No description available.

The first part of the thesis presents the results from unbiased surveys at millimetre (1200 <i>μ</i>m) and radio (1.4 GHz) wavelengths of the ELAIS N2 and Lockman Hole East fields both of which have previously been mapped at 850 <i>μ</i>m. From the first survey the most accurate number counts at 1200 <i>μ</i>m to date are derived and are found to match simple parametric models of galaxy evolution remarkably well. Exploiting the well-matched data in all three wavebands we address the issue of the stability of low signal-to-noise (sub)mm surveys and extract an extremely robust sample of sources detected in the radio and both of the (sub)mm bands. Constraints are also imposed on the redshift distribution of submm sources using spectral templates representative of local starburst galaxies. The radio data is used in conjunction with optical/near-infrared imaging to obtain robust radio counterparts and thereby pinpoint the location of the optical/near-infrared host galaxies for an unprecedented large sample of submm sources. The optical/near-infrared colours and morphologies are summarised revealing that about 60 per cent of the host galaxies display highly structured or complex morphology, suggestive of merging or interacting systems. In the second part of the thesis the potential of the molecule carbonmonoxide (CO) to trace gas and the properties of the interstellar medium of galaxies at high redshifts is explored. A simple numerical code which simulates the non-LTE excitation conditions of CO in a spherical molecular cloud of H₂ is constructed and is subsequently used to constrain the density and kinetic temperature in two case-studies of high redshift galaxies. Finally, the results from a first systematic interferometric CO survey of luminous submm galaxies are presented. The bulk properties such as gas mass and CO linewidths of an unprecedented large sample of bright submm galaxies are derived and compared with local starburst galaxies as well with other galaxy populations at high redshifts. Based on the average dynamical and total baryonic masses as well as the typical gas exhaustion time of submm galaxies an evolutionary scenario is proposed which attempts to link them to massive evolved galaxies at <i>z</i> ~1 and old giant ellipticals at the present day. Lower limits are imposed on the co-moving number density of massive galaxies at high redshifts and a comparison with predictions from semi-analytical models of galaxy formation reveals the shortcomings of current models to explain the rapid assembly of massive galaxies in the early Universe.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.