Astron. Astrophys. 333, 709-720 (1998)

The interstellar cold dust observed by COBE

G. Lagache, A. Abergel, F. Boulanger and J.-L. Puget

Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, F-91405 Orsay Cedex, France

Received 3 June 1997 / Accepted 1 December 1997

Abstract

Using DIRBE and FIRAS maps at high latitude () we derive the spatial distribution of the dust temperature associated with the diffuse cirrus and the dense molecular clouds. For a emissivity law, we find that the equilibrium dust temperature of the cirrus is about 17.5 K with only small variations over the high latitude sky. Comparison of the far Infrared DIRBE maps shows the presence of a colder emission component with a temperature around 15 K, assuming a emissivity law. The lowest values of the temperature found in the cold regions ( K) are compatible with the results recently obtained for dense cores in star forming regions by the balloon-borne experiment SPM-PRONAOS (Ristorcelli et al., 1996, in prep., Serra et al., 1997). This cold component is in particular present in the direction of known molecular complexes with low star forming activity such as Taurus. The association between the cold component and molecular clouds is further demonstrated by the fact that all sky pixels with significant cold emission have an excess IR emission with respect to the high latitude IR/HI correlation. We have deduced a threshold value of the column density, =2.5 H cm^-2, below which cold dust is not detected within the FIRAS beam of . We have re-examined the problem of the existence of a very cold dust component ( K) by combining DIRBE maps of the cold emission with FIRAS spectra, corrected for the isotropic component found in Puget et al. (1996). The warm and cold component deduced from the analysis of DIRBE maps account for the Galactic FIRAS spectra with no need for a very cold component ( K).

Key words: ISM: clouds, dust, extinction, structure, general infrared: ISM: continuum radio continuum: ISM

Send offprint requests to: G. Lagache

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Contents

• 1. Introduction
• 2. Data presentation and preparation
• 3. Large grain temperature maps
• 4. Cold emission maps
  • 4.1. Maps of FIR excess with respect to the 60 µm emission
  • 4.2. Temperature of the excess component in the Taurus, Auriga and Perseus region
  • 4.3. Correlation of the cold component with molecular gas
• 5. FIRAS spectra of the warm and cold components
  • 5.1. Temperature and optical depth of the cold and warm components
  • 5.2. Residual emission
• 6. Discussion
  • 6.1. Warm and cold components
  • 6.2. Very cold dust in the Galaxy ?
• 7. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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