Zooming in on Star-Formation in the Andromeda Galaxy: Molecular Clouds Resolved with Wideband Millimeter Interferometry and Chemical Abundances of HII Regions

The Andromeda Galaxy (M31), the nearest neighbouring large spiral galaxy to the Milky Way, provides a unique external perspective on star formation and the interstellar medium (ISM). Molecular gas is the primary fuel for star formation and is largely contained within giant molecular clouds (GMCs). Observing GMCs with a wide range of properties is more difficult in the Milky Way, due to our position within the Galactic disc and uncertainties in distance measurements. For this, M31 becomes an ideal laboratory. This thesis presents three studies, which together characterise dust and gas properties of M31 GMCs including metallicity, CO conversion factor and the forces acting on cloud and subcloud scales. provide insight into the initial conditions of star formation. Optical spectroscopy of H ii regions is used to measure elemental abundance (metallicity) variation across the disc of M31. Metallicity generally decreases with galactocentric radius, however, significant scatter around this gradient indicates local variation in star formation conditions suggesting M31 has a recent history of galaxy interactions and mergers. Comparing H ii region metallicities with properties of their associated GMCs provides further insight into how cloud properties correlate with local chemical enrichment. Simultaneous submillimetre observations of thermal dust emission and CO isotopologues help constrain the CO-to-H2 conversion factor, �CO, in M31 GMCs. Dust continuum accurately traces H2 properties, enabling a direct measurement of �′ CO, the factor relating CO luminosity to dust mass, independent of H2 measurements. �′ CO is converted to �CO by the gas-to-dust ratio. Results indicate that �′ CO is approximately constant for M31 GMCs, and does not vary significantly with metallicity. Additionally, an assessment of the dynamical state of these GMCs provides further evidence that while GMCs are bound by external forces and not self-gravity, these observations trace dust emission from dense, gravitationally bound regions. Lastly, the nitrogen-to-oxygen abundance ratio (N/O) is examined for the same H ii region sample. Oxygen and nitrogen have different nucleosynthetic origins, and their ratio provides insight into the relative nucleosynthesis rates of stars with different masses. Our findings support recent evidence from observations and simulations suggesting that the M31 disc formed from a more intense and rapid burst of star formation than the MilkyWay disc. The derived N/O−O/H relationship for M31 shows that at high metallicities, N/O increases with increasing O/H, as theory predicts. However, the trend is significantly steeper than the general Milky Way relation for this metallicity range. Altogether these studies reveal that M31’s chemical evolutionary history differs from that of the Milky Way’s, and that star formation occurs in gravitationally bound regions of GMCs.