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The Warm Hot Intergalactic Medium

The Warm Hot Intergalactic Medium. W = 1.02 ± 0.02 (total) W m = 0.268 ± 0.023 (matter) W b = 0.044 ± 0.003 (baryons) but ~50% missing J.W. den Herder, F. Paerels, A. Rasmussen, J. Kaastra, P. de Korte, H. Hoevers, M. Bruin, C. Scharf, S. Kahn. Cen & Ostriker.

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The Warm Hot Intergalactic Medium

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  1. The Warm Hot Intergalactic Medium W = 1.02 ± 0.02 (total) Wm = 0.268 ± 0.023 (matter) Wb = 0.044 ± 0.003 (baryons) but ~50% missing J.W. den Herder, F. Paerels, A. Rasmussen, J. Kaastra, P. de Korte, H. Hoevers, M. Bruin, C. Scharf, S. Kahn J.W.den Herder 1

  2. Cen & Ostriker • Numerical simulations • Standard LCDM model • z = 3 : cold • z = 0: minor fraction hot, most warm • WHIM is evolving J.W.den Herder 2

  3. Near clusters of galaxies • Soft excess (Lieu et al., 1996), in few clusters, complex calibration/background • XMM-Newton: 7 / 21 show soft excess in 0.2-0.3 keV • O VII line in emission (red shifted) • Coma (Finuguenov): filament 3 Mpc x 20 Mpc, kT = 0.2 keV Clusters of galaxies XMM-Newton J.W.den Herder 3

  4. Absorption line forest • Detection of red-shifted higher ionization state species in UV and X-ray bands: bright backlight source • O VII from local group using PKS2155-304 < 800 km/s, T=0.5 MK, 3 Mpc, n = 6 m-3 • O VI absorption FUSE using quasar H1821+643 (z = 0.297) 2 absorbers • But occasionally inconsistent results with different instruments (PKS2155-304) Nicastro et al. Tripp et al. 0.2264 0.2250 J.W.den Herder 4

  5. In emission between clusters NH 1018.5 – 1021.5 cm2 T 104 – 108.4 K Fang et al. Fang et al. Ion density / hydrogen density (solar abundances) line emission per emission measure O VII r O VIII La O VII O VIII O VII f O VII i O VII 1s-3p J.W.den Herder 5

  6. filaments • 12 selected, calculate EW for O VII, O VII, Fe XVII and Ne IX • abundances 0.1 solar • size of filament 4 x 30 Mpc • density contrast d ~ 5 to 10 (lower than usually (10 – 30) • calculate for these filaments EW to detect WHIM in single pixel, in 4 x 4 Mpc box and along filament (4 x 30 Mpc) • Assume 106 s exposure O VII O VIII max median J.W.den Herder 6

  7. Requirements • count rate WHIM: 0.03 ph/cm2/s/sr in a line • countrate galactic: 30 ph/cm2/s/sr/keV foreground + AGNs • angular resolution: 8’ • energy resolution: 2 eV at 600 eV • energy band 570 - 650 eV OVII-OVIII (920 - 1020 eV NeXI - NeX) • Large grasp: but only for O VII and O VIII at 0.5 keV 1000 cm2 with 1.4 x 1.4o FoV J.W.den Herder 7

  8. Key technology • Mirror with large effective area over short energy range with moderate spatial resolution: short focal length + 4-fold reflections • thin filters (> 40% transmission) with reasonable optical blocking • Large detector with good energy resolution (2 eV) at low energy (0.5 keV): small array (12x12) with large pixels (2x2 mm) or larger array with smaller pixels J.W.den Herder 8

  9. Mirrors • Design based on 2/4 reflections • Abbe-sine condition for large FoV • Conical approximation of Wolter I design • Focal length 1 m J.W.den Herder 9

  10. Mirror production and error budget • Number of shells: 82 (2 bounces x 47, 4: 35) • Length shells : 300 mm • Maximum diameter: • Material mirror Slumped glass (300 mm) • Material reflecting surface: Ni • Figure error per mirror: 20” • Relative alignment: xxx J.W.den Herder 10

  11. Mirror simulation • On axis FWHM / HEW: 0.9 / 1.5 ’ • Off axis (42’) FWHM / HEW: 1.9 / 2.4 arcmin • vignetting J.W.den Herder 11

