CAN GALACTIC H-I BE RADIATIVELY SUPPORTED

I explore the effect of the photolevitation process, through which dusty diffuse clouds can rise to considerable high Galactic latitudes, on the global vertical distribution of the H I in the Galaxy. It is shown that the vertical support may be completely provided by the turbulence in the lower effective gravitational potential determined by the Galactic radiation field. The requirement of a population of fast clouds to match the observed profiles can be relaxed to consider only moderate-to-low values of the dispersion velocities of the neutral gas. In addition, the apparent observed constancy of the H I scale height with galactocentric radius is naturally explained by the model in terms of the similar behavior of the Galactic radiative (inclusive of the H II region distribution) and gravitational fields. Some discussion on the general validity of the study and on possible relevant additional effects is also given.