The Narrow-Line Region and Ionization Cone Lei Xu

NLR Importance:  Spacially resolved  Ionizing radiation from the central source  Dynamics--how AGNs are fueled Low density gas: 10^2 – 10^6 cm^-3 Scale: 10 pc – 1 kpc

NLR Narrow-Line Spectra Line Ratio Diagrams Emission Line Region Modelling Interesting Results from Observation

Narrow-Line Spectra FWHM: ~200—900 km/s; typically 350— 400 km/s Low Gas density: emission lines arising from magnetic dipole transitions [OIII], N[II]….

Physical Conditions in Low-Density Gases Electron Density S+S+ [SII] 6716, 6731.

Electron Density Low-density Case High-density Case << >>

Electron Temperature O ++

Basic Parameters Filling factor N L^3= r^3

Line Ratio Diagrams BPT Diagram ( Baldwin, Phillips, & Terlevich 1981) Groves et al. 2006

Emission Line Region Modelling The temperature and ionization are determined by the ionization source. Need to determine the density, temperature, and ionization state of the ionized gas Two main pathways: Photoionization and Shock ionization.

Photoionization The NLR is excited by the UV and X-ray photons from a central source, thought to be the accretion disk surrounding the central black hole in AGN. (Osterbrock 1989; Blandford et al. 1990) Input parameters: the gas abundances and initial density, the size or column depth of the model cloud, the incident ionizing spectrum, and the incident ionizing flux of the radiation. Able to reproduce the ratios well for a limited range of parameters, as well as. Failing to reproduce both low-ionization and high-ionization line strengths simultaneously, e.g. with the same parameter set.

Shock Ionization The gas is excited collisionally through shocks caused by interactions with a jet or winds arising from the central AGN source. Input parameters: the gas abundances, pre-shock density, shock velocity, and a parameter related to the magnetic field strength. Unable to reproduce typical Seyfert NLR line ratios. For some LINER-like objects, they might possibly be the exciting mechanism. Discussed in detail in Allen, Dopita, & Tsvetanov (1998)

Shock + Precursor Combination of both shock and photo-ionization, and the photo-ionization is determined by the shock velocity. Fast shocks (Vs > 150 km s−1) would produce ionizing photons (Dopita & Sutherland 1995, 1996). As post- shock gas cools, it produces ionizing photons. Able to reproduce the observations quite well, and can also produce some of the higher ionization lines. They require shocks throughout the NLR, meaning shock signatures should always be visible. So by themselves these models cannot explain all NLR emission.

Allen, Dopita, & Tsvetanov 1998

Multi-Component Photoionization The combination of two or more photoionization models. Most models limit themselves to two components to minimize the number of free parameters. The main problem with these models is that as you increase the number of clouds, the problem becomes unconstrained. Binette et al. (1996); Ferguson et al. (1997); Groves et al. (2004)

Relationship between NLR size and [OIII] luminosity Bennert et al the open diamond: Seyfeit galaxies the filled square: PG quasars

Quasar Schmitt et al Sample: 39 Seyfert 2s 21 Seyfert 1s 7 Quasars

Bennert et al Type-1 Type-2 Type-1 Type-2

Relationship between and NLR line width Host galaxy spheroid velocity dispersion Since measures the basic gravitational velocity in the near-nuclear regions, a comparison with should show the degree to which the velocity field of the NLR gas has a gravitational origin. Nelson & Whittle 1995, 1996; Greene & Ho 2005; Rice et al. 2006

Greene & Ho 2005 Rice et al. 2006

The mass of a galaxy’s central, supermassive black hole and the stellar velocity dispersion of the host galaxy spheroid have the relationship Greene & Ho 2005

Ionization Cone NGC 5252 [OIII] Afanasiev et al. 2007

NGC 3516 [OIII] Z-shaped pattern Moiseev et al. 2007

Properties  Both bi-cones and single cones are found. A counter- cone may be present but hidden by obscuration in the disk.  Good correlation between the directions of ionized cones and those of radio jets — their symmetry axes coincide to within 5 − 10◦ (Wilson & Tsvetanov 1994; Falcke et al. 1996; Nagar et al. 1999)  No clear relationship between the axes of the cones and those of the host-galaxy disks

Formation Theoretical Scenario:  Collimation of ionizing radiation by the torus of matter accreting onto a supermassive black hole at the nucleus of the galaxy  Shock produced by the intrusion of the jet from the active nucleus into the surrounding clouds of interstellar medium Numerical Simulation:  Rossi et al. (2000): the model of the interaction of the jet with gaseous clouds in the circumnuclear region. Able to explains a number of morphological features, but fails to describe the development of symmetric Z- shaped features.  Afanasiev et al. (2007)

Afanasiev et al NGC 5252 Afanasiev Velocity Map Luminosity map

Summary Spacially resolved; Ionizing radiation from the central source; Dynamics Line Ratio Diagrams are able to distinguish different emission line sources, and test the emission line region modelling. Relationship between NLR size and [OIII] luminosity Relationship between and Ionization cone