High resolution CO imaging of high redshift QSO host galaxies
  We review recent high-resolution CO observations of distant QSOs obtained at the Very Large Array. The aim of these observations is to resolve the molecular gas distribution in these extreme objects both spatially and in velocity space. They provide unique information regarding the small-scale distribution, the extent, and the brightness temperatures of the molecular gas in these early systems. E.g., the structure and dynamics of the molecular gas may reveal whether or not mergers can be the cause of the ongoing starburst activity. The observations also allow for a first estimate of the dynamical gas mass. Currently, only the VLA is able to obtain resolutions in CO of up to 0.15" which is needed to resolve typical galactic structures of sizes ~1 kpc. We present new high-resolution VLA imaging of high-z QSOs (BRI 1335-0417, APM 08279+5255 and J1148+5251). These observations pave the road to future ALMA observations where resolutions of order 0.1'' will be obtained routinely. 
F. Walter (MPIA), D. A. Riechers (MPIA), C. L. Carilli (NRAO), F.   Bertoldi (AIfA Bonn), A. Weiss (MPIfR), P. Cox (IRAM)