SCYON Abstract

Received on December 10 2003

Discovery of Globular Clusters in the Proto-Spiral NGC 2915:
Implications for Hierarchical Galaxy Evolution

AuthorsGerhardt R. Meurer1, J.P. Blakeslee1, M. Sirianni1, H.C. Ford1, G.D. Illingworth2, N. Benítez1, M. Clampin3, F. Menanteau1, H.D. Tran4, R.A. Kimble3, G.F. Hartig5, D.R. Ardila1, F. Bartko6, R.J. Bouwens1, T.J. Broadhurst7, R.A. Brown5, C.J. Burrows5, E.S. Cheng3, N.J.G. Cross1, P.D. Feldman1, D.A. Golimowski1, C. Gronwall8, L. Infante9, J.E. Krist5, M.P. Lesser10, A.R. Martel1, G.K. Miley11, M. Postman5, P. Rosati12, W.B. Sparks5, Z.I. Tsvetanov1, R.L. White1,5, W. Zheng1
Affiliation1 Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218
2 UCO/Lick Observatory, University of California, Santa Cruz, CA 95064
3 NASA Goddard Space Flight Center, Greenbelt, MD 20771
4 W.M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743
5 STScI, 3700 San Martin Drive, Baltimore, MD 21218
6 Bartko Science & Technology, P.O. Box 670, Mead, CO 80542-0670
7 Racah Institute of Physics, The Hebrew University, Jerusalem, Israel 91904
8 Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802
9 Departmento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
10 Steward Observatory, University of Arizona, Tucson, AZ 85721
11 Leiden Observatory, Postbus 9513, 2300 RA Leiden, Netherlands
12 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
To appear inApJL December 20, 2003 edition


We have discovered three globular clusters beyond the Holmberg radius in Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark matter dominated blue compact dwarf galaxy NGC 2915. The clusters, all of which start to resolve into stars, have M_V606 =-8.9 to -9.8 mag, significantly brighter than the peak of the luminosity function of Milky Way globular clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of metal-poor Galactic globular clusters. The specific frequency of clusters is at a minimum normal, compared to spiral galaxies. However, since only a small portion of the system has been surveyed it is more likely that the luminosity and mass normalized cluster content is higher, like that seen in elliptical galaxies and galaxy clusters. This suggests that NGC 2915 resembles a key phase in the early hierarchical assembly of galaxies - the epoch when much of the old stellar population has formed, but little of the stellar disk. Depending on the subsequent interaction history, such systems could go on to build-up larger elliptical galaxies, evolve into normal spirals, or in rare circumstances remain suspended in their development to become systems like NGC 2915.