Accurate Spectral Energy Distributions and Selection Effects for High-redshift Dusty Galaxies: a New Hot Population to Discover with the Spitzer Space Telescope?

The spectral energy distributions (SEDs) of dust-enshrouded galaxies with powerful restframe farinfrared(IR) emission have been constrained by a range of ground-based and space-borne surveys. The IRAS catalog provides a reasonably complete picture of the dust emission from nearby galaxies (redshift z ≃ 0.1) that are typically less luminous than about 10L⊙. However, at higher redshifts, the observational coverage from all existing far-IR and submillimeter surveys is much less complete. Here we investigate the SEDs of a new sample of high-redshift submillimeter-selected galaxies (SMGs), for which redshifts are known, allowing us to estimate reliable luminosities and characteristic dust temperatures. We demonstrate that a wide range of SEDs is present in the population, and that a substantial number of luminous dusty galaxies with hotter dust temperatures could exist at similar redshifts (z ≃ 2− 3), but remain undetected in existing submillimeter surveys. These hotter galaxies could be responsible for about a third of the extragalactic IR background radiation at a wavelength of about 100μm. The brightest of these galaxies would have far-IR luminosities of the order of 10L⊙ and dust temperatures of the order of 60K. Galaxies up to an order of magnitude less luminous with similar SEDs will be easy to detect and identify in the deepest Spitzer Space Telescope observations of extragalactic fields at 24μm. Subject headings: galaxies: evolution – methods: observational – galaxies: interstellar medium – galaxies: starburst – cosmology: observations