A Cyberinfrastructure platform to meet the needs of data intensive radio astronomy on route to the SKA

Resolving the Radio Source Background: Deeper Understanding Through Confusion

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By Samuel George 2351 days ago
We used the Karl G. Jansky Very Large Array (VLA) to image one primary beam area at 3 GHz with 8 arcsec FWHM resolution and 1.0 microJy/beam rms noise near the pointing center. The P(D) distribution from the central 10 arcmin of this confusion-limited image constrains the count of discrete sources in the 1 < S(microJy) < 10 range. At this level the brightness-weighted differential count S^2 n(S) is converging rapidly, as predicted by evolutionary models in which the faintest radio sources are star-forming galaxies; and ~96% of the background originating in galaxies has been resolved into discrete sources. About 63% of the radio background is produced by AGNs, and the remaining 37% comes from star-forming galaxies that obey the far-infrared (FIR) / radio correlation and account for most of the FIR background at 160 microns. Our new data confirm that radio sources powered by AGNs and star formation evolve at about the same rate, a result consistent with AGN feedback and the correlation of black hole and bulge stellar masses. The level of confusion at centimeter wavelengths is low enough that neither the planned SKA nor its pathfinder ASKAP EMU survey should be confusion limited, and the ultimate source detection limit imposed by natural confusion from overlapping extended sources is < 0.01 microJy at 1.4 GHz. If discrete sources dominate the surprisingly bright extragalactic background reported by ARCADE2 at 3.3 GHz, they constitute an unexpected new population of sources that must be two orders of magnitude more numerous than all galaxies brighter than m_AB = +29, cannot be located in or near galaxies, and are typically weaker than 0.03 microJy at 1.4 GHz.