NIHAO XV: The environmental impact of the host galaxy on galactic satellite and field dwarf galaxies

TL;DR

This study uses high-resolution simulations to analyze how the host galaxy influences the properties and evolution of dwarf galaxies, revealing significant mass loss and environmental effects.

Contribution

It provides new insights into the environmental impact on dwarf galaxies by analyzing their properties across different environments using ultra high-resolution simulations.

Findings

Satellites and nearby galaxies show lower velocity dispersions and gas fractions.

Dark matter mass deficits are due to substantial mass loss experienced by satellites.

Even distant dwarfs like Eri II are likely affected by the Milky Way's past influence.

Abstract

We study the impact of the host on dwarf galaxy properties using four new Milky Way-like, ultra high-resolution simulations, ($N_{\rm part} >10^7$) from the NIHAO project. We split our sample in satellite ($R<R_{200}$), nearby ($1<R/R_{200}<2.5$), and field ($R>2.5 R_{\rm 200}$) galaxies. Simulated galaxies from all three groups are in excellent agreement with Local Group dwarf galaxies in terms of: stellar mass-velocity dispersion, stellar mass-metallicity relation, star formation histories, and stellar mass functions. Satellites and nearby galaxies show lower velocity dispersions and gas fractions compared to field galaxies. While field galaxies follow global abundance matching relations, satellites and nearby galaxies deviate from them, showing lower dark matter masses for given stellar mass. The reason for this deficit in dark matter mass is substantial mass loss experienced by satellites and $\sim80$\% of the nearby galaxies, while orbiting inside $R_{200}$ at earlier times. However, both satellites and nearby objects fall back onto the relation for field galaxies if we use the maximum of their virial mass instead of the present-day value. This allows us to provide estimates for the peak masses of observed Local Group galaxies. Finally, using radial velocities, distances, and the velocity dispersion-stellar mass relation from our simulations, we derive a metric to distinguish between galaxies harassed by the central object and unaffected ones. Applying this metric to observed objects we find that even far away dwarf galaxies like Eri II ($D\approx$ 370 kpc) have a strong probability ($\approx 83$\%) of having been affected by the Milky Way in the past. This naturally explains the lack of gas and recent star formation seen in Eri II.