Diffuse Far-Ultraviolet Observations of the Taurus Region

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 Av > 1.5, obscures the background diffuse FUV radiation, while scattered FUV radiation is seen in and beyond the halo region, where Av < 1.5. The total intensity of H2 fluorescence in the cloud halo is I = 6.5 × 104 photons cm-2 s-1 sr-1 in the 1370-1670 Å wavelength band. A synthetic model of the H2 fluorescent emission fits the present observation best with a hydrogen density nH = 50 cm-3, H2 column density N(H2) = 0.8 × 1020 cm-2, and incident FUV intensity IUV = 0.2. H2 fluorescence is not seen in the core, presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region.