The formation and evolution of dust in semi-analytic models of galaxy formation

Clay, Scott Jonathan (2017) The formation and evolution of dust in semi-analytic models of galaxy formation. Doctoral thesis (PhD), University of Sussex.

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The formation and evolution of galaxies is an interesting subject to study because it incorporates
astrophysics from all scales, from the initial perturbations in the early universe
creating the large scale structures that produce galaxies, right down to the evolution of
stellar populations and their manipulation of the host galaxy. Simulations of galaxy formation
allow us to test the various physical recipes against that which is observed in order
to build a true and proper picture of what is happening in the real universe.

L-Galaxies is a semi-analytic model of galaxy formation built on top of the merger
trees from the Millennium dark matter simulation, and is constrained to match certain key
observations at low redshift by applying a Monte Carlo Markov Chain (MCMC) method
to constrain the free parameters. In using the model to make high redshift predictions
of the stellar mass function, UV luminosity function and star formation rate distribution
function we found that the model starts to deviate from observational constraints at the
highest redshifts, particularly in high mass galaxies. In the case of the UV luminosity
function, this is because the current dust model is calibrated at low redshift and lacks
sophistication in that it only depends on the cold gas mass and the density of metals.

To improve on this we implement a physically motivated dust model that traces the
formation of dust from stellar sources, such as in the stellar winds of AGB stars and in
the supernovae remnants of massive stars, the growth of dust inside molecular clouds, and
the destruction of dust due to supernovae explosions. The model is fully integrated into
L-Galaxies such that the evolution of dust is included in all the recipes relevant to the
formation and evolution of galaxies, including: star formation; radiative feedback; cooling
and reheating; and both major and minor mergers.

Our results show a good fit to observations of the dust mass in galaxies both in the
local universe and out to high redshift and we note a similar conclusion as in the literature
that dust growth inside molecular clouds is not only necessary but the dominant source
of the dust mass in these galaxies. However, stellar sources of dust can not be neglected
as molecular clouds must first be seeded by dust grains in order for accretion to occur.
This could be important in the very early universe, perhaps for the first galaxies that
will hopefully be observed by JWST in the future, because these galaxies may not have
had sufficient time to seed their molecular clouds and as such the dust produced by these
stellar sources would be important for calculating the galaxies true observed luminosity.

We finish by discussing the limitations of the model and discuss areas for possible
improvement as well as the next steps in using this to better predict the luminosity of
galaxies in future models.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy > QB0495 Descriptive astronomy > QB0856 Galaxies
Depositing User: Library Cataloguing
Date Deposited: 17 Oct 2017 09:31
Last Modified: 17 Oct 2017 09:31

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