Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf
Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf
Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf
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66 4. The magneto-ionic me<strong>di</strong>um around 3C 449<br />
(a)<br />
(c)<br />
(b)<br />
(d)<br />
Figure 4.11: Comparison between observed and synthetic profiles of rms and mean Faraday<br />
rotation at resolutions of 5.5 arcsec (a and b) and 1.25 arcsec (c and d). The synthetic profiles<br />
are derived from the best-fitting model withΛ max = 65 kpc. The black points represent the data<br />
with vertical bars correspon<strong>di</strong>ng to the rms fitting error. (a) and (c): Profiles ofσ RM . The magenta<br />
crosses represent the mean values from 35 simulations at 5.5-arcsec resolution, and the vertical<br />
bars are the rms scatter in these profiles due to sampling. (b) and (d): Profiles of〈RM〉 derived<br />
from single example realizations at 5.5 and 1.25-arcsec resolutions.<br />
scale. The model withΛ max =65 kpc gives the best representation of the data. The fit is within<br />
the estimated errors except for a marginal <strong>di</strong>screpancy at the very largest (and therefore poorly<br />
sampled) separations. That withΛ max =20 kpc is inconsistent with the observed pseudo-structure<br />
function for any separation> ∼ 20 arcsec (≃6 kpc) where the sampling is still very good, and is firmly<br />
excluded. The model withΛ max =205 kpc has slightly, but significantly too much power on large<br />
scales.<br />
I emphasize that such estimate of the outer scale of the RM fluctuations is essentially<br />
independent of the functional form assumed for the variation of field strength with ra<strong>di</strong>us in the<br />
central region, which affects the structure function only for small separations. The results are<br />
almost identical if I fit the field-strength variation with either the profile of Eq. 4.5 (withη≈0) or<br />
that of Eq. 4.6.<br />
As for the structure functions of in<strong>di</strong>vidual regions, the pseudo-structure function at large<br />
66