KDG 64: a large dwarf spheroidal or a small ultradiffuse satellite of Messier 81

TL;DR

This study presents detailed kinematic and stellar population analysis of KDG 64, suggesting it is a transitional object between dwarf spheroidals and ultradiffuse galaxies, shaped by feedback and tidal interactions.

Contribution

First spatially resolved kinematic measurements of KDG 64, revealing its properties and potential evolutionary link between dSphs and UDGs.

Findings

KDG 64 has an old, metal-poor stellar population.

Dark matter constitutes about 90% within the half-light radius.

KDG 64 is a transitional dSph-UDG object in the M81 group.

Abstract

Low-mass early-type galaxies, including dwarf spheroidals (dSph) and brighter dwarf ellipticals (dE), dominate the galaxy population in groups and clusters. Recently, an additional early-type population of more extended ultradiffuse galaxies (UDGs) has been identified, sparking a discussion on the potential morphological and evolutionary connections between the three classifications. Here, we present the first measurements of spatially resolved stellar kinematics from deep integrated-light spectra of KDG 64 (UGC 5442), a large dSph galaxy in the M 81 group. From these data, we infer stellar population properties and dark matter halo parameters using Jeans dynamical modelling. We find an old, metal-poor stellar population with no young stars and a dark matter mass fraction of ~ 90 per cent within the half-light radius. These properties and the position of KDG 64 on the Fundamental Plane indicate that it is a local analogue of smaller UDGs in the Coma and Virgo clusters and is probably a transitional dSph-UDG object. Its evolutionary path cannot be uniquely established from the existing data, but we argue that supernovae feedback and tidal heating played key roles in shaping KDG 64.