1. Globular Clusters with Gemini
Duncan Forbes
Swinburne University
Mike Beasley (Lick Obs),
Terry Bridges (Queen’s University)
Duncan Forbes (Swinburne)
Favio Feifer, Juan Forte (Argentina)
Karl Gebhardt (Texas)
Dave Hanes (Queen’s University)
Steve Zepf (Michigan)
Ray Sharples (Durham)

2. Science Goals
Long term spectroscopic study of the globular cluster systems of early-type galaxies using the Gemini Multi-Object Spectrographs on the Gemini-North and Gemini-South telescopes. Key science goals:
test specific galaxy formation scenarios (e.g. mergers versus monolithic collapse)
test GC formation scenarios (e.g. presence of young GCs, abundance ratio variations)
investigate possible angular momentum transfer during merging and determine the specific angular momentum of ellipticals
probe dark matter mass distributions out to large radii

3. International Collaboration
Large Gemini program since 2002A
Publicity in local newspapers and ABC Radio
Pros:
Same GMOS instrument North and South
Photometry and spectra
Cons:
Proposal (deadline, PIT, 1 vs 2, abstract, sci case, attachments etc)
Manpower limited (1 paper to date)

4. Gemini Strategy
Obtain colours, magnitudes, kinematics, metal abundances, abundance ratios  and ages for several hundred GCs associated with elliptical (E) and lenticular (S0) galaxies in a range of environments.
Gemini 8m vs Keck 10m
GC kinematics GC ages

5. Sample Selection Galaxy Type MV Environment NGC 4649 E2 -22.4 Cluster
NGC E Group
NGC S Group
NGC S Field
NGC E Cluster
NGC S Field
NGC E Group
IC E Group

6. GMOS Data To Date Galaxy Photometry Spectroscopy
NGC fields: g,i 1 field: 10 hr
NGC fields: g,r,i 1 field: 10 hr
NGC fields: g,r,i fields: 6.5, 8 hr
NGC fields: g,r,i fields: 8, 8 hr

7. NGC 4649 (M60) Virgo cluster, E2, MV= -22.4, D=16 Mpc 480 sec
in g’, i’
for 3 fields
Forbes et al 2004, MNRAS submitted

8. Spatial Location
| arcmin (40 kpc) | X

9. Colour-Magnitude Diagrams

10. Colours: All Clusters NGC 4649 (45-240 arcsec) Blue: (g-i)'=0.87
Red: (g-i)'=1.17
i'<23.5 N=995
90% complete

11. Colours: By Radius

12. Colour & Density Profiles
Galaxy
Galaxy
Red
All
Blue

13. GC Luminosity Function
i’TO = /- 0.15
NTotal = /- 900
SN = 4.1 +/- 1.0

14. NGC 3379 Leo Group, E1, MV= -20.7, D=10 Mpc
10 hours total exposure
B600 grism: ~5 Å FWHM with 1” slit
Å typical coverage
Beasley et al. 2004, in prep

18. Cluster Ages/Metallicities

19. Cluster Dynamics

20. Cluster Dynamics
11 kpc

21. Summary
GMOS is a powerful way to study GC systems photometrically and spectroscopically
Photometry: GC colours, luminosity functions, density profiles for blue/red GCs
Spectroscopy yields GC ages, metallicities, abundance ratios, kinematics, host galaxy M/L ratios
Interesting results already from existing sample; long-term goal is to obtain data for ~10 galaxies, covering range of galaxy luminosity and environment

22. Globular Clusters…may hold the key to understanding the evolution of galaxies and ultimately the Universe. (New Scientist Nov. 2002)