Detecting the Warm-Hot Intergalactic Medium through X-ray Absorption Lines

Details Detecting the Warm-Hot Intergalactic Medium through X-ray Absorption Lines Detecting the Warm-Hot Intergalactic Medium through X-ray Absorption Lines

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011head...12.3620y&link_type=abstract

American Astronomical Society, HEAD meeting #12, #36.20

Astronomy and Astrophysics

Astronomy

Scientific paper

The warm-hot intergalactic medium (WHIM) at temperatures 1E5-1E7 K is believed to contain 30-50% of the baryons in the local universe. However, all current X-ray detections of the WHIM at redshifts z>0 are of low statistical significance (<=3sigma) and/or controversial. In this work, we aim to establish the detection limits of current X-ray observatories and explore requirements for next generation X-ray telescopes in study of the WHIM through X-ray absorption lines. We analyze all available grating observations of Mrk 421 and obtain spectra with signal-to-noise ratios (S/Ns) of 90 and 180 per 50 mA spectral bin from Chandra and XMM observations, respectively. Although these spectra are two of the best ever collected with Chandra and XMM, we cannot confirm the two WHIM systems reported by Nicastro et al. in 2005. Our bootstrap simulations indicate that spectra with such high S/Ns canNOT constrain the WHIM with N(OVII)=1E15 cm^{-2} (corresponding to an equivalent width of 2.5 mA) at >=3sigma significance level. The simulation results also suggest that it would take >60 Ms for Chandra and 140 Ms for XMM to constrain the N(OVII) at >4sigma from a spectrum of a background QSO with flux of 0.2 mCrab. Future X-ray spectrographs need to be equipped with spectral resolution R 4000 and effective area A 100 cm^2 to accomplish the similar constraint with an exposure time of 2 Ms, and would require 11 Ms to survey the 15 QSOs with flux >=0.2 mCrab along which clear intergalactic OVI absorbers have been detected.

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