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Researchers discover distant galactic halos

Very Large Array telescope reveals unique properties of spiral galaxies.

A study of spiral galaxies seen edge-on has revealed that halos of cosmic rays and magnetic fields above and below the galaxies’ disks are much more common than previously thought. Edge-on galaxies, when seen with the naked eye, look like a line in the sky.

An international team of astronomers including lead author and Queen’s postdoctoral student Theresa Wiegert and Queen’s researcher Judith Irwin (Physics, Engineering Physics and Astronomy) used 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 upgraded telescope is more powerful than any used before and allowed researchers to see halos much fainter than before.

“We knew before that some halos existed, but, using the full power of the upgraded VLA and the full power of some advanced image-processing techniques, we found that these halos are much more common among spiral galaxies than we had realized," says Dr. Irwin.

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," says Dr. Wiegert. 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; Jayanne English, University of Manitoba, combined them into a single image. The result, says Dr. 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, the scientists said, confirms a prediction of such halos made in 1961.

The scientists are now making the VLA images available to other researchers to allow them to do their own analyses to explore other aspects of the halos including what they reveal about the evolution of galaxies.

The results from “Continuum Halos in Nearby Galaxies – an EVLA Survey” (CHANG-ES) is appearing in the Astronomical Journal. Researchers working with the CHANG-ES consortium work at institutions around the world.