Astron. Astrophys. 344, 322-332 (1999)

First detection of the warm ionised medium dust emission

Implication for the cosmic far-infrared background

G. Lagache ¹, A. Abergel ¹, F. Boulanger ¹, F.X. Désert ² and J.-L. Puget <sup>1

1</sup> Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, F-91405 Orsay Cedex, France
² Laboratoire d'Astrophysique, Observatoire de Grenoble, B.P. 53, 414 rue de la piscine, F-38041 Grenoble Cedex 9, France

Received 15 July 1998 / Accepted 4 January 1999

Abstract

We present a new analysis of the far-IR emission at high Galactic latitude based on COBE and HI data. A decomposition of the Far-IR emission over the HI, H⁺ and H₂ Galactic gas components and the Cosmic Far InfraRed Background (CFIRB) is described.

For the first time the far-IR emission of dust associated with the Warm Ionised Medium (WIM) is evidenced. This component determined on about 25 of the sky is detected at a 10 level in the [200, 350]  band. The best representation of the WIM dust spectrum is obtained for a temperature of 29.1 K and an emissivity law  3.8  0.8  cm². With a spectral index equal to 2, the emissivity law becomes  1.0  0.2  cm², with a temperature of 20 K, which is significantly higher than the temperature of dust associated with HI gas. The variation in the dust spectrum from the HI to the WIM component can be explained by only changing the upper cutoff of the Big Grain size distribution from 0.1  to 30 nm.

The detection of IR emission of dust in the WIM significantly decreases the intensity of the CFIRB, especially around 200  which corresponds to the peak of energy.

Key words: ISM: dust, extinction ISM: general cosmology: cosmic microwave background cosmology: observations infrared: ISM: continuum submillimeter

Send offprint requests to: G. Lagache

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Data presentation and preparation
• 3. Emission spectrum of dust associated with HI gas
  • 3.1. Variation of the dust emission spectrum with the HI column densities
  • 3.2. Dust emission spectrum in low HI column density regions
• 4. Effects induced by the diffuse ionized gas on the Far-IR/HI correlation
• 5. Emission spectrum of the diffuse H⁺ component
  • 5.1. Detection
  • 5.2. Normalisation and emissivity
  • 5.3. First interpretation
• 6. The extragalactic component
  • 6.1. FIRAS spectra in low HI column density regions: evidence for an extragalactic component
  • 6.2. Isotropy
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999
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