New insights into primeval galaxies in the era of JWST

The properties of galaxies that existed in the early Universe hold the key to understanding not only their formation and evolution but also the broader reionisation process. While the Hubble Space Telescope (HST) was able to identify a small sample of candidate z>7 galaxies, the James Webb Space Telescope (JWST) has revolutionised the field. The sensitivity of the near infrared camera (NIRCam) and spectrograph (NIRSpec) instruments have facilitated the detection and spectroscopic confirmation of galaxies out to z∼14. Moreover, the study of the properties of not just individual, but samples of high-redshift galaxies is now possible. As astronomers utilise the capabilities of this telescope multiple key questions, left over from the HST-era, require answering. Here I present the results of several studies that aim to answer some of these important unanswered questions. I utilise ground-based observations of the intrinsically strongest hydrogen emission line, Lyman-α (Lyα), to constrain the escape fraction of UV-bright galaxies in the early Universe. This shows that UV-bright galaxies appear to have low escape fractions of ionising photons, setting the scene for JWST studies of the ionising capabilities of different galaxy populations. I then use NIRCam observations of Lyα-emitting galaxies to explain the escape of Lyα photons from galaxies by showing that all high-redshift Lyα emitters (LAEs) have close companions, in contrast to typical high-redshift galaxies. The combination of observations and simulations, in this work, shows how interactions between close companion galaxies can both enhance Lyα emission, but also facilitate its escape. The following work I present focuses on observations of one of the highest redshift LAEs with the integral field unit on JWST. These observations reveal both a Lyα halo around this galaxy as well as an abundance of candidate UV-faint emission line galaxies, evidencing the complex escape of Lyα but also the environments within which high-redshift galaxies exist. Following this, I identify a galaxy that shows both strong emission lines and a Balmer break indicating the presence of both a young and old stellar population, and hence a rejuvenating star-formation history (SFH), revealing the complex SFHs of early galaxies. Finally, I discuss these results and future avenues for this work, especially in the context of next generation instruments and simulations. I also point the reader to some additional research conducted as part of my PhD, but not included in this thesis, in Witten et al. 2022. This work focuses on the low-resolution spectrographs on-board the Gaia satellite. This work, completed before the release of Gaia data release 3, addresses the potential information available in these low-resolution spectra to measure the temperature, surface gravity and metallicity of observed stars. I also show that these spectra can be used to identify candidate carbon-enriched metal-poor stars for follow-up high-resolution observations.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Witten, Callum

Advisors dc:contributor.advisor

• Sijacki, Debora
• Laporte, Nicolas

• High-redshift galaxies
• James Webb space telescope
• Lyman-α
• Epoch of Reionisation

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/90be203b-0494-4bce-8308-b5462b62da0d/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0002-1369-6452

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/376829