Investigating the physics of star formation in isolated and perturbed galaxies

• Main Author: Baxter, Keith Michael
• Published: University of Cambridge 2000
• Subjects: 520
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596482

This thesis concentrates on the numerical modelling of star formation in isolated and perturbed systems, with particular emphasis on the effects of feedback. In view of the complicated nature of star formation within an individual molecular cloud, a stochastic approach is adopted in which the timescale for star formation occurring is assumed to be a function of the cloud's mass and temperature. Feedback is included in some models by assuming that star formation may also be triggered as the result of expanding supernova remnants generating shocks in clouds. Two different models for cloud growth are investigated. The first scheme considers the growth of clouds through collisional coalescence, whilst the second assumes that clouds grow by accreting matter from the H<SUB>1</SUB> component as they orbit the galaxy. Models in which clouds grow through collisional coalescence display many properties in good agreement with those observed in galaxies. Specifically, the cluster formation rate, star formation rate and cloud mass spectrum are all within the observational limits. Models in which clouds grow through accretion were, however, inconsistent with observations on a number of points. Most notably, the cloud mass spectrum is considerably shallower and the number of very high-mass clouds considerably lower than that observed in galaxies. The behaviour of interacting galaxies is highly idiosyncratic, making them an ideal candidate for comparison with numerical simulations. The behaviour of the coalescence model when perturbed by the fly-past of a companion galaxy is therefore investigated. The star formation history of the system is found to be heavily dependent on the degree of triggered star formation present in the system. In models that include triggered star formation, the increased spatial density of clouds that arises due to the infall of gas towards the nuclear region is shown to generate a burst of triggered star formation, leading to a rapid increase in the cluster formation rate. The star formation rate in models that did not include triggered star formation was found to rise as the result of the decreased cloud collisional timescale.