Catalogue of far-infrared loops in the Galaxy

Abstract

Aims: An all-sky survey of loop- and arc-like intensity enhancements has been performed in order to investigate the large-scale structure of the diffuse far-infrared emission. Methods: We used maps made of 60 and 100 micrometer processed IRAS data (Sky Survey Atlas and dust infrared emission maps) to identify large-scale structures: loops, arcs or cavities, in the far-infrared emission in the Galaxy. Distances were attributed to a subsample of loops using associated objects. Results: We identified 462 far-infrared loops, analyzed their individual FIR properties and their distribution. This data forms the Catalogue of Far-Infrared Loops in the Galaxy. We obtained observational estimates of f_in~30% and f_out~5% for the hot gas volume filling factor of the inward and outward Galactic neighbourhood of the Solar System. We obtained a slope of the power law size luminosity function {beta}=1.37 for low Galactic latitudes in the outer Milky Way. Conclusions: Deviations in the celestial distribution of far-infrared loops clearly indicate, that violent events frequently overwrite the structure of the interstellar matter in the inner Galaxy. Our objects trace out the spiral arm structure of the Galaxy in the neighbourhood of the Sun and their distribution clearly suggests that there is an efficient process that can generate loop-like features at high Galactic latitudes. Power law indices of size luminosity distributions suggest, that the structure of the ISM is ruled by supernovae and stellar winds at low Galactic latitudes while it is governed by supersonic turbulence above the Galactic plane.