A large population of ultra-compact dwarfs and bright intracluster globulars in the fornax cluster

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Title: A large population of ultra-compact dwarfs and bright intracluster globulars in the fornax cluster
Author(s): Gregg, Michael D.; Drinkwater, Michael J.; Evstigneeva, Ekaterina A.; Jurek, Russell; Karick, Arna M.; Phillipps, Steven; Bridges, Terry J.; Jones, Bryn; Bekki, Kenji; Couch, Warrick J.
Abstract: All the previously cataloged ultracompact dwarf (UCD) galaxies in the Fornax and Virgo clusters have 17.5 < bJ < 20. Using the 2dF spectrograph on the Anglo-Australian Telescope, we have carried out a search for fainter UCDs in the Fornax Cluster. In the magnitude interval 19.5 < bJ < 21.5, we have found 54 additional compact cluster members within a projected radius of 0.◦9 (320 kpc) of the cluster Centre, all of which meet our selection and observational criteria to be UCDs. These newly identified objects, however, overlap in luminosity and spatial distribution with objects classified as globular clusters (GCs) belonging to the central cluster galaxy NGC 1399; in fact, about half of the objects in our sample are included in recent catalogs of NGC 1399/Fornax GCs. The numbers, luminosity function, and spatial distributions of our compact object sample are consistent with being the bright tail of the Fornax cluster-wide GC population. Yet, our present larger sample of intergalactic compact objects forms a dynamically distinct population from both the NGC1399 GCs and the nucleated dwarf ellipticals in Fornax. This supports the interpretation that the UCDs, which populate the bright tail of the GC luminosity function, are, in some respects, a separate class of objects, at least to the extent that they have experienced a distinct dynamical history and origin, which differs from the bulk of the NGC1399 GCs. Correcting for our spectroscopic incompleteness, we estimate that there are ∼105 ± 13 of these brighter compact cluster objects down to bJ < 21.5 in the central region of the Fornax, and hence these UCDs/globulars outnumber other galaxy types in this space. The differences in their dynamics and distribution compared to dwarf ellipticals (dEs) may be consistent with a threshing or tidal destruction origin, if they have
Publication type: Journal article
Research centre: Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing
Source: Astronomical Journal, Vol. 137, no. 1 (Jan 2009), pp. 498-506
Publication year: 2009
Keyword(s): Cluster galaxies; Coma cluster; Dwarf galaxies; Galaxy clusters; Globular clusters; Objects; Origin; Planetary-nebulae; Spectroscopy; Spiral galaxies; Star-clusters; Virgo-cluster
Publisher: Institute of Physics Publishing
ISSN: 0004-6256
Publisher URL: http://dx.doi.org/10.1088/0004-6256/137/1/498
Peer reviewed