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© Katrin Lehle

Cloudy With a Chance of Rain: Simulat­ing the Galac­tic Weather

Katrin Lehle – Hector RCD Awardee Dylan Nelson

Galax­ies are embed­ded in a rich and complex atmos­phere – the circum­galac­tic medium (CGM). Under­stand­ing the processes going on in the CGM is inevitable for a self-consis­tent model for galaxy evolu­tion. Thus, we will shed some light on open questions about galaxy clusters using numer­i­cal simula­tions. We will analyze the already exist­ing cosmo­log­i­cal state-of-the art simula­tion Illus­trisTNG and also write new types of simulation.

Galax­ies are not isolated islands of stars float­ing around in space but surrounded by a rich and complex atmos­phere – the circum­galac­tic medium (CGM). Clearly, a self-consis­tent theory of galaxy evolu­tion is only achiev­able if we under­stand the processes going on in the atmos­pheres of galaxies.

Just as our earth, a galaxy is a complex ecosys­tem and has a weather. Super­mas­sive black holes and super­novae inject massive amounts of energy into the atmos­phere and drive outflows. Obser­va­tions and simula­tions suggest that the gas in the atmos­phere is a multi-phase medium where cool, dense clouds may eventu­ally form within a hot and diffuse phase. These clouds can rain back onto the galaxy and fuel further star forma­tion and black hole accretion.

This baryonic cycle resem­bles similar­i­ties to the water cycle on earth, however, additional processes such as merging satel­lite galax­ies and cosmic inflows need to be consid­ered. Due to the complex­ity of the CGM it is crucial to employ numer­i­cal simula­tions for finding theoret­i­cal models. This is why we work with the state-of-the-art cosmo­log­i­cal hydro­dy­nam­i­cal simula­tion IllustrisTNG.

We focus on the most massive objects in the universe, namely galaxy clusters. Galaxy clusters are well suited for such studies since their gas can be obser­va­tion­ally well studied in X‑ray wavelengths. Further­more, galaxy clusters still bring some unresolved puzzles with them. For example we cannot observe cold gas reser­voirs and exces­sive star forma­tion in the centers even though the observed central cooling timescales suggest that star forma­tion should happen at a high rate.

In this PhD project we will shed some light on these unknown processes by analyz­ing already exist­ing cosmo­log­i­cal simula­tions and on the other hand writing new type of simulations.

Wolkig mit Aussicht auf Regen: Simulationen des galaktischen Wetters

In the figure the most massive dark matter halo of the TNG50 simula­tion is shown. The white circle depicts the virial Radius. The four differ­ent panels show differ­ent proper­ties of this halo. Upper left: stellar column density, upper right: entropy of the gas, lower left: bolomet­ric x‑ray luminos­ity of the gas, lower right: gas temperature.

Katrin Lehle

Heidel­berg University

Super­vised by

Hector RCD Awardee Dr.

Dylan Nelson

Physics, Infor­mat­ics

Disziplinen Dylan NelsonHector RCD Awardee since 2021