Hydrodynamical simulations of galaxy formation with non-Gaussian initial conditions

TL;DR

This study uses hydrodynamical simulations to explore how small-scale primordial non-Gaussianities, especially negative $f_{NL}$, influence galaxy formation and could help address cosmological and galaxy formation tensions.

Contribution

It demonstrates that negative small-scale non-Gaussianities can lead to more disky galaxies, suggesting a potential solution to existing cosmological and galaxy formation tensions.

Findings

Negative $f_{NL}$ delays galaxy assembly.

Simulated galaxies with negative $f_{NL}$ are more disky.

Potential to alleviate cosmological and galaxy formation tensions.

Abstract

Collisionless simulations of structure formation with significant local primordial non-Gaussianities at Mpc scales have shown that a non-Gaussian tail favouring underdensities, with a negative $f_{\rm NL}$ parameter, can significantly change the merging history of galaxy-sized dark matter halos, which then typically assemble later than in vanilla $\Lambda$CDM. Moreover, such a small-scale negative $f_{\rm NL}$ could have interesting consequences for the cosmological $S_8$ tension. Here, we complement our previous work on collisionless simulations with new hydrodynamical simulations of galaxy formation in boxes of 30 Mpc/$h$, using the {\sc RAMSES} code. In particular, we show that all feedback prescriptions being otherwise identical, simulations with a negative $f_{\rm NL} \sim -1000$ on small scales, hence forming galaxies a bit later than in vanilla $\Lambda$CDM, allow to form simulated galaxies with more disky kinematics than in the vanilla case. Therefore, such small-scale primordial non-Gaussianities could potentially help alleviate, simultaneously, tensions in cosmology and galaxy formation. These hydrodynamical simulations on small scales will need to be complemented with larger box simulations with scale-dependent non-Gaussianities, to statistically confirm these trends and explore their observational consequences in further detail.