FAR-ULTRAVIOLET OBSERVATION OF THE AQUILA RIFT WITH FIMS/SPEAR

Abstract

We present the results of far ultraviolet (FUV) observations of the broad region around the Aquila Rift including the Galactic plane. As compared with various wavelength data sets, dust scattering is found to be the major origin of the diffuse FUV continuum in this region. The FUV intensity clearly correlates with the dust extinction level for E(B - V) < 0.2, while this correlation disappears for E(B - V) > 0.2 due to heavy dust extinction combined with the effect of nonuniform interstellar radiation fields. The FUV intensity also correlates well with H alpha intensity, implying that at least some fraction of the observed H alpha emission could be the dust-scattered light of H alpha photons originating elsewhere in the Galaxy. Most of the Aquila Rift region is seen devoid of diffuse FUV continuum due to heavy extinction while strong emission is observed in the surrounding regions. Molecular hydrogen fluorescent emission lines are clearly seen in the spectrum of "Aquila-Serpens," while "Aquila-East" does not show any apparent line features. CO emission intensity is also found to be higher in the "Aquila-Serpens" region than in the "Aquila-East" region. In this regard, we note that regions of star formation have been found in "Aquila-Serpens" but not in "Aquila-East."