  12. Plot Aeff / off axis angle for few energies (0.5, 2 and 6 keV) • Plot Aeff / energy J.W.den Herder 12

  13. Mirror result • effective area: 1950 cm2 (without filters ?) • mass ~ 30 kg • Focal length 1 m • Mirror diameter 1.3 m • FoV 1.4 x 1.4o • Angular resolution 3 / 2 arcmin (HEW / FWHM) • Possible improvement: usage of multi-layer, optimization on auxiliary science (improving high (> 0.5 keV) response) • Optimization between angular scale per pixel, spectral resolution and focal length J.W.den Herder 13

  14. filters • Optimise transmission between O VIII line and O VII triplet • assumed 5 filters, 20 nm Al on 100 nm parylene: T = 0.58 For 50 / 100 nm Al T = 0.48 / 0.35 • Together with filling factor (0.9) a detector efficiency of 0.5 is reasonable J.W.den Herder 14

  15. Optical load • Optical load calculated for composite spectrum • Optical load will deteriorate resolution by: D E = h n I 0.5t0.5 where t is • Limiting magnitude for 1 eV contribution mv > 8 except for hot stars (O stars): mv > 18 (calculate effect of NH on O stars) J.W.den Herder 15

  16. Detectors TES micro-calorimeters can reach 2 eV requirement when optimized at low energies (4 eV at 6 keV proven) large arrays require automated production: micro-machining and NTD-Ge or doped Si thremistors not optimal Challenge: Large detector: large and many pixels, array read-out (FDM) But: • Low countrates • Small energy band J.W.den Herder 16

  17. Array production Bulk • Wet etching (simple) • Thermal link to bath ok (Cu coating on Si-Beams) • # pixels potentially limited by space for electrical wiring surface: • Rugged design • Additional space for wiring • Production process more difficult (surface protection needed during removal of saccrifical Poly-Si) J.W.den Herder 17

  18. Fundamental properties n = TES Joule heating (T3.4), a = the steepness of the transition, g corrects for temperature gradient over G (0.5). • Heat capacitance C= CTES + Cabsorber: comparablefor Ti/Au TES and Cu/Bi absorber (0.3 mm) • x ~ 1 for current devices (excess noise) but G ↓ for slow devices (teff = C T / a P with P = G DT (10 pW) and GTES ↑ : x → 0.2 x J.W.den Herder 18

  19. Large pixels Problem • Small GTES to keep CTES low (not over full area) • Small Cabsorber thus thin, but internal diffusion of electrons a problem Solution • Multiple TES • Different pixel shape • Additional Cu grid J.W.den Herder 19

  20. Multi TES simulations • Results from Marcel: pixel size, nr TES, expected resolution + figures of hexagonal, triangular, … pixels J.W.den Herder 20

  21. Other related missions (adapted from Suto et al. 2004) J.W.den Herder 21

  22. conclusions • Mission within reach with: • 1000 cm2 effective area • 1.4 x 1.4 deg Field of View (detector of 24 x 24 pixels of 1 mm2) • 2 eV resolution • Observing strategy: 10 x 10 degree will be imaged • Detection of filaments in mega-pixels (4 x 4 Mpc) up to z ~ 0.1 • Verification of filaments between clusters up to z ~ 0.25/0.30 • Some improvements compared to other proposed missions (MBE, DIOS) within reach but needs to be demonstrated experimentally (mirror design and large pixels) • International effort is required/sought to make such a mission feasible • A lot of other interesting science ……. J.W.den Herder 22

  23. additional science with arcmin resolution • the heliospheric X-ray emission • super nova remnants • turbulent broadening in cooling flows • accretion of fresh material onto clusters • chemical history of clusters and groups • the diffuse galactic medium: halo, galactic fountains • stellar coronae • hot stars • AGN • timing studies • Dark energy mapping by a cluster surveay J.W.den Herder 23

  24. detections • Calculate for these filaments EW to detect WHIM in single pixel, in 4 x 4 Mpc box and along filament (4 x 30 Mpc) • Assume 106 s exposure Hydrogen column densities low (1020 cm-2) or 2 10-7 cm-3 (TBC) J.W.den Herder 24 Cross section longitudinal selection

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