Deep spectroscopy of the emission‐line populations in NGC 185★

Because dwarf galaxies are the most abundant type of galaxy, they are crucial for our understanding of the formation and evolution of galaxies. Abundance ratios and their variations as a result of star formation are key constraints in chemical evolution models. Thus, the determination of these abundances in the dwarf galaxies of the Local Universe is extremely important. However, these objects are intrinsically faint, and observational constraints to their evolution can be obtained only for very nearby galaxies. NGC 185 is one of the four brightest dwarf companions of M31. However, unlike the other three – NGC 147, 205 and 221 (M32) – it has an important content of gas and dust. We have obtained deep spectroscopic observations of the Hα emitting population of NGC 185 using the Gemini multi-object spectrograph at the Gemini North telescope. As a result, in addition to the bright planetary nebulae (PNe) previously found in the galaxy and reported in the literature, we have found other, much fainter, PNe. We have then recalculated the electron temperatures and chemical abundances of the brightest PNe and, for the first time, we have derived their electron densities. Our characterization of the population properties of the PNe is interpreted in terms of the chemical evolution of NGC 185, which suggests that it has suffered a significant chemical enrichment within the last ∼8 Gyr. We have also discovered the first symbiotic star in the galaxy and we have determined the properties of a known supernova remnant located close to the centre of NGC 185.