UCDs - more massive than allowed?

TL;DR

This paper discusses the surprising high dynamical mass-to-light ratios observed in ultra-compact dwarf galaxies and massive globular clusters, challenging standard models and suggesting they may be more massive than previously thought.

Contribution

It presents observational evidence for high M/L ratios in UCDs and explores potential explanations for these unexpected results.

Findings

High M/L ratios increase with object mass above 10^6 M_sun

Some UCDs have M/L values incompatible with standard stellar models

UCDs deviate from typical globular cluster relations, aligning more with early-type galaxies

Abstract

Dynamical mass estimates of ultra-compact dwarfs galaxies and massive globular clusters in the Fornax and Virgo clusters and around the giant elliptical Cen A have revealed some surprising results: 1) above about 10^6 M_sun the mass-to-light (M/L) ratio increases with the objects' mass; 2) some UCDs/massive GCs show high M/L values (4 to 6) that are not compatible with standard stellar population models; and 3) in the luminosity-velocity dispersion diagram, UCDs deviate from the well defined relation of `normal' GCs, being more in line with the Faber-Jackson relation of early-type galaxies. In this contribution, we present the observational evidences for high mass-to-light ratios of UCDs and discuss possible explanations for them.