# Drivers of disc tilting I: Correlations and possible drivers for Milky Way analogues

## TL;DR

This study uses cosmological simulations to investigate the causes of disc tilting in galaxies, finding that cold gas misalignment, rather than dark matter properties, primarily drives the tilting process.

## Contribution

It demonstrates that cold gas misalignment is the main factor influencing disc tilting, challenging the assumed role of dark matter in this process.

## Key findings

- No correlation between dark halo properties and disc tilting.
- Strong correlation between gas misalignment and disc tilting.
- Gas cooling onto the disc is identified as the principal driver.

## Abstract

The direction of the spin vectors of disk galaxies change over time. We present the tilting rate of a sample of galaxies in the NIHAO suite of cosmological hydrodynamical simulations. Galaxies in our sample have been selected to be isolated and to have well determined spins. We compare the tilting rates to the predicted observing limit of Gaia, finding that our entire sample lies above the limit, in agreement with previous work. To test the role of dark matter and of gas we compare the weighted Pearson's correlation coefficients between the tilting rates and various properties. We find no correlation between the dark halo's tilting rate, shape, or misalignment with respect to the disc, and the tilting rate of the stellar disc. Therefore, we argue that, in the presence of gas, the dark halo plays a negligible role in the tilting of the stellar disc. On the other hand, we find a strong correlation between the tilting rate of the stellar disc and the misalignment of the cold gas warp. Adding the stellar mass fraction improves the correlation, while none of the dark matter's properties together with the cold gas misalignment improves the correlation to any significant extent. This implies that the gas cooling onto the disc is the principal driver of disc tilting.