Signatures of diffuse interstellar gas in the Galaxy Evolution Explorer all-sky survey ^★

AEGORA Research Group, Facultad de CC Matemáticas, Universidad Complutense de Madrid, 28040 Madrid, Spain
e-mail: aig@ucm.es

Received: 9 July 2018
Accepted: 9 September 2019

Abstract

Context. The all-sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped about 85% of the Galaxy at ultraviolet (UV) wavelengths and detected the diffuse UV background produced by the scattering of the radiation from OBA stars by interstellar dust grains. Against this background, diffuse weak structures were detected as well as the UV counterparts to nebulae and molecular clouds.

Aims. To make full profit of the survey, unsupervised and semi-supervised procedures need to be implemented. The main objective of this work is to implement and analyze the results of the method developed by us for the blind detection of ISM features in the GALEX AIS.

Methods. Most ISM features are detected at very low signal levels (dark filaments, globules) against the already faint UV background. We have defined an index, the UV background fluctuations index (or UBF index), to identify areas of the sky where these fluctuations are detected. The algorithm is applied to the images obtained in the far-UV (1344–1786 Å) band since this is less polluted by stellar sources, facilitating the automated detection.

Results. The UBF index is shown to be sensitive to the main star forming regions within the Gould’s Belt, and to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalog with the UBF index values is made available online to the community.