Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals

Details Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals

2008-06-06

arxiv.org/abs/0806.1090v2

Astronomy and Astrophysics

Astrophysics

15 pages, 14 figures, 1 table, submitted to MNRAS 22/5/08, Revised to include data from Mieske etal. (0806.0374), accepted by

Scientific paper

10.1111/j.1365-2966.2008.13739.x

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 ~10$^4$ M_o systems (GCs) to ~10$^11$ M_o systems (elliptical galaxies). The lack of measured velocity dispersions for dwarf ellipticals with -16 > M_K > -18 (~10$^8$ M_o) 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 10$^11$ M_o) 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 are a natural extension of the GC sequence to higher masses, i.e. IMOs are essentially massive star clusters. [Abridged].

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