Scl-dE1 GC1: AN EXTENDED GLOBULAR CLUSTER IN A LOW-LUMINOSITY DWARF ELLIPTICAL GALAXY

We report the discovery from Hubble Space Telescope/ACS images of an extended globular cluster, denoted by Scl-dE1 GC1, in the Sculptor Group dwarf Elliptical galaxy Scl-dE1 (Sc22). The distance of the dE is determined as 4.3 ± 0.25 Mpc from the I magnitude of the tip of the red giant branch in the color-magnitude diagram. At this distance the half-light radius of Scl-dE1 GC1 is ~22 pc, placing it among the largest clusters known, particularly for globular clusters associated with dwarf galaxies. The absolute magnitude of Scl-dE1 GC1 is MV = –6.7 and, to within the photometric uncertainties of the data, the cluster stellar population appears indistinguishable from that of the dE. We suggest that there may be two modes of globular cluster formation in dwarf galaxies, a normal mode with half-light radii of typically 3 pc, and an extended mode with half-light radii of ~10 pc or more.

[1]  Edward J. Shaya,et al.  Tip of the Red Giant Branch Distances. II. Zero-Point Calibration , 2007, astro-ph/0701518.

[2]  WLM-1: A Non-Rotating, Gravitationally Unperturbed, Highly Elliptical Extragalactic Globular Cluster , 2009 .

[3]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

[4]  W. E. Harris,et al.  Structural Parameters for Globular Clusters in M31 and Generalizations for the Fundamental Plane , 2007, 0704.2057.

[5]  Bonn,et al.  Globular cluster systems in nearby dwarf galaxies – I. HST/ACS observations and dynamical properties of globular clusters at low environmental density , 2008, 0810.3660.

[6]  S. Larsen,et al.  New Members of the Cluster Family in Nearby Lenticular Galaxies , 2002, astro-ph/0203454.

[7]  N. R. Tanvir,et al.  A new population of extended, luminous star clusters in the halo of M31 , 2005 .

[8]  A. Sandage,et al.  Comparison of Distances from RR Lyrae Stars, the Tip of the Red Giant Branch, and Classical Cepheids , 2007, 0712.2346.

[9]  Andrew A. West,et al.  A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite? , 2004, astro-ph/0410416.

[10]  J. P. Huchra,et al.  M31 Globular Clusters: Colors and Metallicities* ** *** , 2000 .

[11]  Taft E. Armandroff,et al.  Standard Globular Cluster Giant Branches in the (M(I), (V - I)o) Plane , 1990 .

[12]  K. Woodley,et al.  Sizes of Confirmed Globular Clusters in NGC 5128: A Wide-Field High-Resolution Study , 2007, 0710.1778.

[13]  Thomas H. Puzia,et al.  Hubble Space Telescope imaging of globular cluster candidates in low surface brightness dwarf galaxies , 2005 .

[14]  Peter B. Stetson,et al.  THE CENTER OF THE CORE-CUSP GLOBULAR CLUSTER M15: CFHT AND HST OBSERVATIONS, ALLFRAME REDUCTIONS , 1994 .

[15]  B. Willman,et al.  A Pair of Boötes: A New Milky Way Satellite , 2007, 0705.1378.

[16]  The acs virgo cluster survey. XI. The nature of diffuse star clusters in early-type galaxies , 2005, astro-ph/0511251.

[17]  Andreas Koch,et al.  The Observed Properties of Dark Matter on Small Spatial Scales , 2007 .

[18]  J. Ott,et al.  Detection of Neutral Hydrogen in Early-Type Dwarf Galaxies of the Sculptor Group , 2005, Proceedings of the International Astronomical Union.

[19]  N. Benı́tez,et al.  The Photometric Performance and Calibration of the Hubble Space Telescope Advanced Camera for Surveys , 2000, astro-ph/0507614.

[20]  A. Mackey,et al.  Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo , 2004, astro-ph/0408404.

