The Importance of Interstellar Dust to Astrophysics

Geoffrey C. Clayton

Louisiana State University

Abstract:

Interstellar dust, though containing relatively little mass, has

a profound effect on many physical processes in astrophysics and

on our ability to observe and to understand them. It is the

dominant opacity source for continuum photons with energies

between the microwave and the ionization edge of hydrogen. A

large fraction of these photons is absorbed by dust and

re-emitted in the IR. Unless dust extinction along a particular

line of sight can be predicted and removed, the intrinsic

spectral energy distribution of reddened astrophysical objects

cannot be accurately determined. Correcting for dust becomes

even more difficult for distant galaxies because of the effects

of mixing stars, gas and dust together in an uncertain geometry.

It is crucial to separate the effects of the dust intrinsic to

the galaxy from those associated with the galaxy's stellar age

and metallicity. The accuracy of this separation directly

affects the determination of a galaxy's physical properties (star

formation rate and history, dust content, etc.), as illustrated

by investigations of the star formation rate as a function of

redshift. The correction for dust currently dominates the

uncertainty in the inferred star formation rate in high-z

galaxies and conclusions about the evolution of galaxies.