Moving and changing : using cold gas and spatially resolved spectroscopy to understand galaxies as evolving dynamic systems

Abstract

Galaxies are vast systems which contain stars, gas, and dust, spiralling under the influence of gravity. On human timescales they appear constant and fixed, however these systems are in motion – moving internally at vast speeds, and evolving through life stages. This work considers how the combination of multiwavelength observations can be used to understand these dynamic systems.

For decades, our observations of the motions of stars in these systems have not matched those expected based on the visible matter which is seen to be present. This has necessitated the inclusion of a dark matter component in our theory of galactic structure. This component cannot be directly observed, however dynamical modelling offers an avenue through which the properties of this can be derived. In this work, I use dynamical modelling to aid in the study of a population of galaxies known as red geysers. These galaxies may offer direct signatures of large scale outflows in galaxies which are needed in our theoretical framework to explain how galaxies stop forming new stars. Through this, more evidence was produced which points towards these galaxies exhibiting large scale outflows. Further, I then use dynamical modelling to explore the dark matter content of galaxies, and develop a novel method which incorporates cold gas observations into the process in order to better constrain the dark matter parameters. This method is shown to improve the modelling outcomes, and is an important proof-of-concept test to highlight the potential for future work using cold gas kinematics in dynamical models.

Galaxies are composed of their stellar populations contained within, and the evolutionary processes we see hinge on how these populations are affected. Some of the most extreme evolution processes are seen in so-called jellyfish galaxies, which are experiencing external environmental pressure as they fall into dense cluster environments. The final section of this work presents evidence of ongoing quenching taking place asymmetrically in a sample of these galaxies, demonstrated by spectral signatures of post-starburst formation histories on their leading edges. Using multiple data sources, I make the argument that this effect is being caused by the progressive compression and stripping of gas due to the external pressure.