CLUSTERS OF GALAXIES AND THEIR MASSES IN X-RAYS (AND SZ)

1. CLUSTERS OF GALAXIES AND THEIR MASSES IN X-RAYS (AND SZ) FABIO GASTALDELLO MARIACHIARA ROSSETTI IASF-Milano INAF

2. OUTLINE OF THE LECTURE • Basic properties of Galaxy Clusters • Zero order model for the Intra Cluster Medium • Relaxed (Cool core clusters) vs Unrelaxed (NCC) • Spatially Resolved Spectroscopy • Mass reconstruction through hydrostatic equilibrium equation • SZ effect and X-ray-SZ combination

3. Basic properties of the ICM Setting the context The ICM istenuous, typicaldensities 10-4to a few 10-2 cm-3 . These are very low densities, the taillobesof the earthmagnetospherehavedensitiesof 10-2 cm-3 .

4. Basic properties of the ICM Setting the context The ICM is hot, temperatures are in the range of 107 to 108 K (1-10 keV) highly ionized: H, He completely ionized heavier elements partially ionized Chemically enriched, heavy elements such as O, Si and Fe are present in almost solar proportions

5. X-Ray Imaging X-rays and optical light show us a different picture

6. X-Ray Imaging X-rays and optical light show us a different picture

7. THE COMPONENTS OF GALAXY CLUSTERS Intra-cluster medium (ICM) Thermal plasma X-rays (10-30%) Relativistic particles Radio Galaxies (5%) Dark Matter Gravitational potential 1E 0657-156 THE BULLET CLUSTER Galaxy clusters are the most massive (M~1014-1015 MSUN) objects in the Universe

8. Properties of groups and clusters CLUSTERS GROUPS/POOR CLUSTERS LX (erg/s) 1043 - 1045 1041.5 - 1043 kTX (keV) 2 – 15 ≤ 2 N gal 100-1000 5 – 100 σv (km/s) 500-1200 (median 750) 200 – 500 Mtot (< 1.5 Mpc) 1014 – 5 x 1015 1012.5 - 2 x 1014 Number Density 10-5 – 10-6 Mpc-3 10-3 – 10-5 Mpc-3 Groups and poor clusters provide a natural and continuous extension to lower mass, size, luminosity and richness of rich, massive and rare clusters BHACALL 1999

9. Timescales & other fundamentals Cooling timescale The ICM cools by emitting radiation Except for the innermost regions where np is high, gas cools on timescales > Hubble time In first approx. we may consider the ICM as a stationary ball of hot plasma

10. Heating • No major on-going heating of the gas is necessary (the cooling is very slow) • The ultimate origin of the bulk of the thermal energy of the ICM is the gravitational energy lost by the gas as it falls into the cluster’s potential well • The temperature of the ICM is related to the depth of the potential well and to the total mass of the cluster

11. The ICM is highly ionized Tg ~ 107 – 108 H, Hecompletely ionized • Coulomb interactions are the dominant mechanism for collisions, for Te = Ti the mean free path is: ICM can be treated as a fluid, satisfying hydro-dynamical equations

12. Timescale for a sound-wave to cross the cluster The ICM is in hydrostatic equilibrium

13. Radiation process Continuum emission is dominated by thermal bremsstrahlung spectral shape Tg spectrum normal. ng Optically thin: ngσT L ≈ 10-2 6.65x10-25 3.18x1024 ‹‹ 1

14. Lineemission The Fe Kα complex ~ 7 keV is dominated by emission from He-like (6.7 keV) and H-like (6.9 keV), the ratio of lines intensity depends upon the ionization state of the gas which is a function of the gas temperature.

15. Summary of basic properties • A hot, tenuous and weakly magnetized plasma (ICM) rests in the potential well of galaxy clusters • The temperature of the ICM is related to the total mass of the cluster • The ICM is enriched and heavily ionized • It dissipates energy at a very slow rate by emitting X-rays by thermal bremsstrahlung • It can be treated as a fluid in hydro-static equilibrium • The pressure associated with the weak B field does not drive gas dynamics

16. X-Ray Imaging • Central regions feature approx. constant surface brightness • In outer regions the surface brightness falls off as a power-law with index approx. 3 • Emission is traced out to 1-2 Mpc from the core Mohr et al. (1999)

17. COOL CORES (CC) vs NON-CC (NCC) Relaxed clusters usually feature a centrally peaked density profile, causing a prominent surface brightness peak Flux limit SB limit

18. Concentration parameter (Santos et al 2008) CC vs NCC C=0.30 C=0.02 Abell 2204: CC Abell 2069: NCC

19. Offset between X-ray peak and BCG* position as a dynamical indicator (Hudson et al 2010, Sanderson et al 2009, Mann & Ebeling 12 ) *BCG= Brightest Cluster Galaxy Abell 496 Abell 754 CC vs NCC DISTURBED Large offset RELAXED Small offset )M.ROSSETTI, FG, G. FERIOLI et al (2016) MNRAS 457, 4515

20. Temperature profiles 3 Regions: • T drop in Core of CC clusters • Flat profile • Decreasing profile Leccardi & Molendi (2006) Existence and extension of region 3 have been the subject of considerable controversy (SAX, ASCA) which now (XMM, Chandra) appears to have been resolved.

