Diffuse Far-Ultraviolet Observations of the Taurus Region

Diffuse far-ultraviolet (FUV: 1370-1670 A) flux from the Taurus molecularcloud region has been observed with the SPEAR/FIMS imaging spectrograph. An FUVcontinuum map of the Taurus region, similar to the visual extinction maps,shows a distinct cloud core and halo region. The dense cloud core, where thevisual extinction is A_v > 1.5, obscures the background diffuse FUV radiation,while a scattered FUV radiation is seen in and beyond the halo region where A_v< 1.5. The total intensity of H2 fluorescence in the cloud halo is I_{H2} = 6.5x 10^4 photons cm^{-2} s^{-1} sr^{-1} in the 1370-1670 A wavelength band. Asynthetic model of the H2 fluorescent emission fits the present observationbest with a hydrogen density n_H = 50 cm^{-3}, H2 column density N(H2) = 0.8 x10^{20} cm^{-2}, and an incident FUV intensity I_{UV} = 0.2. H2 fluorescence isnot seen in the core presumably because the required radiation flux to inducefluorescence is unable to penetrate the core region.Comment: Accepted for ApJL, 4 pages, 3 figure