MUSE-ALMA Haloes

XIV. The ALMA Large Programme Data Release

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching near Munich, Germany
² Aix Marseille Univ., CNRS, LAM, (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
³ Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
⁴ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
⁵ CSIRO Space and Astronomy, PO Box 1130, Bentley, WA 6102, Australia
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Max-Planck-Institut für Astrophysik (MPA), Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
⁸ Observatoire Astronomique de Strasbourg – UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
⁹ Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 December 2025
Accepted: 19 February 2026

Abstract

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 < 100 K gas is tracing gas flows. The MUSE-ALMA Haloes survey assembled probes of the neutral atomic gas H 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.