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Session 51 - Interstellar Medium II.
Display session, Thursday, January 08
Exhibit Hall,
Spinning interstellar dust grains produce detectable rotational emission in the 10-100 GHz frequency range. The physical processes responsible for excitation and damping of grain rotation include collisions with atoms and ions, long-range interaction with passing ions, emission of infrared radiation, the recoil following H_2 formation on the grain surface, and photoelectric emission. In addition, the grain rotation is damped by the radiation from the rotating electric dipole moment. We estimate likely dipole moments as a function of grain size. The relative importance of these various excitation and damping processes depends on the environment and on the grain size.
We calculate the rms rotational velocity as a function of grain size including all of the above processes. For reasonable assumptions concerning the grain size distribution, we compute the emission spectrum expected from dust in interstellar diffuse gas as well as dark clouds.
Rotational emission from spinning dust grains in diffuse clouds can account for the "anomalous" Galactic background component which correlates with 100um thermal emission from dust, detected by Kogut et al (1996), de Oliveira Costa et al (1997), and Leitch et al (1997). Implications for cosmic background studies are discussed.
