MUSE-ALMA Haloes

The interactions between gas and galaxies are of paramount importance to our understanding of structure formation. A fundamental element of such baryon cycle studies is a complete census of the condensed matter (stars and cold gas) in both galaxies and their immediate surroundings, the so-called circumgalactic medium. Of particular importance are the processes of converting molecular gas into stars and deciphering whether this I, ionised gas, and stellar component for a sample of 79 z ∼ 0.5 galaxies. This was achieved by combining absorption-line spectroscopy of background quasars with a projected impact parameter as low as 5 kpc and as high as 250 kpc to probe the low-density circumgalactic gas with emission-line tracers of both ionised gas and stars. This paper presents the Large Programme observational setup and releases the data characterising the molecular phase of some of the MUSE-ALMA Haloes targets so as to reach a complete census of their condensed baryons. ALMA’s unique millimetre coverage and high sensitivity are ideal for characterising the CO emission of these z ∼ 0.5 H I-selected galaxies. By measuring the molecular mass, kinematics, gas flows, and gas fractions, this project (i) quantifies the role of molecular gas in H I-rich galaxies, (ii) characterises the molecular phase of gas flows from morpho-kinematics analyses, and (iii) establishes a census of the condensed baryons in the interstellar and circumgalactic media. Ultimately, these results will provide unique insights into the baryon cycle – a crucial component of galaxy formation.