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

By J. Brodie, A. Romanowsky, J. Strader, D. Forbes. 2011

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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 ≳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 (MV = −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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0cf8675c83176a2b66fac2fb81ee91aecf1f01bb

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Citations in the corpus

CO-EVOLUTION OF GALACTIC NUCLEI AND GLOBULAR CLUSTER SYSTEMS (2013, background): “The weak tidal field regime may be especially relevant for giant galaxies, as recent HST observations of Brodie et al. (2011) indicate that many globular clusters in M87 may not be tidally limited.”
The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater (2016, background): “…Milky Way globular clusters (black dots) and dwarf galaxies (open circles) as well as the dwarfs of the M31 (triangles) (McConnachie 2012, updated Sep 2015); this is complemented by measurements collected for various extended companion objects around nearby galaxies (grey dots, Brodie et al. 2011).”
ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, background): “Kinematics data for 55 metal-rich GCs extend to ∼ 12 ae (Romanowsky et al. 2009), where we have removed objects brighter than i = 21.3 owing to their peculiar kinematics, which may imply contamination by ultra compact dwarfs (cf. Brodie et al. 2011).”
The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies (2012, background): “Given the ongoing debate regarding the uncertain separation between GCs and ultracompact dwarfs (UCDs; Mieske et al. 2006; Brodie et al. 2011), we decided to set the upper brightness magnitude at Mi ≈ −11.6 (MI ≈ −12), 1 mag brighter than the integrated magnitude of ω Cen, the brightest GC in the…”
The AIMSS Project I: bridging the star cluster, galaxy divide (2014, methodology): “The principle literature sources for CSSs are the compilations of Misgeld & Hilker (2011) and Brodie et al. (2011) plus the recent update from Forbes et al. (2013), and to these compilations we add additional data for specific systems.”
BEASTS OF THE SOUTHERN WILD: DISCOVERY OF NINE ULTRA FAINT SATELLITES IN THE VICINITY OF THE MAGELLANIC CLOUDS (2015, background): “It is interesting that in the size luminosity plane the ambigiously classified objects in our sample seem to join the sequence of objects observed in other galaxies labelled as faint-fuzzies (FF) or Extended Clusters (EC) (see Larsen et al. 2001; Brodie et al. 2011; Forbes et al. 2013).”
WIDE-FIELD PRECISION KINEMATICS OF THE M87 GLOBULAR CLUSTER SYSTEM (2011, methodology): “This is by far the largest publiclyavailable data set of GCs around any galaxy with both measured sizes and spectroscopic confirmation, and enables us to clarify the relations between UCDs and GCs (§4.4.1 and Brodie et al. 2011).”
Precession of the Sagittarius stream (2013, unknown): “Brodie et al. (2011) discovered apop- c© 2012 RAS, MNRAS000, 1–12 -50 0 50 100 XSGR [kpc] -50 0 50 100 Y S G R [k pc ] Sun Sgr NGC 2419 -50 0 50 100 XSGR [kpc] -50 0 50 100 Y S G R [k pc ] Figure 6.”
Illuminating Low Surface Brightness Galaxies with the Hyper Suprime-Cam Survey (2017, background): “For context, we also show the family of early-type galaxies (Brodie et al. 2011), representative giant LSB spiral galaxies (Sprayberry et al. 1995), UDGs in intermediate to high density environments (van Dokkum et al. 2015; Román & Trujillo 2017a), and H I-bearing UDGs in the field (Leisman et al.…”