An ALMA perspective on high-redshift galaxy evolution

Licentiate thesis, 2022

The processes governing the growth and evolution of high-redshift massive galaxies have long been a subject of intense investigations. Studies of the cosmic star-formation rate density have shown a peak at z ∼ 2 − 3, demonstrating the distinct need to understand the mechanisms by which galaxies acquired the fuel necessary to ignite such intense star formation. Galaxies are expected to transform through a number of phases leading up to and proceeding this peak. Theoretical modelling and simulations have proposed several driving mechanisms to cause these changes, including feedback from active galactic nuclei and merger activity driven by the effect of companion galaxies. However, both of these can be difficult to observe at high-redshift and studies have concluded conflicting results in the past decades. A synergy must exist between the predictions of theoretical simulations and observa- tional realities; with the increased sensitivity and capability of modern telescopes it has become possible to investigate this.

Observations probing the effect of these mechanisms in the high-redshift universe have greatly improved in recent years with the advent of telescopes such as the Atacama Large submillimeter/Millimeter Array. Through observations of the environment of massive high-redshift quasars and starburst galaxies, along with detections of companion galaxies, it has become possible to begin to understand the effect these companions could have. Furthermore, signatures of outflow activity and tracers of the impact of active galactic nuclei on their host galaxy have begun to uncover the significance of feedback in high-redshift galaxies.

This licentiate thesis summarizes the current understanding of massive high-redshift galaxy evolution and presents two (possibly archetypal) examples of massive high-redshift galaxies. Using deep, high-resolution observations of the far-infrared fine structure [CII] 158μm line, faint companions were found in close proximity to both the quasar BRI0952-0115 (z = 4.432) and the sumbillimeter galaxy AzTEC-3 (z = 5.3). Additionally, both BRI0952 and AzTEC-3 exhibit signatures of outflows. The results presented in Paper I provide additional evidence to the hypothesis that massive high-redshift galaxies evolve in over-dense regions and that outflow activity can have a dramatic effect on the host galaxy. Moreover, they demonstrate the necessity of conducting deeper observations necessary to detect these relatively fainter phenomena that are thought to be a crucial aspect of galaxy evolution.