"Observations of active galactic nuclei The names "active galaxies" and "active galactic nuclei" (AGN) are related to the main feature that distinguishes these objects from inactive (normal or regular) galaxies: the presence of supermassive accreting black holes (BHs) in their centers. As of 2011, there were approximately a million known sources of this type selected by their color and several hundred thousand by basic spectroscopy and accurate redshifts. It is estimated that in the local universe, at z <
0.1, about 1 out of 50 galaxies contains a fast-accreting supermassive BH, and about 1 in 3 contains a slowly accreting supermassive BH. Detailed studies of large samples of AGN, and the understanding of their connection with inactive galaxies and their redshift evolution, started in the late 1970s, long after the discovery of the first quasi-stellar objects (hereinafter quasars or QSOs) in the early 1960s. Although all objects containing active supermassive BHs are now referred to as AGN, various other names, relics from the 1960s, 1970s, and even later, are still being used. Some of the names that appear occasionally in the literature, such as "Seyfert 1 galaxies" and "Seyfert 2 galaxies," in honor of Seyfert, who observed the first few galaxies of this type in the late 1940s (see
- Chapter 6 for a detailed discussion of the various groups), are the result of an early confusion between different sources that are now known to have similar properties"-- Provided by publisher. "Research into active galactic nuclei (AGN) - the compact, luminous hearts of many galaxies - is at the forefront of modern astrophysics. Understanding these objects requires extensive knowledge in many different areas: accretion disks, the physics of dust and ionized gas, astronomical spectroscopy, star formation, and the cosmological evolution of galaxies and black holes. This new text by Hagai Netzer, a renowned astronomer and leader in the field, provides a comprehensive introduction to the theory underpinning our study of AGN and the ways that we observe them. It emphasizes the basic physics underlying AGN, the different types of active galaxies and their various components, and the complex interplay between them and other astronomical objects. Recent developments regarding the evolutionary connections between active galaxies and star-forming galaxies are explained in detail. Both graduate students and researchers will benefit from Netzer's authoritative contributions to this exciting field of research"-- Provided by publisher.
Includes bibliographical references (pages 339-348) and index.