High redshift CO line emission: perspectives

Although about a dozen high redshift (z larger than 2) starburst galaxies have been recently detected in the CO lines, spectroscopic detections of molecular gas of very young galaxies are still very difficult. The CO lines are usually optically thick, which limits greatly the increase of emission with redshift, as observed for the dust continuum. However the future instruments (LMT, ALMA, etc..) will allow large progress in this domain, and perspectives are discussed. Computations are based on a simple extrapolation of what is known of starbursting galaxies at lower redshift.