[21]  Ivan R. King,et al.  The structure of star clusters. I. an empirical density law , 1962 .

[22]  K. Freeman,et al.  Surface BR Photometry of Newly Discovered Dwarf Elliptical Galaxies in the Nearby Sculptor and Centaurus A Groups , 2000 .

[23]  Naoyuki Tamura,et al.  AN EXTENDED STAR CLUSTER AT THE OUTER EDGE OF THE SPIRAL GALAXY M 33 , 2008, 0802.0501.

[24]  B. Elmegreen.  Variations in Stellar Clustering with Environment: Dispersed Star Formation and the Origin of Faint Fuzzies , 2007, 0710.5788.

[25]  Sidney van den Bergh,et al.  Globular clusters and the formation of the outer Galactic halo , 2004 .

[26]  Christian Moni Bidin,et al.  Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy ,, , 2007 .

[27]  P. Barmby,et al.  Structural parameters for globular clusters in NGC 5128 - III. ACS surface brightness profiles and model fits , 2007, 0711.2180.

[28]  G. Costa.  Structure and stellar content of globular clusters. I. Surface-brightness profiles for four southern clusters , 1979 .

[29]  B. Miller,et al.  The Globular Cluster Luminosity Function and Specific Frequency in Dwarf Elliptical Galaxies , 2007, 0708.2511.

[30]  K. Freeman,et al.  Surface Brightness Fluctuation Distances to Dwarf Elliptical Galaxies in the Sculptor Group , 1998, astro-ph/9809046.

[31]  P. W. Hodge,et al.  Distances to nearby galaxies in Sculptor , 2003, astro-ph/0302045.

[32]  Rupali Chandar,et al.  The Globular cluster systems of five nearby spiral galaxies: New insights from Hubble Space Telescope imaging , 2004, astro-ph/0407460.

[33]  Jeremiah P. Ostriker,et al.  EFFECTS OF TIDAL SHOCKS ON THE EVOLUTION OF GLOBULAR CLUSTERS , 1998 .

[34]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[35]  WLM-1: An old, Nonrotating, Gravitationally Unperturbed, Highly Elliptical Extragalactic Globular Cluster , 2005, astro-ph/0511502.

[36]  E. Grebel,et al.  Accepted Version Preprint typeset using L ATEX style emulateapj v. 10/09/06 AGE DETERMINATION OF SIX INTERMEDIATE-AGE SMC STAR CLUSTERS WITH HST/ACS * , 2022 .

[37]  Basic N-body modelling of the evolution of globular clusters — I. Time scaling , 1998, astro-ph/9805344.

[38]  Eric W. Peng,et al.  The acs virgo cluster survey. X. half-light radii of globular clusters in early-type galaxies : Environmental dependencies and a standard ruler for distance estimation , 2005 .

[39]  S. Bergh.  The luminosity–diameter relations for globular clusters and dwarf spheroidal galaxies , 2008, 0807.2798.

[40]  B. Yanny,et al.  Cats and dogs, hair and a hero: A quintet of new milky way companions , 2006 .

[41]  W. E. Harris,et al.  Structural parameters from ground-based observations of newly discovered globular clusters in NGC 5128 , 2006 .

[42]  William E. Harris,et al.  A Catalog of Parameters for Globular Clusters in the Milky Way , 1996 .

[43]  Sergey E. Koposov,et al.  Accepted for publication in ApJ Preprint typeset using L ATEX style emulateapj v. 02/07/07 THE DISCOVERY OF TWO EXTREMELY LOW LUMINOSITY MILKY WAY GLOBULAR CLUSTERS , 2022 .

[44]  Patrick Seitzer,et al.  Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1 , 1998 .

[45]  Destruction of the Galactic Globular Cluster System , 1996, astro-ph/9603042.

[46]  Heidelberg,et al.  A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites , 2008, 0805.2945.

[47]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .