Programme by Session

The transformative quality and quantity of MOONS spectroscopy will allow us to extend truly statistical studies of subtle galaxy physical properties out to high redshift. In order to take full advantage of these data it is important to develop correspondingly superior analysis techniques, moving beyond index measurements to obtain stronger constraints through full spectral fitting. In this talk I will introduce the BAGPIPES spectral modelling and fitting tool, which allows the user to fit complex models to spectroscopic data within a fully Bayesian framework. Crucially, BAGPIPES also allows for the modelling and fitting of systematic uncertainties arising from instrumental and atmospheric effects. I will demonstrate the use of BAGPIPES to analyse data from VANDELS, a uniquely deep, recently completed spectroscopic survey, designed to obtain high-SNR continuum spectroscopy for ~2000 galaxies from 1 z 7. In particular I will present the first science results from the VANDELS quiescent sample at 1.0 z 1.3. We consider the trend in mean stellar age with stellar mass, recovering a strong downsizing trend of ~1.5 Gyr per decade in stellar mass, in agreement with similar studies at lower redshifts. This is a strong observational constraint on feedback models in numerical simulations, and we demonstrate that the downsizing trend at z=1 is insufficiently strong in both Simba and IllustrisTNG. We also consider how galaxies which undergo quenching events move across the UVJ diagram towards the red sequence, and hence explore the relationship between the green-valley, post-starburst and quiescent populations.