1. AGN Feedback at the Parsec Scale Feng Yuan Shanghai Astronomical Observatory, CAS with: F. G. Xie (SHAO) J. P. Ostriker (Princeton University) M. Li (SHAO)

2. OUTLINE Intermittent activity of compact radio sources Intermittent activity of compact radio sources Outburst: 10^4 years Outburst: 10^4 years Quiescent: 10^5 years Quiescent: 10^5 years previous interpretation & its problem previous interpretation & its problem thermal instability of radiation-dominated thin disk thermal instability of radiation-dominated thin disk Explaining the intermittent activity with Global Compton scattering feedback mechanism in hot accretion flows Explaining the intermittent activity with Global Compton scattering feedback mechanism in hot accretion flows What is global Compton scattering ? What is global Compton scattering ? When L > 0.02 L_Edd: no steady solutions; BH activity oscillates When L > 0.02 L_Edd: no steady solutions; BH activity oscillates Estimations of durations of active and inactive phases Estimations of durations of active and inactive phases

3. AGN feedback: an important role in galaxy formation & evolution correlation correlation suppression of star formation in elliptical galaxies suppression of star formation in elliptical galaxies Great progress made; still many details need further exploration (Ostriker 2010) Great progress made; still many details need further exploration (Ostriker 2010) seeking direct observational evidence seeking direct observational evidence Feedback often causes intermittent activity of AGNs Feedback often causes intermittent activity of AGNs Investigating feedback at various scales Investigating feedback at various scales

4. Observational evidence (I): Relics and new jets

5. Courtesy: A. Siemiginowska Observational evidence (II): double-double radio sources

6. Population problem of compact young radio sources Many compact young (10^3 year) radio sources found If the total activity lasts for 10^8 yr, the number of sources with the ages < 10^3 yr should be ~ 10^5 times lower than the number of sources older than 10^3 yr But the population studies show far too many compact young sources: what s the reason?

7. Interpretation: intermittent activity Courtesy: A. Siemiginowska

8. Compact radio sources: Age 1. Kinematic age 2. Synchrotron age Czerny et al. 2009 Typical age: <10^4 yr

9. Compact radio sources: Luminosity Czerny et al. 2009 Typical bolometric L: 0.1L_Edd or 0.02 L_Edd (preferred)

10. Existing models for intermittent activity Galaxy merger: 10^8 year Galaxy merger: 10^8 year Ionization instability: 10^8 year Ionization instability: 10^8 year Thermal instability of radiation-pressure dominated thin disk (Czerny et al. 2009) Thermal instability of radiation-pressure dominated thin disk (Czerny et al. 2009) Limit-cycle behavior intermittent activity Limit-cycle behavior intermittent activity But two questions: Can jets be formed in standard thin disk? Can jets be formed in standard thin disk? Is the radiation-dominated thin disk unstable? Is the radiation-dominated thin disk unstable?

11. Jet can only be formed in hard states (hot accretion flows) soft/high state: Standard thin disk No radio emission without jets Low/hard state: Hot accretion flow Strong radio emission with jets

12. Thermal stability of Radiation- dominated standard thin disks It has been thought radiation- dominated thin disk (L>0.2) is thermally unstable (e.g., Piran 1978; Janiuk et al. 2002) It has been thought radiation- dominated thin disk (L>0.2) is thermally unstable (e.g., Piran 1978; Janiuk et al. 2002) However: However: Observations: Observations: Gierlinski & Done (2004): a sample of soft state BHXBs; 0.01< L/L_Edd<0.5; Gierlinski & Done (2004): a sample of soft state BHXBs; 0.01< L/L_Edd<0.5; no variability quite stable no variability quite stable Possible exception: GRS1915+105: L too high? Possible exception: GRS1915+105: L too high? Confirmed by 3D MHD Numerical Simulations Confirmed by 3D MHD Numerical Simulations (Hirose, Krolik & Blaes 2009) (Hirose, Krolik & Blaes 2009) Stable or not??

13. Two interpretations for the stability Time-lag model Time-lag model (Hirose, Krolik & Blaes 2009, ApJ) (Hirose, Krolik & Blaes 2009, ApJ) Fluctuations in thermal energy are correlated to fluctuations in turbulent magnetic and kinetic energies, but with a time lag Magnetic pressure model Magnetic pressure model (Zheng, Yuan, Gu & Lu 2011, ApJ) Assume:, then we have: R BH causality Result: The critical Mdot of instability increases! Advantage: can explain why GRS 1915+105 is unstable

14. We propose: Global Compton heating feedback as an interpretation

15. Hot Accretion (ADAF&LHAF) Hot ( virial) & Geometrically thick Hot ( virial) & Geometrically thick Optically thin in radial & vertical directions: photons will freely escape with little collisions with electrons Optically thin in radial & vertical directions: photons will freely escape with little collisions with electrons Convectively unstable outflow Convectively unstable outflow (no radiation: Stone, Pringle & Begelman 1999; strong radiation: Yuan & Bu 2010) (no radiation: Stone, Pringle & Begelman 1999; strong radiation: Yuan & Bu 2010) \dot{M} low: ADAF; \dot{M} low: ADAF; \dot{M} high: LHAF \dot{M} high: LHAF Radiative efficiency: a function of \dot{M}; can reach 10%L_Edd! Radiative efficiency: a function of \dot{M}; can reach 10%L_Edd! Yuan 2003

