Joint Astrophysics Colloquium

Cosmic Dust: Friend or Foe? New Insights into Galactic evolution from the Planck Surveyor and the Herschel Space Observatory

Peter Martin

CITA

For precision cosmological studies of the cosmic microwave background radiation, thermal emission by cold interstellar dust particles in our Galaxy produces an unwanted polarized foreground, to be removed, thrown in the dust bin. But at the same time, the thermal dust emission is a reliable tracer of Galactic gas and magnetic fields and so benefits investigations of Galactic evolution. A basic question is why, unlike in other galaxies, there is still an interstellar medium (ISM) in the Milky Way in which stars are continually forming. The answers lie in understanding the cycling of the ISM from the diffuse atomic phase to dense molecular clouds, inefficient sites of star formation, and back. By imaging the thermal dust emission, two satellites, the Planck Surveyor and the Herschel Space Observatory, are revolutionizing this field. Each cost about a billion euros and I will report my two cents' worth! Planck's all-sky view is providing special insight into the vast high-latitude regions where we see the first hints of molecular clouds forming. Herschel has targeted spectacular molecular clouds closer to the Galactic plane, peering into stellar nurseries that are closed to investigation by traditional optical astronomy methods because of extinction by dust.