Search for WHIM around A2744 using Suzaku

• Published in: arXiv.org
• Main Authors: Hattori, Shiho, Ota, Naomi, Yu-Ying, Zhang, Akamatsu, Hiroki, Finoguenov, Alexis
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 07.02.2017
• Subjects: Computer simulation; Deposition; Emission analysis; Galactic clusters; Galaxies; Intergalactic media; Line spectra; Photons; Physics - High Energy Astrophysical Phenomena; Predictions; Red shift; Shock heating; Soft x rays; Surface brightness; Temperature distribution; X ray spectra
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1702.02157

We present the results from the Suzaku satellite of the surrounding region of a galaxy cluster, A2744, at \(z=0.3\). To search for oxygen emission lines from the warm-hot intergalactic medium (WHIM), we analyzed X-ray spectra from two northeast regions 2.2-3.3 and 3.3-4.4 Mpc from the center of the cluster, which offers the first test on the presence of a WHIM near the typical accretion shock radius (\(\sim 2r_{200}\)) predicted by hydrodynamical simulations. For the 2.2-3.3 Mpc region, the spectral fit significantly (99.2% significance) improved when we include OVII and OVIII lines in the spectral model. A comparable WHIM surface brightness was obtained in the 3.3-4.4 Mpc region and the redshift of OVIII line is consistent with \(z=0.3\) within errors. The present results support that the observed soft X-ray emission originated from the WHIM. However, considering both statistical and systematic uncertainties, OVIII detection in the northeast regions was marginal. The surface brightness of the OVIII line in \({\rm 10^{-7} photons\,cm^{-2}s^{-1}arcmin^{-2}}\) was measured to be \(2.7\pm 1.0\), \(2.1 \pm 1.2\) for the 2.2-3.3, 3.3-4.4 Mpc regions, giving the upper limit on the baryon overdensity of \(\delta = 319 (<443)\), \(283 (<446)\), respectively. This is comparable with previous observations of cluster outskirts and their theoretical predictions. The future prospect for WHIM detection using the Athena X-IFU micro-calorimeter is briefly discussed here. In addition, we also derived the ICM temperature distribution of A2744 to detect a clear discontinuity at the location of the radio relic. This suggests that the cluster has undergone strong shock heating by mass accretion along the filament.