A Spatially Resolved Study of the Cold Dust in NGC 205

Abstract

We present IRAC and MIPS observations of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The extended dust emission is spatially concentrated in three main emission regions. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2 × 10^4 M_⊙, at a temperature of ~20K. The gas mass associated with this component matches the predicted mass returned by the dying stars from the last burst of star formation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm observations over a small central region or "Core" (18" diameter), suggest the presence of very cold (T ~ 12K) dust and a dust mass 16 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 and without the millimeter observations, suggest a total gas mass range of 3.2 × 10^6 to 5 × 10^7 M_⊙.

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