From the computational to the observed Universe: Studying galaxy formation through stellar kinematics and strong gravitational lensing

• Applicant: Professor Dr. Volker Springel
• Subject Area: Astrophysics and Astronomy
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391742280

• Final Report Year: 2022

Final Report Abstract

In this project, we have analysed three state-of-the-art hydrodynamical simulation projects of galaxy formation, Illustris, Auriga, and IllustrisTNG, and confronted their predictions with observational data. We focussed our study on four different topical areas, which are all particularly timely given both observational progress and the only recently acquired capability of the theoretical models to make robust predictions in these areas based on cosmological simulation models. These topics are the (i) dynamics and stellar kinematical structure of galaxies, the (ii) chemical enrichment processes in disk galaxies, the (iii) density profiles of massive elliptical galaxies as relevant for strong gravitational lensing, and (iv) the formation and impact of magnetic fields on galaxy evolution. In each area, numerous results have been obtained on the many open questions in the field, thereby helping to make progress on the unsolved problems. For example, we could establish that the TNG100 simulation of the IllustrisTNG broadly reproduces the observed fractions of different stellar orbital components and their stellar mass dependencies as observed for the galaxies in the CALIFA survey. But interestingly, several marginal disagreements between the simulation and observations could be established as well, for example the average cold-orbit fractions of the simulated galaxies of low stellar mass are systematically higher than the observational data. We explored the total density profiles of early-type galaxies in the IllustrisTNG simulation, finding that they are close to isothermal. However, the slope values show weak correlations with galactic properties, including stellar mass, effective radius, stellar surface density, central velocity dispersion, central dark matter fraction and in-situ-formed stellar mass ratio. The relations are generally in good agreement with observations, but only if feedback from black holes is included in the simulations. In a pioneering analysis we studied the chemical enrichment of Milky Way-sized galaxies with rapid neutron capture elements (r-process). We could show that that the majority of metalpoor stars are r-process enriched for a broad range of different enrichment models. Also, dwarf galaxies which experience a single r-process event early in their history show highly enhanced r-process abundances at low metallicity, which is seen both in observations and in our simulation models. Finally, we showed that the circum-galactic medium of Milky Way-like galaxies becomes magnetised at early times via galactic outflows that transport magnetised gas from the disk into the halo. At late times an in-situ turbulent dynamo that operates on a timescale of Gigayears further amplifies the magnetic field in the circumgalactic medium, leading to saturation at typical values of 0.1 µG at the virial radius shortly before the present epoch. Interestingly, the resulting Faraday rotation signal is in excellent agreement with recent observations.

Publications

• Gas accretion and galactic fountain flows in the Auriga cosmological simulations: angular momentum and metal redistribution. Monthly Notices of the Royal Astronomical Society, 490(4), 4786-4803.
  Grand, Robert J. J.; van de Voort, Freeke; Zjupa, Jolanta; Fragkoudi, Francesca; Gómez, Facundo A.; Kauffmann, Guinevere; Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker & White, Simon D. M.
  
• Magnetizing the circumgalactic medium of disc galaxies. Monthly Notices of the Royal Astronomical Society, 498(3), 3125-3137.
  Pakmor, Rüdiger; van de Voort, Freeke; Bieri, Rebekka; Gómez, Facundo A; Grand, Robert J J; Guillet, Thomas; Marinacci, Federico; Pfrommer, Christoph; Simpson, Christine M & Springel, Volker
  
• Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies. Monthly Notices of the Royal Astronomical Society, 494(4), 4867-4883.
  van de Voort, Freeke; Pakmor, Rüdiger; Grand, Robert J J; Springel, Volker; Gómez, Facundo A & Marinacci, Federico
  
• The effect of magnetic fields on properties of the circumgalactic medium. Monthly Notices of the Royal Astronomical Society, 501(4), 4888-4902.
  van, de Voort Freeke; Bieri, Rebekka; Pakmor, Rüdiger; Gómez, Facundo A; Grand, Robert J J & Marinacci, Federico