All Figures

$\begin{figure} \par\mbox{\includegraphics[width=8.5cm]{6988f1a.eps}\hspace*{1.2cm} \includegraphics[width=8.5cm]{6988f1b.eps} } \end{figure}$ Figure 1: Left: total intensity contours of NGC 6946 at $\lambda6.2~{\rm cm}$ at 15 $^{\prime \prime }$ resolution, combined from VLA and Effelsberg data. The contour intervals are $1, 2, 3, 4, 6, 8, 12, 16, 32, 64, 128 \times 300~~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the $7~\mu{\rm m}~$ IR emission measured with the ISO satellite with about 6 $^{\prime \prime }$ resolution (Dale et al. 2000). Here and in the following maps, the beam size is shown in the bottom right or left corner of each panel. Right: logarithmic representation of the total intensity at $\lambda6.2~{\rm cm}$ and at 15 $^{\prime \prime }$ resolution.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.5cm]{6988f2a.eps}\hspace*{1cm} \includegraphics[width=8.5cm]{6988f2b.eps} } \end{figure}$ Figure 2: Left: total intensity contours of NGC 6946 at $\lambda20.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution, combined from VLA and Effelsberg data. The contour intervals are $1, 2, 3, 4, 6, 8, 12, 16, 32, 64, 128 \times 200~~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the H $\alpha$ emission (Ferguson et al. 1998). Right: filtered version of the $\lambda20.5~{\rm cm}$ image by subtracting the three brightest sources in the fields and transformation with an isotropic "Mexican hat'' wavelet function with a half-power width of 40 $^{\prime \prime }$ (see Frick et al. 2001).
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f3.eps} } \end{figure}$ Figure 3: Spectral index distribution between $\lambda20~{\rm cm}$ and $\lambda3.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution, determined for points where the intensities at both wavelengths exceed 10 $\times$ the rms noise, so that the maximum error is $\pm$ 0.08.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f4.eps} } \end{figure}$ Figure 4: Contours of thermal intensity of NGC 6946 at $\lambda3.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution. The contour intervals are $1, 2, 3, 4, 6, 8, 12, 16, 32, 64, 128 \times 150~~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the H $\alpha$ emission (Ferguson et al. 1998).
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In the text

