The dust enrichment of galaxies: supernovae and evolved stars

Supernovae occupy a pivotal position in astrophysics, not only because of their importance as standard candles and cosmological probes but also because of the prime role that they play in determining the overall energetics, mass recycling rate and heavy-element enrichment of galaxies. It has been hypothesised that supernovae (SNe) may be a major, or even dominant, source of dust particles in the Universe. Indirect support for this supposition comes from the fact that many of the earliest-formed galaxies known are extremely dusty and IR-luminous, as evidenced by the efficient detection of their redshifted dust emission at submillimetre wavelengths by SCUBA and other instruments. It seems that only massive stars can have produced the observed dust over the short timescales implied, either during during dusty mass-losing phases prior to the SN event or else within the expanding and cooling ejecta from the SN event. Dust formation models confirm that newly formed dust in SN ejecta should become detectable at mid-IR wavelengths within 1-2 years of outburst and that the mid-IR is particularly suitable to trace the onset of dust formation in SNe and to determine the amount of dust formed. With the advent of ground-based 8-m telescopes equipped with sensitive mid-IR instruments, such as Gemini's Michelle and TReCS, and the launch of the Spitzer Space Telescope (SST), sufficient sensitivity has become available to embark on searches for mid-IR emission from supernovae in nearby galaxies. Our SEEDS collaboration (Survey for Extragalactic Emission from Dust in Supernovae), composed of astronomers from North America and Europe, has obtained SST time to search for mid-IR dust emission from nearby supernovae hundreds of days after their outbursts, using the IRAC and MIPS instruments. In addition, we have accessed SINGS Legacy SST data on a number of nearby galaxies that have been obtained with the same instruments, in order to search for mid-IR emission from recent SNe within these galaxies. This proposal seeks continued postdoctoral funding in order to allow completion of the supernova dust project. In addition, new far-infrared and submillimetre mapping observations of extended dust shells around evolved stars will be obtained as part of Herschel Space Observatory Guaranteed Time observations following its launch by ESA in 2007, with the aim of addressing the `missing mass' problem for low and intermediate mass stars.