The Globular Cluster Systems of the Sculptor Group

We use CTIO 4 m Mosaic II images taken with the Washington CM and Harris R filters to identify candidate globular clusters in the six major galaxies of the Sculptor group: NGC 45, 55, 247, 254, 300, and 7793. From follow-up spectroscopy with Hydra-CTIO, we find 19 new globular clusters in NGC 55, 247, 253, and 300, bringing the total number of known Sculptor group globular clusters to 36. The newly discovered clusters have spectroscopic ages consistent with those of old Milky Way globular clusters, and the majority are metal-poor. Their luminosity function closely resembles that of the Milky Way's globular clusters; their metallicity distribution is somewhat more metal-rich, but this may be the result of our color selection of candidates. The mean [α/Fe] ratio in the clusters is -0.2 ± 0.3, which is lower than the Milky Way average. The specific frequencies SN are similar to those of other late-type galaxies. However, if we calculate the specific frequency using the K-band total magnitudes of the host galaxies, we find values that are more than a factor of 2 higher. The kinematics of the globular cluster systems are consistent with rotation with the H I disk in each of the four galaxies; however, only in NGC 253 is this result based on more than seven objects. We suggest that the Sculptor group galaxies add to evidence indicating that many of the first-generation globular clusters formed in disks, not halos.

[1]  P. Côté,et al.  The Formation of Giant Elliptical Galaxies and Their Globular Cluster Systems , 1998, astro-ph/9804319.

[2]  H. Harris,et al.  Integrated colors of globular clusters in the Galaxy, Fornax, and M31. , 1977 .

[3]  P. Dokkum.  Cosmic-Ray Rejection by Laplacian Edge Detection , 2001, astro-ph/0108003.

[4]  David Burstein,et al.  Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters , 1997, astro-ph/9712258.

[5]  Heather L. Morrison,et al.  Mapping the Galactic Halo. I. The Spaghetti Survey , 2000 .

[6]  D. Ottaviani,et al.  Hγ and Hδ Absorption Features in Stars and Stellar Populations , 1997 .

[7]  R. Schommer,et al.  Spectroscopy of Giants in LMC Clusters. II Kinematics of the Cluster Sample , 1992 .

[8]  David Burstein,et al.  Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars , 1994 .

[9]  K. Ashman,et al.  Globular cluster systems formed in galaxy mergers , 1993 .

[10]  E. Bertin,et al.  SExtractor: Software for source extraction , 1996 .

[11]  P. Harding,et al.  Accepted by The Astrophysical Journal Letters HST WFPC2 Color-Magnitude Diagrams of Halo Globular Clusters in M33: Implications for the Early Formation History of the Local Group 1 , 1998 .

[12]  Stephen E. Zepf,et al.  Globular Cluster Systems , 1998 .

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

[14]  Thomas J. Chester,et al.  The 2MASS Large Galaxy Atlas , 2001 .

[15]  M. Bolte,et al.  Hubble Space Telescope Observations of the Oldest Star Clusters in the Large Magellanic Cloud , 1999, astro-ph/9911187.

[16]  K. Freeman,et al.  Discovery of Numerous Dwarf Galaxies in the Two Nearest Groups of Galaxies. , 1997, astro-ph/9704030.

[17]  Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique , 2000, astro-ph/0006411.

[18]  Ivan R. King,et al.  The structure of star clusters. III. Some simple dvriamical models , 1966 .

[19]  J. Tonry,et al.  A survey of galaxy redshifts. I. Data reduction techniques. , 1979 .

[20]  Arlo U. Landolt,et al.  UBVRI Photometric Standard Stars in the Magnitude Range 11 , 1992 .

[21]  The Efficiency of Globular Cluster Formation , 1999, astro-ph/9901283.

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

[23]  M. Barbier-Brossat,et al.  Catalogue général de vitesses radiales moyennes pour les étoiles galactiques. Mean radial velocities catalog of galactic stars , 2000 .

[24]  Stephen E. Zepf,et al.  The Formation of Globular Clusters in Merging and Interacting Galaxies , 1992 .

[25]  Peter B. Stetson,et al.  CCD photometry of the globular cluster M92 , 1988 .

[26]  George H. Jacoby,et al.  What is better than an 8192x8192 CCD Mosaic imager: two Mosaic wide-field imagers, one for KPNO and one for CTIO , 1998, Astronomical Telescopes and Instrumentation.

[27]  R. Zinn,et al.  Compositions of halo clusters and the formation of the galactic halo , 1978 .

[28]  Taft E. Armandroff,et al.  Abundances and Kinematics of the Globular Cluster Systems of the Galaxy and of the Sagittarius Dwarf , 1995 .

[29]  W. Harris,et al.  The Halo Stars in NGC 5128. II. An Outer Halo Field and a New Metallicity Distribution , 2000 .

[30]  P. Schechter,et al.  DOPHOT, A CCD PHOTOMETRY PROGRAM: DESCRIPTION AND TESTS , 1993 .

[31]  A. Walker,et al.  Spectroscopy of Giants in LMC Clusters. III. Velocities and Abundances for NGC 1841 and Reticulum and the Properties of the Metal-Poor Clusters , 1992 .

[32]  N. Caldwell,et al.  Kinematics of Star Clusters in M33 , 1991 .

[33]  Nicholas B. Suntzeff,et al.  Spectroscopy of giants in LMC clusters. I. Velocities, abundances, and the age-metallicity relation , 1991 .

[34]  R. M. Sharples,et al.  Spectroscopy of globular cluster candidates in the Sculptor group galaxies NGC 253 and 55 , 2000 .

[35]  H. Harris,et al.  The Washington system: photometric properties and standard stars. , 1979 .

[36]  D. Geisler.  New Washington System CCD Standard Fields , 1996 .

[37]  M. Irwin,et al.  A dwarf satellite galaxy in Sagittarius , 1994, Nature.

[38]  Konrad Kuijken,et al.  Kinematics, Chemistry, and Structure of the Galaxy , 1989 .

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

[40]  J. Huchra,et al.  Extragalactic globular clusters. I, The metallicity calibration , 1990 .

[41]  D. Geisler,et al.  The Abundance Distribution and Luminosity Function of Globular Clusters in NGC 1399 , 1990 .

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

[43]  S. M. Fall,et al.  Hubble Space Telescope Observations of Candidate Young Globular Clusters and Stellar Associations in the Recent Merger Remnant NGC 3921 , 1996 .

[44]  R. P. Kraft.  ABUNDANCE DIFFERENCES AMONG GLOBULAR CLUSTER GIANTS: PRIMORDIAL VS. EVOLUTIONARY SCENARIOS , 1994 .

[45]  A. Whiting.  Angular Momentum in the Sculptor Group , 1999 .

[46]  G. Costa,et al.  Globular clusters in the sculptor group Galaxy NGC 55 , 1982 .

[47]  W. Liller,et al.  A search for globular clusters around the edge-on spiral galaxy NGC 55 , 1983 .