Science > Event > Radio Astronomy in the LSST Era > Program Abstracts > Extragalactic Source Populations

Extragalactic Source Populations

by Carolyn Hunsinger last modified Apr 25, 2013

Jim Condon (National Radio Astronomy Observatory)

Extragalactic Source Populations

Almost all discrete radio sources are extragalactic and so distant (median redshift <z> ~  1) that the radio sky is extremely isotropic. Sources with log[L(W Hz−1)] > 23 at cm wavelengths are usually powered by AGNs in elliptical radio galaxies, Seyfert galaxies, and QSOs; star-forming spiral and irregular galaxies dominate at lower luminosities. Flux density reflects luminosity more than distance; fainter samples are not “deeper.” Most radio sources stronger than S  1 mJy are powered by AGNs. Galaxies obeying the far-infrared/radio correlation probably dominate below S ~ 0.1 mJy and provide extinction-free tracers of recent star formation. “Radio quiet” QSOs are rarely radio silent, with starbursts powering radio emission at the log[L(W Hz−1)]  ~ 23 level.  About 96% of the sky background is contributed by sources stronger than S ~ 1 μJy. The median angular size of faint sources is only <Ø> ≤ 1", small enough to allow reliable identifications with LSST galaxies by position coincidence alone. Compact radio cores place supermassive black holes with milli-arcsec absolute accuracy within optical emission from host galaxies. Known Extragalactic slow radio transients and variables include SNe, microquasars, gamma-ray burst afterglows, and AGN outbursts caused by tidal disruption events.