Modelling dust scattering in our galaxy

Abstract

I have used Monte Carlo models with multiple scattering to predict the dust scattered light from our Galaxy and have compared the predictions with data in two ultraviolet bands from the Galaxy Evolution Explorer spacecraft. I find that 90 per cent of the scattered light arises from less than 1000 stars with 25 per cent from the 10 brightest. About half of the diffuse radiation originates within 200 pc of the Sun with a maximum distance of 600 pc. Multiple scattering is important at any optical depth with 30 per cent of the flux being multiply scattered even at zero reddening. I find that the global distribution of the scattered light is insensitive to the dust distribution with grains of 0.3 < a < 0.5 and g < 0.6. There is an offset between the model and the data of 100 and 200 ph cm−2 s−1 sr−1 Å−1 in the FUV and NUV, respectively, at the poles rising to 200–400 ph cm−2 s−1 sr−1 Å−1 at lower latitudes. The Monte Carlo code and the models of diffuse radiation for different values of the optical constants are available for download.