1. 1 Astro Particle Cosmology OAR Roma Soft X-ray emission in Large Scale Structures: thermal or non-thermal ? Soft X-ray emission in Large Scale Structures: thermal or non-thermal ? WHIM 2006 WHIM 2006 Jan. 18, 2006 Sergio Colafrancesco Sergio Colafrancesco INAF - Osservatorio Astronomico di Roma INAF - Osservatorio Astronomico di Roma INFN – Roma Tor Vergata INFN – Roma Tor Vergata Email Email: Sergio.Colafrancesco@mporzio.astro.itolafrancesco@mporzio.astro.it

2. 2 Formation of DM halos

3. 3 Extended picture: DM+Hydro Two-dimensional slice of (25h −1 Mpc) 2 around a complex including a cluster of X-ray emission weighted temperature T x ≈ 3.3 at z = 0. [Kang et al. 2003] Mach number surface

4. 4 … + shocks & shocks & shocks … LWIM (T < 10 5 K) V sh < 150 km/s Sheet-like WHIM (T  10 5 - 10 7 K) 150 < V sh < 700 km/s Filamentary Hot gas (T > 10 7 K ) V sh > 700 km/s Knotty Shocks Gas

5. 5 … + B field Magnetic field Baryon density [Sigl et al. 2004]

6. 6 Baryon phase diagram z ~ 0 black curve : fast cooling region, cooled, collapsed structures yellow line : “Ly-α equation of state” Ly-α clouds (photoionized) [Valageas et al. 2002] WHIM: 5 ) ~ 30 [Cen & Ostriker & many others] ~ 25 % of baryonic mass at z = 0 distributed in filaments shock-heated, collisionally ionized LWIM: log T < 5 [Kang et al 2005] ~ 15 % of baryonic mass at z = 0 distributed in sheet-like structures shock-heated mostly collisionally ionized

7. 7 WHIM physics Shock heating [continuous]Heat WHIM Electron-ion equilibration[~ T 3/2 /n]Not complete Heat conduction [ e = t eq (T/m e ) 1/2 ] Timescale matchingNot addressed WHIM magnetic fields [0.01 - 0.1  G] WHIM density 1-1000 WHIM temperatures10 5 -10 7 K

8. 8 Cluster environments DM T EW  WHIM —  diffuse … [Kravtsov et al. 2002] LXLX N OVII N OVIII

9. 9 Warm gas & WHIM around clusters Emission weighted temperature map of one projection of the simulation [Mittaz et al. 2004] Coma Cluster in the EUV extra photon emission in the 0.2 – 0.5 keV by the EUVE mission in 1995 [Lieu et al. 1996] Hot gas SXR halo LWIM WHIM 0 5.6 T

10. 10 6’ – 9’ ROSAT and EUVE DS Solid lines are the expected emission spectra of the hot ICM at: kT = 8.7 +/- 0.4 keV A = 0.3 solar kT = 9.6 keV A = 0.22 solar ROSAT PSPC EUVE Coma: EUVE+ROSAT+XMM XMM-Newton 0’ - 5’ [Nevalainen et al., 2003, ApJ, 584, 716] EPIC PN Spectrum EPIC MOS1+MOS2 Spectra

11. 11 EUV+SXR excess in clusters (5/14) Very extended EUV excess in A2199 [Lieu et al., 1999] SXRO VII

12. 12 Average sky background at high latitudes Coma Systematics Is the soft excess above the known systematic uncertainties in the calibration of XMM ? Could the soft excess be due to an incorrect estimate of the foreground Galactic HI absorption ? Could the cluster soft excess be due to an incorrect subtraction of the background ? [Lieu 2004][Bregman et al. 2001]

13. 13 SXR spatially extended (out to 1-2 deg: XMM + PSPC) Increasing strength at larger radii (… except Coma) Extended SXR emission @ < 0.4 keV Weak or absent line emission OVII triplet at  0.56 keV (Cluster ref. frame ?) Properties of the SXR emission [Kaastra et al 2003]

14. 14 AS1101 (2’-5’) with ICM model (fitted from 2-7 keV) and bkgs. Intrinsic background sky average background [Kaastra] SXR EXCESS REMAINS ROBUST (after subtracting the higher background) Isothermal model kT = 3.08 keV A = 0.194 solar Isothermal model kT = 3.08 keV A = 0.194 solar Fit to the OVII+OVIII complex with no constraint on the line energy Redshifted OVII lines ? Line consistent with zero redshift i.e. Galactic origin [Lieu et al. 2004]

15. 15 Thermal origin Thermal (warm) gas at T  0.2 keV Physical constraints For intracluster origin of the WHIM Radiative cooling time For Rapid cooling of the warm gas !

