A new way to measure the distance to NGC1052-DF2

Michael A. Beasley; Katja Fahrion; Sergio Guerra Arencibia; Anastasia Gvozdenko; Mireia Montes

doi:10.1051/0004-6361/202452446

paper

A new way to measure the distance to NGC1052-DF2

arXiv:2503.03403 · doi:10.1051/0004-6361/202452446

Abstract

We employ a new way to measure the distance to NGC1052-DF2 via internal stellar velocity dispersions ( $σ$ ) of its globular clusters (GCs). We obtained deep (15.1h), R=18,200, Ca Triplet integrated-light spectra for 10 GCs in NGC1052-DF2 using FLAMES GIRAFFE on VLT. For five GCs we measure $σ$ , along with precision velocities for the whole sample. We also present a new photometric analysis based on 40 orbits of archival Hubble Space Telescope imaging for 16 spectroscopically confirmed GCs. Assuming that the NGC1052-DF2 GCs obey the $M_{V}$ -- log( $σ$ ) relation followed by the Milky Way and M31 GCs, the NGC1052-DF2 GCs give a distance, $d = 16.2 \pm 1.3$ (stat.) $\pm 1.7$ (sys.) Mpc. By contrast, using a literature distance of $d = 21.7$ Mpc from forward modelling of the TRGB, the GCs lie above the Milky Way + M31 relation by $\sim 0.6$ magnitudes. For a shorter literature distance of 13 Mpc, the GCs fall below the relation by $\sim 0.4$ mag. At $d = 16.2$ Mpc, we obtain mean dynamical $M / L_{V} = 1.61 \pm 0.44 M_{⊙} / L_{⊙}$ , and median half-light radii, $r_{h} = 3.0 \pm 0.5$ pc. This is entirely consistent with Milky Way GCs, with mean $M / L_{V} = 1.77 \pm 0.10 M_{⊙} / L_{⊙}$ , median $r_{h} = 3.2 \pm 0.6$ pc. For the further distance of 21.7 Mpc, we obtain low $M / L_{V}$ ratios ( $M / L_{V} = 1.19 \pm 0.33 M_{⊙} / L_{⊙}$ ) which could suggest ages of $\sim 6$ Gyr.. Such young ages are inconsistent with our MUSE stellar population (companion paper, Fahrion et al.) analysis of the NGC1052-DF2 GCs which indicates they are $\sim 10$ Gyr old. For $d = 16.2$ Mpc, coupled with our new photometry, we find that the properties of the GCs in NGC1052-DF2 appear entirely consistent with those in the Milky Way and other Local Group galaxies. In order to reconcile the further distance with our results, a mass function more dwarf-depleted than the Milky Way GCs must be invoked for the GCs of NGC1052-DF2.

arXiv commentAccepted for publication in A&A

A new way to measure the distance to NGC1052-DF2

Abstract

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