Below follows a description of the tests. Note that this wiki version is still under development and that the AUTHORITATIVE description of the tests is still given in this Description of the tests.

HII region growth in an isothermal constant density field.

This test is the classical problem of an H II region expansion (Strömgren 1939; Spitzer 1978). A steady, monochromatic (hν = 13.6 eV) source emitting N_γ ionizing photons per unit time is turning on in an initially-neutral, uniform-density, static environment with hydrogen number density n_H.

The numerical parameters are:

• Mesh size: 128³ (cartesian)
• computational box dimension L = 6.6 kpc
• gas number density (hydrogen) n_H = 10^-3 cm^-3,
• gas temperature T=10⁴ K (fixed)
• initial ionization fraction x(HI) = 1.2×10^-3 (given by collisional equilibrium)
• N_γ = 5×10⁴⁸ photons s^-1.
• Spectrum: monochromatic (hν = 13.6 eV)
• Source position (xs, ys, zs) = (1,1,1) cells (i.e. in the corner of the box).
• Running time t_sim = 500 Myr.

For these parameters the recombination time is t_rec = 3.86×10¹⁵ s = 122.4Myr, so the simulation is running for about 4t_rec. Assuming a recombination rate α_B(T) = 2.59×10^-13 cm³s^-1 at T = 10⁴ K, then the Strömgren radius is r_S = 5.4 kpc.

The required outputs are

• The neutral fraction of hydrogen on the whole grid at times t = 10, 30, 100, 200, and 500 Myr.
• The I-front position (defined by x(HI)=0.5) and velocity against time along the x-axis.

Single HII region growth in a constant density field (non-isothermal). This is the same problem as Test 1, except that we now allow the ionizing photons to heat the gas.

The numerical parameters are:

• Mesh size: 128³ (cartesian)
• Box size L = 6.6 kpc
• gas number density (hydrogen) n_H = 10^-3 cm^-3,
• Initial gas temperature T=100 K (fixed)
• initial ionization fraction x(HI) = 0
• N_γ = 5×10⁴⁸ photons s^-1.
• Spectrum: : 10⁵ K black-body
• Source position (xs, ys, zs) = (1,1,1) cells (i.e. in the corner of the box).
• Running time t_sim = 500 Myr.

For these parameters the recombination time is t_rec = 3.86×10¹⁵ s = 122.4Myr, so the simulation is running for about 4t_rec. Assuming a recombination rate α_B(T) = 2.59×10^-13 cm³s^-1 at T = 10⁴ K, then the Strömgren radius is r_S = 5.4 kpc.

The required outputs are

• The neutral fraction of hydrogen (x(HI)) and temperature (T) on the whole grid at times t = 10, 30, 100, 200, and 500 Myr.
• Time (Myr), I-front position (kpc) (defined by x(HI)=0.5), I-front velocity (km/s), along the x-axis. ASCII format II.

HII region penetration into a spherical cloud (non-isothermal). The incident photons are entering the box at the y=0 side in a plane parallel fashion.

The numerical parameters are:

• Mesh size: 128³ (cartesian)
• Box size L=6.6 kpc
• Ionizing photon flux at y=0: F = 10⁶ s^-1cm^-2
• initial ionization fraction x(HI) = 0
• gas number density of environment: n_out = 2×10^-4 cm^-3
• gas temperature of the environment: T = 8,000 K
• gas number density of cloud: nclump = 200n_out = 0.04cm^-3
• gas temperature of the cloud T_clump = 40 K.
• Radius of the cloud: r_clump = 0.8 kpc
• Center of the cloud: (xc,yc, zc) = (5,3.3,3.3) kpc, or (xc,yc, zc) = (97,64,64) cells.
• Running time t_sim = 15 Myr.

• The neutral fraction of hydrogen (x(HI)) and temperature (T) on the whole grid at times t = 1,2,3,5 and 15 Myr. ASCII format I
• Time (Myr), I-front position (kpc) (defined by x(HI)=0.5), I-front velocity (km/s), along the symmetry axis. ASCII format II.

HII region growth in a cosmological density field, multiple sources (non-isothermal)

The numerical parameters are:

• Mesh size: 128³ (cartesian)
• Boundary conditions: transmissive
• Box size L=0.5/h Mpc
• h=0.7
• Ω₀=0.27
• Ω_b=0.043
• Gas density: from ''density.bin'' (in cm^-3)
• Initial gas temperature: T = 100 K.
• Sources: from ''sources.dat'' (16 sources, for each 3 source positions (in cell units) and photon luminosities (in units of 10⁵² ionizing photons s^-1)
• Running time t_sim = 0.4 Myr.

