Validation of Foreground Emission Model using GALEX Medium Observations

Abstract

The study of diffuse ultraviolet (UV) background radiation is vital in the investigation of stellar and galactic evolution. Space-based UV observations are comprised of both foreground and background radiations. The foreground emission in an observation is a result of solar contamination in the direction of observation. In our previous work, we modeled airglow (one of the major constituents of the foreground emission) as a function of 10.7 cm Solar Flux and Sun Angle with great accuracy using GALEX deep observations. We adopt a similar methodology to validate the obtained model and run equivalent experiments here using far-UV (FUV) and near-UV (NUV) GALEX medium imaging surveys (MIS) with a total exposure time greater than 3300 s. We obtained a predictive model having excellent compatibility with the earlier model. Our analysis shows that the total foreground emission varies between 59 and 295 photon units in FUV whereas in NUV, it varies between 671 and 1195 photon units depending upon the date and time of observation. We also noticed a strong correlation between the background emission and optical depth both in FUV and NUV, especially in the low density regions. This clearly indicates that the major contributor in diffuse background radiation is the starlight scattered by interstellar dust grains.