Linking optical IFU data with multi-wavelength data: Probing the evolution of stars, gas, and dust in galaxies

Abstract

Stars form from cold, dense gas and, throughout their lifetimes, produce heavy elements via stellar nucleosynthesis. These elements are ejected into the interstellar medium (ISM) through stellar feedback, such as stellar winds and supernova explosions, contributing to the chemical evolution of galaxies in the form of metals and dust. This thesis investigates the interdependence between ISM physical properties (e.g., atomic/molecular gas, dust, and metal abundance) on resolved regions in nearby galaxies, including dwarf and spiral galaxies. This requires linking spatially-resolved optical spectroscopy (termed 'Integral Field Spectroscopy' or IFS) data with multi-wavelength observations spanning the far-ultraviolet to the far-infrared and radio. We trace the multi-phase ISM, quantify star formation, gas, dust, and metal enrichment, and ultimately provide a holistic view of galaxy ecosystems, essential for understanding how galaxies evolve across cosmic time.

The first Chapter explores the potential of colder (i.e., lower temperature and/or less turbulent) atomic hydrogen (HI) gas components as tracers of star-forming gas in nearby galaxies. We analyse narrow (colder) and broad (warmer) kinematic components by decomposing HI 21 cm data cubes for 7 nearby galaxies (both dwarfs and spirals). A cross-correlation analysis between the narrow HI and molecular gas or star formation rate (SFR) surface density at different spatial scales reveals that dwarf galaxies exhibit the strongest correlation at 500-700 pc. We also find that spatial resolution affects the derived results: higher physical resolution data yield a higher median fraction of narrow HI gas. Accounting for this, dwarf galaxies consistently show a larger fraction of narrow HI gas than spirals. These results underscore the role of colder HI as a possible tracer of cold HI or molecular hydrogen at low metallicities, where traditional tracers such as CO are difficult to use. We also emphasise the need for high-resolution HI observations to better understand atomic-to-molecular gas conversion.

The second Chapter presents the spatially resolved (sub-kiloparsec) relationship between dust and metal abundances in 11 nearby galaxies from the wide field-of-view TYPHOON/PrISM IFS survey. We find significant scatter in dust abundance in low/intermediate metal abundance galaxies, consistent with predictions from dust evolution models. We implement dust evolution models to explain this trend, and they can be explained by: (1) a high supernova dust yield and (2) negligible photofragmentation of dust by ultraviolet radiation. We also propose that gas density may play an important role, possibly enabling early dust grain growth despite the galaxy's low metal abundance.

The third Chapter expands the spatially resolved analysis of dust and metal abundances, focusing on two low-metallicity nearby galaxies: Sextans A and Sextans B. Using new optical IFS observations from the Very Large Telescope with the MUSE instrument, we map --- for the first time --- a wide view of the metal abundance in Sextans B. Combined with multi-wavelength data, we find unusually high dust abundances in both galaxies, prompting investigation into the mechanisms behind such enrichment. We apply dust evolution models to explore possible scenarios driving this elevated dust content.

In the final Chapter, I summarise the thesis, discuss the broader implications of the three studies, and outline potential future work to further advance our understanding of the ISM of galaxies and galaxy evolution. Show more