Asquith, Rachel
(2019)
Star formation and quenching in galaxy formation models.
PhD thesis, University of Nottingham.
Abstract
Galaxies locally have been observed to have a bimodal distribution for many properties, such as colour, star formation rate and morphology. These properties can be used to separate galaxies into two classes - the 'blue cloud' and the 'red sequence'. Galaxies move from the blue cloud to the red sequence in a process called 'quenching'. Learning exactly how and why galaxies are quenched is vital to understanding galaxy evolution. In this thesis, we use galaxy formation models to investigate the processes governing star formation and quenching, with the aim of understanding exactly which mechanisms are needed to produce a realistic population of galaxies.
Firstly, we compare nine different galaxy formation models with recent observational results in Chapter 2, focusing on the evolution of the stellar mass function (SMF) in the redshift range 0.5 < z < 3.0. Although most of the models are able to match the SMF at low redshift, they tend to overproduce the number density of low-mass star-forming galaxies at high redshift. We then look at the haloes these galaxies are in, and find that the average stellar mass in low-mass haloes at high redshift in the models is larger than observations suggest. This means that the star formation is more efficient in these haloes in the models than the real Universe. Together, this suggests that the models struggle to decouple the growth of a galaxy from the growth of its dark matter halo.
We then chose one of these nine models to investigate a rare class of galaxies called post-starbursts (PSBs), which have been rapidly quenched, sometimes following a burst of star formation. Using the LGalaxies semi-analytic model, we construct a mock lightcone survey in Chapter 3, which is designed to mimic the UKIDSS Ultra Deep Survey (UDS). With this mock, we explain in Chapter 4 how the Principal Component Analysis method is used to classify PSBs based on photometry alone. We then compare PSBs from our mock with PSBs identified in the UDS, and find differences in their stellar mass and redshift distribution. In the UDS, PSBs can be broadly split into two populations - high-mass at high redshift and low-mass at low redshift. However, in the mock, although the shape of the SMF is broadly similar to observations, the number of PSBs increases with cosmic time more in the models.
Building on the work from the previous chapters, we investigate the evolution of our population of simulated PSBs in Chapter 5. By tracking their properties in time, we can try and figure out what mechanisms are responsible for quenching these galaxies. PSBs that are satellites or orphans appear to be quenched due to their environment. Their hot gas is stripped so after they have used up their cold gas supply they can no longer form stars. For centrals, it appears that they have a merger which initiates a starburst in the galaxy. However, this also funnels hot gas into the central black hole, switching on radio mode feedback from an active galactic nuclei (AGN). This heats the gas in the galaxy and quenches star formation. Relating this back to the UDS, most of the high-mass PSBs at high redshift in the mock are centrals, so we would expect AGN signatures in their spectra. Most of the low-mass low redshift PSBs are centrals or orphans, the latter of which we would expect to be environmentally quenched. However, the quenching pathway for the low-mass, low redshift centrals in the UDS is less clear. One option may be winds from supernovae heating the gas in a similar way to AGN feedback.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Pearce, Frazer
Almaini, Omar |
| Keywords: |
galaxies, bimodial distribution, blue cloud, red sequence, post-starbursts, PSBs |
| Subjects: |
Q Science > QB Astronomy |
| Faculties/Schools: |
UK Campuses > Faculty of Science > School of Physics and Astronomy |
| Item ID: |
57273 |
| Depositing User: |
Asquith, Rachel
|
| Date Deposited: |
11 Dec 2024 10:42 |
| Last Modified: |
11 Dec 2024 10:42 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/57273 |
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