THE RELATIONSHIPS AMONG COMPACT STELLAR SYSTEMS: A FRESH VIEW OF ULTRACOMPACT DWARFS

Journal Article · Thu Dec 15 04:00:00 EST 2011 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/142/6/199· OSTI ID:22034323

Brodie, Jean P; Romanowsky, Aaron J ^[1]; Strader, Jay ^[2]

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1. UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
2. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

We use a combined imaging and spectroscopic survey of the nearby central cluster galaxy, M87, to assemble a sample of 34 confirmed ultracompact dwarfs (UCDs) with half-light radii of {approx}>10 pc measured from Hubble Space Telescope images. This doubles the existing sample in M87, making it the largest such sample for any galaxy, while extending the detection of UCDs to unprecedentedly low luminosities (M{sub V} = -9). With this expanded sample, we find no correlation between size and luminosity, in contrast to previous suggestions, and no general correlation between size and galactocentric distance. We explore the relationships between UCDs, less luminous extended clusters (including faint fuzzies), globular clusters (GCs), as well as early-type galaxies and their nuclei, assembling an extensive new catalog of sizes and luminosities for stellar systems. Most of the M87 UCDs follow a tight color-magnitude relation, offset from the metal-poor GCs. This, along with kinematical differences, demonstrates that most UCDs are a distinct population from normal GCs, and not simply a continuation to larger sizes and higher luminosities. The UCD color-magnitude trend couples closely with that for Virgo dwarf elliptical nuclei. We conclude that the M87 UCDs are predominantly stripped nuclei. The brightest and reddest UCDs may be the remnant nuclei of more massive galaxies while a subset of the faintest UCDs may be tidally limited and related to more compact star clusters. In the broader context of galaxy assembly, blue UCDs may trace halo build-up by accretion of low-mass satellites, while red UCDs may be markers of metal-rich bulge formation in larger galaxies.

• OSTI ID: 22034323
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 6 Vol. 142; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
CATALOGS
COLOR
CORRELATIONS
DETECTION
DISTANCE
GALAXIES
GALAXY CLUSTERS
GALAXY NUCLEI
IMAGES
LUMINOSITY
MASS
METALS
STAR CLUSTERS
TELESCOPES
VISIBLE RADIATION