2006/10/13 by Yoh Takei, J. P. Henry, J. Patrick Henry +7 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Coma (optics) #Coma Cluster #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Intergalactic travel #Metallicity #Neon #Physics #Redshift #astro-ph
paper · pdf · doi:10.1086/510278
published as Astrophys.J.655:831-842,2007 · 13 pages, 14 figures. Accepted for publication in ApJ
arxiv created 2006/10/13 · openalex publication_date 2007/01/23 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Hydrodynamic simulations predict that low-redshift baryons are predominantly in a warm-hot intergalactic medium (WHIM), which should exhibit absorption and emission lines in the soft X-ray region. The WHIM is predicted to be most dense around clusters of galaxies. We present our XMM-Newton RGS observations of X Comae, an active galactic nucleus behind the Coma Cluster. We detect absorption by Ne IX and O VIII at the redshift of Coma with an equivalent width of 3.3 ± 1.8 and 1.7 ± 1.3 eV, respectively (90% confidence errors or 2.3 and 1.9 σ confidence detections determined from Monte Carlo simulations). The combined significance of both lines is 3.0 σ, again determined from Monte Carlo simulations. The same observation yields a high-statistics EPIC spectrum of the Coma Cluster gas at the position of X Com. We detect emission by Ne IX with a flux of (2.5 ± 1.2) × 10 -8 photons cm -2 s -1 arcmin -2 (90% confidence errors or 3.4 σ confidence detection). These data permit a number of diagnostics to determine the properties of the material causing the absorption and producing the emission. Although a wide range of properties are permitted, values near the midpoint of the range are temperature ~4 × 10 6 K, density ~6 × 10 -6 cm -3 corresponding to an overdensity with respect to the mean of ~32, and line-of-sight path length through it ~41( Z / Z ☉ ) -1 Mpc, where ( Z / Z ☉ ) is the neon metallicity relative to solar. These are properties that have been predicted of the WHIM, so we conclude that we have detected the WHIM associated with the Coma Cluster.