AGN Feedback Andrew King Dept of Physics & Astronomy, University of Leicester Astronomical Institute, University of Amsterdam Heidelberg, July 2014 Tuesday, 15 July 14
galaxy knows about central SMBH black hole mass velocity dispersion galaxy bulge Kormendy & Ho, 2013 Tuesday, 15 July 14
how? SMBH mass is completely insignificant: , M ∼ 10 − 3 M bulge so its gravity affects only a region R inf = GM ∼ 10 M 8 parsec σ 2 σ 2 200 M 8 = M/ 10 8 M � , σ 200 = σ / 200 km s � 1 � � - far smaller than bulge why does the galaxy notice the hole? Tuesday, 15 July 14
well.... SMBH releases accretion energy ∼ 0 . 1 M BH c 2 ∼ 10 61 erg galaxy bulge binding energy M b σ 2 ∼ 10 58 erg galaxy notices hole through energy release: `feedback’ Tuesday, 15 July 14
SMBH – host connection SMBH in every large galaxy (Soltan) but only a small fraction of galaxies are AGN SMBH grow at Eddington rate in AGN M = L = L Edd = 4 π GMc η c 2 ˙ electron scattering opacity , κ = κ AGN should produce Eddington winds Tuesday, 15 July 14
Super-Eddington Accretion most photons eventually escape along cones near axis most mass expelled as wind disc Mv = L Edd on average photons give up all ˙ momentum to outflow after ~ 1 scattering c Tuesday, 15 July 14
Eddington winds momentum outflow rate M out v = L Edd ˙ = η ˙ M Edd c speed v = η c m ∼ 0 . 1 c ˙ m = ˙ M out / ˙ M Edd ∼ 1 where ˙ energy outflow rate 1 M out v 2 = η M out = η 2 . η c 2 ˙ ˙ 2 L Edd ' 0 . 05 L Edd 2 (King & Pounds, 2003: cf later cosmological simulations) Tuesday, 15 July 14
PG1211 + 143 (Pounds & Reeves, 2009) P Cygni profile of iron K- alpha: wind with v ' 0 . 1 c `ultrafast outflow’ -- `UFO’ Tuesday, 15 July 14
outflow affects galaxy bulge SMBH releases accretion energy ∼ 0 . 1 M BH c 2 ∼ 10 61 erg galaxy bulge binding energy M b σ 2 ∼ 10 58 erg even though only a fraction of accretion energy is in ( η / 2) ' 0 . 05 mechanical form, this is more than enough energy to unbind the bulge how does the bulge survive? Tuesday, 15 July 14
wind shock wind must collide with bulge gas, and shock – what happens? either (a) shocked gas cools: `momentum–driven flow’ negligible thermal pressure - most energy lost or (b) shocked gas does not cool: `energy–driven flow’ thermal pressure > ram pressure Compton cooling by quasar radiation field very effective out to cooling radius (cf Ciotti & Ostriker, 1997, 2001) R C ∼ 50 − 500 pc initial expansion into bulge gas is driven by momentum only Tuesday, 15 July 14
swept-up ambient gas, mildly shocked wind shock outer shock driven into ambient gas SMBH Eddington wind, ambient gas v ∼ 0 . 1 c Tuesday, 15 July 14
motion of swept-up shell total mass (dark, stars, gas) inside radius R of unperturbed bulge is M tot ( R ) = 2 σ 2 R G M ( R ) = 2 f g σ 2 R but swept-up gas mass G forces on shell are gravity of mass within R , and wind ram pressure: since gas fraction f g is small, gravitating mass inside R is ' M tot ( R ): equation of motion of shell is d R ] + GM ( R )[ M + M tot ( R )] M out v = L Edd = 4 π R 2 ρ v 2 = ˙ d t [ M ( R ) ˙ R 2 c where M is the black hole mass Tuesday, 15 July 14
using M ( R ) , M tot ( R ) this reduces to � d R ) + GM 1 − M d t ( R ˙ = − 2 σ 2 R M σ M σ = f g κ π G 2 σ 4 where integrate equation of motion by multiplying through by R ˙ R : then � 1 − M R 2 ˙ R 2 = − 2 GMR − 2 σ 2 R 2 + constant M σ Tuesday, 15 July 14
using M ( R ) , M tot ( R ) this reduces to � d R ) + GM 1 − M d t ( R ˙ = − 2 σ 2 R M σ M σ = f g κ π G 2 σ 4 where integrate equation of motion by multiplying through by R ˙ R : then � 1 − M R 2 ˙ R 2 = − 2 GMR − 2 σ 2 R 2 + constant M σ if M < M σ , no solution at large R (rhs < 0) Eddington thrust too small to lift swept-up shell Tuesday, 15 July 14
using M ( R ) , M tot ( R ) this reduces to � d R ) + GM 1 − M d t ( R ˙ = − 2 σ 2 R M σ M σ = f g κ π G 2 σ 4 where integrate equation of motion by multiplying through by R ˙ R : then � 1 − M R 2 ˙ R 2 = − 2 GMR − 2 σ 2 R 2 + constant M σ if M < M σ , no solution at large R (rhs < 0) Eddington thrust too small to lift swept-up shell but if M > M σ , ˙ but if M > M σ , ˙ R 2 → 2 σ 2 , and shell can be expelled completely R 2 → 2 σ 2 , and shell can be expelled completely Tuesday, 15 July 14
