Toward the Mass and Origin of Dust in Early-Type Galaxies

The origin and evolution of the dust in earlytype galaxies are two of the key questions to understanding their evolution at late times. The two main scenarios to produce their dust are in situ formation from the winds of cool giants and the accretion of small, gasrich satellite galaxies. The later scenario appears to be the only viable explanation for the several orders of magnitude variation in the amount of dust at fixed stellar mass, as in situ formation implies that the dust content should approximately scale linearly with stellar mass. Yet our demographic studies of a wellselected sample of earlytypes show that dust is present in roughly half of them, which implies a very high merger rate given the expected short lifetime of dust in their hot ISM. We propose SPIRE photometry of 11 of the 45 earlytype galaxies in our previous Spitzer and HST studies. These 11 galaxies have 3channel MIPS photometry, HST images, and deep groundbased photometry and spectroscopy. There are 12 additional galaxies that meet these criteria and already have executed or planned observations. Our goal is to measure the cold dust masses for these galaxies and thus determine the likelihood that the dust originates from minor, gasrich mergers. The SPIRE data are critical to accurately measure the dust masses in these galaxies as the vast majority are active and thus may have a substantial hot dust component that biases mass estimates from the existing, shorterwavelength IR photometry. These data will be combined with archival SPIRE data for the remaining 12 galaxies with detections in our Spitzer study to measure the distribution of dust masses our representative sample of earlytype galaxies and thereby better constrain the origin of the dust. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]