Probing and Exploring high-redshift Galaxies Spectroscopically Using Svom gamma-ray bursts – PEGaSUS

The study of galaxy formation and evolution is one of the major topics of current extragalactic astrophysics. In the last few years, amazing progress has been made regarding the observational study of galaxy properties up to the highest redshift. JWST is making an impressive leap forward in the exploration of the hot, ionized gas of high-redshift galaxies. However, their neutral gas remains elusive despite it being one of the primary components of such high-redshift galaxies and of their circumgalactic medium. This neutral gas can be detected through its absorption of the light of a bright background source. Long Gamma-ray bursts (LGRBs) are a powerful tool to unveil the properties of the neutral interstellar medium (ISM) of their host galaxies, thanks to the detection of gas absorption lines in the optical/near-infrared spectra of their bright afterglows, independently of the brightness of the host galaxies. Even in the epoch of the ELT and JWST, LGRBs are a unique tool to probe in detail the properties of the neutral gas (such as hydrogen and metal content, kinematics) and dust of faint galaxies, that dominate in number the population of high-redshift galaxies. Furthermore, LGRBs are transients and, once their afterglows disappear, it is possible to detect the emission of the host galaxy's ionized gas as well.
To date, the limit on the use of LGRBs for such studies is the poor number of optical/near-infrared spectroscopic observations of LGRB afterglows and their host galaxies at z>2-3. Within this project, we will significantly increase this statistic thanks to the Sino-French space mission SVOM for GRB detection, and to its ground-based follow-up. We will perform and use spectroscopic observations of the afterglows of LGRBs detected by SVOM to explore the properties of faint high-redshift star-forming galaxies with the goal of answering the following questions:
- What are the properties of the neutral ISM gas? How do these properties evolve?
- What are the properties of dust? How do they evolve?
- How is star-formation connected to such properties?
- How do faint star-forming galaxies at high redshift impact the reionization?
Our project is focused on three Tasks: A) the study of the abundances, metallicity and kinematics of the neutral ISM gas; B) the study of dust in high redshift galaxies; C) the combination of the properties of the cold/warm absorbing gas with those of the emitting ionized gas of LGRB host galaxies. We will exploit our observational results also in synergy with cosmological simulations of galaxies.
Our project will generate, as a by-product, the redshift determination of SVOM-detected GRBs. This is a fundamental information including for the study of the GRB phenomenon itself.
Our results are crucial for the scientific exploitation and impact of the SVOM mission which represents an important effort of the French astrophysical community.