#21cmFAST in MP-Gadget rundown
*Syncpoints are set up every 10 Myr or so (free parameter) in order to trigger the excursion set. *When we reach one of the UV syncpoints, three particle meshes are created for mass, stellar mass, and star formation rate, with the same communication and layout as the long-range force code *We then step through filters of different scales PFFT and count photons in each cell (from stellar mass * photons per baryon) to determine which cells are ionised, and calculate J21 if so. This is the excursion set model presented in Mesinger et al 2011. (astro-ph:1003.3878) with UV background from Sobacchi & Mesinger 2013 (astro-ph:1301.6781). *This J21 is then converted into ionisation and photoheating rates, assuming a certain spectral slope (free parameter) between the HI and HeII ionisation thresholds. This is then passed into the existing cooling functions.
##Notes:
*new parameters: ..*ExcursionSetReionOn : 0 or 1 to disable/enable the excursion set ..*ExcursionSetZStop : redshift at which the cooling code reverts to global ionising background ..*ExcursionSetZStart : redshift at which the excursion set starts ..*UVBGdim : dimension of the excursion set grids (can be different from the force grids) ..*ReionRBubbleMax : largest filter radius for the excursion set ..*ReionRBubbleMin : smallest filter radius for the excursion set ..*ReionDeltaRFactor : relative size of subsequent filter radii ..*ReionGammaHaloBias : UNUSED bias used in the meraxes grid model for calculating reionisation feedback in halos ..*ReionNionPhotPerBary : photons per stellar baryon, usually set to 4000 (TODO: cite) ..*AlphaUV : spectral slope for ionising radiation, currently a global constant ..*EscapeFractionNorm : escape fraction of photons from ionising sources at a 10^10 solar halo mass ..*EscapeFractionScaling : escape fraction power-law scaling with halo mass ..*UVBGTimestep : time in Myr between UVBG timesteps ..*ReionFilterType : Filter to use with 21CMFAST, 0 = real-space top-hat, 1 = k-space top-hat, 2 = gaussian ..*RtoMFilterType : Filter to use with 21CMFAST radius to mass, 0 = top-hat, 1 = gaussian ..*J21CoeffFile : path to the table containing photo-ionisaiton and heating rates versus spectral slope at J21 == 1
This excursion set model takes negligible time compared to the rest of the simulation. Tested up to 100Mpc boxes with 0.25 Mpc UV grid resolution.