Modelling Mg ii resonance doublet spectra from star-forming galaxies at z ∼ 1

We investigate the properties of cold gas at around star-forming galaxies at using Mg ii spectra through radiative transfer modelling. We utilize a comprehensive data set of 624 galaxies from the MAGG and MUDF programmes. We focus on Mg ii emission from galaxies and their outskirts to explore the cold gas within galaxies and the circumgalactic medium (CGM). We model Mg ii spectra for 167 individual galaxies and stacked data for different stellar mass bins. The Mg ii spectrum and surface brightness vary significantly with stellar mass. In low-mass galaxies (M∗), Mg ii emission is observed in both core (Rrm p 10 kpc) and halo regions (10 kpc), strong core absorption and more extended halo emission are prominent. This indicates that more massive galaxies have more cold gas. Radiative transfer modelling allows us to investigate key parameters such as the Mg ii column density 30 kpc), while in higher mass galaxies (10) and the outflow velocity. We identify a negative correlation between and. Since higher stellar mass galaxies exhibit a higher and lower, this suggests an abundance of slowly moving cold gas in massive galaxies. In addition, the fitting results of halo spectra indicate the presence of intrinsic Mg ii absorption and strong anisotropy of the cold gas distribution around massive galaxies. This study is not only a proof-of-concept of modelling spatially varying Mg ii spectra but also enhances our understanding of the CGM and provides insights into the mass-dependent properties of cold gas in and around galaxies.