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تسجيل مستخدم جديدDetections of Warm-Hot Intergalactic Medium
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L. Zappacosta
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Several popular cosmological models predict that most of the baryonic mass in the local universe is located in filamentary and sheet-like structures associated with groups and clusters of galaxies. This gas is expected to be gravitationally heated to ~10^6 K and therefore emitting in the soft X-rays. We have investigated three fields with large scale structures of galaxies at redshifts 0.1, 0.45, 0.79 and found signatures of warm-hot thermal emission (kT< 1 keV) correlated with the distribution of galaxies for the first two. The correlation and the properties of both X-ray and galaxy distribution strongly suggest that the diffuse X-ray flux is due to extragalactic emission by the Warm-Hot Intergalactic Medium (WHIM) predicted by cosmological models.
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We assess the possibility to detect the warm-hot intergalactic medium (WHIM) in emission and to characterize its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIO
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atistics and baryonic content of intervening, low-z O VI and Lya absorption-line systems are presented with some comments on overlap between these two classes of absorbers and consequent baryon double-counting problems. From observations of a sample of 16 QSOs observed with the E140M echelle mode of STIS, we find 44 intervening O VI absorbers and 14 associated O VI systems [i.e, z(abs) ~ z(QSO)]. The implied number of intervening O VI absorbers per unit redshift is dN/dz(O VI) = 23+/-4 for rest equivalent width > 30 mA. The intervening O VI systems contain at least 7% of the baryons if their typical metallicity is 1/10 solar and the O VI ion fraction is <0.2. This finding is consistent with predictions made by cosmological simulations of large-scale structure growth. Recently, a population of remarkably broad Lya lines have been recognized in low-z quasar spectra. If these Lya lines are predominantly thermally broadened, then these H I absorbers likely harbor an important fraction of the baryons. We present and discuss some examples of the broad Lya absorbers. Finally, we briefly summarize some findings on the relationships between O VI absorbers and nearby galaxies/large-scale structures.
We observed the Seyfert I active galaxy/broad line radio galaxy 3C120 with the Chandra high energy transmission gratings and present an analysis of the soft X-ray spectrum. We identify the strongest absorption feature (detected at >99.9% confidence)
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3 sigma and 1.9 sigma confidence detections determined from Monte Carlo simulations). The combined significance of both lines is 3.0 sigma, 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 Comae. We detect emission by NeIX with a flux of 2.5+/-1.2 x 10^-8 photons cm^-2 s^-1 arcmin^-2 (90% confidence errors or 3.4 sigma 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 is permitted, values near the midpoint of the range are T = 4 x 10^6 K, n_H = 6 x 10^-6 cm^-3 corresponding to an overdensity with respect to the mean of 32, line of sight path length through it 41 Z/Zsolar^-1 Mpc where Z/Zsolar is the neon metallicity relative to solar. All of these properties are what has been predicted of the warm-hot intergalactic medium (WHIM), so we conclude that we have detected the WHIM associated with the Coma cluster.
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