Entropy, Feedback, & Conduction in Galaxy Clusters

1. Entropy, Feedback, & Conduction in Galaxy Clusters

2. Intracluster Entropy K = Pr-5/3  Tne-2/3 (keV cm2) • Entropy distribution in ICM determines a cluster’s equilibrium structure • Entropy distribution retains information about cluster’s thermodynamic history • Heating and cooling change K more than T

3. Baseline Entropy Profile Entropy profiles in absence of galaxy formation are self-similar and scale with K200 = Also, K(r) ~ r1.1 Voit, Kay, & Bryan (2005) T200 (200 fb rcr)2/3 Tozzi & Norman (2001) Borgani et al. (2002) Voit et al. (2003)

4. Pure Cooling Model Allow baseline profile to cool for a Hubble time in an NFW potential, and remove gas at r = 0 when K = 0.

5. Chandra Entropy Profiles Cavagnolo et al. (2008) 217 clusters K(r) = K0 + K100 (r/100 kpc)a K100 ≈ 150 keV cm2 , a ≈ 1.2

6. Central Entropy Distribution Distribution of K0 is bimodal with deficit at K0 ~ 40-50 keV cm2 corresponding to a cooling time ~ 1 Gyr Cooling-time distribution is not so clearly bimodal Cavagnolo et al. (2008) See also Hudson & Reiprich

7. K0 and Radio Power Central galaxy of a z < 0.2 cluster can be a strong radio source only if K0 < 30 keV cm2 Radio data from NVSS+SUMMS within 20” of X-ray peak Cavagnolo et al. (2008)

8. K0 and Ha Emission Central galaxy can have emission-line nebulosity only if K0 < 30 keV cm2 Ha data from many diverse sources Cavagnolo et al. (2008)

9. K0 and Central Blue Gradient Central galaxy can have blue gradient indicating star formation only if K0 < 30 keV cm2 Rafferty et al. (2008)

10. Conduction vs. Cooling lF = ≈ 4 kpc (K / 10 keV cm2)3/2 fc1/2 • Field length depends uniquely on K for free-free cooling • Donahue et al. (2005) suggested that this conduction threshold could produce a bifurcation in cluster properties • See also Guo et al. (2008), arXiv:0804.3823 kT ne2L

11. Conductive Stabilization of ICM High-entropy gas can be stabilized by conduction Low-entropy gas is thermally unstable Voit et al. (2008)

12. Conductive Stabilization of ICM Thermal conduction can stabilize cooling in clusters with K0 > 30 keV cm2 as long as fc~ 0.2 Voit et al. (2008)

13. Conductive Stabilization of ICM All of the star forming BCGs from Rafferty et al. (2008) are in clusters with entropy profiles that dip below this stabilization threshold Voit et al. (2008)

14. Conductive Stabilization of ICM All clusters from Rafferty et al. (2008) that host BCGs without star formation or Ha emission have entropy profiles that remain above the threshold Voit et al. (2008)

15. Conduction & Feedback • AGN feedback, nebulosity and BCG star formation appear where conduction can no longer compensate for cooling • If conduction is present, it may be important for distributing AGN energy input throughout the cluster core

16. Chandra Group Survey Survey of 44 groups from Chandra archive (0.8-3.0 keV) Background modeling enables T measurements up to r500 Sun et al. (2008)

17. Scaled Group Entropy Profiles Groups are generally farther from the baseline entropy profile than clusters Entropy excess and dispersion decrease toward larger radii Sun et al. (2008)

18. Dispersion in Group Entropy Intrinsic dispersion of scaled entropy is much smaller at large radii than at small radii Sun et al. (2008)

19. Dispersion in Group Entropy Intrinsic dispersion of scaled entropy is much smaller at large radii than at small radii Sun et al. (2008)

20. Dependence of fgas on T Gas fraction in groups is similar to that in clusters outside of r2500 Sun et al. (2008)

21. Mass-Observable Relations Groups follow same M-T and M-YX relations as clusters down to ~ 1 keV Sun et al. (2008)

22. Chandra Groups • Groups are surprisingly well behaved outside of the core regions • Baryon fraction in groups is similar to that in clusters (good for SZ) • Groups follow same M-T and M-Y scaling relations as clusters to ~ 1 keV

24. MSU Elsewhere Mark Voit Greg Bryan Megan Donahue Stefano Borgani Ken Cavagnolo Scott Kay Ming Sun Brian McNamara David Ventimiglia David Rafferty Brian O’Shea Paul Nulsen