Misc,
Hot gas and magnetic arms of NGC 6946: indications for reconnection heating?
(Mar 2, 2016)
Abstract
The grand-design face-on spiral galaxy NGC6946 is remarkable because of its
high star formation activity, the massive northern spiral arm, and the magnetic
arms, which are observed in polarized radio synchrotron emission and are
located between the optical arms and possibly are magnetic reconnection
regions. X-ray observations of NGC6946 performed with XMM-Newton were used to
study the emission from X-ray point sources and diffuse hot gas, including the
magnetic arms and the halo. Spectral fitting of the diffuse X-ray emission
allowed us to derive temperatures of the hot gas. With assumptions about the
emission volume, this allowed us to estimate gas densities, masses, and cooling
times. To explain the X-ray emission from the spiral arms of NGC6946
two-temperature plasma models are needed to account for the disk and halo
emission. The interarm regions show only one thermal component. We observe that
the temperature of the hot gas in and above the magnetic arm regions increases
slightly when compared to the average temperatures in the areas in and above
the spiral arms. For the southwestern part of the disk, which is depolarized in
the radio range by Faraday rotation, we find more efficient mixing of disk and
halo gas. We propose magnetic reconnection in the magnetic arm regions of
NGC6946 as the possible cause of the additional heating of the gas and ordering
of the magnetic fields. In the southwestern part of the galactic disk we
observed indications of a possible faster outflow of the hot gas. A very hot
gas within the MF16 nebula possibly suggests shock heating by a supernova
explosion.