• The neutral fraction of hydrogen (x(HI)) and temperature (T) on the whole grid at times t = 0.05,0.1,0.2,0.3 and 0.4 Myr. ASCII format I

Dynamical expansion of an HII region into a constant density medium.

The numerical parameters are

• Mesh size: 128³ (cartesian)
• Box size L = 15 kpc,
• Initial gas (hydrogen) number density n_H = 10^-3 cm^-3
• Initial gas temperature T = 100 K.
• initial ionization fraction x(HI) = 0,
• Source spectrum: 10⁵ K black-body.
• Source luminosity: ionizing photon rate N_γ = 5×10⁴⁸ photons s^-1
• The source is at the (0,0,0) corner of the box.
• Running time t_sim = 500 Myr.

For a temperature of the ionized gas T = 104 K and a recombination rate α_B(T) = 2.59×10^-13 cm³s^-1, we find a recombination time t_rec = 3.86×10¹⁵ s = 122.4 Myr an initial Strömgren radius r_S = 5.4 kpc, and a final Strömgren radius r_f≈185 kpc. This final pressure-equilibrium radius is thus well outside our computational volume, which was chosen to resolve well the more physically-interesting transition from R-type to D-type, which occurs around r_S.

The required outputs are

• Neutral fraction of hydrogen, gas pressure and temperature on the whole grid at times t = 10, 30, 100, 200, and 500 Myr (pressure in cgs (dyne/cm²), temperature in K). ASCII format I
• Mach number on the whole grid at times t = 10, 30, 100, 200, and 500 Myr. ASCII format I
• Time (Myr), I-front position (kpc) (defined by x(HI)=0.5), I-front velocity (km/s), along the x-axis. ASCII format II.

Dynamical expansion of an HII region into a flat-topped r^-2 density density field.

The numerical parameters are

• Mesh size: 128³ (cartesian)
• Box size L = 0.8 kpc,
• Initial gas (hydrogen) number density in core n_H(r < r₀) = n₀ = 3.2 cm^-3
• Core radius r₀=91.5 pc
• Initial gas (hydrogen) number density outside the core n_H(r > r₀) = n₀ (r₀/r)²
• Initial gas temperature T = 100 K.
• initial ionization fraction x(HI) = 0,
• Source spectrum: 10⁵ K black-body.
• Source luminosity: ionizing photon rate N_γ = 10⁵⁰ photons s^-1
• Source position at (xs, ys, zs)=(0,0,0) corner of the box.
• Running time t_sim = 75 Myr.

The required outputs are

• Neutral fraction of hydrogen, gas density and temperature on the whole grid at times t = 1, 3, 10, 25, and 75 Myr (density in cm^-3, temperature in K). ASCII format I
• Mach number on the whole grid at times t = 1, 3, 10, 25, and 75 Myr. ASCII format I
• Time (Myr), I-front position (kpc) (defined by x(HI)=0.5), I-front velocity (km/s), along the x-axis. ASCII format II.

Dynamical photo-evaporation of a spherical cloud (analogue of Test 3)

HII region penetration into a spherical cloud (non-isothermal). The incident photons are entering the box at the y=0 side in a plane parallel fashion.

The numerical parameters are:

• Mesh size: 128³ (cartesian)
• Box size L=6.6 kpc
• Ionizing photon flux at y=0: F = 10⁶ s^-1cm^-2
• initial ionization fraction x(HI) = 0
• gas number density of environment: n_out = 2×10^-4 cm^-3
• gas temperature of the environment: T = 8,000 K
• gas number density of cloud: nclump = 200n_out = 0.04cm^-3
• gas temperature of the cloud T_clump = 40 K.
• Radius of the cloud: r_clump = 0.8 kpc
• Center of the cloud: (xc,yc, zc) = (5,3.3,3.3) kpc, or (xc,yc, zc) = (97,64,64) cells.
• Running time t_sim = 15 Myr.

• The neutral fraction of hydrogen (x(HI)), pressure (p) and temperature (T) on the whole grid at times t = 1,5,10,25 and 50 Myr. ASCII format I
• Mach number on the whole grid at times t = 1, 5, 10, 25, and 75 Myr. ASCII format I
• Time (Myr), I-front position (kpc) (defined by x(HI)=0.5), I-front velocity (km/s), along the symmetry axis. ASCII format II.