小型専用Ｘ線ミッションによるダークバリオン探査
DIOS (Diffuse Intergalactic Oxygen Surveyor) 計画の紹介「次世代天文学 －大型観測装置とサイエンスー」
シンポジウム須藤 靖 (東大物理)吉川耕司
河原 創 (東大物理)佐々木 伸 (都立大)河合誠之(東工大)
松下恭子(東京理科大)
鶴剛(京大物理)山崎 典子(JAXA/ISAS)
満田 和久 (JAXA/ISAS)
古庄 多恵 (JAXA/ISAS)
藤本 龍一 (JAXA/ISAS)
竹井 洋 (JAXA/ISAS)
大橋 隆哉 (都立大)石崎 欣尚 (都立大)石田 学 (都立大)田原 譲 (名古屋大)
古澤 彰浩 (名古屋大)（東京大学）Missing Baryon (aka Dark Baryon)
Cosmic Baryon Budget
0.0041
ofHItheis0.0068“DARK”
vs WBBN = 0.04 (h=0.7)
W99%+ Wuniversestar + W
H + WICM =−0.0030
2

Fukugita, Hogan, & Peebles (1998) ApJ, 503, 518

http://map.gsfc.nasa.gov

more than 50% of cosmic baryon is “DARK”
and evaded the direct detection so far.

“Where are the dark baryons and in what form?”

Warm-Hot Intergalactic Medium
30~40% of the cosmic baryon at z=0 is in the form ofdiffuse gas with temperature of 105 K to 107 K.

Warm-Hot Intergalactic Medium (WHIM) [(h)wím]
galaxies

dark matter

30Mpc/h(T<105 K)(T>107 K)

hot gas(T>107K)

WHIM(105K<T<107K)

redshiftCen & Ostriker (1999)

WHIM as Missing Cosmic Baryon
About 40% of the total cosmic baryons may
exist as Warm-Hot Intergalactic Medium(WHIM) with 105K<T<107K
WHIM is supposed to distribute diffusely
in filamentary structures and small
galaxy groups
Direct detection of WHIM is difficult
very faint emission in soft X-ray waveband due tolow temperature and low density– strong contamination in actual observation
foreground : X-ray emission of diffuse gas in our Galaxy
background : Cosmological X-ray Background (CXB)–X-ray Forest: Absorption Features of WHIM
in Spectra of Background BeaconsI

QSO continuum spectrum
metal absorption line0 1 z wavelength

WHIM can be seen as absorption lines of ionized heavy elements(OVI-VIII, NeIX-X, NVI-VII, CV-VI) using XMM-Newton, Chandra,and FUSE.

X-ray Forest : Shadow of WHIM
WHIM associated with Virgo cluster is “detected” with 2.6-s
in the XMM-Newton spectrum of a QSO behind Virgo cluster.
Fujimoto et al. PASJ (2004) in press
OVIII redshifted to Virgo cluster
rest wavelength of OVIIIVirgo cluster

QSO : LBQS 1228+1116

ROSAT All Sky Survey Image

Emission Lines of Oxygen in WHIM
We propose the observation of WHIM
through
7T=10K
its oxygen line emission instead of absorption.

systematic WHIM survey
3-dimensional structure andphysical properties of WHIM

T=106.5K

OVII (561eV, 568eV, 574eV, 665eV)OVIII (653eV)

Why oxygen emission lines ?
Effective tracers of gas with T=106-107K
Most abundant other than H and He
No other prominent lines in E=500-660eV

T=106K

Simulated Surface Brightness on the Sky
0.5-2.0keV X-ray emission

0.0< z < 0.3

0.03 < z < 0.04

0.09 < z < 0.11

OVII and OVIII line emission

0.0< z < 0.3

0.03 < z < 0.04

0.09 < z < 0.118

Requirement for the Instruments
Identification of emission lines from various redshift
X-ray spectrometer with high energy resolution : DE < 5eV
Also important for segregation from Galactic line emission
Superconducting TES micro-calorimeter
DE < 2eV at 0.3<E<1.5keV
16×16 array
Large field-of-view and effective area
Need to grasp very weak emission of spatially diffuse WHIM
High throughput of X-ray telescope : SeffWFOV > 50cm2deg2
Four-reflection X-ray Telescope
SeffWFOV ~ 200hcm2deg2 at E=0.6 keV
WFOV ~ 1°×1°

DIOS Project
Diffuse Intergalactic Oxygen Surveyor (DIOS)
specification of the telescope and detector
SeffWFOV=100cm2deg2, WFOV ~ 1°×1°, DE=2eVlight weight (<500kg) and dedicatedsattelite to observe the WHIM emission⇒ poster p26
Primary observational target
Mapping of a few 100deg2 field in 2-year operation up to z~0.3
Pointing observations of large scale structures in the local universe
Detecting the absorption lines of WHIM in QSO and GRB afterglow spectraExample of Simulated Spectra
1x1 deg2
Texp=3x105 sec

Galactic emssion + CXB + WHIM emission

Observed raw spectra arecontaminated by strong CXB andGalactic emission
After subtracting contaminating
spectra, intrinsic WHIM spectra
can be obtained

residual WHIM spectrum

Example of Simulated Spectra
0.3x0.3 deg2
Texp=106sec

OVIII at z=0.2

WHIM emission is “detectable”
if the assumed specification isrealized

OVIII & OVII at z=0.11OVIII at z=0.04

DIOS View of the Local Universe
OVII and OVIII emission in the Super-Galactic plane
0.5-2.0 keV

OVIII+OVII

Filament and supercluster structures will be detected by DIOS

What Can Be Seen by DIOS
Fraction of detectable baryon for a give limiting flux

20-30% of the cosmic baryon will be newly detected by DIOS
Only high temperature (T>106 K) portion of WHIM can be detected
through its emission
Need for the complementary detection oflow temperature WHIM using its absorption feature

X-ray Forest in GRB Afterglow Spectra
GRB afterglow can be a good background beacon todetect WHIM through its metal absorption features.
Simulated observation of a typical GRB afterglow (~ 40/year)
30ksec exposure from 400sec
after the burst

OVII and OVIII absorption line at z~0.2

X-ray Forest in GRB Afterglow Spectra
Distribution function of equivalent widthof OVII and OVIII absorption lines
After GRB afterglow decayed,
DIOS can try to detect WHIM
through its emission.

Constrains on oxygen metallicity
and filling factor of WHIM using
both of its emission and absorption

3s detection for a typical GRB afterglow

DIOS is planned to be equipped with flexible pointing system for GRBs.

Mission and Science Goal
Detection of WHIM with T>106 K through its emission
blind survey of WHIM by mapping of a few 100deg2 field
pointing observation of known large-scale structures in the local universe
Detection of WHIM metal absorption line systems in GRB spectra
complementary search of low temperature WHIM with T<106 K
detection of WHIM both through its emission and absorption featuresphysical properties of WHIM (density, temperature, metallicity)
ionization states of metals ⇒ thermal history of baryons
WHIM distribution (⇔ dark matter/galaxy distribution)

Dynamics of ISM and ICM
Galactic fountain, ICM turbulence