X-ray Signatures of Feedback in Intracluster Gas

1. X-ray Signatures of Feedback in Intracluster Gas Megan Donahue Michigan State University Collaborators: Mark Voit, Ken Cavagnolo, Steven Robinson, Don Horner (GSFC)

2. X-ray Signatures of Feedback • Metals in the ICM • The ICM Luminosity - Temperature relationship. • ICM entropy profiles and ICM bubbles.

3. Clusters of galaxies • Most massive, gravitationally-bound structures in the universe (~1015 Mo) • Hot gas outweighs the stars by a factor ~10 • Dark matter outweighs the baryons by a factor ~ 8.

4. ICM enriched on all scales • 22 clusters w/Beppo-SAX • Consistent Fe abundances • Central excess consistent w/production by BCG. DeGrandi et al. 2001; 2004

5. ICM enriched at high redshift • Little evolution seen between z=0.3-1.3. Tozzi et al. 2003; Ettori, et al. 2005

6. Abundance Patterns (Tamura et al. 2004) XMM EPIC & RGS spectra, 22 clusters • [Si/Fe], [S/Fe] solar • [O/Fe] 0.4-0.7 solar in core of cool clusters; solar elsewhere. • No trend with T > 2 keV • Consistent with Ia and core-collapse supernova yields + star formation rates scaled from the field. (See ASCA results in Baumgartner et al. astro-ph/0309166 for contrary view.)

7. ICM Luminosity - Temperature Relation Gravity-only physics predicts L ~ T2. Allowing radiation to cool the gas modifies the relation. e.g. Voit & Bryan 2001

8. Galaxy Formation and the ICM • Cooling and condensation into stars brings the L-T relation into agreement w/observations. • However, cooling alone produces too many stars (Rees & White 1978; Balogh 2001). • Star formation contributes metals and energy to the ICM: this feedback alone may regulate star formation in most galaxies.

9. Galaxy Formation and the ICM: Questions • Even with feedback from star formation, simulations still predict too much star formation in central dominant galaxies (e.g. Kravtsov 2005). • Feedback in “cooling flows”: the ICM in the centers of most X-ray clusters are radiating too brightly to be supported without additional energy input.

10. “Cooling Flows” • Clusters with short central cooling times (tc<tH). • Regular, relaxed, luminous X-ray clusters with peaked central X-ray surface brightness. • Fairly common, often with central radio sources and Ha nebulae in their cores. • The radiation losses must be stabilized by feedback.

11. Observed “cooling flow” spectra (XMM) • Peterson et al. 2003 • FeXVII and other lines from 1 keV gas not present. • Two-temperature or “truncated” cooling flow (at ~T/3 - T/2)

12. Cluster gas cools… • Temperature gradients from Chandra and XMM observations. • Mass cooling rates closer to star formation rates. • Gas cooler than ~1 keV not seen or is very faint. • The cooling times are still short. • What keeps this gas from cooling further?

13. Hydra A z=0.0522 50 kpc Abell 2052 z=0.0353 50 kpc Radio Sources & Cluster Cores • Can AGN balance radiative cooling in cluster cores? • Bubbles in the ICM: (McNamara, Sarazin, Blanton) • Heating occurs, but it’s not clear how the AGN compensates for radiative losses. • AGN may be the primary culprit in quenching the cooling in cluster cores: but how to tell?

14. Radio-quiet cluster cores Peres et al. 1998: • 23 clusters with cooling rates > 100 solar masses/year • 13: emission line nebulae & strong central radio source • 2: strong central radio source but no optical line emission (A2029, A3112) • 3: emission lines but weak central radio source. (A478, A496, A2142) • 5: no emission lines and little or no radio activity. (A644, A1650, A1651, A1689, A2244)

15. Radio-quiet cluster cores Peres et al. 1998: • 23 clusters with cooling rates > 100 solar masses/year • 13: emission line nebulae & strong central radio source • 2: strong central radio source but no optical line emission (A2029, A3112) • 3: emission lines but weak central radio source. (A478, A496, A2142) • 5: no emission lines and little or no radio activity. (A644, A1650, A1651, A1689, A2244)

16. Chandra Observations • Chose 2 symmetric, relaxed clusters without radio sources, A1650 and A2244. • ACIS-S observations sufficient to obtain >150,000 counts for radial deprojection of spectra and surface brightness. • Temperature and metallicity gradients measured at lower resolution than density gradient.

17. A2244 & A1650 • Feedback free? • Radio quiet -- upper limits or detections a factor of 30 or more below the others • Z = 0.095 and 0.085 • KT ~ 5-6 keV

18. What might have been: • Fossil radio lobes and/or X-ray cavities suggestive of earlier radio activity. • Temperature gradients sufficient to quench cooling via conduction. • Very low central entropy values, suggesting that these clusters are on the verge of a heating episode.

