Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2009-09-01
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
6 pages, 9 figures, to be published in Astronomische Nachrichten (proceedings of Symposium 6 of the JENAM 2008, Vienna)
Scientific paper
Radio halos require the coexistence of extra-planar cosmic rays and magnetic fields. Because cosmic rays are injected and accelerated by processes related to star formation in the disk, they have to be transported from the disk into the halo. A vertical large-scale magnetic field can significantly enhance this transport. We observed NGC 253 using radio continuum polarimetry with the Effelsberg and VLA telescopes. The radio halo of NGC 253 has a dumbbell shape with the smallest vertical extension near the center. With an estimate for the electron lifetime, we measured the cosmic-ray bulk speed as 300+/-30 km/s which is constant over the extent of the disk. This shows the presence of a "disk wind" in NGC 253. We propose that the large-scale magnetic field is the superposition of a disk (r,phi) and a halo (r,z) component. The disk field is an inward-pointing spiral with even parity. The conical (even) halo field appears in projection as an X-shaped structure, as observed in other edge-on galaxies. Interaction by compression in the walls of the superbubbles may explain the observed alignment between the halo field and the lobes of hot Halpha- and soft X-ray emitting gas. The disk wind is a good candidate for the transport of small-scale helical fields, required for efficient dynamo action, and as a source for the neutral hydrogen observed in the halo.
Beck Rainer
Dettmar Ralf-Jürgen
Heesen Volker
Krause Marita
No associations
LandOfFree
Transport of cosmic rays in the nearby starburst galaxy NGC 253 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Transport of cosmic rays in the nearby starburst galaxy NGC 253, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transport of cosmic rays in the nearby starburst galaxy NGC 253 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-11468