$\begin{figure} {\includegraphics[width=8.7cm,clip]{6988f5.eps} } \end{figure}$ Figure 5: Energy densities and their radial variations in the spiral galaxy NGC 6946.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{6988f6a.eps}\hspace*{2mm} \incl... ...6988f6c.eps}\hspace*{2mm} \includegraphics[width=8.5cm]{6988f6d.eps}\end{figure}$ Figure 6: Top left: Polarized intensity contours and observed B-vectors (E+90 $^\circ$ ) of NGC 6946 at $\lambda3.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution, combined from VLA and Effelsberg data. The contour intervals are $1, 2, 3, 4, 6, 8 \times 40~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 12 $^{\prime \prime }$ length corresponds to 100 $~\mu{\rm Jy/beam~area}~$ . Faraday rotation is low ( $\le$ 10 $^\circ$ ) at this wavelength. The background greyscale image shows the $7~\mu{\rm m}~$ IR emission measured with the ISO satellite with about 6 $^{\prime \prime }$ resolution (Dale et al. 2000). Top right: Polarized intensity contours and B-vectors at $\lambda6.2~{\rm cm}$ , corrected for Faraday rotation (see Fig. 12 left) at 15 $^{\prime \prime }$ resolution, combined from VLA and Effelsberg data. The contour intervals are $1, 2, 3, 4, 6, 8 \times 60~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 12 $^{\prime \prime }$ length corresponds to 100 $~\mu{\rm Jy/beam~area}~$ . Bottom left: Polarized intensity contours and observed E-vectors at $\lambda18.0~{\rm cm}$ , not corrected for Faraday rotation, at 15 $^{\prime \prime }$ resolution, combined from VLA C- and D-array data. The contour intervals are $1, 2, 3, 4, 6 \times 50~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 12 $^{\prime \prime }$ length corresponds to 100 $~\mu{\rm Jy/beam~area}~$ . Bottom right: Polarized intensity contours and B-vectors at $\lambda20.5~{\rm cm}$ , corrected for Faraday rotation (see Fig. 12 right), at 15 $^{\prime \prime }$ resolution, combined from VLA C- and D-array data. The contour intervals are $1, 2, 3, 4, 6 \times 50~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 12 $^{\prime \prime }$ length corresponds to 100 $~\mu{\rm Jy/beam~area}~$ .
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f7.eps} } \end{figure}$ Figure 7: Polarized intensity contours of NGC 6946 at $\lambda20.5~{\rm cm}$ at 20 $^{\prime \prime }$ resolution, observed with VLA. The contour intervals are $1, 2, 3, 4, 6, 8~\times 60~~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the ${\rm H~\scriptstyle I}$ emission measured with the Westerbork telescope at about the same resolution (Boomsma et al. 2005; Braun et al. 2007).
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f8.eps} } \end{figure}$ Figure 8: Polarized intensity contours and B-vectors (E+90 $^\circ$ ) of NGC 6946 at $\lambda6.2~{\rm cm}$ at 2 $.\mkern -4mu^\prime$ 45 resolution, observed with the Effelsberg telescope. The contour intervals are $1, 2, 3, 4, 6, 8, 12, 16, 24~\times 200~~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 20 $^{\prime \prime }$ length corresponds to 1000 $~\mu{\rm Jy/beam~area}~$ . The vector orientations are not corrected for Faraday rotation.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f9.eps} } \end{figure}$ Figure 9: Polarized intensity contours and B-vectors (E+90 $^\circ$ ) of NGC 6946 at $\lambda11.2~{\rm cm}$ at 5 $^\prime$ resolution, observed with the Effelsberg telescope. The contour intervals are $1, 2, 3 \times 2000~~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 1 $^\prime$ length corresponds to 3000 $~\mu{\rm Jy/beam~area}~$ . The vector orientations are not corrected for Faraday rotation.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f10.eps} } \end{figure}$ Figure 10: Degree of field regularity q, the ratio of the regular field strength in the sky plane to the isotropic random field strength, derived from the fractional polarization of the nonthermal intensity of NGC 6946 at $\lambda6.2~{\rm cm}$ at 15 $^{\prime \prime }$ resolution. q was computed only at points where the total nonthermal intensity at $\lambda6.2~{\rm cm}$ exceeds 10 times the rms noise.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f11.eps} } \end{figure}$ Figure 11: Polarized intensity contours and observed B-vectors (E+90 $^\circ$ ) of NGC 6946 at $\lambda3.5~{\rm cm}$ at 8 $.\!\!^{\prime\prime}$ 5 resolution, observed with the VLA D-array. Faraday rotation is smaller than 5 $^\circ$ at this wavelength. The contour intervals are $1, 2, 3, 4, 6, 8, 12 \times 20~~\mu{\rm Jy/beam~area}~$ . The vector length is proportional to polarized intensity, 5 $^{\prime \prime }$ length corresponds to 100 $~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the H $\alpha$ emission (Ferguson et al. 1998). The position of the radio nucleus of the galaxy is RA, Dec(2000 $) = 20^{\rm h} 34^{\rm m} 52\hbox{$.\!\!^{\rm s}$ }25$ , $+60\hbox{$^\circ$ }09\hbox{$^\prime$ }14\hbox{$.\!\!^{\prime\prime}$ }5$ .
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.5cm]{6988f12a.eps}\hspace*{8mm} \includegraphics[width=8.5cm]{6988f12b.eps} } \end{figure}$ Figure 12: Left: Intrinsic Faraday rotation measures RM_ibetween $\lambda3.5~{\rm cm}$ and $\lambda6.2~{\rm cm}$ at 15 $^{\prime \prime }$ resolution at points where the polarized intensities at both wavelengths exceeds 4 times the rms noise (taken from that in Q and U). The contours show the polarized intensity at $\lambda6.2~{\rm cm}$ . The contour intervals are $1, 2, 3, 4, 6 \times 80~~\mu{\rm Jy/beam~area}~$ . The foreground $RM_{\rm fg}$ from our Galaxy of $40~{\rm rad~m^{-2}}~$ has been subtracted. Right: Intrinsic Faraday rotation measures RM_i between $\lambda18.0~{\rm cm}$ and $\lambda20.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution at points where the polarized intensities at both wavelengths exceeds 4 times the rms noise. The contours show the polarized intensity at $\lambda20.5~{\rm cm}$ . The contour intervals are $1, 2, 3, 4 \times 60~~\mu{\rm Jy/beam~area}~$ . The foreground $RM_{\rm fg}$ from our Galaxy of $40~{\rm rad~m^{-2}}~$ has been subtracted.
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In the text

$\begin{figure} {\includegraphics[width=8.5cm]{6988f13a.eps} } {\includegraphics[width=8.5cm]{6988f13b.eps} } \end{figure}$ Figure 13: Structure function (in logarithmic presentation) of the intrinsic Faraday rotation measures RM_i between $\lambda3.5~{\rm cm}$ and $\lambda6.2~{\rm cm}$ ( top) and between $\lambda18~{\rm cm}$ and $\lambda20~{\rm cm}$ ( bottom) at 15 $^{\prime \prime }$ resolution. The scale is measured in arcseconds.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.5cm]{6988f14a.eps}\hspace*{8mm} \includegraphics[width=8.5cm]{6988f14b.eps} } \end{figure}$ Figure 14: Left: ratio between polarized intensities at $\lambda6.2~{\rm cm}$ and $\lambda3.5~{\rm cm}$ at 20 $^{\prime \prime }$ resolution, corrected for spectral index, as a measure of Faraday depolarization. The ratio was computed only at points where the polarized intensities at both wavelengths exceeds 4 times the rms noise (taken from that in Qand U). The contours show the polarized intensity at $\lambda6.2~{\rm cm}$ . The contour intervals are $1, 2, 3, 4, 6 \times 100~~\mu{\rm Jy/beam~area}~$ . Right: ratio between polarized intensities at $\lambda20.5~{\rm cm}$ and $\lambda6.2~{\rm cm}$ at 30 $^{\prime \prime }$ resolution, corrected for spectral index, as a measure of Faraday depolarization. The ratio was computed only at points where the polarized intensities at both wavelengths exceeds 4 times the rms noise. The contours show the polarized intensity at $\lambda6.2~{\rm cm}$ . The contour intervals are $1, 2, 3, 4 \times 200~~\mu{\rm Jy/beam~area}~\!$ .
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In the text

