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Paper: WHIM Environment of Giant Radio Galaxies
Volume: 395, Frontiers of Astrophysics: A Celebration of NRAO's 50th Anniversary
Page: 380
Authors: Subrahmanyan, R.; Saripalli, L.; Safouris, V.; Hunstead, R.W.
Abstract: Simulation studies of the warm-hot intergalactic medium (WHIM) suggest that about half of the baryons at low redshifts—the ‘missing baryons’— reside in a warm-hot phase. This gas is expected to occupy the intergalactic space in unvirialized and moderate overdensities associated with the large scale structure in the universe. Direct detection of these baryons is difficult, and progress in our understanding of the state of the WHIM requires observational probes of the diffuse gas associated with filaments and sheets.

Radio continuum images of the radio galaxy MSH J0505−2835 have been made using the Very Large Array (VLA). The double radio structure of this giant radio source has a projected linear size of 1.8 Mpc, extends well beyond the interstellar medium and any coronal halo associated with the host elliptical galaxy and is interacting with the ambient intergalactic medium. We have examined the 3-D structure in the large scale galaxy distribution in the vicinity of the radio source. The host elliptical galaxy is a member of a sheet-like galaxy overdensity that has a fractional density contrast of order 10. The radio source is located at the boundary between this moderate overdensity and an adjacent void and, therefore, the radio lobes of this giant radio source represent an interaction with ambient WHIM gas.

We present a novel method for estimating the properties of the WHIM. The radio data have been used to infer the evolution in the radio source. A lower limit of 4 × 10−15 N m−2 is derived for the pressure in the synchrotron-emitting gas in the lobes of the radio source, which leads to an estimate of 3×108 K m−3 for the density-temperature product in the ambient WHIM. Assuming that galaxies trace the unseen WHIM gas in these large-scale structures that represent moderate overdensities, the densities and temperatures we may expect for the ambient WHIM environment—based on the local galaxy overdensity and assuming that the WHIM gas is heated by hydrodynamic shocks associated with the forma- tion of large scale structure—falls at least an order of magnitude short of the expectations based on the radio properties of the source.

This leads us to conclude that the heating of theWHIM environment of this radio galaxy is perhaps dominated by astrophysical feedback on the WHIM from nearby galaxy concentrations, which heat gas that is located more than 2 Mpc away from the concentrations. Details of the work are given in Subrahmanyan et al., 2007, ApJ, 677, 63.

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