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We present new MERLIN observations of both the radio continuum and neutral hydrogen absorption against NGC 4194, “the Medusa Merger”, These observations are the highest angular resolution observations, made to date, of the neutral gas within this source. In presenting this new data we discuss the nuclear radio continuum structure of this very efficient starburst galaxy, as well as a further investigation of the dynamics and distribution of HI in the galaxy’s nucleus. We conclude by placing these results into the context of other observations of this source, for example high resolution observations of CO emission, with the intention of further understanding the cold neutral and molecular ISM of this source; the fuel for the ongoing starburst.

Interaction and merging are the two most important driving forces of galaxy evolution. In recent years, much research activity has been focused on ULIRGs, which are the result of a disk‐disk merger, since they are among the most spectacular objects in the universe. However, ULIRGs are rare objects in the local universe. Thus, a study of a sample of merging galaxies of moderate FIR luminosity (∼ 1010 – 1011L⊙) may teach us as much as or even more about galaxy formation and evolution as investigations of the most extreme objects. Mergers having a moderate FIR luminosity can also be produced by merging two gas‐rich galaxies with unequal mass or a spiral and an elliptical (S+E). Alternatively, they can be a result of a faded major merger. As a class, moderate luminosity mergers are poorly studied and their role in the overall process of galaxy evolution is not yet well understood. We have obtained multicolour optical and NIR imaging data, optical spectroscopy, HI and CO (i.e. molecular gas) data for a large p...

Understanding the molecular phase of the ISM in starburst and active galaxies is important for the modelling of the onset and evolution of their nuclear activity. Here, we focus on single dish and high resolution studies of 12CO and 13CO and how to use the 12CO/13CO 1‐0 line intensity ratio as a diagnostic tool for large scale ISM properties in galaxies.Observations of high density gas tracers like HCN, HNC, HC3N, HCO+ and CN are essenatial for probing physical and chemical conditions of the dense, star‐forming gas. These tracers show great potential as indicators of the evolution of star formation as well as probes of X‐ray illuminated molecular gas around and active galactic nucleus.