To appear in Annual Reviews of Astronomy and
Astrophysics (2008)
arXiv:0803.2268
For a PDF version of the article, click here.
NUCLEAR ACTIVITY IN NEARBY GALAXIES
Luis C. Ho
The Observatories of
the Carnegie Institution of Washington,
813 Santa Barbara St., Pasadena, CA 91101;
e-mail: lho@ociw.edu
Key Words: accretion disks, active galactic nuclei, black holes,
LINERs, radio galaxies, Seyfert galaxies
Abstract. A significant fraction of nearby galaxies show evidence
of weak nuclear activity unrelated to normal stellar processes. Recent
high-resolution, multiwavelength observations indicate that the bulk of
this activity derives from black hole accretion with a wide range of
accretion rates. The low accretion rates that typify most low-luminosity
active galactic nuclei induce significant modifications to their central
engine. The broad-line region and obscuring torus disappear in some of
the faintest sources, and the optically thick accretion disk transforms
into a three-component structure consisting of an inner radiatively
inefficient accretion flow, a truncated outer thin disk, and a jet or
outflow. The local census of nuclear activity supports the notion that
most, perhaps all, bulges host a central supermassive black hole,
although the existence of active nuclei in at least some late-type
galaxies suggests that a classical bulge is not a prerequisite to seed a
nuclear black hole.
Table of Contents
INTRODUCTION
- SPECTRAL CLASSIFICATION OF GALACTIC NUCLEI
- Physical Motivation
- Sample Spectra
- Diagnostic Diagrams
- Starlight Subtraction
- Other Classification Criteria
- SURVEYS OF NEARBY GALACTIC NUCLEI
- The Palomar Survey
- Other Surveys
- Detection Rates
- Broad Emission Lines
- Robustness and Completeness
- HOST GALAXY PROPERTIES
- Global Parameters
- Nuclear Stellar Populations
- Influence of Bars and Environment
- NUCLEAR PROPERTIES
- Ionizing Continuum Radiation
- Radio Cores
- X-ray Cores
- Circumnuclear Thermal Plasma
- Broad-line Region
- Torus
- Narrow-line Region Kinematics
- Spectral Energy Distribution
- Luminosity Function
- Bolometric Luminosities and Eddington Ratios
- EXCITATION MECHANISMS
- Nonstellar Photoionization
- Contribution from Fast Shocks
- Contribution from Stellar Photoionization
- Energy Budget
- The Nature of Transition Objects and a Unified View
of LLAGNs
- IMPLICATIONS FOR BLACK HOLE DEMOGRAPHICS
- IMPLICATIONS FOR ACCRETION PHYSICS
- Why Are LLAGNs So Dim?
- The Disk-Jet Connection
- The Central Engine of LLAGNs
- CONCLUDING REMARKS
- REFERENCES