21. CC vs NCC

22. CC vs NCC • CC have lower ENTROPY profiles Specific entropy per particle s=T/n2/3 (keV cm2) Pratt et al., 2009 Entropy profiles in CC are steeper and lower in the inner regions Cool core Non cool core

23. CC vs NCC • CC have central peaks in Metal Abundance distribution CC NCC The metal abundance central excess is consistent with enrichment from the large elliptical central galaxy (BCG=Brightest Central Galaxy) invariably found in those systems

24. EXTENDED RADIO EMISSION IN CLUSTERS Coma cluster Radio halos fill the volume of the clusters, Mpc extension. Given the short synchrotron lifetime electrons can’t simply diffuse. No detected polarization

25. EXTENDED RADIO EMISSION IN CLUSTERS A3376 Radio relics linear structures of Mpc size, usually at the outskirts of the diffuse extended emission. 20%-50% detected polarization

26. CONNECTION WITH CLUSTER MERGERS

27. RELAXED or CC • Peaked SB and spherical symmetry • T drop at the center • Low central cooling time (tcool<tHubble) • Steep entropy profiles • Metal abundance peak • Presence of a BCG at the X-ray peak • MERGERS or NCC • No clear SB peak and distorsions in morphology • Flat T profiles in the center • High central cooling time • Flatter entropy profiles • Flatter metal abundance profiles • Optical substructure • Radio halo and relic emission • Multiple SL+WL mass components CC vs NCC

28. AGN FEEDBACK IN CC Fabian+11

29. DIFFICULTY TO GO AT LARGE RADII Leccardi & Molendi 08

30. X-RAY MASS DETERMINATION • Spectra averaged within circular annuli • Normalization / shape of spectrum gives gas density / temperature

31. THE NEED FOR (DE)PROJECTION • Geometrical deprojection (e.g. Ettori 00) • Spectral Deprojection (e.g. Russell+08)

32. From 3-D temperature to gravitational mass profiles Euler’s equation If the ICM is assumed to be a fluid in Hydrostatic Equilibrium: If the cluster is assumed to be spherically symmetric then: Substituting the equation of state: The total mass enclosed within a certain radius r is:

33. Assume spherical symmetry Deproject surface brightness and fit spectra with coronal plasma models and obtain (deprojected) spectral quantities (Fit parameterized functions to radial profiles of gas density and temperature) Assume hydrostatic equilibrium Calculate the radial mass profile (mass “points”) X-RAY MASS DETERMINATIONa) “Smoothed inversion” method

34. Gas density Total density X-RAY MASS DETERMINATIONa) “smoothed inversion” method Vikhlinin+06 Gas mass Total mass

35. X-RAY MASS DETERMINATIONb) “forward” method The method assumes parameterizations for the density (or temperature) and mass profiles to calculate the temperature (or gas density) assuming HE Gas density solution We considered also the temperature solution Gastaldello+07

36. X-RAY MASS DETERMINATIONb) “forward” method You can also use the entropy solution, enforcing naturally by fitting power laws stability against convection Humphrey+08, Cavaliere+09

37. X-RAY MASS DETERMINATIONb) “forward” method DM Gas Total mass stars NGC 1550 Gastaldello+07

38. X-RAY MASS DETERMINATION Ettori, FG+10

39. Sunyaev-Zel’dovich Effect (SZ) Rashid Sunyaev Yacob B. Zel’dovich (1914-1987)

40. Sunyaev-Zel’dovich Effect (SZ) CMB Spectrum intensity Difference Frequency

41. 30 44 70 100 143 217 353 545 853 GHz Stacked signal of Planck SZcluster (Planck Collaboration 2013)

42. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT The thermal SZ has a uniquespectralsignature. The spectralsignaturedoesnotdepend on any cluster property, noteven on redshift

43. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT y = Compton parameter

44. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT Small optical depth

45. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT Energy exchanged

46. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT PV=NkT The thermal SZ normalization depends on the gas pressure integrated along the line of sight. Milder density dependance than X-ray emission: ne(r) ranges from 10-1 cm-3 in clusters’ cores to 10-4 cm-3 in clusters’ outskirts

47. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT ≈2 10-5 The SZ signal is intrinsically faint: depends mainly on the cluster temperature

48. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT The integrated SZ signalisproportional to the total mass (cosmology!)

49. RECIPE: THE THERMAL SUNYAEV-ZEL’DOVICH EFFECT • Take home messages: • The thermal SZ has a unique spectral signature. The spectral signature does not depend on any cluster property, not even on redshift. “Negative signal” below 217 GHz, positive above. • The thermal SZ normalization depends on the gas pressure integrated along the line of sight, milder density dependance than X-ray emission • The integrated SZ signal is proportional to the total mass

50. COMBINING X-RAY AND SZ BASU+10 ABELL 2204