AGN Feedback at the AGN Feedback at the Parsec ScaleParsec Scale

Feng Yuan Shanghai Astronomical Observatory, CAS

with:

F. G. Xie (SHAO) J. P. Ostriker (Princeton University) M. Li (SHAO)

OUTLINEOUTLINE

Intermittent activity of compact radio sourcesIntermittent activity of compact radio sources Outburst: 10^4 yearsOutburst: 10^4 years Quiescent: 10^5 yearsQuiescent: 10^5 years previous interpretation & its problemprevious interpretation & its problem

thermal instability of radiation-dominated thin diskthermal instability of radiation-dominated thin disk

Explaining the intermittent activity with Global Explaining the intermittent activity with Global Compton scattering feedback mechanism in Compton scattering feedback mechanism in hot accretion flowshot accretion flows What is global Compton scattering ?What is global Compton scattering ? When L > 0.02 L_Edd: no steady solutions; BH When L > 0.02 L_Edd: no steady solutions; BH

activity oscillatesactivity oscillates Estimations of durations of active and inactive Estimations of durations of active and inactive

phasesphases

AGN feedback: an AGN feedback: an important role in galaxy important role in galaxy formation & evolutionformation & evolution

correlationcorrelation suppression of star formation in suppression of star formation in

elliptical galaxieselliptical galaxies Great progress made; still many details Great progress made; still many details

need further exploration (Ostriker 2010)need further exploration (Ostriker 2010) seeking direct observational evidence seeking direct observational evidence

Feedback often causes Feedback often causes intermittent activity of intermittent activity of AGNsAGNs

Investigating feedback at various scalesInvestigating feedback at various scales

BHM

Observational evidence (I): Observational evidence (I): Relics and new jetsRelics and new jets

Courtesy: A. Siemiginowska

Observational evidence (II):Observational evidence (II):double-double radio double-double radio

sourcessources

Population problem of Population problem of compact young radio compact young radio

sourcessources 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?

Interpretation: intermittent Interpretation: intermittent activityactivity

Courtesy: A. Siemiginowska

Compact radio sources: Compact radio sources: AgeAge

1. Kinematic age2. Synchrotron age

Czerny et al. 2009

Typical age: <10^4 yr

Compact radio sources: Compact radio sources: LuminosityLuminosity

Czerny et al. 2009

Typical bolometric L: 0.1L_Edd or0.02 L_Edd (preferred)

Existing models for Existing models for intermittent activityintermittent activity

Galaxy merger: 10^8 yearGalaxy merger: 10^8 year Ionization instability: 10^8 yearIonization instability: 10^8 year Thermal instability of radiation-pressure Thermal instability of radiation-pressure

dominated thin disk dominated thin disk (Czerny et al. 2009)(Czerny et al. 2009) Limit-cycle behavior Limit-cycle behavior intermittent activity intermittent activity But two questions: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 Is the radiation-dominated thin disk

unstable?unstable?

Jet can only be formed in hard Jet can only be formed in hard states (hot accretion flows)states (hot accretion flows)

soft/high state:soft/high state: Standard thin diskStandard thin disk No radio emission No radio emission

without jets without jets Low/hard state:Low/hard state:

Hot accretion flowHot accretion flow Strong radio Strong radio

emission emission with with jetsjets

Thermal stability of Thermal stability of Radiation-dominated Radiation-dominated standard thin disksstandard thin disks

It has been thought It has been thought radiation-dominated thin radiation-dominated thin disk (L>0.2) is thermally disk (L>0.2) is thermally unstable unstable (e.g., Piran 1978; (e.g., Piran 1978; Janiuk et al. 2002)Janiuk et al. 2002)

However:However: Observations: Observations:

Gierlinski & Done (2004): a Gierlinski & Done (2004): a sample of soft state BHXBs; sample of soft state BHXBs; 0.01< L/L_Edd<0.5; 0.01< L/L_Edd<0.5;

no variability no variability quite stable quite stable Possible exception: Possible exception:

GRS1915+105: L too high?GRS1915+105: L too high? Confirmed by 3D MHD Confirmed by 3D MHD

Numerical Simulations Numerical Simulations (Hirose, Krolik & Blaes 2009)(Hirose, Krolik & Blaes 2009)

M

Stable or not??

Two interpretations for the Two interpretations for the stabilitystability

“ “Time-lag” modelTime-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” Magnetic pressure” modelmodel(Zheng, Yuan, Gu & Lu 2011, (Zheng, Yuan, Gu & Lu 2011,

ApJ)ApJ)

Assume: Assume: , ,

then we have:then we have:

BH const.

R BH

r Pcausality

Result: The critical Mdot of instability increases!Advantage: can explain why GRS 1915+105 is unstable

We propose:We propose:Global Compton heating Global Compton heating

feedback as an feedback as an interpretationinterpretation

Hot Accretion (ADAF&LHAF)Hot Accretion (ADAF&LHAF)

Hot ( virial) & Geometrically Hot ( virial) & Geometrically thickthick

““Optically thin” in radial & Optically thin” in radial & vertical directions: vertical directions: photons will photons will freely escape with little collisions with freely escape with little collisions with electronselectrons

Convectively unstable Convectively unstable outflow outflow

(no radiation: Stone, Pringle & Begelman (no radiation: Stone, Pringle & Begelman

1999;1999; strong radiation: Yuan & Bu 2010) 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 Radiative efficiency: a function of

\dot{M}; can reach 10%L_Edd!\dot{M}; can reach 10%L_Edd!

