Masses of Star Clusters in the Nuclei of Bulgeless Spiral Galaxies

By C. Walcher, R. P. van der Marel, D. McLaughlin, Hans-Walter Rix, T. Böker, N. Haering, Luis C. Ho, M. Sarzi, J. Shields. 2004

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In the last decade star clusters have been found in the centers of spiral galaxies across all Hubble types. We here present a spectroscopic study of the exceptionally bright (106-108 L☉) but compact (re ~ 5 pc) nuclear star clusters in very late type spirals with the Ultraviolet and Visual Echelle Spectrograph at the VLT. We find that the velocity dispersions of the nine clusters in our sample range from 13 to 34 km s-1. Using photometric data from the Hubble Space Telescope WFPC2 and spherically symmetric dynamical models, we determine masses between 8 × 105 and 6 × 107 M☉. The mass-to-light ratios range from 0.2 to 1.5 in the I band. This indicates a young mean age for most clusters, in agreement with previous studies. Given their high masses and small sizes, we find that nuclear clusters are among the objects with the highest mean surface density known (up to 105 M☉ pc-2). From their dynamical properties we infer that, rather than small bulges, the closest structural kin of nuclear clusters appear to be massive compact star clusters. This includes such different objects as globular clusters, "super star clusters," ultracompact dwarf galaxies (UCDs), and the nuclei of dwarf elliptical galaxies. It is a challenge to explain why, despite the widely different current environments, all different types of massive star clusters share very similar and structural properties. A possible explanation links UCDs and massive globular clusters to nuclear star clusters through stripping of nucleated dwarf galaxies in a merger event. The extreme properties of this type of cluster would then be a consequence of the clusters' location in the centers of their respective host galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/67947c1f7c96a7d5ac9bc9179df2e1e09aba0e50

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Citations in the corpus

Resolved Massive Star Clusters in the Milky Way and Its Satellites: Brightness Profiles and a Catalog of Fundamental Parameters (2005, background): “…by studies of the mass-radius relations for young massive clusters in merging galaxies (e.g., Zepf et al. 1999) and relatively nearby spiral disks (Larsen 2004), and, on a somewhat different scale, for the (young) nuclear clustersin very late-type spirals (Böker et al. 2004; Walcher et al. 2005).”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. II. “CUSP” ELLIPTICALS (2008, background): “If we include the limited subsample of stellar nuclei with velocity dispersions measured in Geha et al. (2002) and Walcher et al. (2005), we find similar results in fundamental projections involving σ .”
Quantifying the coexistence of massive black holes and dense nuclear star clusters (2009, methodology): “From the K-band MBH-L bulge relation in Graham (2007), the expected BH mass is 3 × 10 6 M⊙, equal to the NC's stellar mass (Walcher et al. 2005).”
NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. II. DYNAMICAL MODELS (2009, background): “Indeed, the nuclei of galaxies have very similar structural properties to globular clusters (these nuclei are therefore also referred to as nuclear star clusters; e.g., Walcher et al. 2005).”
Nuclear star clusters (2009, background): “The mass of these young populations is of order 105M , sufficient to explain the total mass of the NSC if they had formed through similar formation episodes repeated every ∼100 Myr over a Hubble time (Walcher et al. 2006; Seth et al. 2006).”
THE DISRUPTION OF GIANT MOLECULAR CLOUDS BY RADIATION PRESSURE & THE EFFICIENCY OF STAR FORMATION IN GALAXIES (2009, background): “Finally, high-mass clusters withMcl & 106M⊙ have β = 0.6 andm0 = 106 M⊙ in equation (5) (Walcher et al. 2005; Evstigneeva et al. 2007; Barmby et al. 2007; Rejkuba et al. 2007; Murray 2009).”
Stellar Populations in the Nuclei of Late-Type Spiral Galaxies (2006, result): “Combining these results with those from Walcher et al. (2005), we have thus shown that the stellar nuclei of these bulge-less galaxies are massive and dense star clusters that form stars 1Max Planck Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany 2ESA/ESTEC, Keplerlaan 1, 2200…”
Families of dynamically hot stellar systems over 10 orders of magnitude in mass (2011, background): “These objects might have already formed more compact than isolated star clusters via recurrent gas inflow, which causes repeated star formation events (e.g. Walcher et al. 2005; Rossa et al. 2006).”
OPTICAL DISCOVERY OF PROBABLE STELLAR TIDAL DISRUPTION FLARES (2010, background): “The nuclear star clusters reported by Walcher et al. (2005) in nine late-type spirals range from 8 × 105 − 6 × 107M⊙ with a median ≈ 10 6.5M⊙; the mean age of the last star formation burst is 34 Myr with the youngest stellar population having a mean mass of 105.5M⊙(Walcher et al. 2006).”
THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, background): “…distinct stellar components in their cores.44 This is true for galaxies across the Hubble sequence (Carollo et al. 1998; Böker et al. 2002, 2004; Walcher et al. 2005, 2006; Seth et al. 2008) and along the luminosity function (e.g., Côté et al. 2006; Turner et al. 2012), suggesting that a…”
Hubble Space Telescope STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass on Hubble Type (2006, methodology): “Walcher et al. (2005, 2006) observed a sample of nine NCs in late-type spiral galaxies using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT).”
The Coincidence of Nuclear Star Clusters and Active Galactic Nuclei (2008, methodology): “For the late-type spiral galaxies, Walcher et al. (2005) has shown that the typical I-band M/L ratio is 0.50 ± 0.37.”