Radiation from the Interstellar Hydrogen Atoms

The interstellar hydrogen atoms can be excited or ionized by the suprathermal particles. The resulting production rates of two photon raditation (due to 2s - 1s transition), Lyman alpha, Balmer alpha, and Paschen alpha photons are calculated in this paper. The energy spectrum of the suprathermal particles, of which protons of energies between 0.1 MeV and 10 MeV are supposed to be the major component, is estimated by extrapolation to lower energies from various cosmic ray evidences. It is shown that the particle flux so obtained can explain fairly well the fact that the interstellar clouds of neutral hydrogen have the mean temperature of about . Production rates of similar radiations by recombinations in the ionized hydrogen regions are also calculated. Possibility of observing those radiations from active clouds is discussed. It is also pointed out that in such active interstellar clouds particles could be accelerated by the violent motion of magnetic fields and may contribute to a source of cosmic rays to significant extent. When the acceleration in the cloud ceases to operate, the rapid cooling will follow. This will favour the formation of stars, as pointed out by HATANAKA, UNNo and TAKEBE.