X-ray study of clusters at the outer edge and beyond

Abstract

We report on recent Suzaku results on cluster outer regions. Relaxed clusters show a monotonous temperature decline to the virial radii, reaching 1/3 to 1/4 of the central levels. Significant temperature jumps have been confirmed for a number of radio relics, including A 3667, A 3376, and CIZA J2242.8+5301. This confirms that the radio relics generally correspond to shock fronts with the Mach numbers around 3. New filament junctions are identified by a new algorithm applied to the SDSS galaxy distribution and show significant X-ray emission with Suzaku. The emission agrees with the L_X-kT relation for elliptical galaxies and galaxy groups, and the junctions can be a important baryon reservoir. We propose a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), equipped with microcalorimeters with a wide field of view (∼ 50 arcmin), which will detect the emission from warm-hot intergalactic medium (WHIM) and measure detailed thermal and dynamical properties of the gas accreting onto clusters from the filaments.