Distance Estimation using Globular Clusters and Ultra-Compact Dwarfs
Abstract
The tight scaling relation between absolute magnitude and internal velocity dispersion (σ) for globular clusters (GCs), referred to as the GC velocity dispersion (GCVD) relation, has shown great potential as a distance estimator. However, at the high-luminosity end of the GC luminosity function, GCs mix with ultra-compact dwarfs (UCDs). As GCs appear to smoothly transition into UCDs with dynamical mass, we investigate the possibility of a unified distance estimation relation applicable to both GCs and UCDs. To this end, we exploit the transition between scaling relations with dynamical mass, using the Milky Way and M31 GCs alongside literature UCDs. Additionally, we look at the influence of UCDs, and of GC size, on GCVD-derived distances. Using the GCVD for UCDs gives a systematic distance underestimation of ∼33 per cent, but a cut to select UCDs with GC-like sizes can eliminate this bias. The minor systematics on GC size produce systematic offsets smaller than the uncertainty of the GCVD. Using the bilinear relation formed by the GCs and UCDs in the absolute magnitude - log dynamical mass plane for distance estimation yields per-object distance uncertainties of ∼30-35 per cent (0.12-0.16 dex). We find that the GC - UCD division occurs at MV ≃ −10.8 mag and Mdyn ≃ 3.1×106 M⊙, consistent with previous findings. Applied to the dwarf galaxy NGC1052-DF2, whose distance is strongly debated, the relation returns 19.1 ± 4.3 Mpc, consistent with literature values.
Related
- The Ejection and Detectability of High- and Hypervelocity Stars by Compact Object Binaries in Globular Clusters
- Introducing AuriGLOBES: The effects of compressive tides, compact object-induced mass loss, and size evolution on modelling globular clusters
- Puzzling Ultra-Diffuse Galaxy Evolution (PUDGE). II. A transformation pathway from ultra-diffuse galaxies to compact dwarfs in galaxy clusters
- Playing CHESS with stars. II. Homogeneous analysis of high-resolution optical spectra for a sample of 135 giants in 14 bulge globular clusters
- A Cosmological Framework for Stellar Collisions at High Redshift in Proto-globular Clusters, Nuclear Star Clusters, and Little Red Dots
BibTeX
@misc{heumen2026distance,
title = {{Distance Estimation using Globular Clusters and Ultra-Compact Dwarfs}},
author = {Bas van Heumen and Jonah S. Gannon and Duncan A. Forbes and Jean P. Brodie and Aaron J. Romanowsky},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27432},
eprint = {2609.27432},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27432},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Distance Estimation using Globular Clusters and Ultra-Compact Dwarfs
AU - Bas van Heumen
AU - Jonah S. Gannon
AU - Duncan A. Forbes
AU - Jean P. Brodie
AU - Aaron J. Romanowsky
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.27432
UR - https://arxiv.org/abs/2609.27432
AB - The tight scaling relation between absolute magnitude and internal velocity dispersion (σ) for globular clusters (GCs), referred to as the GC velocity dispersion (GCVD) relation, has shown great potential as a distance estimator. However, at the high-luminosity end of the GC luminosity function, GCs mix with ultra-compact dwarfs (UCDs). As GCs appear to smoothly transition into UCDs with dynamical mass, we investigate the possibility of a unified distance estimation relation applicable to both GCs and UCDs. To this end, we exploit the transition between scaling relations with dynamical mass, using the Milky Way and M31 GCs alongside literature UCDs. Additionally, we look at the influence of UCDs, and of GC size, on GCVD-derived distances. Using the GCVD for UCDs gives a systematic distance underestimation of ∼33 per cent, but a cut to select UCDs with GC-like sizes can eliminate this bias. The minor systematics on GC size produce systematic offsets smaller than the uncertainty of the GCVD. Using the bilinear relation formed by the GCs and UCDs in the absolute magnitude - log dynamical mass plane for distance estimation yields per-object distance uncertainties of ∼30-35 per cent (0.12-0.16 dex). We find that the GC - UCD division occurs at M_V ≃ −10.8 mag and M_dyn ≃ 3.1×10^6 M_⊙, consistent with previous findings. Applied to the dwarf galaxy NGC1052-DF2, whose distance is strongly debated, the relation returns 19.1 ± 4.3 Mpc, consistent with literature values.
ER -