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

Abstract

We report on the first results of the Narrow-band Ultraviolet Imaging Experiment for Wide-field Surveys (NUVIEWS), a sounding rocket experiment designed to map the far-ultraviolet background in four narrow bands. This is the first imaging measurement of the UV background to cover a substantial fraction of the sky. The narrow band responses (145, 155, 161, and 174 nm, 7-10 nm wide) allow us to isolate background contributions from dust-scattered continuum, H2 fluorescence, and CIV 155 nm emission. In our first flight, we mapped one quarter of the sky with 5-10 arcminute imaging resolution. In this paper, we model the dominant contribution of the background, dust-scattered continuum. Our data base consists of a map of over 10,000 sq. degrees with 468 independent measurements in 6.25 by 6.25 sq. degree bins. Stars and instrumental stellar halos are removed from the data. We present a map of the continuum background obtained in the 174 nm telescope. We use a model that follows Witt, Friedman, and Sasseen (1997: WFS) to account for the inhomogeneous radiation field and multiple scattering effects in clouds. We find that the dust in the diffuse interstellar medium displays a moderate albedo (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 star forming regions. We also have discovered a significant variance from the model.