CHANG-ES IX: Radio scale heights and scale lengths of a consistent sample of 13 spiral galaxies seen edge-on and their correlations

摘要

The vertical halo scale height is a crucial parameter to understand thetransport of cosmic-ray electrons (CRE) and their energy loss mechanisms inspiral galaxies. Until now, the radio scale height could only be determined fora few edge-on galaxies because of missing sensitivity at high resolution. We developed a sophisticated method for the scale height determination ofedge-on galaxies. With this we determined the scale heights and radial scalelengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey intwo frequency bands. The sample average value for the radio scale heights of the halo are 1.1 +/-0.3kpc in C-band and 1.4 +/- 0.7kpc in L-band. From the frequency dependenceanalysis of the halo scale heights we found that the wind velocities (estimatedusing the adiabatic loss time) are above the escape velocity. We found that thehalo scale heights increase linearly with the radio diameters. In order toexclude the diameter dependence, we defined a normalized scale height which isquite similar for all sample galaxies at both frequency bands and does notdepend on the star formation rate or the magnetic field strength. However, thenormalized scale height shows a tight anticorrelation with the mass surfacedensity. The sample galaxies with smaller scale lengths are more spherical in theradio emission, while those with larger scale lengths are flatter. The radioscale height depends mainly on the radio diameter of the galaxy. The samplegalaxies are consistent with an escape-dominated radio halo with convectivecosmic ray propagation, indicating that galactic winds are a widespreadphenomenon in spiral galaxies. While a higher star formation rate or starformation surface density does not lead to a higher wind velocity, wedeceleration of CRE outflow, e.g. a lowering of the wind velocity from thegalactic disk.