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

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posted on 2023-06-09, 08:19 authored by Scott Jonathan Clay
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.


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University of Sussex

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