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Mapping and Mass Measurement of the Cold Dust in NGC 205 with Spitzer

F. R. Marleau·A. Noriega-Crespo·K. A. Misselt·K. D. Gordon·C. W. Engelbracht·G. H. Rieke·P. Barmby·S. P. Willner·J. Mould·R. D. Gehrz·C. E. Woodward
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Abstract

We present observations at 3.6, 4.5, 5.8, 8, 24, 70 & 160um of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The point sources subtracted images at 8 and 24um display a complex and fragmented infrared emission coming from both very small dust particles and larger grains. The extended dust emission is spatially concentrated in three main emission regions, seen at all wavelengths from 8 to 160um. These regions lie approximately along NGC 205's semi-major axis and range from ~100 to 300 pc in size. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2e4 solar masses, mainly 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 (~12K) dust and a dust mass about sixteen 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 3.2e6 to 5e7 solar masses.

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F. R. Marleau, A. Noriega-Crespo, K. A. Misselt, K. D. Gordon, C. W. Engelbracht, G. H. Rieke, P. Barmby, S. P. Willner, J. Mould, R. D. Gehrz, C. E. Woodward. 2006-04-10. Mapping and Mass Measurement of the Cold Dust in NGC 205 with Spitzer. https://doi.org/10.1086/504975

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