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The spectacular halos of spiral galaxies

Submitter: George Heald
Description: The "Continuum Halos in Nearby Galaxies - an EVLA Survey" (CHANG-ES) project has been highlighted here twice before. Now, this detailed study of edge-on spiral galaxies has revealed that "halos" of cosmic rays and magnetic fields above and below the galaxies' disks are much more common than previously thought.

The CHANG-ES collaboration is an international team of astronomers including ASTRON scientist George Heald. The survey made use of the Karl G. Jansky Very Large Array (VLA) to study 35 edge-on spiral galaxies at distances from 11 million to 137 million 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, although we know that careful observations with the venerable WSRT can reveal the low-density gaseous outskirts of a broad range of galaxies.

To see how extensive a "typical" radio continuum halo is, the CHANG-ES team scaled their images of 30 of the galaxies to the same diameter, then Jayanne English, of the University of Manitoba in Canada and a previous honored guest at ASTRON, combined them into a single image which is highlighted as today's Daily Image. The result, said project PI Judith Irwin (from Queen's University in Canada), 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 CHANG-ES collaboration is now also making their first batch of survey images available online for other researchers. The data are available at this website.

The NRAO has released a press release on this spectacular image, and it can be found here.
Copyright: Jayanne English and the CHANG-ES collaboration
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