19. What is A2244 • No fossil lobes out to ~100 kpc A1650 Donahue, et al. 2005

20. What is • No temperature gradients: limited, if any, conduction. Donahue, et al. 2005

21. Entropy • Specific entropy (Tn-2/3) is more closely related to heating and cooling than temperature alone. • DS = D(Heat)/T = (3/2) Nk D[ ln(Tn-2/3)] • Only radiative cooling can reduce entropy • Only heat input (e.g. shocks) can increase entropy • Compression in a gravitational potential changes T but not Tn-2/3 (adiabatic). • S is directly related to tcool (small S(T), short tcool) • Convective stability condition: dS/dr > 0 • Cooling time tc = (14 Gyr) (S/81 keV cm2)3/2 (TkeV)-1

22. Entropy Gradients • Cool cores with feedback evidence show a remarkable consistency in their entropy profiles: • S(r) = S0 + (r/r1)a • S0 ~ 10 keV cm2 • a ~ 0.9 - 1.3 • a is about what one expects as a result of structure formation outside the core (but not necessarily inside the core). • Almost all have non-zero S0.

25. Interpretation of profiles • Similarity of profiles could be used to argue against episodic heating. • No evidence for entropy inversions r > 10 kpc: suggests energy injection can’t just happen at the center. • Entropy floors, small entropy inversions, bubbles show current energy injection.

26. Iron Gradients • Significant iron gradients, increasing toward the core measured in most of these systems. • The presence of a gradient suggests lack of disturbance (e.g. major mergers.) Quasi-stable core gas?

27. What do we see? • High central entropy! 35-50 keV cm2

28. What do we see? • T~5-6 keV => tcool > 109 years

29. Comparison LR vs. Central Entropy LR vs. Power-Law Slope

30. Significant Iron Gradients

31. What happened? • These cluster cores have not yet cooled to low entropy, and will trigger an outburst in the future. OR • The AGN in these clusters have a very low duty cycle, requiring enormous energy injection by AGN in the past.

32. Do radio jets heat the ICM? 10 kpc Perseus Cluster & 3C 84 Sound Waves in Perseus

33. Dramatic Heating Events MS0735 (McNamara et al.) Hydra A (Nulsen et al.)

34. AGN Heating in Groups Radio-loud groups (circles) tend toward the low-L, high-T side of L-T relation Croston et al. 2004

35. Chandra Entropy Profiles Core entropy profiles very regular Entropy inversions are minor and lie at r < 10 kpc

36. Episodic Heating Dt  108 yr (K / 10 keV cm2)3/2 (T / 5 keV)-1 • Heating episodes required every ~108 yr • Central entropy level remains near input level for most of duty cycle • Central entropy input cannot greatly exceed 10-20 keV cm2

37. Entropy Jump Condition K2 + 0.84 K1 DK  - 0.16 K1 v2 3(4r)2/3 v2 3(4r)2/3

38. Core Density Structure • Core density profile: • r(r) ~ 1/r • S(r) = r r(r) • S ~ 3 x10-3 g cm-2

39. Zones of AGN Heating for rr ~ const. • Luminosity dominated: L~rr2v3 DK ~ 29 keV cm2L452/3S3-4/3 • Energy dominated: E ~ rr3v2 DK ~ 22 keV cm2 E59S3-5/3r10-4/3 • Bubble dominated: DE ~ Vbub |dP/dr| Dr DK ~ 6 keV cm2 E59S3-5/3 (r/rinj)-0.18 r10-4/3

40. Chandra Entropy Profiles Core entropy profiles very regular Entropy inversions are minor and lie at r < 10 kpc

41. Beyond the Core (rr2 ~ const) • Sustained Luminosity: L~rr2v3 v ~ 1600 km s-1L461/3 (T/5 keV)-1/3 DK / K ~ 0.4 L462/3 (T/5 keV)-5/3

42. Beyond the Core (rr2 ~ const) • Sustained Luminosity: L~rr2v3 v ~ 1600 km s-1L461/3 (T/5 keV)-1/3 DK / K ~ 0.4 L462/3 (T/5 keV)-5/3 Preserves shape of original K profile!

43. Entropy Profiles • Cooling: Breaks self-similarity Its entropy scale determines M-T, L-T relations • Feedback: Prevents overcooling What elevates entropy at large radius? • Core Profiles: Suggest AGN heating (~1045 erg s-1 , ~108 yr) Extended outburst can elevate entire profile

44. AGN heating? • Yes! • AGN are almost certainly the primary stabilizing mechanisms for cooling cores at z~0.

45. Next Work • Complete entropy profile extraction on other radio quiet clusters (almost done). • Test idea that cooling rates ~ star formation rates with RGS and Astro E-2 spectra (faint Fe XVII and O VII lines should be present.) • Test deprojection assumptions with realistic hydro simulations.

46. Conclusions • Recent ICM abundance measurements show enrichment throughout the cluster. • ICM abundance evolution since z~1.3 slow; consistent with supernova rates. • Central entropies of nearby clusters with short central cooling times are higher in clusters without radio sources. • Cooling and star formation explain the ICM L-T relation (at least at high T). • AGN are required to complete the story to regulate star formation in cDs and stabilize cool core clusters.