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

We study the impact of the host on dwarf galaxy properties using four new Milky Way (MW)-like, ultra-high-resolution simulations (N_part > 10⁷) from the NIHAO project. We split our sample into satellite (R < R₂₀₀), nearby (1 < R/R₂₀₀ < 2.5), and field (R > 2.5R₂₀₀) galaxies. Simulated galaxies from all three groups are in excellent agreement with Local Group dwarf galaxies in terms of the stellar mass-velocity dispersion and stellar mass-metallicity relations, 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 a given stellar mass. The reason for this deficit in dark matter mass is the substantial mass loss experienced by satellites and ∼80 per cent of the nearby galaxies while orbiting inside R₂₀₀ at earlier times. However, both satellites and nearby objects fall back on to 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 ≈ 370 kpc) have a strong probability (≈83 per cent) of having been affected by the MW in the past. This naturally explains the lack of gas and recent star formation seen in Eri II.