AGN Unification Diagram

Schematic representation of our understanding of AGN in the orientation unified scheme. The type of object seen depends on the viewing angle, whether or not the AGN produces a significant jet (radio loud or radio quiet), and the rate of accretion onto the central SMBH (low or high electromagnetic power). The centre of the schematic shows the typical components of an AGN but we note that the geometry of many of these components are still unknown. Radio-loud objects are generally thought to display bipolar jet emission whereas it is only shown on the radio-loud side here. Note radio-quiet is not the same as radio-silent as many galaxies have low level radio emission, which is not significantly above that expected from star-formation and therefore it is unknown if these host radio jets or not. The upper left and upper right quandrants are commonly referred to as low and high excitation radio galaxies (LERG/HERG) respectively. LERGs are also known as hot mode, radio mode, jet mode, and radiatively inefficient sources, while HERGs are also known as cold mode, quasar mode, radiative mode, and radiatively efficient sources. We include some of the most commonly used names for different classes of AGN including broad line radio galaxy (BLRG), narrow line radio galaxy (NLRG), narrow emission line galaxy (NELG), flat spectrum radio quasar (FSRQ), steep spectrum radio quasar (SSRQ), optically violent variables (OVV), and quasi-stellar objects (QSO). Note that while we separate quasars and QSOs as being radio loud and radio quiet respectively, these names are often used interchangeably. Surrounding the central schematic we show whether a particular combination of power, radio emission, and geometry is expected to produce broad or narrow emission lines, or MIR, radio, X-ray, or gamma-ray emission. The transparency of the colour in each ring corresponds to the increasing strength or prevalence of a particular emission type.