Ultracompact Dwarf Galaxies in the Fornax Cluster

By Steve Phillipps, Michael Drinkwater, M. Gregg, J. B. Jones. 2001

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By utilizing the large multiplexing advantage of the Two-degree Field spectrograph on the Anglo-Australian Telescope, we have been able to obtain a complete spectroscopic sample of all objects in a predefined magnitude range, 16.5 < bj < 19.7, regardless of morphology, in an area toward the center of the Fornax Cluster of galaxies. Among the unresolved or marginally resolved targets, we have found five objects that are actually at the redshift of the Fornax Cluster; i.e., they are extremely compact dwarf galaxies or extremely large star clusters. All five have absorption-line spectra. With intrinsic sizes of less than 1.″1 HWHM (corresponding to approximately 100 pc at the distance of the cluster), they are more compact and significantly less luminous than other known compact dwarf galaxies, yet much brighter than any globular cluster. In this paper we present new ground-based optical observations of these enigmatic objects. In addition to having extremely high central surface brightnesses, these objects show no evidence of any surrounding low surface brightness envelopes down to much fainter limits than is the case for, e.g., nucleated dwarf elliptical galaxies. Thus, if they are not merely the stripped remains of some other type of galaxy, then they appear to have properties unlike any previously known type of stellar system.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/576e9e4e320cd618ef5862ac53579a6876b57656

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In Astronomy and Astrophysics

1. P. Hopkins
2. M. Cappellari
3. L. Hernquist
4. Luis C. Ho
5. D. Merritt
6. Alister W. Graham
7. J. Strader
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In Instrumentation

1. J. Strader
2. J. Brodie
3. M. Cappellari
4. D. Merritt
5. L. Ferrarese
6. Pavel Kroupa
7. P. Côté
8. E. Peng

Citations in the corpus

• THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, background): “…a new clue to the origin of cEs is the discovery of numerous UCD galaxies in cluster environments (e.g., Hilker et al. 1999; Drinkwater et al. 2000, 2003; Phillipps et al. 2001; Haşegan et al. 2005; Jones et al. 2006; Blakeslee & Barber DeGraaff 2008; Madrid et al. 2010; Chiboucas et al. 2011).”
• The AIMSS Project I: bridging the star cluster, galaxy divide (2014, background): “These objects, known as ultracompact dwarfs (UCDs; Phillipps et al. 2001), became the first in a series of stellar systems found to exist with properties between star clusters and galaxies.”
• Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters (2005, background): “For example, the Ultra-Compact Dwarfs (UCDs) (Phillipps et al. 2001; Drinkwater et al. 2003) have comparable luminosities to the brightest GCs, small linear sizes, and could be the remnant nuclei of disrupted dE’s.”
• The ACS Virgo Cluster Survey. I. Introduction to the Survey (2004, background): “…of any intergalactic GCs (West et al. 1995; Jordán et al. 2003) associated with this diffuse component would be straightforward.15 Finally, spectroscopic surveys of the Fornax Cluster have produced a number of candidate ‘‘ultracompact dwarfs’’ (e.g., Phillipps et al. 2001; Drinkwater et al. 2003).”
• The formation of ultracompact dwarf galaxies (2001, background): “1 shows that the predicted spheroidal dwarf galaxies fall in the region of the Kormendy diagram that the UCD data of Phillipps et al. (2001) cover, nicely verifying the prediction.”
• The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies (2005, background): “Phillipps et al. (2001) and Drinkwater et al. (2003) examine the various possibilities and argue that the compact objects in Fornax are either the stripped remains of nucleated dwarfs or a genuinely new class of galaxy.”
• From star clusters to dwarf galaxies: the properties of dynamically hot stellar systems (2008, background): “Phillipps et al. (2001) were the first ones to call them ultra compact dwarf galaxies (UCDs), a term which is widely in use for this type of objects at the present.”
• THE RELATIONSHIPS AMONG COMPACT STELLAR SYSTEMS: A FRESH VIEW OF ULTRACOMPACT DWARFS (2011, background): “In the decade or so since the discovery (Hilker et al. 1999; Drinkwater et al. 2000) and naming (Phillipps et al. 2001) of Ultra Compact Dwarfs (UCDs), numerous observational studies have sought to understand where these curious objects fit in the multi-dimensional parameter space for hot…”