The interstellar medium in Andromeda's dwarf spheroidal galaxies: I. Content and origin of the interstellar dust

TL;DR

This study investigates the dust content and origin in the dwarf spheroidal galaxies of Andromeda, revealing the significance of grain growth and dust survival times in explaining their interstellar medium properties.

Contribution

The paper provides new Herschel observations of NGC147 and NGC185, constrains their dust masses, and highlights the role of grain growth in their dust evolution, expanding understanding of ISM in dwarf galaxies.

Findings

NGC147 has a dust mass less than 128 Msun.

NGC185's dust mass is about 5.1 x 10^3 Msun, higher than previous estimates.

Dust production from stars is insufficient to explain observed dust, indicating grain growth is essential.

Abstract

Dwarf spheroidal galaxies are among the most numerous galaxy population in the Universe, but their main formation and evolution channels are still not well understood. The three dwarf spheroidal satellites (NGC147, NGC185, and NGC205) of the Andromeda galaxy are characterised by very different interstellar medium (ISM) properties, which might suggest them being at different galaxy evolutionary stages. While the dust content of NGC205 has been studied in detail by De Looze et al. (2012), we present new Herschel dust continuum observations of NGC147 and NGC185. The non-detection of NGC147 in Herschel SPIRE maps puts a strong constraint on its dust mass (< 128 Msun). For NGC185, we derive a total dust mass M_d = 5.1 x 10^3 Msun, which is a factor of ~2-3 higher than that derived from ISO and Spitzer observations and confirms the need for longer wavelength observations to trace more massive cold dust reservoirs. We, furthermore, estimate the dust production by asymptotic giant branch (AGB) stars and supernovae (SNe). For NGC147, the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population. In NGC185 and NGC205, the observed dust content is one order of magnitude higher compared to the estimated dust production by AGBs and SNe. Efficient grain growth, and potentially longer dust survival times (3-6 Gyr) are required to account for their current dust content. Our study confirms the importance of grain growth in the gas phase to account for the current dust reservoir in galaxies.