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
Circumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available... Show moreCircumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available to form planets. Studying the evolution of circumstellar discs can then help us understand planet formation and the diversity of observed planetary systems. These discs develop almost immediately after star formation, as a direct consequence of the collapse of a molecular cloud and angular momentum conservation. Their surroundings are rich in gas and neighbouring stars, which can be hostile to the discs and affect their evolution in different ways: dynamical encounters with nearby stars can truncate the discs; stellar winds and supernovae explosions can truncate, tilt, or completely destroy the discs; and the presence of bright, massive stars in the vicinity of circumstellar discs can heat their surface enough to evaporate mass from them. This process, known as external photoevaporation, is arguably one of the most important environmental mechanisms in depleting mass from young circumstellar discs. The work performed for this thesis consisted of simulating the early evolution of circumstellar discs in star clusters and the effects of the environment, in particular, truncations due to close encounters and photoevaporation. The results show that photoevaporation is extremely efficient in removing mass from the discs, greatly limiting the amount of material and time available to form planets. Show less
Levy, R.C.; Bolatto, A.D.; Leroy, A.K.; Emig, K.L.; Gorski, M.; Krieger, N.; ... ; Zwaan, M.A. 2021
In this PhD thesis, I describe work done in the CosmoGrid and AMUSE projects. CosmoGrid is a _CDM N-body simulation containing 8.5 billion dark matter particles within a volume of only (30 Mpc)^3,... Show moreIn this PhD thesis, I describe work done in the CosmoGrid and AMUSE projects. CosmoGrid is a _CDM N-body simulation containing 8.5 billion dark matter particles within a volume of only (30 Mpc)^3, resulting in very high mass resolution. In order to run such a large simulation, we investigate a method of combining multiple supercomputers via a fast network; combining them into one large machine for the final calculation. We compare the results of CosmoGrid to previous _CDM simulations, and use the finalised CosmoGrid data to investigate how an aligned group of galaxies in a void region might have formed. Combining CosmoGrid with the Astrophysical Multipurpose Software Environment (AMUSE), we investigate a method to embed simulated star clusters in a large-scale environment such as a dark matter halo. Finally, we use this method to run self-consistent simulations of open star clusters embedded in a forming Milky Way-like galaxy. Show less
