Universität zu Köln

Brugaletta, Vittoria ORCID: 0000-0003-1221-8771 (2025). Self-Regulation of Star Formation and Outflows in the Low-Metallicity Interstellar Medium. PhD thesis, Universität zu Köln.

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Abstract

The evolution of the interstellar medium (ISM) and the self-regulation of star formation in low-metallicity environments remain open questions. These processes are crucial for understanding galaxy evolution in nearby dwarf galaxies, in the outer regions of the Milky Way, and in high-redshift galaxies. This thesis investigates the structure and evolution of the metal-poor ISM using magneto-hydrodynamic simulations of stratified ISM patches within the SILCC framework. The simulations include non-equilibrium chemistry, ISM heating and cooling, anisotropic cosmic ray (CR) transport, and comprehensive stellar feedback (stellar winds, far-UV and ionising radiation, supernovae, and CR injection). Following a bottom-up approach, we first examine the role of CR heating in the metal-poor gas by introducing a novel model that self-consistently derives the CR ionisation rate from the simulated CR energy density, allowing for spatial and temporal variability. We find that, due to the low dust content, CR heating can dominate over photoelectric heating in such environments. We then explore the effect of varying metallicity (from 0.02 to 1 Z_sun ) on the ISM structure and star formation. We find that lower metallicities reduce the mass fraction of cold and molecular (H2) gas, but the star formation and mass outflow rates remain similar for Z higher than 0.1 Z_sun, with a decline only at lower metallicities. Building on these results, we apply our CR heating model in a broader investigation of star formation self-regulation and the possibility of the ISM reaching a steady state. We test with our simulations the "Pressure-Regulated, Feedback-Modulated" (PRFM) star formation theory, which assumes the ISM to be in a steady state, reproducing its numerical predictions. However, we argue that the ISM in our simulations is not in true steady state, as we observe strong feedback-driven outflows. We also analyse the properties of these outflows and find that the mass outflow rate at 1 kpc lags the star formation rate by approximately 15 Myr. Overall, this work highlights the importance of metallicity in shaping the ISM, and contributes to our understanding of the self-regulation of star formation and feedback-driven outflows, across galactic environments.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Brugaletta, Vittoria brugaletta@ph1.uni-koeln.de orcid.org/0000-0003-1221-8771 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-789761
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Interstellar medium English Star formation English Galactic outflows English
Date of oral exam:	1 October 2025
Referee:	Name Academic Title Walch-Gassner, Stefanie Prof. Dr. Schilke, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78976