Discovery of Ultracompact Dwarf Galaxies in the Virgo Cluster

Jones, Bryn; Drinkwater, Michael J.; Jurek, Russell J.; Phillipps, Steven; Gregg, Michael D.; Bekki, Kenji; Couch, Warrick J.; Karick, A. M.; Parker, Quentin A.; Smith, Rodney

doi:10.1086/497960

Cited by 86 publications

(126 citation statements)

References 57 publications

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“…Ultra compact dwarf (UCD) galaxies such as those observed by Hasegan et al (2005) and Jones et al (2006) are Virgo cluster objects with a point-like aspect and are thus generally unresolved in ground based optical imaging (Evstigneeva et al 2008) 11 . The star-galaxy classification based on SDSS optical imaging is thus unable to resolve and identify these objects as galaxies.…”

Section: Ultra Compact Dwarf Galaxiesmentioning

confidence: 99%

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

Boselli

Boissier

Heinis

et al. 2011

A&A

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The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering ∼40 sq. deg in the far UV (FUV, λ eff = 1539 Å, Δλ = 442 Å) and ∼120 sq. deg in the near UV (NUV, λ eff = 2316 Å, Δλ = 1060 Å). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared -submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early-and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (α ∼ −1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.

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Section: Ultra Compact Dwarf Galaxiesmentioning

confidence: 99%

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

Boselli

Boissier

Heinis

et al. 2011

A&A

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“…Within the past decade, a new class of compact stellar systems, called "ultra-compact dwarf galaxies" (UCDs), has been discovered in the cores of the Fornax, Virgo, Centaurus and Hydra galaxy clusters (Hilker et al 1999;Drinkwater et al 2000;Mieske et al 2004;Haşegan et al 2005;Jones et al 2006;Evstigneeva et al 2007b;Hilker et al 2007;Mieske et al 2007Misgeld et al 2008). UCDs are characterized by evolved stellar populations, half-light radii of 10 < ∼ r h < ∼ 100 pc and masses of 2 × 10 6 < m < 10 8 M .…”

Section: Introductionmentioning

confidence: 99%

Two formation channels of ultra-compact dwarf galaxies in Hickson compact groups

Rocha

Mieske

Georgiev

et al. 2010

A&A

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Context. The formation of ultra-compact dwarf galaxies (UCDs) is believed to be driven by interaction, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-point of galaxy evolution. Nothing is known about the properties of UCDs in compact groups of galaxies, environments where most of galaxy evolution and interaction is believed to occur and where UCDs in an intermediate stage in their evolution may be expected. Aims. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups of galaxies. For that, two nearby groups in different evolutionary stages, HCG 22 and HCG 90, were targeted. Methods. We selected about 40 UCD candidates from pre-existing photometry of both groups, and obtained spectra of these candidates using the VLT FORS2 instrument in MXU mode. Archival HST/ACS imaging was used to measure their structural parameters. Results. We detect 16 and 5 objects belonging to HCG 22 and HCG 90, respectively, covering the magnitude range −10.0 > M R > −11.5 mag. Their integrated colours are consistent with old ages covering a broad range in metallicities (metallicities confirmed by the spectroscopic measurements). Photometric mass estimates put 4 objects in HCG 90 and 9 in HCG 22 in the mass range of UCDs (>2 × 10 6 M ) for an assumed age of 12 Gyr. These UCDs are on average 2−3 times larger than the typical size of Galactic GCs, covering a range of 2 < ∼ r h < ∼ 21 pc. The UCDs in HCG 22 are more concentrated around the central galaxy than in HCG 90, at the 99% confidence level. They cover a broad range in [α/Fe] abundances from sub-to super-solar. The spectra of 3 UCDs (2 in HCG 22, 1 in HCG 90) show tentative evidence of intermediate age stellar populations. The clearest example is the largest and most massive UCD (∼10 7 M ) in our sample, which is detected in HCG 22. Its properties are most consistent with a stripped dwarf galaxy nucleus. We calculate the specific frequency (S N ) of UCDs for both groups, finding that HCG 22 has about three times higher S N than HCG 90. Conclusions. The ensemble properties of the detected UCDs supports two co-existing formation channels: a star cluster origin (lowluminosity, compact sizes, old ages, super-solar α/Fe), and an origin as tidally stripped dwarf nuclei (more extended and younger stellar populations). Our results imply that the UCDs detected in both groups do not, in their majority, originate from relatively recent galaxy interactions. Most of the detected UCDs have likely been brought into the group along with their host galaxies.

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“…Ultra-compact dwarfs (UCDs) are massive but compact gravitationallybound stellar systems discovered in the nearby Fornax [1][2] [3][4] [5] and Virgo [6] galaxy clusters. Several UCD formation theories have emerged -that they are ultra-massive examples of globular clusters (GCs) [4]; or stellar superclusters created in gas-rich galaxy mergers [7]; or the remnant cores of tidallystripped nucleated dwarf galaxies [8].…”

Section: Observing the Ucd/gc Interfacementioning

confidence: 99%