# Presentation: 164352

## AGN Feedback Heating inClusters of Galaxies

**Fulai Guo, UCSB  **

- Fermilab ---- December 8, 2008

**Notes:**
Line 1 heating source
Line 2 AGN heating mechanisms 

## Collaborators

**S. Peng Oh (PhD advisor), UCSB**
**Mateusz Ruszkowski, Michigan**

- Papers

- Guo & Oh, 2008, MNRAS, 384, 251
- Guo, Oh & Ruszkowski, 2008, ApJ, 688, 859

## Outline

- Introduction --
-       --cool core clusters
-       --why AGN feedback in Galaxy Clusters?
- Heating the ICM -- Conduction vs AGN heating?
- Part I: Cosmic-ray Feedback
- Part II: Global Stability Analysis
- Open Questions and Future Work

## A typical cool core cluster -- Abell 2029 

- DSS Optical

- Chandra X-ray

- 4 arcmin on each side

- (Peterson & Fabian 2006)

## Why AGN Feedback?(1) The Cooling Flow Problem

- Strong X-ray emission in cluster cores
-  Short cooling time at the cluster center (as short as 0.1 - 1 Gyr)

- Chandra image of Hydra A

- For review papers, see
- Fabian 1994
- Peterson & Fabian 2006

## Why AGN Feedback?(1) The Cooling Flow Problem

- Cool core clusters: lack of emission lines from the gas at temperatures below 1/3 of the ambient T
- Heating is required to suppress strong cooling flows in cool cores

- Sanderson et al. 2006

- (see Peterson & Fabian 2006 for a review)

## Why AGN Feedback (2)?

- The flattening of the entropy
-    profile near the cluster center

-  AGN feedback may be needed to explain the high-luminosity
-     cutoff in the galaxy luminosity function (Croton et al 2006)

-    (Donahue et al. 2006)

## Most importantly, we see AGN-induced bubbles (AGN-ICM interactions)!

- Perseus Cluster, Chandra image

- Fabian et al 2003

## Heating the ICM

- Peterson & Fabian 2006

- Two main heating mechanisms:

- AGN Heating
- Thermal conduction
-      (Bertschinger & Meiksin 1986,
-          Narayan & Medvedev 2001,
-          Zakamska & Narayan 2003,
-          Voigt & Fabian 2004)

## Heating Source: Thermal Conduction?

- (Zakamska & Narayan 2003)

- Abell 1795

-           (Kim & Narayan 2003)

- Equilibrium models work well for many clusters

- But, tend to be globally unstable !

## and require fine-tuning of conductivity !

- (Guo & Oh   2008)

- f= 0.8
- f= 0.6
- f= 0.4
- f= 0

## Previous Studies on AGN Heating

- Analytical studies on spatial distribution of AGN heating
-        “bubble” heating with a Gaussian profile (Brighenti & Mathews 2003)
-         Effervescent heating (Begelman 2001)
-         Cosmic ray heating   (Guo & Oh 2008)
- Simulations of the bubble evolution and its heating effect
-      bubble expansion and mixing e.g., Brüggen & Kaiser (2002)
-      viscous dissipation of AGN-induced waves, Ruszkowski et al. (2004)
-         Outflows, e.g., Vernaleo & Reynolds 2006
-      Shocks, Brüggen et al. 2007
-      Preventing bubble from disruption:
-                viscosity --- Reynolds et al. 2005
-                magnetic fields -- Ruszkowski et al. 2008

## How does AGN heat 

- Chandra image of  the Perseus Cluster

- X-ray cavities or bubbles
-     are seen clearly.

- How does AGN heat
- the ICM?

- The buoyantly-rising bubble expands
-     and heats the ICM through PdV work.
-     This is the effervescent heating model
-     proposed by Begelman (2001).
- The cosmic rays may leak out from the bubbles into the ICM,
-     and heat it (Guo & Oh 2008)

## AGN Effervescent Heating

-  AGN luminosity is proportional
- to the central mass accretion rate:

- Ruszkowski & Begelman 2002

- The bubble loses energy only
- through PdV work

- Spherically integrated bubble
- flux :

## Part I: Cosmic ray heating  (Guo & Oh 2008)

## Why Cosmic Rays?

- Bubbles may be disrupted
- Cosmic rays may leak into
- the ICM.

