Mapping and Mass Measurement of the Cold Dust in NGC 205 withSpitzer

We present observations at 3.6, 4.5, 5.8, 8, 24, 70 & 160um of NGC 205, thedwarf elliptical companion of M31, obtained with the Spitzer Space Telescope.The point sources subtracted images at 8 and 24um display a complex andfragmented infrared emission coming from both very small dust particles andlarger grains. The extended dust emission is spatially concentrated in threemain emission regions, seen at all wavelengths from 8 to 160um. These regionslie approximately along NGC 205's semi-major axis and range from ~100 to 300 pcin size. Based on our mid-to-far infrared flux density measurements alone, wederive a total dust mass estimate of the order of 3.2e4 solar masses, mainly ata temperature of ~20K. The gas mass associated with this component matches thepredicted mass returned by the dying stars from the last burst of starformation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined withprevious 1.1mm observations over a small central region or "Core'' (18"diameter), suggest the presence of very cold (~12K) dust and a dust mass aboutsixteen times higher than is estimated from the Spitzer measurements alone.Assuming a gas to dust mass ratio of 100, these two datasets, i.e.with andwithout the millimeter observations, suggest a total gas mass range of 3.2e6 to5e7 solar masses.Comment: PDF, 10 pages, simulated ApJ, accepted for publicatio