The ultra-diffuse galaxy NGC 1052-DF2 with MUSE: II. The population of DF2: stars, clusters and planetary nebulae

TL;DR

This study uses MUSE spectroscopy to analyze the stellar population, globular clusters, and planetary nebulae of the ultra-diffuse galaxy NGC 1052-DF2, providing insights into its composition, age, and metallicity, and discussing its distance estimates.

Contribution

First systematic spectroscopic analysis of NGC 1052-DF2's stars and clusters, revealing their ages, metallicities, and supporting its placement on the dwarf galaxy mass-metallicity relation.

Findings

The galaxy's stellar population is old (~8.9 Gyr) and metal-poor.

Globular clusters share similar ages but are more metal-poor.

Distance estimates of 13 and 20 Mpc are both plausible based on planetary nebulae.

Abstract

NGC 1052-DF2, an ultra diffuse galaxy (UDG), has been the subject of intense debate. Its alleged absence of dark matter, and the brightness and number excess of its globular clusters (GCs) at an initially assumed distance of 20Mpc, suggested a new formation channel for UDGs. We present the first systematic spectroscopic analysis of both the stellar body and the GCs (six of which were previously known, and one newly confirmed member) of this galaxy using MUSE@VLT. Even though NGC 1052-DF2 does not show any spatially extended emission lines we report the discovery of three planetary nebulae (PNe). We conduct full spectral fitting on the UDG and the stacked spectra of all GCs. The UDG's stellar population is old, 8.9$\pm$1.5 Gyr, metal-poor, with [M/H] = $-$1.07$\pm$0.12 with little or no $\alpha$-enrichment. The stacked spectrum of all GCs indicates a similar age of 8.9$\pm$1.8 Gyr, but lower metallicity, with [M/H] = $-$1.63$\pm$0.09, and similarly low $\alpha$-enrichment. There is no evidence for a variation of age and metallicity in the GC population with the available spectra. The significantly more metal-rich stellar body with respect to its associated GCs, the age of the population, its metallicity and alpha enrichment, are all in line with other dwarf galaxies. NGC 1052-DF2 thus falls on the same empirical mass-metallicity relation as other dwarfs, for the full distance range assumed in the literature. We find that both debated distance estimates (13 and 20 Mpc) are similarly likely, given the three discovered PNe.