- Observational Signatures?
- .......

## Slide 17

## Slide 18

## Slide 19

## Slide 20

## Method

**Method**

-  1D ZEUS code: solve hydrodynamic equations + CR heating
-    and CR transport, CR energy evolution
-  Assume CR energy density in bubbles is a power law with radius
-   (cosmic ray injection rates depend on gas cooling---feedback)

- Slope is a free parameter, implicitly specifies CR injection rate

## Bubble expansion  vs.   bubble disruption

- * Bubbles also heat the ICM through PdV work. For a range of ,
-     bubble disruption dominates. We ignore PdV work.

## Cosmic-ray physics

- Cosmic rays provide pressure support.
- CR energy-loss mechanisms:
-            Coulomb interactions      ------  heat the ICM
-             Hadronic Collisions       ------- most energy will escape
-             Generation of  Hydromagnetic waves  --- heat the ICM

- Cosmic ray transport : advection and diffusion in radial direction

- Cosmic ray heating  (Guo & Oh 2008)

## Simulation Setup

- Spherical symmetry,  From 1  -  200 kpc
- Resolution N=400
- Boundary Condition: constant T,  E at outer boundary

- Code:  ZEUS-3D   modifed to include additional physics:
- 	Radiative cooling
- 	background potential----a dark matter NFW profile
-                                                    a King profile for central galaxy
- 	thermal conduction
- 	Cosmic-ray heating
- 	Cosmic-ray pressure support
- 	Cosmic-ray transport
- 	Cosmic-ray energy equation

- Cosmic ray heating  (Guo & Oh 2008)

## Cooling catastrophe quenched

Cooling flow strongly suppressed---------           final accretion rate     about 2 solar mass/yr

- Cooling flow strongly suppressed---------           final accretion rate     about 2 solar mass/yr

- RESULTS

- Comparison between our model
- With a cooling flow model

- Our model: efficiency 0.003
-                     f=0.3 (Abell 2199)

- Cosmic ray heating  (Guo & Oh 2008)

## Evolution of the simulated cluster (1)

- Abell 2199

## Initial State of our simulations -- solid line:

- Cosmic ray heating  (Guo & Oh 2008)

## IT WORKS!!!

## Final Steady State

- Thermal pressure support dominates over the whole cluster
- Cosmic ray heating is dominated by wave heating

- CR pressure gradients OK!

## Parameter Study (1) -- No fine-tuning!

- (Guo & Oh   2008)

- --  works for range of thermal conductivity and
-                         the AGN feedback efficiency

- f=0.3, = 0.05
- f= 0.4, = 0.003
**f=0.3, ********= 0.003**
- f=0.1, = 0.003
- f=0.3, = 0.0003

## Parameter Study (2)

- --  works for a range of cosmic ray profiles

- (Guo & Oh   2008)

- Our results are also quite robust
- to CR diffusion coefficient and
- magnetic field profile.

## Slide 32

## Part II:Global Stability Analysis of Feedback Models

- A successful model for the ICM must be globally stable
-  Stability analysis allows for quick parameter study and helps
-      to build physical intuition.
- To understand what the role of AGN feedback in stably
-     maintaining the ICM at keV temperatures
-       -- Is a feedback mechanism really required?

- Motivation:

## Background States

- They are chosen to be steady-state cluster profiles.
- Why not equilibrium states?

- Because AGN heating is a feedback mechanism!

## Slide 35

## Background profiles

- Guo et al. 2008

- Abell 1795

- Abell 2597

- fit observations quite well.

## Then perform a Lagrangian global stability analysis......

- Then perform a Lagrangian global stability analysis......
-    No WKB!

- * Growth rate is an eigenvalue of the analysis
- * Explore parameter space rapidly!

## Globally unstable modes

-   suppressed by AGN!

