\begin{table}%t2
\caption{\label{Table2}Magnetic phenomena in NGC~6946 and their probable origins.}
\small%\centering
\par
\begin{tabular}{ll}
\hline\hline
Total magnetic energy density $\simeq$ turbulent energy density in inner galaxy & Field amplification by turbulent gas flows \\
Total magnetic energy density dominates in outer galaxy & Magneto-rotational instability ?\\
Low degrees of polarization in gas spiral arms & Field tangling due to star-formation activity \\
Large-scale pattern in Faraday rotation & Coherent fields \\
Magnetic arms with regular, almost completely aligned fields & Efficient dynamo action in interarm regions \\
Two inner magnetic arms & Superposition of dynamo modes $m=0$ and $m=2$ \\
No large-scale field reversals & Higher dynamo modes weak or absent in inner galaxy \\
Outer magnetic arms & Higher dynamo modes or shear flows in outer galaxy \\
Alignment of ordered fields along spiral structure & Interaction between gas flow and magnetic field \\
Magnetic arms are phase-shifted images of gas arms & Magnetic field may trigger the formation of gas spiral arms \\
North-south asymmetry in Faraday rotation & Spiral field points inwards in both inner magnetic arms \\
Enhanced magnetic field along inner edge of inner gas spiral arm & Compression or shear by density waves \\
Smooth turning of field lines into inner gas spiral arm & No shock \\
Mild field compression in inner gas spiral arm & Magnetic field connected to warm, diffuse gas \\
Anti-correlation of $RM$ and field pitch angle & Helical fields \\
$RM$ structure function flat until 6\kpc\ scale & Uncorrelated field structures below 6\kpc\ scale \\
$RM$ structure function rising for scales larger than 6\kpc & Large-scale coherent fields \\
Depolarization rings at \wave{20} & Differential Faraday rotation in $\HII$ complexes \\
Strong Faraday depolarization at \wave{18} and \wave{20} & Faraday dispersion by random fields \\
Large-scale asymmetry in Faraday depolarization & Helical fields ?\\
\hline
\label{tab2}
\end{tabular}
\end{table}