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Title: Hadronic processes of energetic particles in star-forming galaxies and high-redshift protogalactic environments
Author: Owen, Ellis Richard
ISNI:       0000 0004 8500 3533
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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In this thesis, the heating and feedback effect of energetic cosmic rays (CRs) in star-forming galaxies and protogalaxies is investigated. Galaxies undergoing violent starburst episodes are expected to be rich in CRs. This is due to an abundance of stellar end-products (which are able to accelerate CRs up to PeV energies), coupled with the rapid development of a µG interstellar magnetic field soon after the onset of star-formation, which is able to contain CRs inside the host galaxy. Hadronic CR particles can undergo interactions with photons and baryons. In star-forming galaxies, target photons are supplied by stellar radiation and the cosmological microwave background, while target baryons comprise the interstellar and circumgalactic medium. CR interactions enable their deposition of energy, causing the surrounding medium to be heated. This occurs either by the Coulomb thermalisation, or by the inverse Compton X-ray emission, of CR secondary particles (which are injected by the hadronic CR interactions). CR heating processes are found to attain a power of 10−25 erg cm−3s−1 in an idealised galaxy with 1 core collapse SN event per decade. This falls to 10−28 erg cm−3s−1 if concentrated starburst activity in the system leads to the development of a galactic-scale outflow. It is argued that CR-driven heating processes can lead to quenching and/or stunning of subsequent star-formation activity in the host. The level of CR feedback in 16 observed starburst/post-starburst high-redshift galaxies is estimated, based on the star-formation rates they could have sustained during their starburst episodes. It is found that CR feedback cannot be neglected in these systems: it has the strength to suppress star-formation, and can even maintain a post-starburst period of quiescence which is consistent with their inferred star-formation histories.
Supervisor: Wu, K. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available