PROBING DENSITY-FLUCTUATIONS AT LOW AND HIGH-REDSHIFT

We discuss cosmological inference from galaxy surveys at low and high redshifts. Studies of optical and IRAS redshift surveys with median re dshift (z) over bar similar to 0.02 yield measurements of the density parameter Omega and the power-spectrum of density fluctuations? but bo th cannot easily be related to the properties of the underlying mass d istribution due to the uncertainty in the way galaxies are biased rela tive to the mass distribution. Moreover, currently little is known abo ut fluctuations on scales intermediate between local galaxy surveys (s imilar to 100h(-1) Mpc) and the scales probed by COBB (similar to 1000 h(-1) Mpc). We focus here on several issues, as examples of clustering on different scales: the extent of the Supergalactic Planer, an optim al reconstruction method of the density and velocity fields, the effec t of biasing on determination of Omega from redshift distortion, the f uture big surveys SDSS and 2dF (with median redshift (z) over bar simi lar to 0.1) and radio sources and the X-Ray Background as useful probe s of the density fluctuations at higher redshift ((z) over bar similar to 1).