First we constructed a parent simulation of sufficient size to include thousands of Milky Way sized systems but also of sufficient resolution to construct good Lagrangian volumes. We decided on ~10,000 particles per Milky Way-sized host and a 100 Mpc/h volume. Our `level_max=10`

, which means our parent simulation’s effective resolution is (2^10)^3 = 1024^3, i.e. a parent particle mass,

$m_p = 8.72 \times 10^7 M_\odot$

# parentics.conf[setup]boxlength = 100zstart = 127levelmin = 10levelmin_TF = 10levelmax = 10padding = 8overlap = 4ref_center = 0.5, 0.5, 0.5ref_extent = 0.2, 0.2, 0.2align_top = yesbaryons = nouse_2LPT = nouse_LLA = noperiodic_TF = yes[cosmology]Omega_m = 0.3175Omega_L = 0.6825Omega_b = 0.049H0 = 67.11sigma_8 = 0.8344nspec = 0.9624transfer = eisenstein[random]seed[10] = 34567[output]format = gadget2filename = ./icsgadget_num_files = 128[poisson]fft_fine = yesaccuracy = 1e-5pre_smooth = 3post_smooth = 3smoother = gslaplace_order = 6grad_order = 6