Fluorescent ultraviolet spectra of molecular hydrogen in star forming clouds

Abstract

The far-UV photons from the newly born stars make Photo-dissociation Regions (PDRs) on the surfaces of the nearby molecular clouds. In the PDRs, molecular hydrogens which absorb the far-UV photons in the Lyman-Werner bands are electrically excited, and then de-excited to the ground electrical states, emitting far-UV lines. These observations are only possible from space telescopes and can be one of the scientific purposes of the first Korean scientific satellite. In order to prove the feasibility of observations for various celestial sources, we run a radiative transfer code to simulate the H-2 fluorescent lines with various physical conditions, i.e., gas density, gas temperature, external far-UV field strength, and spectral energy distribution of the external UV field. The code considers bound-continuum transitions as well as bound-bound transitions. The total fluorescent intensities and the spectral shapes depend on the physical conditions. By observing the far-UV spectra from the PDRs, we can study the interaction of the young stars with the ambient clouds and the evolution process of the star forming clouds.