Nebular free-bound continuum

A nebular free-bound continuum is emitted when a free electron is captured into a bound atomic level and its excess energy leaves as a photon. The threshold energies produce recombination edges such as the Balmer discontinuity. Its spectrum depends on electron temperature, ionic abundances, capture cross-sections and emission measure; it is distinct from bound-bound recombination lines and free-free bremsstrahlung.