MPIfR: Swirling Electrons in the Whirlpool Galaxy

bystander · Post by **bystander** » Wed Aug 20, 2014 9:35 pm

Swirling Electrons in the Whirlpool Galaxy
Max Planck Institute for Radio Astronomy | 2014 Aug 20

Cosmic particles and magnetic fields in the galaxy M51 observed with the LOFAR radio telescope

[i]LOFAR radio map of the whirlpool galaxy M51 and its neighbourhood at a frequency of 150 MHz. The field covers 4 by 2.6 degrees. The observations were performed with the Dutch LOFAR high-band antennas. The map shows the distribution of hot electrons in M51 and also a large number of background galaxies.The inlay shows an enlarged view of M51 at 150 MHz (white contour lines) overlayed onto an optical image of M51 from the Digital Sky Survey (DSS). [b](© David Mulcahy et al., Astronomy & Astrophysics)[/b][/i]
The whirlpool galaxy Messier 51 (M51) is seen from a distance of approximately 30 million light years. This galaxy appears almost face-on and displays a beautiful system of spiral arms.
A European team of astronomers was able to observe M51 with the International LOFAR Telescope in the frequency range 115-175 MHz, just above the normal commercial FM radio frequency band of 88-108 MHz. The team obtained the most sensitive image of any galaxy at frequencies below 1 GHz so far.

With LOFAR's high sensitivity, the disk of M51 in the radio regime could be traced much further out than before. The astronomers detected cosmic electrons and magnetic fields 40,000 light years away from the center of M51. With LOFAR’s high angular resolution, the spiral arms are clearly visible. Magnetic fields and cosmic rays are densest in spiral arms. Compared to higher radio frequencies, spiral arms appear broader due to the diffusion of cosmic electrons away from the spiral arms where they have been formed.

The view of galaxies in the radio regime is different to their optical appearance. Whereas optical images show predominantly the visible light from stars, the radio waves unravel two constituents of galaxies that are invisible to optical telescopes: electrons, almost as fast as light, and magnetic fields. Their role for the stability and evolution of galaxies is increasingly under discussion. The electrons are "cosmic ray" particles produced in the shock fronts of giant supernova explosions. Magnetic fields are generated by dynamo processes driven by gas motions. When the electrons spiral around the magnetic field lines, radio waves are emitted, a process called synchrotron emission. Its intensity increases with the number and energy of the electrons and with magnetic field strength. ...

First LOFAR observations of the “Whirlpool Galaxy”
University of Southampton | 2014 Aug 20

The nature of the low-frequency emission of M51:
First observations of a nearby galaxy with LOFAR - D. D. Mulcahy et al

Astronomy & Astrophysics 578 A74 (20 Aug 2014) DOI: 10.1051/0004-6361/201424187
arXiv.org > astro-ph > arXiv:1407.1312 > 04 Jul 2014 (v1), 22 Jul 2014 (v2)