Search for warm-hot gas associated with the Virgo cluster

The amount of baryons detected so far at z0 is only about 2030% of thatdetected at z2, or calculated from the standard bigbang nucleosynthesis.This missing baryon. problem is now one of the most important topics incosmology. Recent simulations predict that most of the baryons in the presentUniverse reside in a warmhot intergalactic medium with temperatures of10^5 10^7 K, associated with clusters of galaxies. In order to probe thiswarmhot gas, we propose to observe a quasar behind the Virgo cluster withRGS, and measure the resonant absorption line of O VIII Ly alpha at 653.6eV.This provides a unique opportunity to settle the missing baryon problem andto understand the formation of the largescale cosmological structure. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]