Composite image of an edge-on spiral galaxy with a radio halo produced by fast-moving particles in the galaxy’s magnetic field. In this image, the large, grey-blue area is a single image formed by combining the radio halos of 30 different galaxies, as seen with the Very Large Array. At the center is a visible-light image of one of the galaxies, NGC 5775, made using the Hubble Space Telescope. This visible-light image shows only the inner part of the galaxy’s star-forming region, outer portions of which extend horizontally into the area of the radio halo. Credit: Jayanne English (U. Manitoba), with support from Judith Irwin and Theresa Wiegert (Queen’s U.) for the CHANG-ES consortium; NRAO/AUI/NSF; NASA/STScI (Science credit: Theresa Wiegert, Judith Irwin and the CHANG-ES consortium)
Improved sensitivity shows faint radio emission above and below the disks of spiral galaxies and appear to be more common than previously thought. An international team of astronomers used the Karl G. Jansky Very Large Array (VLA) to study 35 edge-on spiral galaxies at distances from 11 – 137 M light-years from Earth. The study took advantage of the ability of the VLA, following completion of a decade-long upgrade project, to detect radio emission much fainter than previously possible.
Spiral galaxies, like our own Milky Way, have the vast majority of their stars, gas, and dust in a flat, rotating disk with spiral arms. Most of the light and radio waves seen with telescopes come from objects in that disk. Learning about the environment above and below such disks has been difficult. “Studying these halos with radio telescopes can give us valuable information about a wide range of phenomena, including the rate of star formation within the disk, the winds from exploding stars, and the nature and origin of the galaxies’ magnetic fields,” said Theresa Wiegert, Queen’s University. The paper provides the first analysis of data from all 35 galaxies in the study.
To see how extensive a “typical” halo is, the astronomers scaled their images of 30 of the galaxies to the same diameter, then Jayanne English, of the University of Manitoba in Canada, combined them into a single image. The result, said Irwin, is “a spectacular image showing that cosmic rays and magnetic fields not only permeate the galaxy disk itself, but extend far above and below the disk.” The combined image confirms a prediction of such halos made in 1961.
“The results from this survey will help answer many unsolved questions in galactic evolution and star formation,” said Marita Krause of the Max-Planck Institute for Radioastronomy in Bonn, Germany. https://public.nrao.edu/news/pressreleases/galaxy-halos
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