Observational Evidence of the WHIM

Details Observational Evidence of the WHIM Observational Evidence of the WHIM

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.0732f&link_type=abstract

American Astronomical Society, HEAD meeting #9, #7.32; Bulletin of the American Astronomical Society, Vol. 38, p.354

Mathematics

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Scientific paper

About a year ago, we presented the first observational evidence for the existence of the Warm-Hot Intergalactic Medium (WHIM). Two WHIM filaments at cosmological distances were found to to lie along our line of sight to the nearby blazar Mkn 421, through the detection, in the exceptionally high-quality Chandra-LETG spectrum of this source, of two absorption line systems by highly ionized intervening gas clouds.
Although by no mean conclusive, such evidence confirmed for the first time the predictions of all hydro-dynamical simulations for the formation of structures in a Λ-CDM Universe and suggested a definitive solution to the long-standing paradox of the Missing Baryons.
Recently, the significance of these detections has been questioned in two companion articles lead by XMM-RGS calibrators, on the basis that: (a) the same systems are non detected in the RGS spectrum of Mkn 421, and (b) the systems present in the Chandra-LETG spectrum of Mkn 421 would have a significance much lower than that reported by us originally.
Here we demonstrate that (a) the quality of the XMM-RGS spectrum is not sufficient to disprove the Chandra detections, and (b) proper Montecarlo simulations asses the significance of the Chandra detections to levels very close to those originally published and based on F-tests.
We conclude based on our re-analysis of the Chandra-LETG and XMM-RGS spectrum of Mkn 421 and on the new comparative analysis of other Chandra and XMM continuum-spectra that, due to its worse resolving power, the XMM-RGS is about 3-4 times less efficient than the Chandra-LETG for the detection of unresolved, faint absorption lines.
In this contribution we will also discuss future possibilities for WHIM studies and presnt a new MIDEX concept called Pharos.
F.N. acknowledges support from NASA-LTSA, Chandra and XMM-Newton funds.

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