1. Probing the IMF
Star Formation in Massive Clusters

2. Probing the IMF: Goals
Quantify the IMF in rich, dense star-forming regions
Understand the relationship between IMF; initial conditions
locate the stellar birthline/region
link to mass accretion rate
explore linkage to thermal + turbulent pressure
Critical to modeling star-formation in the early universe

3. Probing the IMF: Measurements
JHK photometry
MCAO images at high Strehl (~0.5 at J-band)
IFU spectroscopy at R ~ 1000
MCAO photometry can probe
0.3 to 100 Msun in Arches cluster; R 136
define birthline location + IMF
5 to 100 Msun in clusters out to ~1 Mpc
quantify slope of upper IMF
IFU spectroscopy can probe brightest stars

4. Probing the IMF: Measurements
Galactic Center Superclusters: d = 10 kpc
= 7”
Stellar density ~ 100x Orion Nebula Cluster

5. Probing the IMF: Measurements
LMC Massive Cluster: d = 200 kpc
R 136
20”
Stellar density ~ 10x Orion Nebula Cluster

6. Probing the IMF: Measurements
M82 Superclusters: d = 4 Mpc

7. Probing the IMF: Measurements
Stellar Birthlines for Differing dMacc/dt
High dMacc/dt
Low dMacc/dt
How is dMacc/dt related to [Fe/H]; stellar density?

8. Probing the IMF: Ancillary Science
Quantify the spatial distribution for stars of different masses & ages
Do massive stars form preferentially near the cluster center?
If so, does this imply a different formation mechanism?
Quantify stellar multiplicity in dense clusters
What role do dynamical interactions play in influencing multiplicity?
What are the relevant timescales and environmental conditions?

9. Probing the IMF: Current Status
With current 6-10m class telescopes + HST:
Crowding limits IMF probe to M > 2 Msun in Arches; R 136
IMF probes in regions more distant than ~1 Mpc is precluded by crowding

10. Probing the IMF: Need for GSMT
Key issue is crowding (not photon collection)
With a 30m GSMT, K-band diffraction limit is 0.015”
Arches clusters can be studied throughout the M33 disk
Probe birthlines; IMF for wide range of metallicities
R 136 clusters can be studied out to M82 (upper end of IMF)

11. Probing the IMF: Requirements
MCAO-fed near IR imager with ~1’ FOV
Deliver Strehl ~ 0.5 at J-band
MCAO-fed IFU spectrograph with R ~ 3000

12. Probing the IMF: Trades
Ability to probe IMF to larger distances; lower masses increases dramatically as aperture increases
Directly linked to reduced crowding
Adequate sampling of IMF may not require MCAO correction over maximum achievable field (~2’)

13. Effects of Crowding on Photometry
20”
M 32 (Gemini/Hokupaa)
NGST
GSMT with MCAO

14. Probing the IMF: GSMT v NGST et al
NGST is limited by crowding (see previous slide)
ALMA could probe initial conditions in Galactic regions

15. Probing the IMF: Needed Simulations
Quantify crowding vs aperture trade
Simulate variable extinction & nebular background
Understand Strehl vs photometric precision trade
Understand optimum field of view
Model time variations of Strehl during exposure