A&A 405, 813-819 (2003)
DOI: 10.1051/0004-6361:20030545
The large-scale anomalous microwave emission revisited by WMAP
G. LagacheIAS, Bât. 121, Université Paris-Sud, 91435 Orsay, France
(Received 24 March 2003 / Accepted 8 April 2003 )
Abstract
We present a new study of the high latitude galactic contributions to the millimeter sky, based on an analysis of the WMAP data combined with several templates of dust emission
(DIRBE/COBE and FIRAS/COBE) and gas tracers (HI and H
).
To study the IR to millimeter properties of the diffuse
sky at high galactic latitude, we concentrate on the emission correlated with the HI gas.
We compute the emission spectrum of the dust/free-free/synchrotron components associated with
HI gas from low to large column densities.
A significant residual WMAP emission over the free-free, synchrotron and
the dust contributions is found from 3.2 to 9.1 mm.
We show that this residual WMAP emission (normalised to 10
atoms/cm
) (1) exhibits a constant
spectrum from 3.2 to 9.1 mm and (2) significantly decreases in amplitude
when
increases,
contrary to the HI-normalised far-infrared emission which stays rather constant.
It is thus very likely that the residual WMAP emission is not
associated with the Large Grain dust component.
The decrease in amplitude with increasing opacity ressembles in fact to the decrease of the
transiently heated dust grain emission observed in dense interstellar clouds.
This is supported by an observed decrease of the HI-normalised 60
m
emission with HI column densities.
Although this result should be interpreted with care due to residual zodiacal contaminations
at 60
m, it suggests that the WMAP excess emission is associated with the small
transiently heated dust particles.
On the possible models of this so-called "anomalous microwave emission" linked
to the small dust particles are the spinning dust and the excess
millimeter emission of the small grains, due to the cold temperatures
they can reach between two successive impacts with photons.
Key words: ISM: general -- cosmology: miscellaneous -- radio continuum: general
© ESO 2003