Elliptical galaxies and globular clusters (GCs) have traditionally
been regarded as physically distinct entities due to their
discontinuous distribution in key scaling diagrams
involving size, luminosity and velocity dispersion.
Recently this distinctness has been challenged by the discovery of stellar systems with mass intermediate between those of GCs and dwarf ellipticals (such as Ultra Compact Dwarfs and Dwarf Galaxy Transition Objects).
Here we examine the relationship between the virial and
stellar mass for a range of old stellar systems, from
GCs to giant ellipticals, and including such Intermediate Mass
Objects (IMOs).
Improvements on previous work in this area
include the use of (i) near-infrared magnitudes
from the 2MASS survey, (ii) aperture corrections to velocity dispersions,
(iii) homogeneous half light radii
and (iv) accounting for the effects of non-homology in galaxies. We find a virial-to-stellar mass relation that ranges from ~104
M(sun) systems (GCs) to ~1011 M(sun) systems
(elliptical galaxies).
The lack of measured velocity dispersions for dwarf ellipticals
with -16 > MK > -18 (~108 M(sun))
currently inhibits our ability to determine how, or indeed if,
these galaxies connect continuously
with GCs in terms of their virial-to-stellar mass ratios.
We find elliptical galaxies to have roughly equal fractions of dark and
stellar matter within a virial radius;
only in the most massive (greater than 1011 M(sun))
ellipticals does dark matter dominate the virial mass.
Although the IMOs
reveal slightly higher virial-to-stellar mass ratios than
lower mass GCs, this may
simply reflect our limited understanding of their IMF (and hence their stellar mass-to-light ratios) or structural properties.
We argue that most of these intermediate mass
objects have similar properties to massive GCs, i.e. IMOs
are essentially massive star clusters.
Only the dwarf spheroidal galaxies exhibit behaviour notably distinct from the other stellar systems examined here, i.e. they display
a strongly increasing virial-to-stellar mass ratio
(equivalent to higher dark matter fractions) with decreasing stellar mass. The data used in this study is available in electronic format.