16. 16 Supercluster medium Giant ¼ keV Halo centered at Coma (as detailed by the ROSAT sky survey) The warm gas here may be part of the WHIM, not in physical contact with the hot ICM (B confinement ?) SXR halo around A1795 Bootes Supercluster [Kaastra et al. (2003)]

17. 17 WHIM solves some problems with thermal soft excess model. Cluster SXR shows characteristics of the WHIM near the nodes Thermal emission with T ~ few 10 6 K Increases in importance on the outskirts of clusters SXR & cluster environment

18. 18 If emission is caused by warm intercluster filaments, can avoid the need for pressure balance with the hot intracluster gas so the warm gas density can have which is fixed by observations (i.e. lower n w implies higher L). For a given value of EM, the line-of-sight COLUMN DENSITY of warm filaments is which can be observationally constrained Constraints to this scenario: for example, the emission measure EM is given by …but: do WHIM models give rise to a Soft X-ray Excess ? SXR & LSS filaments

19. 19 Low-T IGM component is predicted to be very weak [Mittaz et al. 2004] Emission from cells < 1 keV Factor of ~ 10 4 Maximum possible emission SXR & WHIM models SimulatedObserved Hot component8 x 10 44 2 x 10 44 Warm component3 x 10 40 3 x 10 43 Luminosity comparison

20. 20 When compared with > 1  soft excesses observed with ROSAT: [Bonamente et al. 2002] Simulated luminosities Generally no strong source of soft excess at centre of simulated cluster (max possible fraction explained by model ~ 30%) Maximum (preferred direction)

21. 21 Simulating the Soft X-ray excess in clusters of galaxies L.-M. Cheng, S. Borgani, P. Tozzi, L. Tornatore, A. Diaferio, K. Dolag, X.-T. He, L. Moscardini, G. Murante, G. Tormen astro-ph/0409707 The detection of excess of soft X-ray or Extreme Ultraviolet (EUV) radiation, above the thermal contribution from the hot intracluster medium (ICM), has been a controversial subject ever since the initial discovery of this phenomenon. We use a large--scale hydrodynamical simulation of a concordance LambdaCDM model, to investigate the possible thermal origin for such an excess in a set of 20 simulated clusters having temperatures in the range 1--7 keV. Simulated clusters are analysed by mimicking the observational procedure applied to ROSAT--PSPC data, which for the first time showed evidences for the soft X-ray excess. For cluster--centric distances 0.4< R/R_{vir}< 0.7 we detect a significant excess in most of the simulated clusters, whose relative amount changes from cluster to cluster and, for the same cluster, by changing the projection direction. In about 30 per cent of the cases, the soft X-ray flux is measured to be at least 50 per cent larger than predicted by the one-- temperature plasma model. We find that this excess is generated in most cases within the cluster virialized regions. It is mainly contributed by low--entropy and high--density gas associated with merging sub--halos, rather than to diffuse warm gas. Only in a few cases the excess arises from fore/background groups observed in projection, while no evidence is found for a significant contribution from gas lying within large--scale filaments. We compute the distribution of the relative soft excess, as a function of the cluster--centric distance, and compare it with the observational result by Bonamente et al. (2003) for the Coma cluster. Similar to observations, we find that the relative excess increases with the distance from the cluster center, with no significant excess detected for R<0.4R_{vir} Recent cluster simulations seem to find SXR excess in outer regions of merging clusters. SXR & cluster merging “… low-entropy & high-density gas associated to sub-halos rather than diffuse warm gas …”

22. Minimum required warm gas column density is contradicted by absorption line measurements of quasar spectra OVII emission lines found on top of the soft excess spectra at the outskirts of some clusters could be NOT real (associated to Galactic emission) Thermal origin troubles Outer soft excess NOT associated with the WHIM if the origin is outlying filaments seen in projection  required column density will be enormous if intracluster warm gas  problem with cooling time Outside a cluster’s core Inside a cluster’s core

23. 23 Non-thermal origin Coma XMM-Newton MOS1+2 and PN fits to 0’-5’ region Single temperature Single temperature + Power-law Assuming a power-law soft excess in Coma dramatically improves the fit ! ComaMKW3sA2052A2199A1795Sersic 159-03A3112 SXRStrongWeak Strong LinesNo?????? HXRYesNo Yes No

24. 24 SXR vs HXR in clusters ICS of CMB photons by intracluster cosmic rays (relativistic e ± with E  100-300 MeV) RadioEUVHXR Coma Require cosmic rays (with E > 300 MeV) in clusters atmospheres

25. 25 Indications SXRHXRCooling flow ComaYes No A1795Yes Quenched Sersic 159-03Yes?Quenched A3112Yes?Quenched [Feretti 2003] [Fusco-Femiano et al. 2004] [Colafrancesco et al. 2004]

