Radio Loud and Radio Quiet Quasars

Radio Loud and Radio Quiet Quasars

Ken Kellermann, NRAO

It has been half a century since the discovery of quasars and the subsequent recognition of the much larger radio quiet quasar population. Although all quasars are thought to contain a SMBH as the source of their enormous OIR luminosity, it has not been clear if the radio loud quasars are a distinctly different class of object from the radio quiet quasars or if they are just the high end of a smooth radio luminosity function, and why only a small fraction of optically selected quasars are strong radio sources. I will first discuss the bizarre circumstances surrounding the discovery of quasars through their strong radio emission followed by the recognition of their more populous radio quiet counterpart.  I will then describe the results of a VLA study of quasars selected from the Sloan digital Sky Survey which suggest that the radio emission from radio quiet quasars is mostly due to star formation in the host galaxy and is not directly related to the SMBH, and why previous radio studies were unable to unambiguously recognize the separate population of radio quiet quasars. Finally, I will review what we have learned from VLBA observations of radio loud quasars as well as the challenges presented by the recent space VLBI observations of the high brightness temperatures in some quasars which greatly exceed the limits set by inverse Compton scattering.