Unveiling massive galaxy evolution in the high-redshift universe
Doctoral thesis, 2025
The processes governing the rapid formation and evolution of massive galaxies in the early universe is one of the most profound and unresolved questions in modern extragalactic astronomy. Observations show that the cosmic star formation rate peaked at z ~ 2 - 3, demonstrating the distinct need to understand how galaxies acquired fuel for such vigorous star formation. Simulations point to galaxy mergers and active galactic nuclei (AGN) as the primary drivers of this buildup, but direct observational evidence for this at high redshift is limited and often ambiguous. This thesis summarizes our current understanding of the growth of massive high- redshift galaxies, focusing on how the interplay between their environments, gas content, feedback, and star formation influences their evolution. Deep, high angular resolution observations of far-infrared and submillimeter gas tracers, primarily [CII] and CO emission, were used to study a sample of five galaxies: the quasar BRI0952-0115 (z = 4.432), and the submillimeter galaxies SPT0125-47 (z = 2.51), SPT 2134-50 (z = 2.77), G09v1.97 (z = 3.63), and AzTEC-3 (z = 5.3). Four of these galaxies are strongly gravitationally lensed, allowing for detailed studies of their interstellar medium and environments.
Small companion galaxies were identified nearby both BRI 0952-0115 and AzTEC- 3, supporting the hypothesis that massive galaxies evolve in over-dense environments. Direct observational evidence of a gas exchange between a small companion and AzTEC-3 suggested that interactions with smaller galaxies can trigger and fuel intense star formation. Both systems exhibited gas outflows, though the driving mechanism behind them is uncertain. High-resolution imaging of G09v1.97 revealed a massive, rotating disk, challenging the conclusions of previous studies claiming the source was a merger. Observations of SPT 0125-47 and SPT 2134-50 showed tentative velocity gradients, suggesting that recent interactions and/or mergers may have triggered their high star-formation rates.
Overall, the results of this thesis underscore the importance of feedback, the environment, and support the hypothesis that massive high-redshift galaxies evolve in over-dense regions. This work highlights the role of gravitational lensing in uncovering faint structures and dynamical features that would otherwise be unobservable. Together, these findings provide new insight into massive galaxy evolution in the early universe.
Small companion galaxies were identified nearby both BRI 0952-0115 and AzTEC- 3, supporting the hypothesis that massive galaxies evolve in over-dense environments. Direct observational evidence of a gas exchange between a small companion and AzTEC-3 suggested that interactions with smaller galaxies can trigger and fuel intense star formation. Both systems exhibited gas outflows, though the driving mechanism behind them is uncertain. High-resolution imaging of G09v1.97 revealed a massive, rotating disk, challenging the conclusions of previous studies claiming the source was a merger. Observations of SPT 0125-47 and SPT 2134-50 showed tentative velocity gradients, suggesting that recent interactions and/or mergers may have triggered their high star-formation rates.
Overall, the results of this thesis underscore the importance of feedback, the environment, and support the hypothesis that massive high-redshift galaxies evolve in over-dense regions. This work highlights the role of gravitational lensing in uncovering faint structures and dynamical features that would otherwise be unobservable. Together, these findings provide new insight into massive galaxy evolution in the early universe.
Galaxies: evolution – Galaxies: high-redshift – Galaxies: AGN – Galax- ies: starbursts – techniques: interferometric – techniques: gravitational lensing
Author
Kiana Kade
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Exploring the environment, magnetic fields, and feedback effects of massive high-redshift galaxies with [CII]
Astronomy and Astrophysics,;Vol. 673(2023)
Journal article
Probing the interstellar medium of the quasar BRI 0952−0115 An analysis of [C ii], [C ii], CO, OH, and H<inf>2</inf>O
Astronomy and Astrophysics,;Vol. 684(2024)
Journal article
Kade K., Yang C., Yttergren M., Knudsen K. K., König S., Amvrosiadis A., Dye S., Nightingale J., Zhang L., Zhang Z., Cooray A., Cox P., Gavazzi R., Ibar E., Michalowski M. J., van der Werf P. P., Xue R.: Detailed lens modeling and kinematics of the dusty star forming galaxy G09v1.97: An analysis of CO(6–5), H2O, H2O+, and dust continuum emission
Kade K., Bredberg M., Knudsen K.K., König S., Drouart G., Romeo A., Bakx T.J.L.C.: Resolving the molecular gas emission of the z ~ 2.5 - 2.8 starburst galaxies SPT 0125-47 and SPT 2134-50
Galaxer är enorma kosmiska sammansättningar av gas, damm, stjärnor, och planeter. Vi bor i en av miljarder sådana sammansättningar, nämligen Vintergatan. Att förstå hur galaxer bildas och utvecklas över kosmisk tid är en av de viktigaste frågorna inom modern astronomi. Eftersom galaxer utvecklas över miljarder år kan vi inte titta på dem och se dem förändras, dock kan vi genom att observera en fjärran del av universum också se tillbaka på ett avlägset förflutet i universums ungdom. I denna avhandling studeras galaxers omgivande miljö samt deras inre gasrörelser vid en tidpunkt då universum endast var ett par miljarder år gammalt. Genom att titta på galaxernas omgivningar kan vi se om de existerar i avskildhet eller om de har följeslagargalaxer omkring sig. Detta hjälper oss i sin tur att förstå om dessa avlägsna galaxer är stillsamt roterande skivor likt Vintergatan, eller om de är inbegripna i sammanslagningar eller andra slags interaktioner med andra galaxer. Genom att studera gasen i dessa galaxer kan vi studera deras inre utveckling och de centrala supermassiva svarta hålens roll i denna utveckling. På grund av de extrema avstånden till dessa avlägsna galaxer använder vi ett fenomen som kallas gravitationslinsning och som fungerar som ett naturligt förstoringsglas, för att kunna studera dem i rikare detalj. I avhandlingen studeras egenskaperna hos fem galaxer, varav fyra är förstorade genom gravitationslinsning, i syfte att placera in dessa galaxer i en evolutionär kontext och därigenom kunna koppla dem till det vi ser i vårt närliggande universum.
Galaxies are massive cosmic collections of gas, dust, stars, and planets. We live in just one of billions, namely the Milky Way. Understanding how galaxies form and evolve over cosmic time is one of the central questions in modern-day astronomy. It is impossible to watch a galaxy evolve since they change over billions of years; however, by looking into the distant universe, we also look into the dis- tant past when the universe was still young. This thesis studies the environments in which galaxies evolved and the internal behavior of their gas at a time when the universe was only a few billion years old. Through looking at a galaxy’s environment, it is possible to see if the galaxy is solitary or whether it has companion galaxies around it. This, in turn, helps us understand if the galaxy is a calmly rotating disk like the Milky Way, or if there are on-going mergers or other types of interactions with other galaxies. By studying the gas in a galaxy, we can study its internal evolution, including the role of the central supermassive black hole. Due to the extreme distances to these galaxies, a phenomenon known as gravitational lensing, which acts as a natural magnifying glass, is used to study these galaxies in better detail. This thesis examines the properties of five galaxies, four of which are gravitationally lensed, in order to place these sources into an evolutionary context and thereby connect them to what we see in the nearby universe.
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
ISBN
978-91-8103-245-1
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5703
Publisher
Chalmers