NIHAO project I: Reproducing the inefficiency of galaxy formation across cosmic time with a large sample of cosmological hydrodynamical simulations

TL;DR

The NIHAO project uses 100 cosmological hydrodynamical simulations to successfully reproduce the observed inefficiency of galaxy formation across cosmic time, emphasizing the role of stellar feedback.

Contribution

This study introduces a large, unbiased sample of high-resolution simulations with consistent physics, demonstrating stellar feedback's key role in galaxy formation inefficiency.

Findings

Simulated galaxies match observed stellar mass-halo mass relation.

Star formation rates in simulations align with observations across cosmic time.

Stellar feedback is essential to reproduce galaxy formation inefficiency.

Abstract

We introduce project NIHAO (Numerical Investigation of a Hundred Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical simulations performed using the gasoline code, with an improved implementation of the SPH algorithm. The haloes in our study range from dwarf to Milky Way masses, and represent an unbiased sampling of merger histories, concentrations and spin parameters. The particle masses and force softenings are chosen to resolve the mass profile to below 1% of the virial radius at all masses, ensuring that galaxy half-light radii are well resolved. Using the same treatment of star formation and stellar feedback for every object, the simulated galaxies reproduce the observed inefficiency of galaxy formation across cosmic time as expressed through the stellar mass vs halo mass relation, and the star formation rate vs stellar mass relation. We thus conclude that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than the Milky Way.