X-Ray Absorption by the Warm-Hot Intergalactic Medium in the Hercules Supercluster

Abstract

The "missing baryons", in the form of warm-hot intergalactic medium (WHIM), are expected to reside in cosmic filamentary structures that can be traced by signposts such as large-scale galaxy superstructures. The clear detection of an X-ray absorption line in the Sculptor Wall demonstrated the success of using galaxy superstructures as a signpost to search for the WHIM. Here we present an XMM-Newton Reflection Grating Spectrometer (RGS) observation of the blazar Mkn 501, located in the Hercules Supercluster. We detected an O VII K$\alpha$ absorption line at the 98.7 % level ($2.5\sigma$) at the redshift of the foreground Hercules Supercluster. The derived properties of the absorber are consistent with theoretical expectations of the WHIM. We discuss the implication of our detection for the search for the "missing baryons". While this detection shows again that using signposts is a very effective strategy to search for the WHIM, follow-up observations are crucial both to strengthen the statistical significance of the detection and to rule out other interpretations. A local, $z\sim 0$ O VII K$\alpha$ absorption line was also clearly detected at the $4\sigma$ level, and we discuss its implications for our understanding of the hot gas content of our Galaxy.

5 pages, 2 figures, 2 tables, Accepted for publication on ApJ Letters

References in corpus (6)

• X-Ray Absorption from the Milky Way Halo and the Local Group
• Physical Properties, Baryon Content, and Evolution of the LyαForest: New Insights from High Resolution Observations at z < 0.4
• Chi-square and Poissonian Data: Biases Even in the High-Count Regime and How to Avoid them
• The Void Phenomenon Explained
• On the Putative Detection of z>0 X-ray Absorption Features in the Spectrum of Markarian 421
• Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304

Cited by in corpus (11)

• XMM-Newton Survey of Local O VII Absorption Lines in the Spectra of Active Galactic Nuclei
• X-Ray Detection of Warm Ionized Matter in the Galactic Halo
• Missing baryons traced by the galaxy luminosity density in the large-scale WHIM filaments
• A possible Chandra and Hubble Space Telescope detection of extragalactic WHIM towards PG 1116+215
• Oxygen, neon, and iron X-ray absorption in the local interstellar medium
• X-ray absorption towards high-redshift sources: probing the intergalactic medium with blazars
• Hot WHIM counterparts of FUV OVI absorbers: Evidence in the line-of-sight towards quasar 3C 273
• Diffuse Low-Ionization Gas in the Galactic Halo Casts Doubts on $z\simeq 0.03$ WHIM Detections
• Implications of an updated ultraviolet background for the ionization mechanisms of intervening Ne VIII absorbers
• Systematic errors in the maximum likelihood regression of Poisson count data: introducing the overdispersed chi-square distribution
• A search for the missing baryons with X--ray absorption lines towards the blazar 1ES 1553+113