Ice Emission and the Redshifts of Submillimeter Sources

Abstract

Observations at submillimeter wavelengths have revealed a population ofsources thought to be at relatively large redshifts. The position of the850 {μ}m passband on the Rayleigh-Jeans portion of the Planck functionleads to a maximum redshift estimate of z~4.5, since sources will notretain their redshift-independent brightness close to the peak of thePlanck function and thus drop out of surveys. Here we review evidencethat ice absorption is present in the spectra of local ultraluminousinfrared galaxies, which are often taken as analogs for the 850 {μ}msource population. We consider the implication of this absorption forice-induced spectral structure at far-infrared wavelengths and presentmarginal astronomical evidence that amorphous ice may have a featuresimilar to crystalline ice near 150 {μ}m. Recent corroborativelaboratory evidence is supportive of this conclusion. It is argued thatearly metal enrichment by pair-instability supernovae may lead to a highice content relative to refractory dust at high redshift, and a fairlyrobust detection of ice emission in a z=6.42 quasar is presented. It isfurther shown that ice emission is needed to understand the 450 {μ}msources observed in the GOODS-N field. We are thus encouraged to applyfar-infrared ice emission models to the available observations of HDF850.1, the brightest submillimeter source in the Hubble Deep Field. Wesuggest that a redshift as large as 13 may need to be considered forthis source, nearly a factor of 3 above the usual top estimate.Inclusion of the possibility of far-infrared ice emission in thespectral energy distributions of model sources generally broadens therange of redshifts to be considered for submillimeter sources comparedto models without ice emission.