underlying density field (pixel by pixel) + reionisation parameters? 17/02/2025 Réunion GT ICR 30 It is a very high dimension problem: we use gradient descent Things get messy when there are ionised “bubbles” = gaps in data Need to impose a prior on the density in these missing pixels a. Matter power spectrum (known theoretically, e.g., inpainting) b. Cross-correlations (e.g., with CO maps, see Zhou & Mao 2023)