Outflow from hot accretion flows ------Nature, origin and properties (arxiv:1206.4173) Feng Yuan Shanghai Astronomical Observatory Chinese Academy of Sciences
Accretion physics Motivation Outflow: important ingredient of accretion physics Crucial to understand accretion-related phenomena in AGNs & BH binaries AGNs feedback Outflow has been observed in AGN-host galaxies Origin of wind: hot accretion flow? (Hot flow also exist in luminous AGNs!) Constrain parameters of winds: mass flux, velocity, density
OUTLINE Introduction to hot accretion flow radial profile of Mdot: decreasing inward Nature of the Mdot profile Outflow (ADIOS) or CDAF (convection)? Origin & Properties of outflow Observational implications Fermi Bubble Winds from AGNs: magnetic centrifugal force origin?
Hot Accretion Flows Two series of accretion: Cool (e.g., the standard thin disk) Hot (e.g., ADAF) Two hot accretion solutions When Mdot < α 2 Mdot_Edd: ADAF When Mdot > α 2 Mdot_Edd: LHAF Yuan 2001
Numerical Simulation: Mdot decreases inward Igumenshchev & Abramowicz 1999; Stone, Pringle & Begelman 1999; Stone & Pringle 2000; Hawley & Balbus 2002; Machida et al 2003;.Yuan & Bu 2010 M r = M (r out )(r/r out ) 0.5 0.8 Inflow rate Net rate Stone, Pringle & Begelman 1999 Outflow rate Stone, Pringle & Begelman 1999
Density profile flattens In original analytical model (with a constant Mdot): ρ r 1.5 ρ r 0.85 When Mdot decreases inward Yuan, Wu & Bu 2012
Confirmed by Observations of Sgr A* & NGC 3115 Chandra observations + Bondi theory give the Bondi rate: (consistent with numerical simulation of Cuadra et al. 2006) High linear polarization at radio waveband requires innermost region accretion rate (rotation measure requirement): 7 9 (10 10 ) M yr So Mdot must decrease inward Density profile consistent with numerical simulation Sgr A*: NGC 3115: Yuan, Quataert & Narayan 2003; Wong et al. 2011 10 5 M yr 1 1
Question one: Why does Mdot decrease inward?
Model One: Adiabatic inflow-outflow solution (ADIOS) Blandford & Begelman 1999; 2004; Begelman 2012 mass loss in outflow Mdot decreases Outflow is produced because of Bernoulli parameter Be>0 However: When Be<0, we still found outflow In the most updated version (Begelman 2012), the mechanism of producing outflow is not specified but leaves open.
Model Two: Convection-dominated accretion flow (CDAF) Narayan, Igumenshchev & Abramowicz 2000; Quataert & Gruzinov 2000 Hot hydro accretion flow is convectively unstable Because entropy increases inward (Narayan & Yi 1994) It is true even when radiation is strong (Yuan & Bu 2010) A convective envelope solution is found Gas then circulates in convective eddies Mdot decreases Debate on MHD flows: applicable to MHD flow or not? No (Hawley, Balbus, Stone): dynamics of MHD flow is controlled by magnetic field & MRI Yes (Narayan, Abramowicz, Quataert): there is a convection component in the instability criteria
Our Plan If the decrease of Mdot is due to circular convective turbulence, we should expect the properties of inflow & outflow roughly same So we systematically study the properties of inflow & outflow using simulation Analyze the convective stability of MHD flow Effect of different initial conditions
Hydro & MHD simulations Hydro MHD
Hydro & MHD simulations Hydro MHD
Result: Not CDAF, but ADIOS (I) Mdot decreases because of mass loss in outflow
Result: Not CDAF, but ADIOS (II) Mdot decreasing NOT because of convective or turbulent eddies, because: Mdot decreases inward & no mass accumulation Properties of inflow & outflow completely different! MHD accretion flow is convectively stable
Properties of inflow & outflow (I) (Hydro Case) Yuan, Bu & Wu 2012
Properties of inflow & outflow (II) (Hydro Case) Yuan, Bu & Wu 2012
Properties of inflow & outlow (III) (MHD Case) Yuan, Bu & Wu 2012
Properties of inflow & outflow (IV) (MHD Case) Yuan, Bu & Wu 2012
An MHD accretion flow is convectively stable The Hoiland criteria: Here: Result: Most of the region is convectively stable! Yuan, Bu & Wu 2012
Question Two: What is the origin of outflow?
Origin of outflow in hydro flows: Buoyant force (thermal) Hydro Flow is convectively unstable Temperature & Be of outflow is higher than inflow Convection: buoyant force driving outflow Temperature of Fluid element increases due to fluctuation It then feels buoyant force moves outward
Origin of outflow in MHD flows: Micro-Blandford & Payne mechanism (magnetic) Not because of Be>0 & convection Early ADIOS not correct Simulation: Angular momentum of outflow >> inflow Magnetic stress transfer angular momentum magnetic centrifugal force Different from Blandford & Payne mechanism: Don t need large-scale poloidal field! Don t need B dominance Black hole Differential rotation B line This fluid element gets angular momentum from the other one
Other properties of outflow: mass Mass flux of outflow flux Mdot_out(r_out)=Mdot_in(r_out) Angular distribution
Terminal velocity of outflow Whether outflow can reach infinity depends on the sign of Be Sign of Be depends on initial condition of simulations, which is poorly cnstrained We speculate Be>0. Then: since so
Observational application: (I) Fermi Bubble Su et al. 2010
Fermi Bubble Su et al. 2010 Total energy within the bubble: 10 54 ~10 55 erg Age: 10 7 (v/1000km s -1 ) yrs Power: 3 10 39 erg/s Scale: 8 kpc
Two existing models Jet model (Guo & Mathews 2011a, 2011b). However: Not collimated, only a jet nozzle Mass loss rate in the jet: Eddington rate Eddington outflow model (Zubovas, Nayakshin, & King 2011, 2012) Outflow: Spherical distribution Eddington rate: quasar phases of Sgr A*
Modeling the Fermi bubble: Energetics Power of outflow: Mou, Yuan, Bu, 2012, in preparation To produce the required power, we need (for r_out=1000r_s) Mdot_out=0.1Mdot_Edd This implies: the past activity of Sgr A* is 10^4-10^5 times stronger than the present (roughly consistent with Totani 2006).
Next one: M 87? Direction of Jet Two Bubbles
Observational application: (II) Origin of AGNs Winds? Winds detected in AGNs with various L E.g., NGC 4395: Lbol=10^{-3} Ledd (Crenshaw & Kraemer 2012) Hot outflow directly detected (Brian s talk) Comments on other two models of wind production Detailed study to some sources rules out radiation & thermal driving mechanisms: NGC 4151 (Kraemer et al. 2005) GRO J1655-40 (Miller et al. 2006; Neilsen & Homan 2012) Blandford & Payne (1982) model: large-scale poloidal B field exists or not? arxiv:1205.4222: jet & wind have the same origin
Inward decrease of Mdot: Summary not because of convective motions, but outflow (ADIOS) Origin of outflow Hydro: convection or buoyant force MHD: magnetic centrifugal force Properties of outflow Wide range of angular distribution; High mass flux Terminal velocity: unknown; but likely ~v_k (r_out) Applications Fermi Bubble origin of winds in AGNs & BH binaries