critical value M σ = f g κ π G 2 σ 4 ' 2 ⇥ 10 8 M � σ 4 200 remarkably close to observed relation despite effectively M − σ no free parameter (King, 2003; 2005) ( f g ∼ 0 . 1) SMBH mass grows until Eddington thrust expels gas feeding it Tuesday, 15 July 14
shells confined to vicinity of BH until M = M σ R . R inf ∼ few × GM ∼ 10 − 50 σ 2 200 pc σ 2 Tuesday, 15 July 14
transition to energy-driven flow once M σ reached close to quasar shocked gas cooled by inverse Compton effect (momentum-driven flow) but once M > M σ , R can exceed R C : wind shock no longer cools wind shock is adiabatic: hot postshock gas does P d V work on surroundings bulge gas driven out at high speed � 1 / 3 2 ησ 2 c ' 1000 σ 2 / 3 200 km s − 1 v e = 3 f g Tuesday, 15 July 14
Zubovas & King, 2012a once BH grows to , shock passes cooling radius M > M σ => large-scale energy-driven flow Tuesday, 15 July 14
2500 2000 Velocity / kms -1 1500 1000 500 energy--driven outflows rapidly converge to 0 10 3 10 4 10 5 10 6 10 7 10 8 � 1 / 3 2 η f c 200 ( f c /f g ) 1 / 3 km s − 1 Time / yr ' 925 σ 2 / 3 σ 2 c v e ' 3 f g 2500 and persist even after central quasar turns off 2000 Velocity / kms -1 1500 high velocity outflow at large radius 1000 500 also for other potentials: Zubovas & King, 2012b 0 0.01 0.10 1.00 10.00 Radius / kpc Tuesday, 15 July 14
density contrast => energy-driven outflow shock may be Rayleigh-Taylor unstable two—phase medium: gamma—rays and molecular emission mixed large--scale high speed molecular outflows, e.g. Mrk 231: galaxy bulge should produce gamma-ray emission Tuesday, 15 July 14
outer shock runs ahead of contact discontinuity into ambient ISM: velocity jump across it is a factor ( γ + 1) / ( γ � 1): fixes velocity as ◆ 1 / 3 ✓ lf c v out = γ + 1 R ' 1230 σ 2 / 3 ˙ km s − 1 200 2 f g and radius as R out = γ + 1 R 2 outflow rate of shocked interstellar gas is = ( γ + 1) f g σ 2 M out = d M ( R out ) ˙ ˙ R d t G 200 l 1 / 3 M � yr � 1 M out ' 3700 σ 8 / 3 ˙ Tuesday, 15 July 14
AGN feedback: Herschel (molecular outflows) Mrk 231 – OH Outflow terminal velocity (obs): ~1.100 km/s R out (model) ~1.0 kpc Mrk 231 outflow rate (dM/dt): ~1.200 M /yr SFR: ~100 M /yr gas mass (from CO): 4.2 x 10 9 M depletion time scale (M gas /M): ~4 x 10 6 yr mechanical energy: ≥ ¡10 56 ergs mechanical luminosity: ≥ ¡1% ¡L IR Tuesday, 15 July 14
Eddington winds momentum outflow rate M out v = L Edd ˙ = η ˙ M Edd c speed v = η c m ∼ 0 . 1 c ˙ m = ˙ M out / ˙ M Edd ∼ 1 where ˙ energy outflow rate 1 M out v 2 = η M out = η 2 . η c 2 ˙ ˙ 2 L Edd ' 0 . 05 L Edd 2 Tuesday, 15 July 14
Maiolino et al., 2013 Fig. 12. Correlation between the kinetic power of the outflow and the AGN bolometric luminosity. Symbols and colour-coding as in Fig. 8. The grey line represents the theoretical expectation of models of AGN feedback, for which P K , OF = 5% L AGN . The red dashed line represents the linear fit to our data, excluding the upper limits. The error bar shown at the bottom-right of the plot corresponds to an average error of ± 0.5 dex. Tuesday, 15 July 14
spirals: bulge outflow pressure => disc star formation expanding shocked bulge gas galaxy disc bulge outflow pressurizes central disc, and stimulates star formation bulge quenched, disc briefly fired up? Tuesday, 15 July 14
inhomogeneous ISM? if ISM is patchy, of two-temperature effects important, not obvious that wind shocks always cool could outflows be energy-driven at all radii? (Faucher-Giguere & Quataert, 2012, Bourne & Nayakshin 2013, 2014) if most of mass in dense blobs, these feel only drag of wind Tuesday, 15 July 14
inhomogeneous ISM? if most of mass in dense blobs, these feel only drag of wind in simple cases this is dimensionally ~ ram pressure - maybe M-sigma OK? but not obvious -- e.g. D’Alembert’s paradox -- no drag on smooth objects Tuesday, 15 July 14
inhomogeneous ISM? calculation of drag => boundary layer; unstable, numerically difficult instabilities producing blobs also numerically difficult two-fluid effects on Compton cooling also difficult! but observational distinction is clear: momentum-driven = small-scale energy-driven = large-scale Tuesday, 15 July 14
Recommend
More recommend