16. Two effects of Compton scattering in accretion flows Consider collision between photons and electrons in hot accretion flow, two effects: Consider collision between photons and electrons in hot accretion flow, two effects: Momentum Momentum Radiation force: Radiation force: Balance with grav. force Eddington luminosity Balance with grav. force Eddington luminosity Energy Energy For : Compton up-scattering or Comptonization, which is the mechanism of producing X-ray emission in BH systems For photons: Compton up-scattering or Comptonization, which is the mechanism of producing X-ray emission in BH systems For electrons: they can obtain or loss energy due to the scattering with photons (e.g., Compton radiative cooling) For electrons: they can obtain or loss energy due to the scattering with photons (e.g., Compton radiative cooling)

17. Assume the electrons have T e and the photon energy is Є, after each scattering on average the electron will obtain energy: We will focus on electrons and non-local scattering (because hot accretion flow is optically thin in radial direction) Thompson limit:

18. The spectrum received at radius r It is difficult to directly calculate the radiative transfer when scattering is important. So we use two-stream approximation, calculate the vertical radiative transfer in a zone around r. The spectrum before Comptonization is: The spectrum after Comptonization is calculated based on Coppi & Blandford (1990)

19. The spectrum received at radius r When calculating the radiative transfer from dr to r, we neglect for simplicity the scattering. Then from the region inside of r: From the region outside of r:

20. The Compton heating/cooling rate The number of scattering at The number of scattering at radius r with unit length and radius r with unit length and optical depth is : optical depth is : So the heating/cooling rate (per unit volume of the accretion flow) at radius r is: So the heating/cooling rate (per unit volume of the accretion flow) at radius r is: unit length in r

21. When Compton heating/cooling important? Result: Cooling is important when Mdot>0.01 Heating is important when Mdot>0.2 (function of r!) We compare Compton heating/cooling with viscous heating Yuan, Xie & Ostriker 2009

22. Getting the self-consistent solutions δ~0.5 (from the modeling to Sgr A*) The new Compton heating/cooling term

23. Get the self-consistent solutions using the iteration method procedure: procedure: guess the value of Compton heating/cooling at each radius, guess the value of Compton heating/cooling at each radius, solve the global solution, solve the global solution, compare the obtained Compton heating/cooling with the guessed value to see whether they are identical. compare the obtained Compton heating/cooling with the guessed value to see whether they are identical. If not, use the new value of Compton heating and get the new solution until they are identical. If not, use the new value of Compton heating and get the new solution until they are identical.

24. Electron temperature Compton heating/cooling rate The self-consistent solutions (I): dynamics Self-consistent solution

25. When Mdot is large: oscillation When L >~0.02 L_Edd, Compton heating is so strong that electrons at r_virial~10^5r_s will be heated above T_virial When L >~0.02 L_Edd, Compton heating is so strong that electrons at r_virial~10^5r_s will be heated above T_virial Thus gas will not be captured by BH, no steady hot solution exists! Thus gas will not be captured by BH, no steady hot solution exists! Accretion resumes after cooled down oscillation of the activity of BH Accretion resumes after cooled down oscillation of the activity of BH

26. Oscillation scenario: general picture Active phaseInactive phase

27. Active phase Duration of active phase: Duration of active phase: accretion timescale at r_virial accretion timescale at r_virial why more luminous sources tend to be younger: why more luminous sources tend to be younger: So:

28. Inactive phase What is the spatial range of heated gas during the active phase? The energy equation of electrons: The solution is: From: We get the range of heated gas:

29. Inactive phase Properties of heated gas: Properties of heated gas: temperature: T= T_x ~ 10^9K temperature: T= T_x ~ 10^9K Density=? Density=? From pressure balance with ISM: From pressure balance with ISM: n_inact T_x = n_ISM T_ISM (T_ISM~10^7 K) n_inact T_x = n_ISM T_ISM (T_ISM~10^7 K) (how to know n_ISM? L ~ 2%L_Edd Mdot n_ISM) (how to know n_ISM? L ~ 2%L_Edd Mdot n_ISM) Duration of inactive phase Duration of inactive phase Cooling timescale: Cooling timescale: for T_x & n_ISM, t_cool~10^5 yr for T_x & n_ISM, t_cool~10^5 yr accretion time at 10^6r_s: >> 10^5 yr accretion time at 10^6r_s: >> 10^5 yr We should choose the shorter one We should choose the shorter one

30. Summary The global Compton scattering feedback can explain: L~0.02 L_Edd L~0.02 L_Edd More luminous sources are younger More luminous sources are younger Duration of active phase: 3 10^4 yr Duration of active phase: 3 10^4 yr Duration of inactive phase: 10^5 yr Duration of inactive phase: 10^5 yr

31. Thank you!

32. Comparison with other works: questions Other works of feedback: scales & mechanisms Other works of feedback: scales & mechanisms Proga et al.: also small scale; momentum feedback Proga et al.: also small scale; momentum feedback Ciotti & Ostriker et al.: larger scales Ciotti & Ostriker et al.: larger scales Di Matteo et al. : mainly energy feedback Di Matteo et al. : mainly energy feedback Murray, Quataert & Thompson 2005 Murray, Quataert & Thompson 2005 Springel et al …..Croton et al. ….. Springel et al …..Croton et al. ….. Questions: Questions: Momentum & energy feedback: when & which one is dominant? Momentum & energy feedback: when & which one is dominant? Small & large scales: is there any characteristic scale? Or they play their roles at various scales? Small & large scales: is there any characteristic scale? Or they play their roles at various scales? If so, pc-scale feedback in this work should be taken into account If so, pc-scale feedback in this work should be taken into account