New research indicates that early galaxies contain large amounts of gas and dust, essential for star formation, more than theoretical models would indicate. In a recently published paper, a team of scientists from the NCBJ Astrophysics Division used observations from the ALPINE-ALMA program to investigate the presence of gas and dust in galaxies that formed within the first billion years after the Big Bang.

The evolution of galaxies is governed by many processes, related to the presence of gas and dust in the interstellar medium (ISM). The cooling of the gas leads to star formation, while stars in turn enrich the ISM with heavier elements, e.g. through supernova explosions or stellar winds. Also, processes such as galactic outflows, supernova shock waves or dust growth in the ISM affect the composition and amount of gas and dust in galaxies in differing magnitudes. And although this dust accounts for only 1% of interstellar matter, it significantly influences physical and chemical processes, e.g. by attenuating ultraviolet and optical light from young stars and its subsequent re-emission at different wavelengths. In order to fully understand the evolution of galaxies well, it is necessary to precisely describe and characterize all these processes.

Recent decades have seen tremendous developments in this field, including emergence of advanced telescopes such as the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), and the Atacama Large Millimeter/submillimeter Array (ALMA) observatory. The observations available from these instruments allow scientists to look back into the past, going back to times close to the Big Bang. Studies based on those observations found a significant amount of gas and dust in the ISM of galaxies formed within the first billion years since the Big Bang, thus posing a challenge to the theoretical models.

In a recent study, just published in the journal Astronomy & Astrophysics, an international team of astrophysicists along with members from the NCBJ’s Astrophysics Division analysed the composition of dust and gas in a sample of galaxies that formed around a billion years after the Big Bang. For this purpose, the team used observations from the ALPINE program (ALMA Large Program to INvestigate[CII] at Early times), which traced the light emitted by a specific ion of carbon, „[CII]”. These ions are formed by UV radiation from young stars, so the intensity of their emission carries information about the star formation process and activity in the galaxies from which they originate. This in turn enables us to estimate the content of the gas and dust through spectral energy distribution (SED) fitting techniques.

From a theoretical perspective, astrophysicists employed state-of-the-art chemical evolution models that allowed them to quantify the mechanisms responsible for the production or destruction of dust and gas in galaxies, including the effects of inflows of pristine gas, or galactic outflows. „We discovered that even at such an early stage in cosmic history, galaxies had already accumulated significant amounts of gas and dust” says Prasad Sawant, a PhD student in the NCBJ’s Astrophysics Division and first author of the paper. „Our study suggests that observed dust content in older galaxies can be explained by contributions from the supernova explosions. Although, in the case of the youngest galaxies, this process seems inadequate and hence requires an additional contribution from growth of the dust particles to reproduce the observed dust content.”

Another part of this study was testing the hypothesis of the variational initial mass function (IMF). This empirical function describes the initial distribution of masses for stars in a galaxy and the inferred physical properties of galaxies, including star formation rate, stellar mass, and dust mass, depend strongly on its assumed form. ’’Typically, studies adopt a canonical IMF ’’ – explains Prasad Sawant. „In our case, we also test a ’top-heavy’ IMF, which favours the formation of a greater proportion of massive stars, leading to an increased rate of supernovae and dust production.” The aim of this analysis was to reproduce the observed dust content in the youngest galaxies by assuming a top-heavy IMF where canonical forms of IMF were not adequate. Results of this analysis have shown that assuming a top-heavy IMF improves the agreement between model predictions and observational data, compared to a standard Chabrier IMF.

The work of astrophysicists led by Mr. Sawant has shown important mechanisms governing the formation and destruction of dust in galaxies of the early Universe, especially the dominant role of supernovae explosions and dust growth in the ISM. Moreover, the improved agreement of the model with observations after using the revised form of the IMF warrants further investigation, particularly with upcoming JWST observations.

This work was done under project „DINGLE – Dust IN Galaxies: Looking through its Emission (P.I: dr hab. Ambra Nanni)” which was funded by NCN.

The full results of the study are available in the publication: „The ALPINE-ALMA[CII] Survey: Unveiling the baryon evolution in the interstellar medium of z ∼ 5 star-forming galaxies”; P. Sawant, A. Nanni, M. Romano, D. Donevski, G. Bruzual, N. Ysard, B. C. Lemaux, H. Inami, F. Calura, F. Pozzi, K. Małek, Junais, M. Boquien, A. L. Faisst, M. Hamed, M. Ginolfi, G. Zamorani, G. Lorenzon, J. Molina, S Bardelli, E. Ibar, D. Vergani, C. Di Cesare, M. Béthermin, D. Burgarella, P. Cassata, M. Dessauges-Zavadsky, E. D’Onghia, Y. Dubois, G. E. Magdis, H. Mendez-Hernandez; A&A 694 A82 (2025); DOI: https://doi.org/10.1051/0004-6361/202451542

To learn more about ALPINE-ALMA[CII] survey: http://alpine.ipac.caltech.edu/

Illustration: Composite image of a galaxy situated at redshift ~ 4.5 (formed around 1.3 billion years after the Big Bang), created from F090W (blue), F200W (green), and F444W (red) filters of James Webb Space Telescope – NIRCam which highlights regions of intense star formation. Overlaid contours are detection from the Atacama Large Millimeter/submillimeter Array (ALMA): pink shows dust continuum, tracing the galaxy’s dust, and yellow depicts[CII] 158 µm emission, revealing the distribution of ionized carbon[CII] gas.