26. 26 CRs in clusters p p Primary e ± Direct acceleration (shocks) Injection (AGNs) Re-acceleration Primary e ± Direct acceleration (shocks) Injection (AGNs) Re-acceleration Secondary e ± Hadronic collisions DM annihilation Secondary e ± Hadronic collisions DM annihilation

27. 27 SXR & primary CRs F ICS /F th should increase at large radii [Lieu & Sarazin 1998]  data indicate that F ICS /F th = constant in Coma [Bowyer et al. 2004] If F EUV  F RH  B increase outwards If F EUV is produced by merging shocks  [Lieu et al. 1998] Two-phase model [Brunetti et al. 2001] 1) AGN injection 2) Turbulent re-acceleration  strong tuning of physical conditions (high-E cutoff,  acc < 0.3 Gyr, …) Additional CR population [Colafrancesco, Marchegiani, Perola 2005]

28. 28 SXR & Hadronic collisions F EUV-SXR  due to secondary electrons produced in hadronic (pp) collisions [Bowyer et al. 2004] [Marchegiani, Perola, Colafrancesco 2006] [Marchegiani 2005, PhD Thesis] Fit EUV brightness

29. 29 SXR & Dark Matter F EUV-SXR  due to secondary electrons produced in DM annihilation [Colafrancesco et al. 2005]

30. 30 SXR & Dark Matter F EUV-SXR  due to secondary electrons produced in DM annihilation [Colafrancesco et al. 2005]

31. 31 XMM-Newton observations of Clusters in the 0.4-7 keV range confirm ‘beyond reasonable doubt’ [Lieu 2004] the existence of a soft excess first noticed by the EUVE and ROSAT teams. is strong and in XMM extends to E=1-2 keV, at a level beyond the uncertainties of the detector responses is seen in regions where the cluster low energy flux is 10-100 times above background cannot be explained as a Galactic absorption anomaly The thermal interpretation in terms of missing warm baryonic filaments of the IGM suffers from a large discrepancy in col.dens. Recent cosmological simulation reproduced the SXR by high-density, low-S gas clumps associated to merging process. At the outskirts of clusters, the OVII detection claimed by Kaastra, Lieu et al. (2003) is a questionable result (at least for now). Non-thermal models require very high cosmic ray pressure/density. Cluster SXR: the status

32. 32 Diagnostics Direct Spectral resolution at EUV / SXR energies Spatial resolution of SXR (core vs. outskirts) Indirect Multi- observations SZ effect

33. 33 SZ effect of warm & rel. plasma thermal e - relativistic e - [Colafrancesco et al. 2003 ]

34. 34 Intensity change Spectral shape Thermal Relativistic SZE: general derivation Redistribution function Pressure [Colafrancesco & al. 2003, A&A, 397, 27]

35. 35 The e - distributions in Coma 50GeV = M  100 GeV 200 GeV 500 GeV T=0.1 keV T=8.2 keV Radio-halo electrons

36. 36 If V r =0 km/s there is no room for an additional non- thermal population in Coma (1  c.l.) Best fit: Plot 0 Thermal + Non-thermal SZE [ OVRO + MITO ] Thermal population The Case of Coma

37. 37 A possible SZ kin in Coma There is evidence of a peculiar velocity of Coma [Bernardi et al. 2002] The presence of a positive SZ kin allows for an additional (thermal or non-thermal) component of the total SZ signal Approaching Coma

38. 38 Best fit: b.f. Including a non-thermal population in Coma improves the fit Thermal + non-thermal SZE

39. 39 b.f. Hot (T ~ 8.2 keV) + Warm (T ~ 0.1 keV) Thermal SZE improves the fit Hot (T ~ 8.2 keV) + Warm (T ~ 0.1 keV) Thermal SZE improves the fit A warm component in Coma

40. 40 Hot + Warm + Non-thermal EUV excess in Coma b.f. The complete assembly

41. 41 SZE & WHIM Using the SZE (l.o.s. integral of the electron distribution in whichever form) to probe the WHIM distribution in LSS [Colafrancesco et al. 2006] density velocity temperature OVI density [Fang & Bryan (2001)]

42. 42 THANKS for your attention !

43. 43 Simulation of WHIM material. Weak signal in 10 5 seconds

44. 44 Just not enough low temperature material: Total column densityColumn density < 1keV Column density of low temperature components is much less than that of the hot component at the cluster 1 Mpc

45. 45 WHIM physics Shock heating [continuous]Heat WHIM Electron ion equilibration[~ T 3/2 /n]Not complete Heat conduction [ e = t eq (T/m e ) 1/2 ] WHIM magnetic fields [0.01 - 0.1  G] WHIM density 1-1000 WHIM temperatures10 5 -10 7 K

46. 46 Shock heating

47. 47 Equilibration

48. 48 Timescales

49. 49 Heat conduction

50. 50

51. 51 Magnetic field role