On the lack of strong O-line excess in the Coma cluster outskirts from Suzaku

Abstract

About half of the baryons in the local Universe are thought to reside in the so-called warm-hot intergalactic medium (WHIM) at temperatures of 0.1-10 million K. Thermal soft excess emission in the spectrum of some cluster outskirts that contains OVII and/or OVIII emission lines is regarded as evidence of the WHIM, although the origin of the lines is controversial due to strong Galactic and solar system foreground emission. We observed the Coma-11 field, where the most prominent thermal soft excess has ever been reported, with Suzaku XIS in order to make clear the origin of the excess. We did not confirm OVII or OVIII excess emission. The OVII and OVIII intensity in Coma-11 is more than 5 sigma below that reported before and we obtained 2 sigma upper limits of 2.8 and 2.9 photons cm^-2 s^-1 sr^-1 for OVII and OVIII, respectively. The intensities are consistent with those in another field (Coma-7) that we measured, and with other measurements in the Coma outskirts (Coma-7 and X Com fields with XMM-Newton). We did not confirm the spatial variation within Coma outskirts. The strong oxygen emission lines previously reported are likely due to solar wind charge exchange.

arXiv comment5 pages, 3 figures. Accepted for publication in ApJ

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• Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction
• Suzaku X-Ray Observations of the Accreting NGC 4839 Group of Galaxies and the Radio Relic in the Coma Cluster
• Search for X-Ray Emission Associated with the Shapley Supercluster with Suzaku
• Suzaku Observations of Iron K-lines from the Intracluster Medium of the Coma Cluster
• The diffuse soft excess emission in the Coma cluster from the ROSAT All-Sky Survey
• Joint analysis of X-ray and Sunyaev Zel'dovich observations of galaxy clusters using an analytic model of the intra-cluster medium
• Suzaku Constraints on the Soft and Hard Excess Emissions from Abell 2199
• A new way of detecting intergalactic baryons
• Soft X-ray excess of clusters: a thermal filament model, and the strong lensing of background galaxy groups
• Characterization of the warm--hot intergalactic medium near the Coma cluster through high--resolution spectroscopy of X Comae