence, while the
former is only present in supersonic turbulence. We show that supersonic
and subsonic turbulence exhibit different distributions as well as
different morphologies in the maps of |∇P|. Particularly,
filaments produced by shocks show a characteristic "double jump" profile
at the sites of shock fronts resulting from delta function-like
increases in the density and/or magnetic field, while those produced by
subsonic turbulence show a single jump profile. In order to
quantitatively characterize these differences, we use the topology tool
known as the genus curve as well as the probability distribution
function moments of the image distribution. We find that higher values
for the moments correspond to cases of |∇P| with larger sonic Mach
numbers. The genus analysis of the supersonic simulations of |∇P|
reveals a "swiss cheese" topology, while the subsonic cases have
characteristics of a "clump" topology. Based on the analysis of the
genus and the higher order moments, the SGPS test region data have a
distribution and morphology that match subsonic- to transonic-type
turbulence, which confirms what is now expected for the warm ionized
medium. |
| Tags |
ISM: General, Magnetohydrodynamics: MHD, Polarization, shock waves, turbulence |