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Title: Resolved studies of the dynamics, star formation and chemical properties of high-redshift galaxies
Author: Gillman, Steven Richard
ISNI:       0000 0004 9348 8745
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2020
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Understanding the physical mechanisms that drive the evolution of galaxies through cosmic time is one of the fundamental pillars of modern-day observational astronomy. Developing a robust theory of galaxy formation enables us to address vital questions connected to the structural and dynamical evolution of galaxies, Why are the kinematic and morphological properties of high-redshift galaxies much more turbulent and irregular than those we see in the local Universe? What drives the galaxies towards the well-ordered, stable systems which ultimately lead to the emergence of the Hubble Sequence? To answer these questions, we must first empirically constrain the fundamental properties (e.g. mass, energy, and angular momentum) of galaxies across cosmic time. This thesis presents an analysis of the dynamics and morphologies of star-forming galaxies from z = 0.8 to z = 3.5. We include both seeing-limited near-infrared integral field spectroscopy observations from the K-band Multi Object Spectrograph (KMOS) as well as adaptive optics integral field observations from the Gemini Northern Integral Field Spectrograph (Gemini-NIFS), the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) and the OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS). We first analyse the connection between a galaxy’s dynamics and its rest-frame optical morphology by exploiting seeing-limited KMOS observations from the KMOS Galaxy Evolution Survey (KGES) that probe the Hα and [Nii] emission lines in 288 star-forming galaxies at z ∼ 1.5. We combine the integral field data with high-resolution CANDELS HST near-infrared imaging to constrain the morphology of the galaxies in the sample. We identify that low-mass, compact galaxies have lower specific angular momentum whilst more massive disc galaxies have higher angular momentum. At fixed mass, peculiar galaxies have similar levels of angular momentum to that of disc galaxies whilst having higher star formation rate surface densities. We propose that the peculiar morphologies are driven by higher gas fractions leading to a more clumpy interstellar medium. We then explore the chemical abundance properties of ∼700 high-redshift star-forming galaxies that make up the KGES and KROSS surveys. Using the [Nii] / Hα emission line ratio we analyse the connection between gas-phase metallicity, stellar mass and fundamental galaxy properties. We establish that peculiar galaxies have a lower metallicity for a given stellar mass compared to disc and spheroidal systems, which we attribute to their higher gas fractions. The metallicity gradients of the galaxies correlate negatively with stellar mass and positively with specific star formation rate. This agrees with the inside-out model of galaxy formation whereby galaxies first form stars at their centres, enriching the surrounding interstellar medium. On average, we identify flat metallicity gradients which we demonstrate agrees with other studies of high-redshift galaxies and numerical models in which feedback processes are important. Finally, we use high-resolution adaptive optics observations to map out the Hα, [Nii] and [Oiii] nebula emission lines in 34 star-forming galaxies from z = 0.8 to z = 3.5. We explore the evolution of the normalisation of the specific angular momentum – stellar mass plane across ∼ 5Gyr, and constrain the internal distribution of specific angular momentum in each galaxy. We establish that the specific angular momentum becomes less centrally concentrated in galaxies with higher stellar mass due to a combination of stellar feedback and gas accretion. This leads to an evolution in the morphologies of the galaxies towards more a late-type dominated population.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available