New Data Produce Radio Map of North Galactic Pole
The new map, which covers over 50 square degrees of sky, reveals several new features that haven’t been seen before.
“You might have thought that the radio sky has been well imaged,” said Philipp Kronberg, of Los Alamos National Lab, who led the research project. But in fact there are holes in our picture of the sky, he said.
The image, the researchers report, provides the first detailed view of foreground galactic and extragalactic features that might contribute to CMB backgrounds on scales to be imaged by the PLANCK cosmic microwave background explorer.
Kronberg and colleagues produced the image by combining data from Arecibo, the world’s largest radio telescope, located in Puerto Rico, and the Dominion Radio Astrophysical Observatory in British Columbia, Canada. The DRAO is an array of 7 telescopes, each 9 meters across, in an east-west line. The telescopes shift along the line over twelve days in such a way that the combined data simulate a single 600 meter telescope.
The researchers chose the region of sky above the north galactic pole in order to be minimally affected by the Milky Way, said Kronberg. The new map’s field of view is centered on the Coma cluster of galaxies.
They were looking for areas of faint, 0.4 GHz synchrotron emission at low surface brightness levels on angular scales from 3 minutes to 8 degrees. In producing the map, they subtracted out known point sources, cosmic microwave background radiation, and smooth Milky Way foreground.
They found several interesting features, which Kronberg reported at the April Meeting of APS.
For instance, they found no correlation between the faint radiation produced by particles accelerated in the magnetized plasma of space and the distribution of bright stars and galaxies.
“We see signals all over this piece of sky,” said Kronberg in a press conference at the April Meeting. There are some patches of what is probably Milky Way foreground throughout much of the mapped area, though the new view identifies some areas that are relatively foreground-free. The Planck CMB explorer, which will be launched later this year, might want to concentrate on those spots, suggested Kronberg.
The new map revealed a large (about 9 million light years across) region of magnetized plasma near the Coma cluster, probably at the distance of the Great Wall of galaxies. The magnetic field is about 0.3 micro gauss, about 1/10th the strength of the Milky Way’s magnetic field. How that field is generated and maintained is not known, he said. This is the first known large diffuse patch that’s not associated with any galaxy, said Kronberg.
They found another large diffuse source. This feature, which has never been seen before, could be a giant radio galaxy that had not previously been observed because it was obscured by other nearby sources of radio waves, said Kronberg.