Dark Flow 2D: Recovering a Coherent Bulk Motion from Noisy Cluster Velocities

Some surveys of distant galaxy clusters report a small coherent drift on top of the ordinary Hubble expansion — a "dark flow" that does not average away across the sky the way random peculiar velocities should. This simulator scatters a configurable number of galaxy clusters through a projected 3D volume, gives each one an outward Hubble-flow velocity plus a peculiar-velocity component built from a shared coherent vector and independent per-cluster noise, and then runs the same vector-averaging estimator real surveys use to try to recover that coherent vector from the noisy individual measurements. A convergence panel plots the running estimate against the number of clusters averaged so the 1/√N noise suppression is visible directly, and a histogram shows the live spread of one velocity component across the sampled field. Tune the injected flow speed, the noise dispersion, and the sample size, and drag the sky view to inspect the field from any angle.