A tomographic reconstruction of intergalactic gas in the low-redshift Cosmic Web

• Applicant: Professor Dr. Philipp Richter
• Subject Area: Astrophysics and Astronomy
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 585782421

Modern cosmology predicts that matter in the Universe has evolved into a vast network of filamentary structures on Megaparsec scales, known as the Cosmic Web. A central unresolved question in astrophysics concerns how the diffuse intergalactic medium (IGM), which permeates the Cosmic Web, influences galaxy formation and evolution over cosmic time. Cosmological simulations suggest that large-scale gas flows between galaxies and the IGM are shaped by the surrounding cosmological environment. To study these processes observationally at statistically significant levels, extensive spectroscopic datasets are essential. In this PhD project, we will carry out a systematic and fully automated spectral analysis of over a thousand ultraviolet spectra obtained with HST/COS. Using advanced statistical techniques, we aim to construct a tomographic map of the low-redshift IGM (z < 0.5) and its components. We will analyze more than 30,000 absorption-line systems to investigate the properties of HI Lyman  and metal-ion absorption, allowing us to reconstruct the cross-section and physical conditions of the gas as a function of its cosmological environment, with an unprecedented statistical depth. Additionally, we will combine this absorption line dataset with archival information on several million galaxies to examine the space density and distribution of Lyman  and metal absorbers within individual filaments and voids. Our analysis will employ sophisticated statistical tools to characterize their spatial and physical properties. Special focus will be placed on studying HI Lyman  and metal absorbers in and around low-mass galaxy groups, which host the bulk of the Universe‘s star-forming galaxies. Through this, we aim to explore the impact of AGN feedback on large-scale gas circulation and the redistribution of baryons beyond the group‘s virial radii. Ultimately, this new HST/COS survey will provide critical insights into the nature of intergalactic gas within the Cosmic Web and deepen our understanding of the relationship between intergalactic absorbers and the large-scale structures in which they reside.

• DFG Programme: Research Grants