2006ApJ...644L.181L

Diffuse far-ultraviolet (FUV; 1370-1670 Å) flux from the Taurus molecular cloud region has been observed with the SPEAR/FIMS imaging spectrograph. An FUV continuum map of the Taurus region, similar to the visual extinction maps, shows a distinct cloud core and halo region. The dense cloud core, where the visual extinction A_v>1.5, obscures the background diffuse FUV radiation, while scattered FUV radiation is seen in and beyond the halo region, where A_v<1.5. The total intensity of H₂fluorescence in the cloud halo is I_H2=6.5x10⁴ photons/cm2/s/sr in the 1370-1670 Å wavelength band. A synthetic model of the H₂fluorescent emission fits the present observation best with a hydrogen density n_H=50/cm3, H₂column density N(H₂)=0.8x10²⁰/cm2, and incident FUV intensity I_UV=0.2. H₂fluorescence is not seen in the core, presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region.