Strong magnetic spiral pattern in a ringed galaxy NGC 4736

Abstract

We present high sensitivity radio polarimetric (VLA) observations of a galaxy with strong orbital resonances NGC 4736. The total radio intensity at 8.4 GHz covers smoothly the whole galaxy bulge and reveals a distinct ring of radio emission closely related to the ring morphology visible in infrared, CO and H emission. However, the magnetic field reveals a very coherent spiral pattern. The magnetic field vectors are crossing the inner starbursting ring, the dust lanes within the ring and other rather circularly shaped features visible in other gas traces. Either the magnetic field uncovers the pattern of gas motions not seen in other spectral ranges, or the spiral magnetic field is of a pure dynamo origin, ignoring the ringed morphology of the galaxy. © 2008 Copyright International Astronomical Union 2008.