Using radio polarimetry we study the connection between the transport of cosmic rays ( CR ’ s ) , the three-dimensional magnetic field structure , and features of other ISM phases in the halo of NGC 253 .
We present a new sensitive radio continuum map of NGC 253 obtained from combined VLA and Effelsberg observations at \lambda 6.2 { cm } .
We find a prominent radio halo with a scaleheight of the thick radio disk of 1.7 kpc .
The linear dependence between the local scaleheight of the vertical continuum emission and the cosmic ray electron ( CRE ) lifetime requires a vertical CR bulk speed of 270 { km s ^ { -1 } } . The magnetic field structure of NGC 253 resembles an “ X ” -shaped configuration where the orientation of the large-scale magnetic field is plane-parallel only in the inner regions of the disk and at small distances from the galactic midplane .
At larger galactocentric radii and further away from the midplane the vertical component becomes important .
This is most clearly visible at the location of the “ radio spur ” southeast of the nucleus , where the magnetic field orientation is almost vertical .
We made a simple model for the dominant toroidal ( r, \phi ) magnetic field component using a spiral magnetic field with prescribed inclination and pitch angle .
The residual poloidal ( r, \phi,z ) magnetic field component which was revealed by subtracting the model from the observations shows a distinct “ X ” -shaped magnetic field orientation centered on the nucleus .
The orientation angle of the poloidal magnetic field is consistent with a magnetic field transport described by the superposition of the vertical CR bulk speed and the rotation velocity . Hence , we propose a disk wind which transports cosmic rays , magnetic field , and ( partially ) ionized gas from the disk into the halo .