Revisiting the globular clusters of NGC 1052-DF2^⋆

¹ Department of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Wien, Austria
² European Space Agency, European Space Research and Technology Centre, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³ Instituto de Astrofísica de Canarias, Calle Vía Láctea, E-38206 La Laguna, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Spain
⁵ Centre for Astrophysics and Supercomputing, Swinburne University, John Street, Hawthorn, VIC 3122, Australia
⁶ Department of Physics, Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, Brno 611 37, Czech Republic
⁹ Univ. Lyon, ENS de Lyon, Univ. Lyon1, CNRS, Centre de Recherche Astrophysique de Lyon, UMR5574, 69007 Lyon, France

^⋆⋆ Corresponding author: katja.fahrion@univie.ac.at

Received: 1 October 2024
Accepted: 14 March 2025

Abstract

The ultra-diffuse galaxy (UDG) NGC 1052-DF2 has captured the interest of astronomers ever since the low velocity dispersion measured from ten globular clusters (GCs) suggested a low dark matter fraction. Also, its GC system was found to be unusually bright, with a GC luminosity function peak at least one magnitude brighter than expected for a galaxy at a distance of 20 Mpc. In this work we present an updated view of the GC system of NGC 1052-DF2. We analysed archival MUSE data of NGC 1052-DF2 to confirm the membership of four additional GCs based on their radial velocities, thereby raising the number of spectroscopically confirmed GCs to 16. We measured the ages and metallicities of 11 individual GCs, finding them to be old (> 9 Gyr) and with a range of metallicities from [M/H] = −0.7 to −1.8 dex. The majority of GCs are found to be more metal-poor than the host galaxy, with some metal-rich GCs sharing the metallicity of the host ([M/H] = −1.09_−0.07^+0.09 dex). The host galaxy shows a flat age and metallicity gradient out to 1 R_e. Using a distance measurement based on the internal GC velocity dispersions (D = 16.2 Mpc), we derived photometric GC masses and find that the peak of the GC mass function compares well with that of the Milky Way. From updated GC velocities, we estimated the GC system velocity dispersion of NGC 1052-DF2 with a simple kinematic model and find σ_GCS = 14.86_−2.83^+3.89 km s⁻¹. However, this value is reduced to σ_GCS = 8.63_−2.14^+2.88 km s⁻¹ when the GC that has the highest relative velocity based on a low S/N spectrum is considered an interloper. We discuss the possible origin of NGC 1502-DF2, taking the lower distance, spread in GC metallicities, flat stellar population profiles, and dynamical mass estimate into consideration.