Test 1: HII region expansion in a uniform gas at fixed temperature. Radially averaged neutral fraction plots at t = 10, 100, and 500 Myr. Shown are the results from SPHRAY (red), CRASH (purple), RSPH (green), C²-Ray (light blue), and all the other radiative transfer codes that completed this test (orange).

Test 1: HII region expansion in a uniform gas at fixed temperature. Neutral fraction surface plots produced by SPHRAY at t = 10, 100, and 500 Myr. The contours are at xHI = 0.1 and xHI = 0.9. This is one way to define the thickness of the ionization front. Note the color bar here is slightly different than those in the comparison project paper. (* the SPH particles were interpolated onto a 128x128 grid to make this plot and so the axes are measured in grid cells)