Diffuse UV Observations near Taurus Molecular cloud with GALEX data

Abstract

We have studied the diffuse ultraviolet radiation in the vicinity of the Taurus Molecular Cloud employing the latest Galaxy Evolution Explorer data. We also have studied the dust-reddening as evident from E(B-V) data in the region with three different dust maps. The Planck Collaboration XI et al. 2014 dust map was used for correlation studies between the diffuse background and the dust reddening. A strong correlation (r=0.9) between the diffuse far ultraviolet and near ultraviolet shows maximum contri- bution comes from dust-scattered starlight. We have also confirmed the earlier reported anti-correlation between the diffuse background and the reddening (Hurwitz 1994; Lee et al. 2006) with the latest diffuse GALEX data of Murthy 2014b. We used a Monte Carlo dust code to model dust scattered radiation in the region using HIPPARCOS stars as the sources of ultraviolet photons. We have tried modified dust distribution in the Taurus Molecular Cloud with Planck Collaboration XI et al. 2014 (Model-1) and with Green et al. 2015 (Model-2) reddening maps separately. Both models give similar results in general and show little effects on dust distributions. We have run a series of Monte Carlo simulation models to constrain dust grain albedo (a) and phase-factor (g). The best _t model is found to occur for an albedo value of 0.3. Many stars with a broad range of positions and distances significantly contribute towards the total ux, and hence the level of scattered radiation is appeared to be independent of the phase-factor values. Our dust scattered models shows that the observed anti-correlation between the diffuse background and the dust reddening is in-fact due to shadowing of the thick molecular clouds in front. Additionally, a more detailed analysis shows that the coincidental presence of bright HIPPARCOS stars (accidental) towards the optical thin side (lower galactic longitude side) of the cloud complex exacerbate the anti-correlation between the diffuse background and the dust reddening. newline