$\begin{figure} \par\mbox{\includegraphics[angle=270,width=8.5cm]{6988f15a.eps}\hspace*{8mm} \includegraphics[angle=270,width=8.5cm]{6988f15b.eps} } \end{figure}$ Figure 15: Polarized intensity and observed E-vectors at $\lambda20.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution in the regions showing ring-like "canals''.
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In the text

$\begin{figure} {\includegraphics[width=8.7cm]{6988f16.eps} } \end{figure}$ Figure 16: Pitch angles of the magnetic field vectors at 20 $^{\prime \prime }$ resolution and contours of polarized intensity at $\lambda6.2~{\rm cm}$ .
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In the text

$\begin{figure} {\includegraphics[width=8.8cm]{6988f17.eps} } \end{figure}$ Figure 17: Average polarized intensity at $\lambda18.0~{\rm cm}$ and $\lambda20.5~{\rm cm}$ at 20 $^{\prime \prime }$ resolution.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f18.eps} } \end{figure}$ Figure 18: Deep 60 ks ROSAT HRI image of NGC 6946 (Ehle, priv. comm.) overlaid onto an optical image.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm]{6988f19.eps} } \end{figure}$ Figure 19: Polarized intensity at $\lambda20.5~{\rm cm}$ at 30 $^{\prime \prime }$ resolution, averaged in sectors of 10 $^\circ$ width in azimuthal angle in the galaxy plane and between 1 kpc and 10 kpc radius from the centre of NGC 6946. The azimuthal angle is counted counterclockwise from the galaxy's north-eastern major axis (at 60 $^\circ$ position angle). Errors due to rms noise are $\simeq$ $5~\mu{\rm Jy/beam~area}~$ , smaller than the symbol sizes.
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In the text

$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f3.eps} } \end{figure}$	Figure 3: Spectral index distribution between $\lambda20~{\rm cm}$ and $\lambda3.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution, determined for points where the intensities at both wavelengths exceed 10 $\times$ the rms noise, so that the maximum error is $\pm$ 0.08.
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$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f4.eps} } \end{figure}$	Figure 4: Contours of thermal intensity of NGC 6946 at $\lambda3.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution. The contour intervals are $1, 2, 3, 4, 6, 8, 12, 16, 32, 64, 128 \times 150~~\mu{\rm Jy/beam~area}~$ . The background greyscale image shows the H $\alpha$ emission (Ferguson et al. 1998).
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$\begin{figure} {\includegraphics[width=8.7cm,clip]{6988f5.eps} } \end{figure}$	Figure 5: Energy densities and their radial variations in the spiral galaxy NGC 6946.
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$\begin{figure} {\includegraphics[width=8.5cm]{6988f13a.eps} } {\includegraphics[width=8.5cm]{6988f13b.eps} } \end{figure}$	Figure 13: Structure function (in logarithmic presentation) of the intrinsic Faraday rotation measures RM_i between $\lambda3.5~{\rm cm}$ and $\lambda6.2~{\rm cm}$ ( top) and between $\lambda18~{\rm cm}$ and $\lambda20~{\rm cm}$ ( bottom) at 15 $^{\prime \prime }$ resolution. The scale is measured in arcseconds.
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$\begin{figure} \par\mbox{\includegraphics[angle=270,width=8.5cm]{6988f15a.eps}\hspace*{8mm} \includegraphics[angle=270,width=8.5cm]{6988f15b.eps} } \end{figure}$	Figure 15: Polarized intensity and observed E-vectors at $\lambda20.5~{\rm cm}$ at 15 $^{\prime \prime }$ resolution in the regions showing ring-like "canals''.
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$\begin{figure} {\includegraphics[width=8.7cm]{6988f16.eps} } \end{figure}$	Figure 16: Pitch angles of the magnetic field vectors at 20 $^{\prime \prime }$ resolution and contours of polarized intensity at $\lambda6.2~{\rm cm}$ .
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$\begin{figure} {\includegraphics[width=8.8cm]{6988f17.eps} } \end{figure}$	Figure 17: Average polarized intensity at $\lambda18.0~{\rm cm}$ and $\lambda20.5~{\rm cm}$ at 20 $^{\prime \prime }$ resolution.
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$\begin{figure} {\includegraphics[width=8.8cm,clip]{6988f18.eps} } \end{figure}$	Figure 18: Deep 60 ks ROSAT HRI image of NGC 6946 (Ehle, priv. comm.) overlaid onto an optical image.
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