X-Ray Large Scale Structure and XMM

The formation of Large Scale Structures (LSS) in the universe was first studied at optical wavelengths as the galaxy spatial distribution appeared to be far from homogeneous. Considerable effort has been invested in semi-analytical approaches and in numerical simulations (DM + hot gas) to explain the observed structures, given some set of initial conditions and using additional constraints provided by the COBE results. It is now clear however, that these two extreme data set are not sufficient to discriminate between the possible remaining cosmological scenarios. It is thus timely to investigate LSS at a much higher redshift than the present survey limits both in the optical and in other wavebands. In this context, the X-ray band will certainly become a hot field with the advent of the XMM observatory. The next section briefly summarizes what is known about LSS from optical wavelengths and simulations. Sect. 3 reviews the particular points that can be addressed in the X-ray band. Last section presents realistic prospects for mapping LSS with XMM.