8th HEAD Meeting, 8-11 September, 2004
Session 3 Surveys and the Cosmic X-ray Background
Poster, Wednesday, September 8, 2004, 9:00am-10:00pm

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[3.07] Autocorrelation Function Using XMM-Newton for the Detection of the WHIM

E. Ursino, M. Galeazzi (University of Miami)

The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ''warm-hot'' (105 - 107 K) filamentary gas, distributed in the intergalactic medium (WHIM). It is currently believed that a significant fraction (~ 10 %) of the diffuse x-ray background in the energy band 0.5-1 keV is due to thermal emission from this intergalactic medium.

Due to the filamentary structure of the WHIM, its X-ray emission should have a characteristic angular distribution. Measuring the autocorrelation function is therefore an ideal tool for the detection of the WHIM. So far, using data from the ROSAT satellite it has been possible to probe angular scales of more than 2'. Models of the WHIM distribution predict a characteristic scale for soft X-Ray emission between 7'' and 10'. Using observation data from XMM-Newton, we intend to determine the angular correlation at scales in the 0'.2-30' range.

Our investigation includes the analysis of data from the XMM-Newton archive, as well as two dedicated observations in the direction of MBM-20 and an ''empty'' field nearby. The criteria of choice for the archival data are high galactic latitude (b>30o), long observing time (t>70000 s), and absence of bright sources in the field of view. The analysis is focused on events in the energy range 0.5-1 keV, where the majority of the WHIM contribution is expected.

We present here the first results from our analysis, our treatment of point sources and of background noise. We finally confront our results with data from previous analysis, to check the validity of our approach.

The author(s) of this abstract have provided an email address for comments about the abstract: ursino@physics.miami.edu

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