Old Massive Globular Clusters and the Stellar Halo of the Dwarf Starburst Galaxy NGC 4449

Abstract

We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters. Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H] ~ -1) and subsolar Mg enhancement ([Mg/Fe] ~ -0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the other is very massive (~ 3 x 10^6 M_sun). We have also identified a population of remote halo globular clusters. NGC 4449 is consistent with an emerging picture of the ubiquity of stellar halos among dwarf galaxies, and study of its globular clusters may help distinguish between accretion and in situ scenarios for such halos.

15 pages, AJ in press

References in corpus (19)

• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
• The Dual Origin of Stellar Halos
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• The nucleus of the Sagittarius dSph galaxy and M54: a window on the process of galaxy nucleation
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
• Clues to Nuclear Star Cluster Formation from Edge-on Spirals
• Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca
• Star Clusters in M31: I. A Catalog and a Study of the Young Clusters
• The Globular Cluster Luminosity Function and Specific Frequency in Dwarf Elliptical Galaxies
• Globular Cluster Systems in Nearby Dwarf Galaxies: I. HST/ACS Observations and Dynamical Properties of Globular Clusters at Low Environmental Density
• A Comparison of Optical and Near-Infrared Colours of Magellanic Cloud Star Clusters with Predictions of Simple Stellar Population Models
• The cluster population of the irregular galaxy NGC 4449 as seen by the Hubble Advanced Camera for Surveys
• The ACS Survey of Galactic Globular Clusters XI: The Three-Dimensional Orientation of the Sagittarius Dwarf Spheroidal Galaxy and its Globular Clusters
• Photometry of Magellanic Cloud clusters with the Advanced Camera for Surveys - II. The unique LMC cluster ESO 121-SC03
• Star Clusters in M 31. IV. A Comparative Analysis of Absorption Line Indices in Old M 31 and Milky Way Clusters
• The Connection Between X-ray Binaries and Star Clusters in NGC 4449
• Evidence for Blue Straggler Stars Rejuvenating the Integrated Spectra of Globular Clusters
• First SDO/AIA Observation of Solar Prominence Formation Following an Eruption: Magnetic Dips and Sustained Condensation and Drainage

Cited by in corpus (7)

• Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream Around NGC 4449 and Hierarchical Galaxy Formation on Small Scales
• A Catalog of Extended Clusters and Ultra-Compact Dwarf Galaxies - An Analysis of their Parameters in Early- and Late-Type Galaxies
• Star Formation Histories of the LEGUS dwarf galaxies. II. Spatially resolved star formation history of the Magellanic irregular NGC 4449
• The Star Cluster System in the Local Group Starburst Galaxy IC 10
• The In-situ Origins of Dwarf Stellar Outskirts in FIRE-2
• New Surface Brightness Fluctuations Spectroscopic Technique: NGC4449 and its Stellar Tidal Stream
• LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449