# Signatures of diffuse interstellar gas in the Galaxy Evolution Explorer all sky survey

## TL;DR

This paper presents a new automated method to detect diffuse interstellar medium features in GALEX UV survey data, revealing structures like star-forming regions and loops with low signal levels.

## Contribution

We developed and applied an unsupervised algorithm utilizing the UV background fluctuations index to identify faint ISM features in GALEX FUV images, providing a new tool for astrophysical analysis.

## Key findings

- Detection of ISM features at very low UV signal levels
- Identification of star-forming regions and loops like Loop I
- Creation of an online catalogue of UBF index values

## Abstract

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 are detected as well as the UV counterparts to nebulae and molecular clouds. 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 . 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 FUV (1344 -1786 Angstroms) band since this is less polluted by stellar sources, facilitating the automated detection. The UBF index is shown to be sensitive to the main star forming regions within the Gould's Belt, as well as to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalogue with the UBF index values is made available on-line to the community.