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 ( NGC 147 , NGC 185 , and NGC 205 ) 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 NGC 205 has been studied in detail by De Looze et al .
( 38 ) , we present new Herschel dust continuum observations of NGC 147 and NGC 185 .

The non-detection of NGC 147 in Herschel SPIRE maps puts a strong constraint on its dust mass ( \leq 128 ^ { +124 } _ { -68 } M _ { \odot } ) .
For NGC 185 , we derive a total dust mass M _ { \text { d } } = 5.1 \pm 1.0 \times 10 ^ { 3 } M _ { \odot } , which is a factor of \sim 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 NGC 147 , the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population .
In NGC 185 and NGC 205 , 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 .