Yuan 2003

Two effects of Compton Two effects of Compton scattering in accretion scattering in accretion

flowsflows Consider collision between photons and Consider collision between photons and

electrons in hot accretion flow, two effects:electrons in hot accretion flow, two effects: Momentum Momentum

Radiation force: Radiation force: Balance with grav. force Balance with grav. force Eddington luminosity Eddington luminosity

Energy Energy For For photons: Compton up-scattering or : Compton up-scattering or

Comptonization, Comptonization, which is the mechanism of producing X-which is the mechanism of producing X-ray emission in BH systemsray emission in BH systems

For For electronselectrons: they can obtain or loss energy due : they can obtain or loss energy due to the scattering with photons (e.g., Compton to the scattering with photons (e.g., Compton radiative cooling)radiative cooling)

Tcc

U

Assume the electrons have Te and the photon energy is Є, after each scattering on average the electron will obtain energy:

We will focus on electrons and We will focus on electrons and “non-local”“non-local” scattering scattering (because hot accretion flow is optically thin (because hot accretion flow is optically thin in radial directionin radial direction))

Thompson limit:

The spectrum received at The spectrum received at radius rradius 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)

The spectrum received at The spectrum received at radius rradius 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:

The Compton The Compton heating/cooling rateheating/cooling rate

The number of scattering at The number of scattering at

radius r with unit length andradius r with unit length and

optical depth is :optical depth is :

So the heating/cooling rate (per unit volume of the So the heating/cooling rate (per unit volume of the accretion flow) at radius r is:accretion flow) at radius r is:

es

unit length in r

When Compton heating/cooling important?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

Getting the self-consistent Getting the self-consistent solutionssolutions

ieii

ieee

k

s

out

out

qqdr

dp

dr

dv

qqqdr

dp

dr

dv

prjrv

dr

dpr

dr

dvv

R

RMvRHM

)1(

)(

1

4

2

2

2

22

..

compq

δ~0.5 (from the modeling to Sgr A*)

The new Compton heating/cooling term

Get the self-consistent Get the self-consistent solutions using the solutions using the iteration methoditeration method

procedure: procedure: guess the value of Compton guess the value of Compton

heating/cooling at each radius, heating/cooling at each radius, solve the global solution,solve the global solution, compare the obtained Compton compare the obtained Compton

heating/cooling with the guessed value heating/cooling with the guessed value to see whether they are identical. to see whether they are identical.

If not, use the new value of Compton If not, use the new value of Compton heating and get the new solution until heating and get the new solution until they are identical.they are identical.

When Mdot is large: When Mdot is large: oscillationoscillation

When L >~0.02 L_Edd, Compton heating When L >~0.02 L_Edd, Compton heating is so strong that electrons at is so strong that electrons at r_virial~10^5r_s will be heated above r_virial~10^5r_s will be heated above T_virialT_virial

Thus gas will not be captured by BH, Thus gas will not be captured by BH, no no steadysteady hot solution exists! hot solution exists!

Accretion resumes after cooled down Accretion resumes after cooled down “oscillation” of the activity of BH“oscillation” of the activity of BH

2/15 )%2/L(10~ Eddsvirial Lrr

Oscillation scenario: Oscillation scenario: general picturegeneral picture

Active phase Inactive phase

Active phaseActive phase

Duration of active phase: Duration of active phase:

accretion timescale at r_virialaccretion timescale at r_virial

why more luminous sources tend to why more luminous sources tend to be younger:be younger:

svirialEdd rrLL 510~,%2~for

2/15 )%2/L(10~ Eddsvirial Lrr

So:

Inactive phaseInactive phase

What is the spatial range of heated gas during What is the spatial range of heated gas during the active phase?the active phase?

The energy equation of electrons:

The solution is:

From:

We get the range of heated gas:

Inactive phaseInactive phase Properties of heated gas:Properties of heated gas:

temperature: T= T_x ~ 10^9Ktemperature: 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 (how to know n_ISM? L ~ 2%L_Edd Mdot Mdot n_ISM) n_ISM) Duration of inactive phaseDuration of inactive phase

Cooling timescale: Cooling timescale:

for T_x & n_ISM, t_cool~10^5 yrfor T_x & n_ISM, t_cool~10^5 yr accretion time at 10^6r_s: >> 10^5 yraccretion time at 10^6r_s: >> 10^5 yr We should choose the shorter oneWe should choose the shorter one

SummarySummary

The global Compton scattering feedback The global Compton scattering feedback can explain:can explain:

L~0.02 L_EddL~0.02 L_Edd More luminous sources are youngerMore luminous sources are younger Duration of active phase: 3 10^4 yrDuration of active phase: 3 10^4 yr Duration of inactive phase: 10^5 yrDuration of inactive phase: 10^5 yr

Thank you!Thank you!