The far-infrared continuum spectrum of the Milky Way explained by a dust and gas model

Max-Planck-Institut für Astrophysik - 85740 Garching, Germany

Received: 11 September 1995
Accepted: 15 February 1996

Abstract

The far-infrared continuum spectra observed in the FIRAS-COBE mission are explained by a one-component dust source in the Galaxy and a cold excess due to radiation of molecular hydrogen gas in the outer Galaxy. The dust model is based on an empirically tested temperature-dependent mass absorption coefficient and a reasonable dust density distribution close to the galactic plane. The temperature of the dust along the line of sight is determined by a fit curve. The gas source is conceivable as a small part of cold molecular hydrogen and helium gas in the outer Galaxy which is only observable in a small temperature interval at 11 K and at corresponding (equilibrium ) condensation densities of about . It is assumed that the high densities occur in very small and short-living inhomogeneities of the fractal-structured gas due to self-gravitation, turbulence and starting condensation in the elementary fragments, i.e. the gas is at a stage close to star formation. Preliminary tests show that the gas sources are very likely correlated with the well-known HI sources in the outer Galaxy. The gas sources contribute to the spectra still at latitudes up to |b| < 25–30 degrees, while the instrument noise is larger at higher latitudes.