2008/06/30 by Duncan Forbes, Duncan A. Forbes, P. D. Lasky +5 · 3 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Dark matter #Elliptical galaxy #Fundamental plane (elliptical galaxies) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Globular cluster #Lenticular galaxy #Physics #Star formation #Stellar mass #Stellar, planetary, and galactic studies #Velocity dispersion #Virial mass #Virial theorem #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2008.13739.x
15 pages, 14 figures, 1 table, submitted to MNRAS 22/5/08, Revised to include data from Mieske etal. (0806.0374), accepted by MNRAS 22/7/08. See http://astronomy.swin.edu.au/dforbes for full Table
arxiv created 2008/07/29 · openalex publication_date 2008/09/04 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 ultracompact 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 Two Micron All Sky Survey (2MASS), (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 ∼104M⊙ systems (GCs) to ∼1012M⊙ systems (elliptical galaxies). The lack of measured velocity dispersions for dwarf ellipticals with −16 > MK > −18 (∼108M⊙) 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 1012M⊙) 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 initial mass function (and hence their stellar mass-to-light ratios) or structural properties. We argue that most of these IMOs 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 are available in electronic format.