Active versus non-active galaxies: The seagull wings

AGN Zoo and Classications of Active Galaxies

We review the variety of Active Galactic Nuclei (AGN) classes (so-calledAGN zoo") and classification schemes of galaxies by activity types based on their optical emission-line spectrum, as well as other parameters and other than optical wave-length ranges. A historical overview of discoveries of various types of active galaxies is given, including Seyfert galaxies, radio galaxies, QSOs, BL Lace...

Active Galaxies: Overview

Active Galaxies as Particle Accelerators

We present the theoretical arguments and describe the accumulating experimental evidence that jets, powered by supermassive black holes, are true cosmic accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. The features of the multiwavelength emission spectrum are dictated by the interactions of electrons and proton...

Stellar Populations in Active Galaxies

The role of stars and starbursts in AGN has been a recurring issue for nearly as long as AGN have been recognized as hosts of interesting phenomena. The heated “starburst versus monster” controversy of the 80’s and 90’s was gradually replaced by “starburst plus monster” studies, as observational work in the past decade has firmly established that accretion onto a super-massive black-hole and st...

Active galaxies and radiative heating.

There is abundant evidence that heating processes in the central regions of elliptical galaxies have both prevented large-scale cooling flows and assisted in the expulsion of metal rich gas. We now know that each such spheroidal system harbours in its core a massive black hole weighing ca. 0.13% of the mass in stars and also know that energy was emitted by each of these black holes with an effi...