Deep spectroscopy of the emission-line populations in NGC185

TL;DR

This study provides a detailed spectroscopic analysis of planetary nebulae in NGC 185, revealing their chemical properties, electron densities, and recent chemical enrichment, along with discovering a symbiotic star and analyzing a supernova remnant.

Contribution

First detailed spectroscopic characterization of PNe in NGC 185, including electron densities and chemical abundances, and discovery of a symbiotic star and analysis of a supernova remnant.

Findings

Detected new, fainter planetary nebulae in NGC 185.

Recalculated electron temperatures and chemical abundances.

Indicated significant chemical enrichment in NGC 185 over the last 8 Gyr.

Abstract

Dwarf galaxies are crucial to understand the formation and evolution of galaxies, since they constitute the most abundant galaxy population. Abundance ratios and their variations due to star formation are key constraints to chemical evolution models. The determination of these abundances in the dwarf galaxies of the Local Universe is thus of extreme importance. 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, but unlike than the other three, NGC 147, NGC 205, and NGC 221 (M32) it has an important content of gas and dust. We obtained deep spectroscopic observations of the H$\alpha$ emitting population of NGC 185 using GMOS-N at Gemini. As a result, in addition to the bright planetary nebulae (PNe) previously found in the galaxy and reported in the literature, we found other, much fainter, PNe. We then re-calculated the electron temperatures and chemical abundances of the brightest ones, and derived, for the first time, their electron densities. Our characterisation of the PN population properties is interpreted in terms of the chemical evolution of NGC 185, which suggests that it has suffered a significant chemical enrichment within the last $\sim$8 Gyr. We also discovered the first symbiotic star in the galaxy and enlightened the properties of a known supernova remnant located close to the centre of NGC 185.