A new approach to determine optically thick H2 cooling and its effect on primordial star formation

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We present a new method for estimating the H2 cooling rate in the optically thick regime in simulations of primordial star formation.

• Our new approach is based on the TreeCol algorithm, which projects matter distributions onto a spherical grid to create maps of column densities for each fluid element in the computational domain.
• We have improved this algorithm by using the relative gas velocities, to weight the individual matter contributions with the relative spectral line overlaps, in order to properly account for the Doppler effect.
• We compare our new method to the widely used Sobolev approximation, which yields an estimate for the column density based on the local velocity gradient and the thermal velocity.