Active galaxies, thermal conduction and gas in galaxy groups and clusters

1. Active galaxies, thermal conduction and gas in galaxy groups and clusters Suparna Roychowdhury Collaborators: Mitchell Begelman, JILA Mateusz Ruszkowski,JILA Biman Nath, RRI Astronomy Group, Raman Research Institute Bangalore, India Groups of galaxies in nearby universe, Santiago, Chile, 5 - 9 december, 2005

2. Groups and clusters of galaxies • Most galaxies found in groups (<50 members) or clusters (100-1000) • Mass range between 1013 -- 1015 M • Size varies between 1--few Mpc • Contains large amount of hot gas (intracluster gas)--~10% of the total mass • Temperature between 1--10 keV Coma cluster NGC 2300(central part)

3. Properties of ICM • ICM self-gravity negligible • Adiabatic gas infall into dark matter clumps(no dissipation) similar scaling laws as dark matter • S = T/ne2/3 • ICM temp. determined by dark matter potential well • Thermal speed of protons~ velocity dispersion of galaxies

4. Expected Scaling relations • Lx n2T1/2R3  T2 (since T  M/R) • S  T (since objects forming at the same epoch have same mean density) Voit & Bryan(2001) • S  T0.65--> density in groups is lower than expected • Steeper relation observed : Lx  T2.8 • Observations Show Deviations From Scaling Relations!!

5. Preheating by supernovae or AGNs? SR & BBN (2003) • fresh look at ICM (with universal temp. profile(Lokenet.al (2002)) in hydrostatic equilibrium • find excess entropy requirement Need ~ 0.5 - 1keV per particle Bialek et.al (2001)

6. AGNs in clusters • A large fraction of the mechanical energy of jets is deposited in the ambient medium • Buoyant bubbles of relativistic plasma can also deposit energy • Cosmic rays from AGNs can also preheat • the gas in groups – possibly connected to Li-6 • abundance (Nath, Madau & Silk 2005) • Radio galaxies preferentially reside in poor clusters (Bahcall & Chokshi 1992; Best 2004)

7. Buoyant bubbles and effervescent heating (Dalla Vecchia et al 2004) • Buoyant bubbles of relativistic plasma can rise and deposit energy by doing pdV work • For a large flux of bubbles, the `effervescent’ heating rate can be related to AGN luminosity (Begelman 2001) • Believed to be effective in quenching cooling flows---can they also explain the excess entropy at large radii? A2597 (McNamara et al 2001)

8. Energy requirements • Time evolution of ICM with effervescent heating, cooling and thermal conduction--compare entropy with observations after Hubble time • Required energy input EAGN Mcl1.5 Deduced relation: MBH  Mcl5/3 (extension of MBH– Mhalorelation?) (Ferrarese & Merritt 2000)

9. Roychowdhury et. al, 2005, ApJ • gas density decreases with time when heating • is on and decreases after heating has been • switched off. • effects of heating and thermal conduction • are seen even at large radii (beyond 0.5 rvir)!

10. (Ponman et al 2002) • No obvious entropy cores in poor clusters • In conflict with expectations from earlier preheating models • First heating model with AGNs, radiative cooling and thermal conduction which does not produce isentropic cores – gentle positive gradient in the entropy profiles Roychowdhury et. al (2005)

11. Support for radio loud AGN heating (Croston et al 2005) • Gas in groups with radio loud AGNs is at a higher entropy (than gas in groups with radio quiet AGNs)

12. Sunyaev-Zel’dovich effect and cluster gas • CMB photons are inverse Compton scattered by hot electrons decreasing the CMB flux in the RJ region in the direction of the cluster • Enhanced entropy decreases the amount of distortion !!

13. SZ angular power spectrum • Effervescent heating decreases the power spectrum more than previously thought

14. Summary • Feedback from AGNs may explain the excess entropy in galaxy groups and clusters • Effervescent heating is a viable model. • Predict MAGN Mcl 5/3. • Recent observations reveal the connection between excess entropy and the presence of radio loud AGNs in groups. • Decrease in SZ power spectrum larger than previously thought.