Periodic Reporting for period 5 - FEEDGALAXIES (A new vantage point on how gas flows regulate the build-up of galaxies in the early universe)
Periodo di rendicontazione: 2022-11-01 al 2024-01-31
As part of this action, we have reached three transformative goals by leading some of the most ambitious observational campaigns on novel instruments. First, we have acquired direct images of the shape and chemical content of the gas filaments and gas envelopes near galaxies. Second, we have obtained new evidence on how this gas phase – an essential ingredient for the assembly and evolution of galaxies – evolves with time and changes with the number of close neighbors near galaxies. Finally, we have expanded our view of the gas-galaxy connection into a novel region of parameter space, reaching smaller galaxies that have remained elusive in the past but that account for most of the galaxies that populate the Universe. This project has thus added critical information to our appreciation of how galaxies assemble and evolve into the objects we see today in the Universe, contributing to a more complete picture of the events that lead to the assembly of the general galaxy populations, including our own Galaxy.
First, we have uncovered the emission from the gas surrounding galaxies, revealing for the first time gas filaments connecting multiple galaxies feeding from the cosmic fuel through which they actively form stars. The cosmic web we observed resembles the filaments predicted by computer simulation based on the current cosmological model, thus confirming this prediction strongly. Furthermore, we have detected, for the first time, the light from the heavy elements produced within stars and subsequently ejected in their gaseous envelopes. This new detection opens an exciting prospect for studying the poorly constrained feedback processes: an ensemble of mechanisms that regulate the efficiency with which galaxies convert gas in stars. This is a vital step for the build-up and evolution of galaxies.
Second, we have unveiled how the galaxy environment shapes the halo gas distribution. Galaxies are well-known to exhibit different properties according to the number of close neighbors, whereas systems living in the busiest environment have older stars and are devoid of gas. Our observations have added fresh clues to understanding the origin of these different properties by detecting a clear excess of gas near galaxies in rich environments compared to isolated systems across a large interval of cosmic times. For more evolved galaxies, this excess can be attributed to mechanisms actively removing gas from the galaxies. In contrast, for the galaxies observed in the younger universe, we linked this excess to a more intense gas accretion phase, leading to a rapid evolution.
Finally, our study has provided an expanded view of the gas environment of low-mass galaxy populations that have remained elusive in the past but that account for the large majority of the galaxies that inhabit the Universe. Our study has led to a picture in which these low-mass galaxies are connected by gas filaments that contain the majority of the dense gas. These are the most likely channels through which galaxies acquire gas. Extended pockets of more diffuse and enriched gas are also present, which we link to past galaxy assembly episodes that have spread heavy elements in the surrounding environment. With modeling from simulations, this action has, therefore, broadened our understanding of the baryon cycle of galaxies across approximately 6 billion years of cosmic time.
From the technical point of view, a significant contribution of this action has been the development of novel analysis techniques to exploit the ground-breaking nature of integral field spectrographs at large telescopes (in particular, the MUSE instrument at VLT). Specifically, we have developed one of the most advanced end-to-end pipelines to maximize the information content of the MUSE data, including numerical techniques to improve the sensitivity. Furthermore, we have put forward the basis of new ways to consistently connect detailed modeling of the gas surrounding galaxies with observations, thus paving the ground for more systematic and self-consistent comparisons between data and models.