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Title: Studying the growth of galaxies with JWST
Author: Kemp, Thomas William
ISNI:       0000 0004 8500 8625
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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The James Webb Space Telescope (JWST or Webb) is a large (6.5m diameter primary mirror) infrared (0.6 < λ < 30μm) space telescope. It impressive size and wavelength coverage will revolutionise the field of galaxy formation and evolution, enabling the community to push back the observational frontier to within a few 100 million years of the Big Bang. With JWST expected to launch in 2021, a detailed understanding of its capabilities is essential to guarantee the success of the mission. In this thesis, I present a new analysis of how best JWST can be utilised to study the evolution and formation of galaxies across cosmic time. Primarily this work uses simulated JWST and ancillary HST observations in an attempt to assess JWST's capabilities, specifically its ability to study high-mass, high-redshift, dusty star-forming galaxies in the Universe. Additionally, I use currently available data from the UV/optical to sub-mm to perform a new study of the prevalence of high-mass, high-redshift, dusty star-forming galaxies accessible before the launch of JWST. Firstly, I introduce a piece of software that I have built to simulate observations that will be made using the Mid-infrared Instrument (MIRI) onboard JWST. This piece of software is capable of simulating all of MIRI's available observing modes: MIRI Imager, Low-Resolution Spectrograph (LRS), Medium Resolution Spectrometer (MRS). I then use this software to show the potential for measurements of the Hα emission line in high-redshift star-forming galaxies using the MRS IFU. At redshifts z > 6.7, MIRI is the only instrument onboard JWST that can directly observe Hα, a sensitive star-formation indicator, tracing very recent star-formation. I show that with approximately ≃ 6-hour integration time with the MIRI MRS, the Hα emission line in the brightest known z ≃ 7 galaxies can be detected to a SNR of approximately ≃ 11. Therefore, I conclude that the MIRI MRS could be an impressive tool for determining the star-formation rates of high-redshift galaxies in the epoch of reionisation. Secondly, I present an overview of the Public Release Imaging for Extragalactic Research (PRIMER) proposal submitted as part of the Director's Discretionary Early Release Science (DD-ERS) programme for Cycle-1 of JWST. PRIMER is a large (52hr), deep, fully-sampled NIRCam and MIRI imaging programme, designed to efficiently (≈ 75% observing efficiency) observe the faintest galaxies in the best-studied available (Non-GTO Covered) equatorial HST CANDELS field, COSMOS. As well as detailing the science goals and observational design of this programme, I place it in the context of other planned JWST programmes (ERS & GTO) focussed on observations of high-redshift galaxies. Thirdly, I present a new analysis of the potential power of deep, near-infrared, imaging surveys with the JWST to improve our knowledge of galaxy evolution. In this work, I properly simulate what can be achieved with realistic survey strategies, and utilise rigorous signal:noise calculations to calculate the resulting posterior constraints on the physical properties of galaxies. I explore a broad range of assumed input galaxy types (> 20,000 models, including extremely dusty objects) across a wide redshift range (out to z ≃ 12), while at the same time considering a realistic mix of galaxy properties based on our current knowledge of the evolving population (as quantified through the Empirical Galaxy Generator: EGG). While our main focus is on imaging surveys with NIRCam, spanning λobs = 0:8 - 5:0 μm, an important goal of this work is to quantify the impact/added-value of: i) parallel imaging observations with MIRI at longer wavelengths and ii) deeper supporting optical/UV imaging with HST (potentially prior to JWST launch) in maximising the power and robustness of a major extragalactic NIRCam survey. I show that MIRI parallel 7.7-μm imaging is of most value for better constraining the redshifts and stellar masses of the dustiest (AV > 3) galaxies, while deep B-band imaging (reaching mAB ' 28:5mag) with ACS on HST is vital for determining the redshifts of the large numbers of faint/low-mass, z < 5 galaxies that will be detected in a deep JWST NIRCam survey. Finally, I attempt to assess the prevalence of the dusty subset of galaxies that MIRI will observe, utilising the current deepest UV/optical/near-IR and far- IR/sub-mm observations. The data collected from numerous telescopes covers a total of 1.8 deg2 in the UDS and COSMOS fields. Combining the UV and IR data, I assess the total number density as a function of cosmic time and compare the methods of detecting/selecting high-redshift, high mass dusty galaxies. I calculate the total star-formation rate (SFR) as a function of redshift and compare the contribution from sub-mm galaxies and UV/optically-selected dusty galaxies. I also calculate the star-formation rate density (SFRD) across cosmic history in an attempt to extend the Madau & Dickinson (2014) plot to higher redshifts for obscured star-formation. I show that both the UV/optical and (sub)-mm approach to detecting high-redshift dusty galaxies both produce a consistent estimation of their evolving comoving number density at high redshift. I find clear evidence of a rapid decline in the total comoving number density of these objects beyond z > 3, which results in a similarly steep decline in the SFRD of the Universe contributed by obscured star-formation. Comparing to recent work through in the literature, my results strengthen the existing evidence for a transition between unobscured & obscured star formation as the dominant mode of star-formation activity at z ≃ 2-3.
Supervisor: Dunlop, James ; McLure, Ross Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: James Webb Space Telescope ; JWST ; galaxy formation ; dusty star-forming galaxies ; high-redshift star-forming galaxy ; Mid-infrared Instrument software