A Study of the Extragalactic UV Radiation in Helix Nebula using GALEX

Abstract

We have studied the ultraviolet sources using Galaxy Evolution Explorer medium imaging surveys in Helix Nebula and estimated UV fluxes by using aperture photometry in distant and near ultraviolet bands. The aperture photometric method produces reliable, accurate flux measurements and found inconsistent with the merged catalog of Galaxy Evolution Explorer. From the current results, the fluxes are consistent with brighter absolute magnitude up to 24.5 and the measurement error increases gradually to more than 50 % at the fainter magnitude side. Percentage of error in far UV is greater than near UV, due to the fact that brighter galaxies are more visible than the near UV sources. The diffuse UV contributors of zodiacal light, airglow contribution in the nebula were estimated. The total extragalactic UV radiation from the detected sources to the diffuse background in the nebula is of the order of 50 ± 14 photons cm-2sr-1s-1Å-1 in NUV band and 28 ±10 photons cm-2sr-1s-1Å-1 in FUV band. HIGHLIGHTS GALEX observations have the potential to find extragalactic UV sources Helix Nebula is first identified for distinct source detection Aperture photometric method can detect fainter sources up to the magnitude of 27 Extragalactic sources in the Helix nebula contribute to diffuse UV emission in the nebula GRAPHICAL ABSTRACT