Periodic Reporting for period 1 - ECOGAL (ECOology for Galaxies using ALMA archive and Legacy surveys)
Reporting period: 2023-10-01 to 2025-09-30
Galaxy formation and evolution are closely linked to the surrounding environment and to the properties of their host dark-matter haloes. To advance our understanding, it is essential to measure the non-stellar baryonic components in and around galaxies across a range of environments, thereby enabling a more complete characterisation of the connection between baryonic (normal) matter and dark matter halos. Motivated by this, ECOGAL (ECOology for Galaxies using ALMA Archive and Legacy surveys) aims to exploit the wealth of observations accumulated in the ALMA archive over the past decade to constrain the cold interstellar medium and to investigate both the cold and hot phases of the circumgalactic medium (CGM).
The first major achievement of ECOGAL is a public data release built from processing more than 200 ALMA programs accumulated over the past decade, and linking these products with ancillary data from facilities such as the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). Secondly, using the ECOGAL data products, we measured the cold-gas content of a red-and-dead galaxy in the early universe (~10.3 Gyr ago) through its dust continuum emission, finding evidence that additional gas accretion from the cosmic web may be required. Thirdly, we attempted to measure the gaseous content in the outer disk regions of galaxies to connect these measurements with those obtained within galaxies -- including the second ECOGAL result -- although the data did not reveal significant emission from either the cold or hot gas phases, even in the deepest ALMA observations available. Finally, we explored potential solutions by assessing the limitations of current facilities. Our analysis suggests that a large single-aperture submillimetre telescope could substantially advance our ability to probe the gaseous components around galaxies.
A number of ECOGAL results advance beyond the current state of the art. First, the ECOGAL public data release constitutes the largest ALMA compilation assembled to date for extragalactic studies, and its linkage with publicly available JWST and HST data significantly enhances its legacy value. Second, the detection of dust in some of the most massive red-and-dead galaxies challenges existing paradigms of galaxy evolution, especially given conflicting reports of negligible dust content in similar systems; this tension highlights the need for dedicated follow-up studies. Finally, the non-detection of cold and hot gas-phase components -- even in some of the deepest ALMA maps -- underscores the limitations of current facilities and points to the need for next-generation submillimetre observatories.