2.1  :  Simulations

This site makes the results of two main simulations available to the public. The first of these is the Millennium Simulation, performed by Volker Springel (MPA) using a specially customized version of the GADGET-2 simulation code. The second is the Millennium-II Simulation, perfomed by Mike Boylan-Kolchin (MPA) using Volker Springel's GADGET-3 code. Both are pure dark matter simulations in a periodic cube using 10,077,696,000 simulation particles. The main differences between the two are the size of the box (500 Mpc/h for Millennium, 100 Mpc/h for Millennium-II), the force resolution (Plummer-equivalent softening of 5 kpc/h for Millennium, 1 kpc/h for Millennium-II), and the particle mass (8.6 x 10⁸ M_sun/h for Millennium, 6.9 x 10⁶ M_sun/h for Millennium-II). A smaller version of the Millennium Run, the milli-Millennium Simulation, is also available on this site. This simulation used the same cosmology and resolution as the Millennium Simulation but in a 62.5 Mpc/h box with 19,683,000 particles.

The simulation parameters for the Millennium and Millennium-II Simulations are as follows:

• Ω_m = Ω_dm+Ω_b = 0.25
  density parameter (ρ_m/ρ_crit) in total matter
• Ω_b = 0.045
  density parameter in baryons
• Ω_Λ = 0.75
  density parameter of dark energy
• h = H₀/100 km/s/Mpc = 0.73
  Hubble parameter in units 100 km/s/Mpc
• n_s = 1
  spectral index of the primordial power spectrum
• σ₈ = 0.9
  mass density fluctuation amplitude in 8 Mpc/h sphere at redshift zero
• Number of particles = 2160³ = 10,077,696,000
• m_p = 8.6 x 10⁸ M_sun/h (Millennium)
  m_p = 6.9 x 10⁶ M_sun/h (Millennium-II)
• L = 500 Mpc/h (Millennium)
  L = 100 Mpc/h (Millennium-II)
  size of the cubic simulation box
• ε = 5 kpc/h (Millennium)
  &epsilon = 1 kpc/h (Millennium-II)
  Plummer-equivalent force softening