The role of mass and environment in the quenching and structural transformation of galaxies up to z ~3

Fernandes Ramos, Marta Sofia (2021) The role of mass and environment in the quenching and structural transformation of galaxies up to z ~3. MRes thesis, University of Nottingham.

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It is not very well understood how galaxies quench their star formation and undergo morphological transformation. It is hard to separate how both the internal structure of galaxies and their environment affect their star formation properties. Furthermore, the observed morphological and size evolution of galaxies is still a topic of much research.

In this thesis, we investigate the role of mass and environment in the quenching of star formation and size evolution of galaxies in the redshift range 0.5<z<3, using data from the 11th data release (DR11) of the UKIDSS Ultra-Deep Survey (UDS). We do this by studying the fraction of quiescent galaxies and the mass-size relation as a function of environment. We define environment as the normalized galaxy counts in a fixed aperture of 250 or 400 kpc and use a Principal Component Analysis (PCA) to identify star-forming (SF), passive and post-starburst (PSB) galaxies. The environmental measurements and the PCA technique are explained in Chapter 2, where the structural parameters are also explained.

We find that the fraction of quiescent galaxies increases with both mass and local galaxy density at all redshifts, extending the trends observed at lower redshifts. From the mass-size relation, in agreement with previous studies, we confirm that massive passive galaxies at 2 < z < 3 are approximately a factor of two smaller on average than their counterparts at 0.5 < z < 1. When comparing the mass-size relation in different environments, however, at a given epoch we find that passive galaxies are on average larger in dense environments than their counterparts of comparable mass in less dense regions. In the redshift range 1 < z < 2, high mass (log M^*/M_\odot > 11) quiescent galaxies are ~ 50 per cent larger in the highest density environments compared to the least dense environments. These trends may be explained by an increased rate of minor dry mergers in dense environments. In addition, we also confirm previous findings that the most recently quenched "post-starburst" galaxies are the most compact of all galaxy types, extending these findings to z=3. Combining these results, we propose a scenario in which massive galaxies initially become exceptionally compact immediately prior to being rapidly quenched at high redshift. Thereafter, these galaxies accrete satellites at a rate dependent on their environment, and gradually grow into the larger passive galaxies we observe in the local Universe.

Item Type: Thesis (University of Nottingham only) (MRes)
Supervisors: Almaini, Omar
Keywords: galaxy growth, galaxies, redshift
Subjects: Q Science > QB Astronomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 64344
Depositing User: Ramos, Marta
Date Deposited: 13 Sep 2023 10:40
Last Modified: 13 Sep 2023 10:40

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