The formation of disk galaxies in a cosmological context: Populations, metallicities and metallicity gradients

TL;DR

This study uses cosmological simulations to explore the formation and metallicity distribution of different stellar populations in disk galaxies, revealing gradients and correlations with initial density fluctuations.

Contribution

It presents the first simulation results incorporating detailed physics to reproduce galaxy components and their metallicity gradients within a cosmological context.

Findings

The simulated galaxy has a metal-rich bulge, metal-poor halo, and a disk with a metallicity gradient.

Halo and bulge stars are predominantly old (>10.5 Gyr).

The disk's metallicity gradient is approximately -0.05 dex/kpc.

Abstract

We present first results concerning the metallicities and stellar populations of galaxies formed in a cosmologically motivated simulation. The calculations include dark matter, gas dynamics, radiation processes, star formation, supernovae feedback, and metal enrichment. A rotating, overdense sphere with a mass of $8\,10^{11}\,$\Msol\ serves as initial model. Converging and Jeans unstable regions are allowed to form stars, which get their metallicity from the gas they are formed from. Via supernovae, metal enriched gas is given back to the interstellar medium. The forming galaxy shows the main properties of spiral galaxies: A metal rich bulge, a metal poor stellar halo and a disk of nearly solar composition. Halo and bulge consist predominantly of old stars ($>10.5\,$Gyrs). The disk has a metallicity gradient of $\dd(\log Z) / \dd r = - 0.05\,$kpc$^{-1}$, whereas the halo shows none. The models also exhibit a correlation between the metallicity of Pop~II stars and the power of small scale fluctuations. The stars of the bulge form from gas which is initially located in the largest maxima of the primordial density fluctuations, whereas the halo stars originate from gas accumulated in less pronounced maxima.