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TRACING BRIGHT AND DARK SIDES OF THE UNIVERSE WITH X-RAY OBSERVATIONS
SUTO YASUSHI,YOSHIKAWA KOHJI,DOLAG KLAUS,SASAKI SHIN,YAMASAKI NORIKO Y.,OHASHI TAKAYA,MITSUDA KAZUHISA,TAWARA YUZURU,FUJIMOTO RYUICHI,FURUSHO TAE,FURUZAWA AKIHIRO,ISHIDA MANABU,ISHISAKI YOSHITAKA The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
X-ray observations of galaxy clusters have played an important role in cosmology, especially in determining the cosmological density parameter and the fluctuation amplitude. While they represent the bright side of the universe together with the other probes including the cosmic microwave background and the Type Ia supernovae, the resulting information clearly indicates that the universe is dominated by dark components. Even most of cosmic baryons turns out to be dark. In order to elucidate the nature of dark baryons, we propose a dedicated soft-X-ray mission, DIOS (Diffuse Intergalactic Oxygen Surveyor). Recent numerical simulations suggest that approximately 30 to 50 percent of total baryons at z = 0 take the form of the warm-hot intergalactic medium (WHIM) with $10^5K < T < 10^7K $which has evaded the direct detection so far. The unprecedented energy resolution (${\~} 2eV$) of the XSA (X-ray Spectrometer Array) on-board DIGS enables us to identify WHIM with gas temperature $T = 10^6 {\~} 10^7K$ and overdensity $\delta$ = 10 ${\~}$ 100 located at z < 0.3 through emission lines of OVII and OVIII. In addition, WHIMs surrounding nearby clusters are detectable with a typical exposure time of a day, and thus constitute realistic and promising targets for DIOS.
Searching for cosmic missing baryons with DIOS - Diffuse Intergalactic Oxygen Surveyor -
Yasushi Suto,Akihiro Furuzawa,Kazuhisa Mitsuda,Manabu Ishida,Noriko Y. Yamasaki,Ryuichi Fujimoto,Shin Sasaki,Tae Furusho,Takaya Ohashi,Yoshitaka Ishisaki,Yuzuru Tawara 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
Approximately 30 to 50 percent of the total baryons in the present universe is supposed to take the form of wa arm/hot intergalactic medium (WHIM) whose X-ray continuum emission is very weak. In order to carry out a direct and homogeneous survey of elusive cosmic missing baryons, we propose a dedicated soft-X-ray mission, DIOS (Diffuse Intergalactic Oxygen Surveyor). The unprecedented energy resolution ( 2eV) of the XSA (X-ray Spectrometer Array) on-board DIOS enables us to identify WHIM with gas temperatures T = 106က7K and overdensity = 10က100 located at z < 0:3 through emission lines of Ovii and Oviii. DIOS, which will hopefully be launched in several years time, promises to open a new window of detection and characterization of cosmic missing baryons and to provide yet another important and complementary tool to trace the large-scale structure of the universe.