| Summary: | <p>Star forming galaxies (SFGs) are expected to be the sources responsible for reionising the Universe, but detailed study of these within the Epoch of Reionisation (EoR, z>6), will only become possible with the long-wavelength coverage and sensitivity of the James Webb Space Telescope (JWST). One approach to understanding these systems is to study lower-redshift galaxies which share similar properties and are potential analogues to galaxies in the reionisation era. In this Thesis I study star forming galaxies that exhibit large nebular emission line equivalent widths (EW), consistent with what has been inferred at high redshifts, using HST/WFC3 slitless spectroscopy to select galaxies at z~1-3 directly on their emission line strength.</p>
<p>VLT/FORS2 spectroscopic follow-up on z~1 emission line selected galaxies from the WFC3 WISPS survey confirms the slitless spectroscopic redshift of 95% of galaxies with emission line detections, and those galaxies with large rest-frame H-alpha EWs not only have high specific star formation rates but also high [OIII]/H-beta and [OIII]/[OII] ratios, suggesting lower metallicities or higher ionisation parameters than low-EW SFGs. I measure a strong EW evolution with redshift from WISPS, which I also confirm with a spectroscopic study of z~2 SFGs from the 3D-HST survey where I determine the distribution of [OIII]5007 rest-frame EWs. The abundance of extreme emission line galaxies (EELGs) increases rapidly with redshift, and while abundance of these EELGs and their contribution to the ionising background at intermediate redshifts is minimal (only 3.6% of z~2 SFGs have [OIII]5007 EWs above 750A), EELGs may dominate the ionising output of the SFG population during the EoR.</p>
<p>I am a member of the JWST Advanced Deep Extra-galactic Survey (JADES), a joint NIRSpec and NIRCam instrument science team GTO programme whose main science goals are to trace galaxy evolution from z~1 to within the EoR by measuring star formation rates, metallicities and stellar masses of a large sample of galaxies. As part of JADES, I re-analysed multi-band imaging in the GOODS fields to draw up a list of robust high redshift candidates and a prioritisation of these targets, in particular SFGs in the EoR, for NIRSpec spectroscopic follow-up. I confirm through simulations of JADES NIRSpec deep spectroscopy that our key science goals can be met with the achieved signal-to-noise from our observational strategy (in particular redshift confirmation, and metallicity measurements from line ratio diagnostics).</p>
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