Multi-wavelength correlation studies of diffuse emission from the Aquila Rift

Abstract

We present a multi-wavelength correlation study of diffuse ultraviolet radiation using GALEX observations towards the Aquila Rift. Apart from airglow and zodiacal emissions, we find a diffuse background of 1300 -3700 ph cm −2 s −1 sr −1Å−1 in the far-ultraviolet (FUV: 1350 -1750Å) band and 1300 -2800 ph cm −2 s −1 sr −1Å−1 in the near-ultraviolet (NUV: 1750 -2850Å) band. The observed diffuse UV emissions are saturated with total as well as neutral hydrogen column density in the region due to high optical depth in UV (τ : 0.91-23.38). Higher values of FUV/NUV ratio in the region, greater than the threshold value of 0.6, along with the positive correlation between the ratio and FUV intensity are due to excess emission in the FUV band which is absent in the NUV band. We estimated the excess emission to be in the range ∼ 400 -2700 ph cm −2 s −1 sr −1Å−1 , plausibly due to H 2 fluorescence, ion line emissions and two-photon continuum emissions from the region in the FUV band, which also shows saturation in optically thick regions with N(H 2 ) as well as Hα emissions. Since N(H 2 ) and Hα emissions spread all over the region, the excess emission from the field is composite in nature and a detailed spectroscopic analysis is needed to disentangle the contribution from individual components.