The interstellar cold dust observed by COBE
G. Lagache, A. Abergel, F. Boulanger, J. L. Puget;
AaA, 1998, 333, 709
ABSTRACT:Using DIRBE and FIRAS maps at high latitude (|b|>10degr ) we derive the spatial distribution of the dust temperature associated with the diffuse
cirrus and the dense molecular clouds.
For a nu (2) 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 nu (2) emissivity law.
The lowest values of the
temperature found in the cold regions ( ~ 13 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, N_{H_I}=2.5 10(20) H
cm(-2) , below which cold dust is not detected within the FIRAS beam of ~ 7degr
.
We have re-examined the problem of the existence of a very cold dust
component (T ~ 7 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 (T ~ 7 K).
KEYWORDS: ism: clouds, dust, extinction, structure, general, infrared: ism: continuum, radio continuum: ism
PERSOKEY:dust, dirbe, extinction, fir, ,
CODE: lagache98