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Studying Galaxy Clusters with Astro -H

Studying Galaxy Clusters with Astro -H. Silvano Molendi IASF-Milano/INAF. ICM in Galaxy Clusters. Largest gravitationally bound structures in the local universe . Subject of intense research as cosmological tools interesting structures

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Studying Galaxy Clusters with Astro -H

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  1. Studying Galaxy Clusters withAstro-H Silvano Molendi IASF-Milano/INAF

  2. ICM in Galaxy Clusters Largest gravitationally bound structures in the local universe. Subjectof intense research • as cosmological tools • interesting structures a) and b) are of course connected as some understanding of the structures is required to use clusters as cosmological tools.

  3. Basic properties of the ICM Setting the context The ICM istenuous, typicaldensities 10-4 to a few 10-2 cm-3 hot, temperatures from 107 to 108 K (1-10 keV) highlyionized: H, He completelyionizedheavierelementspartiallyionized Chemicallyenriched, heavyelementssuchas O, Si and Fe are present in almostsolarproportions

  4. Thermal bremsstrhalung + line emission X-ray emission

  5. Basic properties of the ICM Setting the context X-ray emission form clusters is extended

  6. We have had high resolution spectroscopy in X-ray for more than decade now, so is ASTRO-H really going to be a major step forward? ASTRO-H The large improvement in collecting area at Fe K line will afford considerable insight for many astrophysical sources. ASTRO-H will carry the first micro-calorimeter However, for extended sources, for which high res. spectroscopy has been possible only in the most limited sense, SXS will produce a true quantum leap

  7. The importance of motion Show movies

  8. Disclaimer Many things can and will be done, in this presentation I will cover some of the most important. Not an exhaustive presentation.

  9. Motions in the ICM Indirect evidence of motions is now abundant

  10. Shocks in the ICM Bullet cluster Best example of shock Core of sub-structure already gone through cluster From RH conditions and density jump Mach number ~ 3 Vshock ~ 4700 km/s Markevitch & Vikhlinin (2007)

  11. Motions in the ICM These are rare systems, one of the reasons is the shocks occur exactly in the plane of the sky Shocks now seen in a few systems point to mildly supersonic gas motions There are likely similar systems seen at different angles (e.g. A576 Dupke+07) these will be accesible with SXS

  12. Motions in cores Indirect evidence of gas motions in the cores of many “relaxed” (Cool Core) systems

  13. Core of Perseus cluster Highly structured Enhanced emission Cavities Fabian+03

  14. Radio Bubbles Cavities coincide with radio lobes associated to the AGN at the center Fabian+03

  15. Ripples and weak shocks • Radio cavities expand and rise buoyantly, in doing so they set the ICM in motion, generating ripples and weak shocks Fabian+03

  16. ColdFronts Ghizzardi, Rossetti &SM 2010 • CF are contact discontinuities (SB jumps) discovered by Chandra (Markevitch & Vikhlinin 2007) • Found in merging systems where they mark dense subcluster cores that have survived a merger

  17. ColdFronts Ghizzardi, Rossetti &SM 2010 • Found in non merging systems were they result from the displacement of lowest entropy gas from the bottom of the potential well. • Small pressure jump across the CF point to subsonic motions • Search for cold fronts in a representative sample of nearby systems shows that ALL relaxed clusters host at least 1 CF

  18. Gas Motions in clusters • Indirect evidence for ubiquitous subsonic gas motion in cluster cool cores • Subsonic motions are quite likely one of the defining traits of these systems, (the reason this statement is seldom made is that we have, thus far, lacked direct observations of gas motions) • Open questions are: • what is the kinetic energy vs. thermal energy? • is the flow laminar or turbulent? • what is the viscosity of the ICM? • Indirect evidence for mildly supersonic motion in a few systems, typically those were shock is propagating in the plane of the sky.

  19. SXS on ASTRO-H • A 6eV resol @ Fe Kαline corresponds to a velocity resolution of 300 km/s • The sound speed in the ICM is • cs = (5/3·p/ρ)1/2 = 1460 km/s·(kT/8 keV) 1/2 ASTRO-H well suited to measure subsonic motions in ICM • Most important line is the Fe Kα • For most T He-like Fe Kα is the most prominent

  20. Fe He-like Kα

  21. Laminar flow Different regions with Δv=200km/s

  22. Turbulent flow Region with vTurb=200km/s

  23. Laminar vs Turbulent flow • Some line broadening may be present even if turbulence is completely absent (limited angular resolution & line of sight effects) • The combination of high spectral resolution and moderate angular resolution should allow us to distinguish between flows dominated by laminar and turbulent motions. • Intermediate cases will be more difficult but not impossible to characterize.

  24. ICM Thermo-dynamicstructure • XMM-Newton Grating (Peterson+01 ) and CCD data (SM & Pizzolato01) falsified the cooling-flow model that predicted strong multi-phaseness of ICM in cluster cores (temperatures from a few keV down to 0.1 keV). • Evidence, in some instances, of suppression of conduction, presence of multi-temperature structure: suppression of conduction across cold fronts e.g. A3667, Ettori & Fabian 2001 presence of blobs/filaments of cooler gas in the radio arms of M87 (SM 2002, etc.)

  25. ICM Thermo-dynamicstructure The limited spectral resolution of CCDs and spatial resolution of gratings does not allow us to address the issue of moderate multi-phaseness in the ICM at large SXS will change this

  26. ICM Spectraat CCD resolution • 1 keV • 2 keV • 4 keV • 8 keV

  27. ICM Spectraat SXS resolution • 1 keV • 2 keV • 4 keV • 8 keV

  28. Fe L-shellemission T up to 3keV

  29. Ar Kα line emission He-like H-like Ratio of H to He-like 2keV<T < 8keV

  30. Fe Kα line emission He-like H-like Ratio of H to He-like 2keV<T < 10keV

  31. ICM Thermo-dynamicstructure • The relative intensity of Fe L-shell lines and the ratio of H-like Kalpha to He-like Kalpha lines for O,Mg,Si,S,Ar,Ca & Fe are all dependent upon temperature and can be used to provide independent estimates of T and assess presence of even modest multiphase-ness. • As for the study of line broadening some apparent multi-T will be present even if the gas is single phase (limited angular resolution & line of sight effects), however these effects can be accounted for

  32. Summary The SXS will produce a quantum leap in our understanding of the ICM It will: • directly detect motions within the ICM for the first time • characterized the thermodynamic structure of the ICM • improve our understanding of metals in the ICM

  33. NuSTAR • The relative intensity of Fe L-shell lines and the ratio of H-like Kalpha to He-like Kalpha lines for O,Mg,Si,S,Ar,Ca & Fe are all dependent upon temperature and can be used to provide independent estimates of T and assess presence of even modest multiphase-ness. • As for the study of line broadening some apparent multi-T be present even if turbulence is the gas is single phase (limited angular resolution & line of sight effects), however these effects can be accounted for 10 arcsec (FWHM) 13 x 13 arcmin 1 keV @ 60 keV 0.5 keV @ 6 keV < 48 h

  34. NuSTAR • Launched on June 13th in LEO • First Light on June 28th • Thus far everything has gone well • Mast deployment successful • Instruments functioning within expectations

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