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Abstract

Starburst galaxies are characterized by intense star formation at high star formation rate Surface densities and short gas depletion times. Strong stellar feedback drives galaxy-scale winds and outflows in all gas phases, i.e. ionized, neutral and molecular. The extreme conditions in local starburst galaxies are thought to be similar to those in typical high-redshift star forming galaxies, e.g. at the peak of the cosmic star formation history.

In this thesis, we present and analyze 0.15'' (~2.5pc) resolution ALMA CO(3–2) observations of the nuclear starburst in NGC253. Using this data, we study the molecular outflow in unprecedented detail, zoominto NGC253’s super star clusters (SSCs) and compare the starburst to the similar but more quiescent center of the MilkyWay.

Firstly, we kinematically decompose the molecular gas emission in NGC253 into a disk and non–disk component to then separate out the molecular outflow.We systematically improve on previous measurement and obtain mass outflow rates M ~ 14-39 Msun yr^-1 for the starburst. The kinetic energy and momentum of the molecular outflow dominates over the other gas phases and is consistent with being supplied by the starburst at a few percent efficiency.

Secondly, we study the physical and chemical conditions in the molecular gas in the (proto-)SSCs in NGC253, the places where future outflows will be launched from. The SSCs differ significantly in chemical complexity and show up to 55 lines belonging to 14 different chemical species. Spectral modelling allows us to infer spectral line ratios and physical properties. The molecular gas in the SSCs is hot, consistent with UV photon-dominated chemistry and permeated by intense infrared radiation.

Thirdly, we compare the molecular cloud properties in the starbursting center of NGC253 and the MilkyWay Galactic Center (GC), that shares similar properties as NGC253. Using a structure identification algorithmon resolution-, area- and noise-matched datasets allows for a direct comparison of the kinematic structure. Through common cloud scaling relations, we infer a high external pressure (Pext ~ 10^7-7.5 K cm^-3) in NGC253 and a significant amount of unbound (non-self-gravitating) molecular gas that is characterized by high velocity dispersion.

In summary, in this thesis we could follow the life cycle of a molecular outflow from an actively star forming molecular cloud before the launching of an outflow all the way out to distances that are hundreds of parsecs above the starburst disk where the outflow fades away.