VINTERGATAN-GM: How do mergers affect the satellite populations of MW-like galaxies?

TL;DR

This study uses hydrodynamical simulations to show that a galaxy's recent merger history influences its satellite population, but these effects diminish over time, affecting how we interpret galaxy properties.

Contribution

The paper introduces the VINTERGATAN-GM suite of simulations to analyze how specific merger events impact satellite populations over time.

Findings

Smaller mergers lead to up to 60% more satellites shortly after the event.

Differences in satellite populations fade by redshift zero.

Recent merger history significantly contributes to scatter in galaxy satellite properties.

Abstract

We investigate the impact of a galaxy's merger history on its system of satellites using the new \textsc{vintergatan-gm} suite of zoom-in hydrodynamical simulations of Milky Way-mass systems. The suite simulates five realizations of the same halo with targeted `genetic modifications' (GMs) of a $z \approx 2$ merger, but resulting in the same halo mass at $z=0$. We find that differences in the satellite stellar mass functions last for $2.25-4.25$ Gyr after the $z \approx 2$ merger; specifically, the haloes that have undergone smaller mergers host up to 60\% more satellites than those of the larger merger scenarios. However, by $z=0$ these differences in the satellite stellar mass functions have been erased. The differences in satellite numbers seen soon after the mergers are driven by several factors, including the timings of significant mergers (with $M_{\rm 200c}$ mass ratios $>1:30$ and bringing in $M_{\rm *} \geq 10^{8}{\rm M}_{\odot}$ at infall), the masses and satellite populations of the central and merging systems, and the subsequent extended history of smaller mergers. The results persist when measured at fixed central stellar mass rather than fixed time, implying that a host's recent merger history can be a significant source of scatter when reconstructing its dynamical properties from its satellite population.