Chemodynamical Adaptive Mesh Refinement Simulations of Disk Galaxies

Few, Christopher Gareth (2012) Chemodynamical Adaptive Mesh Refinement Simulations of Disk Galaxies. Doctoral thesis, University of Central Lancashire.

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In this thesis I bring together three projects that comprise my postgraduate studies; using numerical simulations of galaxy formation in a cosmological context. The first of these projects involves the simulation of a suite of galaxies in loose group and field environments. This suite of galaxies is used to compare properties such as the metallicity gradients and morphology to determine if systematic differences are apparent as a function of subtle environmental differences. Almost no distinction is seen between galaxies in the field and the loose group environments: individual assembly histories of the galaxies dominate over ambient environmental effects with the exception of the vertical velocity dispersion of the stellar disc where loose group galaxies tend to exhibit a greater number of instances of impulsive heating of the disc.

In the second project I present further analysis of this suite of galaxies and a comparison with other galaxies simulated using contrasting methodologies, in ad- dition to several semi-numerical galaxy formation models. The focus of this work is the evolution of metallicity gradients and star formation profiles, finding that galaxies form in an inside-out fashion. This leads to steeper metallicity gradients in young stellar populations at high redshift compared with the present day. By considering present day stellar populations with different ages in these galaxies the converse is found, older populations have flatter gradients. This suggests that while the metallicity gradient starts out steep, it flattens over time due to stellar migra- tion/mixing. This flattening due to stellar migration happens at a faster rate than the flattening of the gas phase metallicity gradient.

Finally, I present an update to the N-body and adaptive mesh refinement hydrodynamical code ramses that introduces a more sophisticated feedback treatment, this code is dubbed ramses-ch. Under the new scheme, energetic and elemental feedback is contributed by stars throughout their lifetime rather than (as previously) in a single burst. This relaxation of the ‘instantaneous feedback approximation’ in ramses-ch opens up the opportunity for studying chemical evolution using adaptive mesh refinement hydrodynamics where previous studies were limited to smoothed particle hydrodynamical codes or semi-numerical models. The new code is applied to the simulation of a typical disc galaxy using different stellar initial mass functions and supernovae type-Ia progenitor models. The influence of these model inputs on the ratio of elemental abundances and supernovae rates in the simulated galaxies are compared as a means of constraining chemical evolution models. The conclu- sions drawn from this work are discussed in the broader context of galaxy formation simulations.

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