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Shutting Down AGN

Shutting Down AGN. Nick Cowan University of Washington October 20, 2006. AGN: A Primer. Active Galactic Nuclei are super-massive black-holes accreting gas from a disk in the center of a galaxy. Astronomers have come up with a dozen different names for AGN depending on how we see them.

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Shutting Down AGN

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  1. Shutting Down AGN Nick Cowan University of Washington October 20, 2006

  2. AGN: A Primer • Active Galactic Nuclei are super-massive black-holes accreting gas from a disk in the center of a galaxy. • Astronomers have come up with a dozen different names for AGN depending on how we see them. • I’ll call them AGN, quasars and QSOs interchangeably.

  3. Why AGNs? • Apparently (according to Rich) they can ionize gas all the way to the outer edges of a galaxy. • That sounds dangerous.

  4. Outline • Background Info • MORGANA • Feedbacks and Accretion • Results (lots of plots) • Conclusions

  5. Some Background • The M- relation (BH-bulge relation) is an empirical observation that bulges with larger velocity dispersions (masses, luminosities, whatever) tend to host more massive black holes. • AGN exhibit an “anti hierarchical” behavior.

  6. Solutions to the M- Relation :SN Feedback vs AGN Feedback

  7. MORGANA • … is a truly stupid acronym: MOdel for the Rise of GAlaxies aNd Active nuclei. • Seriously, though, it’s a Semi-Analytical Model

  8. Semi Analytic Models (SAMs) • …as opposed to SPH, or N-body simulations. • Don’t need to understand the underlying physics as well. • Need to know which empirical effects are relevant. • Computationally easier. • Easier to analyze the results. • Output and input are closely related (incestuous?).

  9. More on MORGANA • Each DM halo forms from the merger of progenitor halos, each of which has one galaxy in it. • Baryons have three components: • Halo • Bulge • Disk • Each component has three phases: • Cold Gas • Hot Gas • Stars

  10. Yet More About MORGANA! • The DM halos are treated using merger trees. • After merging DM halos, dynamical friction, tidal stripping and tidal shocks on smaller halos (and their galaxy) leads to either tidal destruction or merger with the central galaxy. • Infalling IGM is shock-heated. • The hot halo gas is treated using a polytropic EoS with =1.2 • Cooling of the hot halo phase is treated as a series of concentric shells which cool radiatively and are heated from AGN or SN feedback from the central galaxy. • Also consider hot gas injected in by central galaxy.

  11. MORGANA keeps on goin’ • The cool gas falls into central galaxy and is divvied up between the bulge and the disk. • Gas falling onto disk keeps its angular momentum. • Disk instabilities and major mergers lead to bulges. • In minor mergers the small galaxy’s mass is given to the larger’s bulge. • Star formation treated using something like the Schmidt Law. • Hot gas ejected to halo at a rate equal to the SFR (except for bulges with v>300 km/s, which can hold on to hot gas).

  12. MORGANA: thank God! • Star-forming bulges eject cold gas by kinetic feedback. • If the hot gas is heated above the DM halo’s virial temperature, it is blown out in a galactic super-wind. • Metal enrichment is treated self-consistently assuming instantaneous recycling.

  13. Accretion onto Black Holes • Each DM halo starts with a 103 Msun BH. • BHs merge when halos merge. • Gas accretes onto BH only when it has lost nearly all its angular momentum. • Only bulge cold gas can accrete due to additional J-loss connected to B-fields, turbulence, radiation drag, which are all caused by star formation.

  14. Two Kinds of Winds • Drying Wind (DW): moves all ISM from bulge to halo. (results from kinetic energy being injected directly by BH) • Accreting Winds (AW): triggers further accretion onto BH (results from SN-winds throughout the galaxy) • In either case, SF as a result of winds is neglected in MORGANA.

  15. Quasar-Triggered Winds Preconditions: • AGN evaporation of ISM matches SFR • Can’t remove too much cold gas from the bulge. • Accretion is efficient (>1% Eddington rate)

  16. Stellar (SN) Feedback:Two Flavors • Super-bubbles easily blow out of thin/diffuse disks: most energy injected into halo. • In thicker/denser systems, energy injected into ISM, then dissipated through turbulence. This “kinetic feedback” leads to cold gas with large velocity dispersion. • Inflow of cold IGM can switch you from one limit to the other.

  17. Forced Quenching • AGN in the radiatively inefficient (<1% Eddington) regime heat hot halo gas, quenching cooling flows in large DM halos at low z. • Implemented in all their models.

  18. The Goals of this Paper • Self-consistent modeling of accreting BHs and their feedback on host galaxies. • Reproduce the properties of the AGN population (their luminosity and mass functions). • Reproduce the soft and hard x-ray background (not in this talk).

  19. Soft X-ray Luminosity Function Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  20. Hard X-ray Luminosity Function Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  21. B-band Luminosity Function Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  22. QSO Number Density with z Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  23. QSO Density for DW Model Velocity Dispersion of Cold gas: Solid Black: 0=0 km/s Magenta Dotted: 0=30 km/s Blue Dashed: 0=60 km/s Red Dot-Dashed: 0=90 km/s

  24. Cumulative Source Number Counts Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  25. BH-Bulge Relation • Models look good for large masses (slight over-estimate with the wind models). • Not enough scatter in STD model. • BHs in small bulges are too small.

  26. Black Hole Mass Function Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  27. BH Mass Accretion Black: STD Model Red: DW Model Blue: AW Model

  28. Evolution of the BH-Bulge Relation • Only the massive bulges are plotted here. Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  29. Accretion Rates Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  30. Eddington Ratios Solid Black: STD Model Red Dashed: DW Model Blue Dot-Dashed: AW Model

  31. Conclusions • Quasar triggered winds (Dry Winds) are needed to reproduce the number density of bright quasars. • Kinetic feedbacks in star-forming bulges is a very good candidate for downsizing the AGN population.

  32. Some Bold Predictions • The BH-bulge relation is in place at high-redshift. • Low-redshift faint AGN are responsible for the bulk of the hard x-ray background. • BH mass is acquired through accretion rather than mergers.

  33. Some Big Problems • The BH-bulge relation is steeper than observed for Mbulge<1011 Msun or MBH<108MSun • The BH mass function in this low-mass range is lower than observed. • There must be some additional downsizing mechanism for elliptical galaxies.

  34. References • F. Fontanot, astro-ph/0609823 • C. Megan Urry, ASPC…311…49U

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