1. Courtesy Jason Harris, Steward Observatory Two Tails of a Distribution : The Initial Mass Functions of Extreme Star Formation Michael R. Meyer Steward Observatory The University of Arizona with Julia Greissl, Morten Andersen, and Alan Aversa

2. Stellar Initial Mass Function (Chabrier, 2003; Kroupa, 2001)

3. Chabrier (2003) Initial Mass Function for unresolved binaries plotted in linear units.

4. No local variations in stellar IMF (e.g. Meyer et al. 2000).

5. What about the sub-stellar IMF ? cf. Luhman et al. PPV (2007)

6. HST/NICMOS Observations of Mon R2: Multi-Color Photometry and H2O Filter Andersen, Meyer, Oppenheimer, Dougados, and Carpenter (2006)

7. H-R Diagrams for Sub-stellar Objects in NGC 1333 Greissl, Meyer, Wilking, Fanetti, Greene, Schneider, Young (2007) *

8. Bottom Line: The Sub-stellar IMF is falling! (cf. Allen et al. 2005) Where dN/dm ~ M -  0.0 >  > -2.3 (with 90 % C.I.) Brown dwarfs do not outnumber stars. Meyer et al. (in prep)

9. Spatial Variations in the Ratio of Stars to Sub-stellar Objects? The HST Orion Treasury Program (Robberto et al.)

10. Color-Magnitude Diagrams as a Function of Cluster Radius 0 1 2 3 (J-H) 0 1 2 3 Andersen et al. (in prep) R=0.6-1.0 pc R=1-2 pc R=2.2-2.9 pc MHMH

11. Color-Magnitude Diagrams as a Function of Cluster Radius 0 1 2 3 (J-H) 0 1 2 3 Andersen et al. (in prep) R=0.6-1.0 pc R=1-2 pc R=2.2-2.9 pc MHMH Stars Sub-stellar

12. No strong radial variation in IMF detected in Orion. N(0.01-1.0 Mo)/N(0.02-0.08 Mo) 1 2 3 4 0.8 1.0 1.2 1.4 1.6 1.8 Radius (parsecs) Andersen et al. (in prep)

13. Is the IMF different in super-star clusters?

14. Unresolved Super Star Clusters in NGC 4038/4039 Mengel et al. (2002) * * * * * * * * * * * * * * * * * * * * * *

15. Meyer & Greissl (2005); Greissl et al. (2007) Integrated Spectra of Super-star Clusters: Can distinguish Chabrier (2003) from Salpeter (1955)

16. What is going on? Siess et al. (2000); Ali et al. (1995) CaI+CO(2-0) < 0.5 Msun MgI > 1.0 Msun 1 Myr isochrone

17. Greissl, Meyer, Christopher, & Scoville (2007) See Poster this session! IMF in Antennae Very Young SSC #6 Consistent with Chabrier (2003) IMF

18. “UD” HII Regions (Proto-SSCs) Johnson et al. (2001) 12”

19. Conspectus 1)The sub-stellar IMF in young clusters is consistent with field and a turnover below 0.1 Mo! (Meyer et al. 2007). 2)No strong evidence for radial variation in ratio of stars to sub-stellar objects in Orion between 0.8-1.8 parsecs (Andersen et al. 2007). 3)Preliminary results suggest IMF in very young Antennae super-star clusters consistent with field star IMF (Greissl, Meyer, Christopher, & Scoville, 2007).

20. The Search for Variations: A Six-Parameter IMF 1. Mean Mass 2. Variance 3. High Mass Break 4. High Mass Slope 5. Sub-stellar Break 6. Sub-stellar Slope -2 -1 0 1 2 log[M * /M o ] log[N * ]

21. Epilogue 1)Need surveys for the sub-stellar IMF down below minimum mass for fragmentation. Will require surface gravity information (multi-object near-IR spectra) to sort out background stars (Gorlova et al. 2003; Mohanty et al. 2004) and kinematic studies to probe dynamics. 2)Determine companion mass ratio distribution as a function of primary star mass/separation down to planetary mass regime (e.g. Joergens, 2006; Metchev & Hillenbrand, 2005; Apai et al.). Could this help discern the difference between brown dwarfs and planets? 3)Surveys for ratio of high to low mass stars as a function of [Fe/H], B- field, and ISM pressure in Milky Way and local group galaxies (Andersen et al., Meyer et al.) to search for variations in Jeans Mass. 4)Further modelling of integrated light in ultra-compact HII regions in M33 ([Fe/H] vs. Galactocentric radius) and very young Super-Star Clusters in starburst galaxies (J. Greissl, PhD thesis @ UofA).

22. NICMOS Color-Magnitude Diagram for NGC 1333 Greissl, Meyer, Wilking, Fanetti, Greene, Scheider, Young (2007)

23. Ratio of Stars to Sub-stellar Objects in NGC 1333 Greissl, Meyer, Wilking, Fanetti, Greene, Scheider, Young (2007)

24. Results

25. Ca Mg CO(2-0) 3 Myr 1 Myr 3 Myr 1 Myr Age 6.44 +/- 0.30Ch03 6.27 +/- 0.44Ch03 11.01 +/- 0.44S55 8.98 +/- 0.82S55 EW(CaI + CO(2-0))/EW(MgI)IMF S55 1 Myr S55 3 Myr Ch03 1 Myr Ch03 3Myr

26. MMT-AO Engineering PSF Simulated Trapezium Observations R(Sky Noise) = 1 Rc = 0.2 pc from Close et al. 2003. using Hillenbrand & Carpenter (2000). Hcomp(at Rc) < 24 mag R(sky noise) = 2.5 Rc = 0.5 pc R(Sky Noise) = 4 Rc = 0.8 pc R(Sky Noise) > 20 Rc = 4-5 pc Hcomp(at Rc) < 17.8 mag. Hcomp(at Rc) < 15.3 mags. Core Radius not resolved. 25 kpc50 kpc0.5 Mpc 5 kpc PSF 0.5 kpc The Trapezium on the Bleeding Edge: Sensitivity vs. Confusion...

27. Narrow-band Filters Provide Estimates of Teff Andersen et al. (2006)

28. J-H versus J CMD for MonR2

29. Ratio of “low mass stars ” to brown dwarfs Andersen et al. 2006, AJ

30. The similar ratio for other regions  Mon R2: 8.5+-6.4  Taurus: 6.9+-2.0  IC348: 11.6+-3.4  Orion: 4.3+-0.6  Chabrier:4.3 All measurements within 2sigma of each other

31.  To understand chemical evolution.  Interpret the integrated light of other galaxies.  Constrain contribution to baryonic dark matter The shape of the initial mass function provide crucial information concerning the origins of stellar masses. ● Are there characteristic masses? ● Is the IMF truly universal? Prologue: Why Study the IMF?