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

2. 2 Most galaxies found in groups (<50 members) or clusters (100-1000) Mass range between 10 13 -- 10 15 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 NGC 2300(central part) Coma cluster

3. 3 ICM self-gravity negligible Adiabatic gas infall into dark matter clumps (no dissipation)  similar scaling laws as dark matter  S = T/n e 2/3 ICM temp. determined by dark matter potential well Thermal speed of protons~ velocity dispersion of galaxies

4. 4 Expected Scaling relations L x  n 2 T 1/2 R 3  T 2 (since T  M/R) S  T (since objects forming at the same epoch have same mean density) Voit & Bryan(2001) Steeper relation observed : L x  T 2.8 S  T 0.65 --> density in groups is lower than expected  Observations Show Deviations From Scaling Relations!!

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

6. 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 Radio galaxies preferentially reside in poor clusters (Bahcall & Chokshi 1992; Best 2004) Cosmic rays from AGNs can also preheat the gas in groups – possibly connected to Li-6 abundance (Nath, Madau & Silk 2005)

7. 7 Buoyant bubbles and effervescent heating 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? (McNamara et al 2001) (Dalla Vecchia et al 2004) A2597

8. 8 Energy requirements Time evolution of ICM with effervescent heating, cooling and thermal conduction--compare entropy with observations after Hubble time Required energy input E AGN  M cl 1.5 Deduced relation: M BH  M cl 5/3 (extension of M BH – M halo relation?) (Ferrarese & Merritt 2000)

9. 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 r vir )!

10. 10 (Ponman et al 2002) Roychowdhury et. al (2005) 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

11. 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. 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. 13 SZ angular power spectrum Effervescent heating decreases the power spectrum more than previously thought

14. 14 Feedback from AGNs may explain the excess entropy in galaxy groups and clusters Effervescent heating is a viable model. Predict M AGN  M cl 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.