Pinpointing Radio Wave Origins In The Distant Universe
May 1, 2013

Jansky Very Large Array Looks Deep Into The Distant Universe

April Flowers for - Your Universe Online

For the first time, astronomers have identified discrete sources that account for nearly all of the radio waves coming from distant galaxies. This was achieved by more than 50 hours of observations with the ultra-sensitive Karl G. Jansky Very Large Array (VLA). The researchers found that approximately 63 percent of the background radio emission comes from galaxies with gorging black holes at their cores. The remaining 37 percent emanates from galaxies that are rapidly forming stars.

"The sensitivity and resolution of the VLA, following its decade-long upgrade, made it possible to identify the specific objects responsible for nearly all of the radio background emission coming from beyond our own Milky Way Galaxy," said Jim Condon, of the National Radio Astronomy Observatory (NRAO). "Before we had this capability, we could not detect the numerous faint sources that produce much of the background emission," he added.

The amount of radio emission coming from the distant Universe has been measured by prior studies, but they were incapable of attributing all the radio waves to specific objects. In these studies, emissions from two or more faint objects are often blurred or blended into a single, stronger source of radio waves.

"Advancing technology has revealed more and more of the Universe to us over the past few decades, and our study shows individual objects that account for about 96 percent of the background radio emission coming from the distant Universe," Condon said. "The VLA now is a million times more sensitive than the radio telescopes that made landmark surveys of the sky in the 1960s," he added.

The research team studied a region of the sky in February and March of 2012 that had previously been observed by the original, pre-upgrade, VLA. This region had also been surveyed by the Spitzer Space Telescope, which observes infrared light. Condon and his colleagues carefully analyzed and processed the data to produce an image that revealed the individual, radio-emitting objects within their field of view.

The team´s field of view, which encompassed about one-millionth of the whole sky, is located in the constellation Draco. They identified about 2,000 discrete radio-emitting objects in that region, indicating that there are about 2 billion such objects in the whole sky. These 2 billion objects account for approximately 96 percent of the background radio emission. The final four percent, the researchers point out, could be coming from as many as 100 billion very faint objects.

The scientists performed further analysis to determine which of the objects are galaxies containing massive central black holes that are actively consuming surrounding material and which are galaxies undergoing rapid bursts of star formation. Their results, published in the Astrophysical Journal, indicate that the two types of galaxies evolved at the same rate in the early Universe. This confirms previously proposed theories.

"What radio astronomers have accomplished over the past few decades is analogous to advancing from the early Greek maps of the world that showed only the Mediterranean basin to the maps of today that show the whole world in exquisite detail," Condon said.