The origin and evolution of galaxies are closely tied to the cyclic feedback processes between stars and the interstellar medium (ISM). The aim of this thesis is to explore characteristics of the... Show moreThe origin and evolution of galaxies are closely tied to the cyclic feedback processes between stars and the interstellar medium (ISM). The aim of this thesis is to explore characteristics of the ISM, on global (galactic) scales down to sub-cloud (pc) scales. We explore new methods to investigate the ISM in external galaxies, through radio recombination line observations, and develop the tools and strategies needed to process new low-frequency observations with the Low Frequency Array. We also infer the presence of massive stars and characterize their properties and influence on the ISM. This thesis addresses the questions:- How does low-density ionized gas affect the evolution of the massive, galactic star-forming region, Cygnus X? Are the same fingerprints present in surveys of low-density ionized gas in our Galaxy?- What are the properties of star formation (star clusters) in the central starburst of the galaxy NGC 4945?- Can the ISM be explored outside of the local universe through radio recombination line observations? What are the ISM properties of a dwarf-like galaxy at z=1.1?- What techniques are best suited to detect faint radio recombination lines (at a previously unknown redshift) in extragalactic sources? Show less
