The Narrow-Line Region and Ionization Cone

1. The Narrow-Line Region and Ionization Cone Lei Xu

2. 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

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

4. 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]….

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

6. Electron Density • Low-density Case • High-density Case << >>

8. Electron Temperature O++

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

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

11. 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.

12. 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.

13. 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)

14. 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.

15. Allen, Dopita, & Tsvetanov 1998

16. Multi-Component Photoionization • The combination of two or more photoionization models. • Most models limit themselves to two components to minimizethe 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)

17. Relationship between NLR size and [OIII] luminosity the open diamond: Seyfeit galaxies the filled square: PG quasars Bennert et al. 2002

18. 0.33 0.31 0.41 Quasar 0.42 Sample: 39 Seyfert 2s 21 Seyfert 1s 7 Quasars Schmitt et al. 2003

19. Type-1 Type-2 Type-1 Type-2 Bennert et al. 2006

20. 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

21. Rice et al. 2006 Greene & Ho 2005

22. 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

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

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

25. 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

26. 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)

27. Afanasiev Luminosity map NGC 5252 Velocity Map Afanasiev et al. 2007

28. 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