- * Suppression depends on the feedback efficiency

## Local Stability Analysis

- Consider local WKB perturbations ~ exp(ikr + t)
- Simplifications:
- Plane-parallel approximation; wavelength much shorter than
- any spatial scale; ignore high-frequency sound waves.
- Results:
- Without any heating, X-ray emitting gas is thermally unstable
- Thermal conduction stabilizes short-wavelength perturbations
- AGN heating (~∂P/∂r) reduces the growth rate of local thermal
-        instability.

- First consider....

## Results: Globally Unstable Modes

- Guo et al. 2008

- Consider Abell 2199
- –Model B1: pure conduction model with
-   instability growth time 2.8 Gyr.
- –Model B2: efficiency = 0.05 with
-   instability growth time 4.4 Gyr.
- –Model B3: efficiency = 0.2 with
-   instability growth time 16.9 Gyr.
- –Model B3 without feedback:
-    instability growth time 2.2 Gyr.
**Thus, AGN feedback mechanism is essential to suppress global instability**

## Dependence of Stability on Feedback Efficiency

- For a specific cluster model, the cluster becomes stable when the feedback
- efficiency is greater than a lower limit.

- A2597

- holds for different conductivity

## Parameter Study (1) -- No fine-tuning!

- (Guo & Oh   2008)

- --  works for range of thermal conductivity and
-                         the AGN feedback efficiency

- = 0.05
- f= 0.4
- f=0.3, = 0.003
- f=0.1
- = 0.0003

## Dependence on background profiles:bimodality

- Fix the outer temperature, density,
- AGN efficiency and conductivity,
- while varying the central temperature

- –Non-cool core models (Tin>4.5 keV) are
-   stable
- –Models with Tin<1.7 keV are stable
- –Intermediate central temperatures typically
-   lead to globally unstable solutions

- A1795

## Bimodality

- A2199

- Globally stable clusters are expected
- to have either
- 1) cool cores stabilized by both AGN
-      feedback and conduction
- 2) non-cool cores stabilized primarily
-     by conduction.

- Intermediate central temperatures
- typically lead to globally unstable solutions

- Guo et al 2008

## Bimodality

- A1795

- Guo et al 2008

- Another cluster, still bimodality

## Slide 46

## Dunn & Fabian 2008

- X-ray-deficient bubbles--

- No radio activity---

- Central radio activity--

- OBSERVATION

## Open Questions and Future Work

- Black-hole accretion and AGN feedback: How to get gas to black hole?
-      Is Bondi accretion the whole story (outflows, angular momentum,
-      hot vs cold accretion, etc)?
- 2D and 3D simulations of cosmic-ray bubbles: the bubble
-     evolution and cosmic-ray heating. Preliminary studies on the bubble
-     evolution with CR pressure support and diffusion has been performed
-     by Mathews & Brighenti (2008).
- Bubble stability: what is bubble disruption rate? Viscosity,
-    magnetic shielding, cosmic ray diffusivity.....
- How to distribute heat isotropically? 3D jet-heating simulations show
-    anisotropic heating, resulting in cooling catastrophe. Weak shocks,
-    sound waves, spinning jets?

## Open Questions and Future Work

- Topology of magnetic fields? Could it be regulated by cooling flows,
-    AGN outflows? Could cool, non-cool core clusters be the two aspects
-    Of the same phenomenon, viewed at different times?
- Effect of AGN feedback in cosmological simulations of clusters
- What determines the final state the cluster relaxes toward (fastest
-    decaying eigenfunction)?
- Thermal balance in galaxy groups: very shorter central cooling times.
-     Conduction is not sufficient to offset cooling.

## The Bottom Line

-   Cosmic ray heating can be important in clusters ----- rising
-    bubbles (eventually disrupted) provides a fast means of
-    transport them.
-  Global stability analysis provides a fast way of exploring parameter
-    space. Predict (1) minimum level of heating efficiency (2) bimodal
-    central temperatures.

## AGN heating seems to be consistent with BH accretion!

- Bondi accretion
- near black hole