1. T. Ohashi (Tokyo Metropolitan University)
IXO and WHIM
T. Ohashi (Tokyo Metropolitan University)
Science of WHIM
Status of WHIM search (X-ray and UV)
Suzaku results on LSS and cluster outskirts
Expectation with IXO XGS
Summary

2. Thermal history of the universe
Big bang
Light elements
Recombination
1st stars
Reionization
Galaxies
Clusters
Large –scale structure
Present
Metal synthesis
Shock heating
Cooling by expansion
102 K 3m
0.38M
0.2G
0.8G 5G
13.7Gyr
Age of the Universe
104 K
Reionization by UV and X
106 K
IGM temperature
WHIM (warm-hot intergalactic medium) will tell us the evolution of the hot-phase material in the universe

3. Baryon phase Wide area in the baryon phase space is unexplored
Branchini et al. 09
Oxygen line probes the dark baryon efficiently
EDGE consortium
Bregman 07

4. Cosmic structure Dark matter Galaxies (~104K)
WHIM ( K) traces the cosmic large-scale structure = “Missing baryon”
Typical matter density: d (=n/nB) =
Yoshikawa et al. 2001, ApJ, 558, 520
size = 30 h-1 Mpc  5 deg at z=0.1
IGM ( K)
Cluster gas (107K)

5. Sculptor Wall by Chandra and XMM
Fang et al. 2010, ApJ 714, 1715
Scupltor wall (z = 0.03  0.002) via absorption of blazar H (z = 0.165)
XMM RGS (130 ks) + Chandra LETG (520 ks) combined
OVII (21.6 A) absorption line detected at z = 0.03 with 4.0s significance (EW = 26 mA)
If depth of L = 15 Mpc (filling the wall) and ZO = 0.1 solar assumed, overdensity becomes d  30
Consistent with WHIM filling the filament
Chandra

6. FUSE and XMM detection of WHIM
Nicastro et al. 2010, ApJ 715, 854
XMM RGS
PKS (z = ) shows OVIII (XMM) and HI Lyb (FUSE) absorption lines at z = 0.117
XMM RGS data with 900 ksec in total show 2.8s significance
FUSE data show Lyb (4s) but no OVI feature  T > 3.3  106 K
Metallicity 1% - 4% solar (absorption unlikely to be AGN outflow) and NH  1.5  1021 cm-2
Estimated T infers overdensity  300 and L  5 Mpc
OVIII (z = 0.116)
FUSE
HI Lyb (z = 0.118)

7. COS detection of nearby WHIM
Narayanan et al ApJ, 721, 960
Broad Lya (COS) and OVI (FUSE) at z = against Mrk 290 (z = )
Line width: T = 1.4  105 K
OVI is likely to be photoionized (combination of non-equilibrium coll. ion. and photoionization necessary)
Large-scale filament (20) exists
Possible connection with NGC5987, at about 400 kpc away from the absorption system

8. COS study of distant WHIM
Narayanan et al ApJ, 730, ---
NeVIII and OVI (both with COS) absorption at z = against PKS (z = 0.57)
Line data: T  5  105 K, NH = cm-2, ZNe  0.25 solar
NeVIII probes collisionally ionized gas, while OVI is likely to be photoionized
Hot halo of a galaxy or WHIM
NeVIII useful in studying coll. ion. gas

9. Suzaku search for WHIM
Suzaku is searching for WHIM in cluster outskirts and in superclusters, with no positive detection of redshifted O lines yet
Suzaku is giving fairly low upper limits (d < 300 assuming line-of-sight depth of 2 Mpc and ZO = 0.1 solar)
Suzaku will continue searching for WHIM in all possible locations

10. Cluster outskirts with Suzaku
Rvir (2.7 Mpc)
A2142 outskirt
Akamatsu et al in prep
A1413 outskirt
Rvir
Hoshino et al PASJ
Significant X-ray emission detected out to Rvir
Systematic errors due to fluctuation of CXB, Galactic background, non X-ray background, XIS filter contamination evaluated
Effect of stray light from bright center less than 7% of the observed flux

11. Cluster outskirts with Suzaku
"Uniform" temperature profile
by Burns et al. 2010, ApJ 721, 1105
Akamatsu et al in prep
A2142
r1.1
K = kT/n2/3
Entropy drop at > 0.5 rvir is seen in several clusters
Clumpiness explains only a few % drop
Non equilibrium (Ti > Te) more likely?
Nagai and Lau 2011 ApJL

12. Filament junction by Suzaku
Search for (and detection of ) X-ray emission from large-scale junction of filaments
Kawahara et al ApJL 727, L38
DisPerSE : filament extractor
Sousbie 2010, Sousbie, Pichon, & Kawahara 2010
RASS map with SDSS galaxies
LOS

13. Suzaku J1552+2739: a group of galaxies
X-ray intensity contour
Hardness ratio map
1.64 keV
"hot spot" 3.91 keV
NXB subtracted & vignetting corrected image
LX = 2.4  1043 erg/s
Likely to be a group undergoing major merger
Filament junction could host many undetected X-ray groups
These should explain some of the missing baryons

14. IXO: grating spectrometer
Big jump from Chandra and XMM-Newton grating spectrometers by factor of > 10 in effective area and times higher resolution
Sensitive to Equivalent Width  2 meV
R = 3000 can resolve v = 100 km/s, such as structures of galactic winds
l/Dl

15. IXO: absorption study
OVII, OVIII absorptions: WHIM presence beyond any doubt
Predicted dN/dz of OVII, OVIII clouds (normalized with OVI results): several absorption systems per AGN will be detected
There are > 100 useful AGNs for absorption study (FX > 5  cgs), and observation of 30 AGNs will reveal 100 WHIM clouds
IXO: 600 ksec
OVII
OVI
OVIII 1 10
100
0.1
IXO
dN/dz
EW (mÅ)
Bregman et al. IXO-WP

16. WHIM emission study
Grasp of XMS: equally large as those of dedicated missions
5” angular resolution resolves 16 kpc at z = 0.2 (galactic outflow scale)
Grasp
/ORIGIN
Simulated spectrum
WHIM
Galactic

17. WHIM search using resonance scatting
Churazov et al. 2001, MN 323, 93 Churazov, 2010, Space Sci. Rev. 157, 193
WHIM can be surrounding bright AGNs or groups
Part of continuum X-rays undergoes resonant scattering by WHIM gas
For d ~ 30, a few Mpc region around bright AGNs will shine in OVII and/or OVIII lines
Rough estimation shows that an AGN with LX = 1046 erg/s at z = 0.2 can produce about 100 OVII counts with IXO over ~ 5 arcmin region in 100 ksec observation
Weaker or comparable to the thermal line intensity, but this is an additional emission scaling with n

18. Resonance scattering from WHIM
AGN/group
WHIM
O line
Mpc scale halo
AGN (or gal. group) X-rays will be resonantly scattered by OVII and OVIII ions in surrounding WHIM
A few Mpc scale extended halo of O lines is expected
Radial profile is much flatter than thermal emission from group gas
S. brightness
OVII from group
r-3
r-1
WHIM halo r

19. Summary
WHIM will give us unique information about thermal and chemical evolution of the universe
Absorption and emission studies with IXO will reveal all phases of warm-hot baryons within z  0.5
Absorption study with IXO will probe low-density WHIM clouds (d < 100)
Emission measurement will also show us the spatial structure (filaments, outflows) of WHIM
Resonance scattering may show oxygen-line halos with ~ Mpc scale around bright objects