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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
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

slide2

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

slide3

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

absorption line forest
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

in emission between clusters
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

filaments
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

requirements
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

key technology
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

mirrors
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

mirror production and error budget
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

mirror simulation
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

slide12
Plot Aeff / off axis angle for few energies (0.5, 2 and 6 keV)
  • Plot Aeff / energy

J.W.den Herder

12

mirror result
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

filters
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

optical load
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

slide16

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

array production
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

fundamental properties
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

large pixels
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

multi tes simulations
Multi TES simulations
  • Results from Marcel: pixel size, nr TES, expected resolution + figures of hexagonal, triangular, … pixels

J.W.den Herder

20

other related missions
Other related missions

(adapted from

Suto et al. 2004)

J.W.den Herder

21

conclusions
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

slide23

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

detections
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