Radio Galaxies and the Star Formation History of the Universe

Gopal Krishna

National Centre for Radio Astrophysics

Tata Institute of Fundamental Research

Pune, India

Abstract

Multi-wavelength observations made in the last decade strongly suggest that the universe underwent an intense phase of star-formation in the past (z > 1). This intensive activity is commonly attributed to a higher galaxy merger rate when the universe was a fraction of its present age. Here we examine the role of the powerful radio galaxies whose comoving density is known to be a few orders of magnitude higher at z ~ 2 ( the so called `quasar era'). Taking into account the recent theoretical models for the temporal evolution of the size and luminosity of a powerful double radio source, as well as advanced Lambda-CDM simulations of the cosmic web of baryonic material at different redshifts, it is argued that during the quasar era a high fraction of the volume of the web was occupied by the lobes of double radio galaxies. Widespread compression of proto-stellar clouds, triggered by the high pressure of the synchrotron plasma of the radio lobes, can thus be expected to have played a significant role in the star formation history of the universe, and also in causing a rather high level of magnitization of the galactic and intergalactic material at early epochs.