The Narrow-band Ultraviolet Imaging Experiment for Wide-field Surveys (NUVIEWS)-I: Dust scattered continuum

摘要

We report on the first results of the Narrow-band Ultraviolet ImagingExperiment for Wide-field Surveys (NUVIEWS), a sounding rocket experimentdesigned to map the far-ultraviolet background in four narrow bands. This isthe first imaging measurement of the UV background to cover a substantialfraction of the sky. The narrow band responses (145, 155, 161, and 174 nm, 7-10nm wide) allow us to isolate background contributions from dust-scatteredcontinuum, H2 fluorescence, and CIV 155 nm emission. In our first flight, wemapped one quarter of the sky with 5-10 arcminute imaging resolution. In thispaper, we model the dominant contribution of the background, dust-scatteredcontinuum. Our data base consists of a map of over 10,000 sq. degrees with 468independent measurements in 6.25 by 6.25 sq. degree bins. Stars andinstrumental stellar halos are removed from the data. We present a map of thecontinuum background obtained in the 174 nm telescope. We use a model thatfollows Witt, Friedman, and Sasseen (1997: WFS) to account for theinhomogeneous radiation field and multiple scattering effects in clouds. Wefind that the dust in the diffuse interstellar medium displays a moderatealbedo (a=0.55+/-0.1) and highly forward scattering phase function parameter(g=0.75+/-0.1) over a large fraction of the sky, similar to dust in starforming regions. We also have discovered a significant variance from the model.