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

Abstract

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.

Metallicity gradients in local Universe galaxies: Time evolution and effects of radial migration

“…In Fig. 1 (Richer & McCall 2008;Gonçalves et al 2014), NGC 185 (Gonçalves et al 2012), and NGC 147 (Gonçalves et al 2007). The sample also includes three of the spiral galaxies studied in the present paper: M33 (Magrini et al 2009b;Bresolin et al 2010), NGC 300 (Stasińska et al 2013), and M81 2 .…”

The ionization mechanism of NGC 185: how to fake a Seyfert galaxy?★

“…North is up and east points to the left. The original version of this figure with all the objects we detected can be found in Gonçalves et al (2011).…”

NGC 55: a disc galaxy with flat abundance gradients

“…The spectra of the candidate symbiotic systems will be discussed in a forthcoming paper. The method to derive the physical and chemical condition in H ii regions is described in the previous papers of this series, as for instance Magrini & Gonçalves (2009);Gonçalves et al (2012Gonçalves et al ( , 2014: the temden and ionic tasks of IRAF 3 are used to derive first electron temperature (from the ratio of the [O iii] lines at 500.7 nm and 436.3 nm), and density (from the lines of the [S ii] doublet at 671.7 nm and 673.1 nm) of the gas, then ionic abundances. Ionic abundances are combined with the ionisation correction factors for H ii regions from Izotov et al (2006) ) might imply a maximum underestimation of about ∼700 K and up to a maximum overestimation of ∼400 K of the temperature adopted for the [O ii] ionic abundance.…”

“…The present work is part of our study of the structure and evolution of Local Group and nearby galaxies through the spectroscopy of their emission-line populations (see, e.g., Magrini et al 2005;Gonçalves et al 2007;Magrini & Gonçalves 2009;Gonçalves et al 2012Gonçalves et al , 2014Stanghellini et al 2015). In this framework, we have carried on a deep spectroscopic campaign with the multi-object spectrograph GMOS@Gemini-South telescope of the strong-line emitters of NGC 55, as illustrated in Figure 1.…”