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Microwave Emission from Spinning Dust Grains
There is strong evidence for a substantial population of ultrasmall dust
grains (see Draine & Lazarian 1999a, and references therein).
These grains will be spinning, will have electric dipole moments, and
will therefore produce electric dipole radiation.
The rotational excitation of such grains has been discussed by Draine
& Lazarian (1998a,b), and the rotational emission spectrum has been
predicted (see Figure below).
for reasonable assumptions concerning the size distribution of
the ultrasmall grains.
It appears that the rotational emission from these grains has already
been detected, in the form of a dust-correlated microwave background.
Figure:
Emissivity per H atom due to vibrational emission from large
grains plus rotational emission from small spinning grains.
The emission spectrum for the small spinning grains is taken
from Draine & Lazarian 1998b, and is computed
assuming ``Cold Neutral Medium'' conditions
(, ), and
5% of the cosmic carbon abundance in a population of ultrasmall
grains with a log-normal size distribution given by eq.(62) of
Draine & Lazarian 1998b, with , , and
(for these parameters the ``half-mass'' point of the log-normal
size distribution is at ).
From Draine & Lazarian 1999a, but with new observational
data from de Oliveira-Costa et a. (1999) added to plot
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References
- de Oliveira-Costa, A., Kogut, A, Devlin, M.J., Netterfield, C.B.,
Page, L.A., & Wollack, E.J. 1997, Astrophys. J. (Letters),
482, L17.
- de Oliveira-Costa, A., Tegmark, M., Gutiérrez, C.M.,
Jones, A.W., Davies, R.D., Lasenby, A.N., Rebolo, R.,
& Watson, R.A. 1999,
Astrophys. J. (Letters), 527, L9.
- de Oliveira-Costa, A., Tegmark, M., Page, L.A., & Boughn, S.P. 1998,
Astrophys. J. (Letters), 509, L9.
- Draine, B.T., & Lazarian, A. 1998a,
Astrophys. J. (Letters), 494, L19-22.
- Draine, B.T., & Lazarian, A. 1998b,
Astrophys. J., 508, 157-179.
- Draine, B.T., & Lazarian, A. 1999,
in Microwave Foregrounds,
ed. A. de Oliveira-Costa & M. Tegmark (San Francisco: Astr. Soc.
Pacific)], pp. 133-149.
- Kogut, A., et al. 1996b, Astrophys. J. (Letters),
464, L5.
- Leitch, E.M., Readhead, A.C.S., Pearson, T.J., & Myers, S.T. 1997,
Astrophys. J. (Letters), 486, L23.
- Lim, M.A., et al. 1996, Astrophys. J. (Letters),
469, L69.
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Bruce Draine
1/18/2000