Radio galaxies are cosmic beacons, with the brightest ones beaming nearly a trillion solar-luminosities of radiation into space at radio wavelengths. The origin of this intense emission is the environment of the massive black hole at the galaxy's nucleus -- a so-called active galactic nucleus (AGN). It is thought that electrons moving rapidly in strong magnetic fields produce the radio emission, but at the same time high temperature regions near the AGN also radiate intensely at other wavelengths. Astronomers are interested in understanding the physics underway in these extreme cosmic radio sources, and whether they are cosmic oddities or a normal evolutionary stage of galaxies like our own Milky Way.
SAO astronomers Giovanni Fazio and Steve Willner, along with nine of their colleagues, used the Spitzer Space Telescope to study two well known radio galaxies whose light has been traveling for over eleven billion years -- more than 80% of the lifetime of the universe. Formed when the universe was still relatively young, these objects demonstrate that whatever physical processes are at work in radio galaxies, they also were effective in the early universe. Vigorous star formation in local galaxies, for example, is usually accompanied by emission from
small, carbon-rich grains called polyaromatic hydrocarbons, or PAHs.
The scientists report finding the first evidence for PAHs in distant radio galaxies, a clear indication that in addition to their luminous AGN, these ancestral galaxies also are busy making new stars. The results help to show that these early radio galaxies look quite similar to modern ones despite the youth of the cosmos. Because they are particularly bright (and hence detectable by us), their presence also suggests that there may be many more, less dramatic but nonetheless still active, radio galaxies contributing to this early epoch of cosmic development.