The dichotomy of early-type galaxies from their globular cluster systems
Received 28 May 1996 / Accepted 1 October 1996
Growing evidence for the existence of two classes of ellipticals calls for a comparison of the properties of their globular cluster systems. I compiled information on the properties of 53 globular cluster systems of faint and bright early-type galaxies, and investigated them in the light of the properties of the parent galaxies. The properties of globular cluster systems appear to separate into two classes rather than to follow continuous relations with their host galaxy properties.
The "faint" systems have a low specific frequency (less than about 5), less than roughly 1500 globular clusters, a relatively low metallicity ([Fe/H] ), and a steep density profile that follows the galaxy light. These systems appear essentially unperturbed, and are hosted by faint (about ), disky early-type galaxies with unresolved cores.
On the other hand, "bright" globular cluster systems had a higher efficiency in producing globular clusters and have higher specific frequencies (higher than 5). They have larger number of globular clusters (more than 2000), have flat density profiles () and their color distributions are often broad, and show several peaks or gradients in many cases. Finally the mean metallicity is higher than in "faint" globular cluster systems. "Bright" globular cluster systems show all signs predicted for globular cluster systems that experienced a merger event, and are associated with bright (about ) boxy ellipticals with resolved cores.
I conclude that every galaxy is likely to have formed globular clusters during the early proto-galactic collapse, but "bright" systems were enriched and disturbed during merger events. These two classes of globular cluster systems support the idea that major merger events could be a cause for the dichotomy of early-type galaxies.
Key words: globular clusters galaxies: elliptical and lenticular galaxies: star clusters
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© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998