Theoretical calculations of the HI, HeI and HeII free-bound continuous emission spectra

We present coefficients for the calculation of the continuous emission spectra of H I, He I and He II due to electron-ion recombination. Coefficients are given for photon energies from the first ionization threshold for each ion to the n = 20 threshold of hydrogen (36.5 mu m), and for temperatures 100 <= T <= 10(5) K. The emission coefficients for He I are derived from accurate ab initio photoionization data. The coefficients are scaled in such a way that they may be interpolated by a simple scheme with uncertainties less than 1 per cent in the whole temperature and wavelength domain. The data are suitable for incorporation into photoionization/plasma codes and should aid with the interpretation of spectra from the very cold ionized gas phase inferred to exist in a number of gaseous clouds.