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What do we know about the birth of super star clusters?

What do we know about the birth of super star clusters?. Collaborators: Indraneil Biswas (UVa) Amy Reines (UVa) Rémy Indebetouw (UVa) Bill Vacca (NASA-Ames) Leslie Hunt (INAF) Barb Whitney (SSI) Chip Kobulicky (UWy) Kenny Wood (St.Andrews).

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What do we know about the birth of super star clusters?

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  1. What do we know about the birth of super star clusters? Collaborators: Indraneil Biswas (UVa) Amy Reines (UVa) Rémy Indebetouw (UVa) Bill Vacca (NASA-Ames) Leslie Hunt (INAF) Barb Whitney (SSI) Chip Kobulicky (UWy) Kenny Wood (St.Andrews) Kelsey Johnson (UVa, NRAO)

  2. Why are Super Star Clusters Interesting? • Plausibly proto-globular clusters • Extreme mode of star formation • Formation common in early universe • Luminous “simple stellar populations” for probing galaxy evolution • Impact on the ISM & IGM How were these incredible clusters formed?

  3. Can we learn from Galactic Star Forming Regions? From Ultracompact HII Regions to Proto Globular Clusters Key Questions: How do the properties of star formation scale between these regimes? How do the cluster properties depend on environment?

  4. Compact, “inverted spectrum” sources Very dense HII regions non-thermal Sn free-free optically-thick free-free 100 1 l (cm) Strategy: Look for sources with similar SEDs to Ultracompact HII regions Wood & Churchwell 1989

  5. continuum of sources Comparison of Radio SEDs (individual clusters) SBS 0335-052 He 2-10 NGC 5253 W49A Johnson et al. in prep, Johnson & Kobulnicky 2003, Mezger et al. 1967, Turner et al. 1998, 2004

  6. Comparison of Radio SEDs (individual clusters) • Radii of HII regions < a few pc • Electron densities >104 - 106 cm-3 Pressures > 108 kB • Ionizing Luminosities > 1052-53 s-1  > 1000s O7-type stars SBS 0335-052 He 2-10 NGC 5253 W49A Johnson et al. in prep, Johnson & Kobulnicky 2003, Mezger et al. 1967, Turner et al. 1998, 2004

  7. What can we learn from radio recombination lines?(e.g. Mohan, Anantharamaiah, & Goss 2001) • Densities: ne > 104 cm-3 • Radii: r ~ 2-10 pc • Ionizing Flux: Nlyc > 1052 Nearly perfect agreement with simple models! Example: prediction for H92a line

  8. What do we (maybe?) know about their lifetimes? *Caveat: Star formation must be continuous over at least ~10 Myr *Caveat: The external pressure could be much higher

  9. IC 4662 (2Mpc) Different wavelengths probe different environments “Young” (<10 Myr) optically selected clusters and ultra-young radio selected clusters are exclusive Linear Resolution ~ 10 pc NLyc  20 - 2001049 s-1 Large OB associations Johnson, Indebetouw, & Pisano 2003

  10. What can we learn from the near-infrared? Haro 3 Radio clusters also have an “infrared excess” Hot dust near the ionizing stars Color scale: HST V-band Contours: VLA X-band Johnson, Indebetouw, Watson, & Kobulnicky 2004 (other examples in: Vanzi & Sauvage 2004, Cresci et al. 2005, Cabanac et al. 2005)

  11. NLyc 5,000 1049 s-1 5,000 O7* stars SBS 0335-052ultra-low metallicity (Z  1/40 Z) Color scale: HST ACS F140LP Contours: VLA + Pie Town X-band Color scale: HST NICMOS Paa Contours: VLA + Pie Town X-band Johnson & Hunt in prep. (See also: Hunt, Vanzi, & Thuan, 2001; Plante & Sauvage, 2002)

  12. VLA 2 cm contour, Gemini 10mm color (Vacca, Johnson, & Conti 2002) What can we learn from the mid-infrared? He2-10 He2-10 He 2-10 VLA 2 cm contour, HST V-band color (Kobulnicky & Johnson 1999) The radio sources alone account for at least 60% of the mid-IR flux from the entire galaxy

  13. Ionizing source(s) Fractal Structure Cocoon Mass (SFE) % Clumpy Dust Dust Composition Rout Rin Can we use infrared observations to probe the natal environment? New Models: 3D Monte-Carlo Radiation Transfer (à la Barb Whitney) Fractal dust structure consistent with the actual ISM

  14. Near-IR J, H, K Spitzer IRAC 3.6, (4.5+5.8), 8.0 mm Spitzer MIPS 24, 70, 160 mm Rin = 5 pc Rin = 10 pc Rin = 20 pc Rin = 30 pc Rin = 45 pc Geometric Sequence with Rin increasing (pseudo-evolutionary sequence) Example: 90% clumpy, Rout=50pc, SFE=10% Johnson, Whitney, Indebetouw, & Wood submitted.

  15. Near-IR J, H, K Spitzer IRAC 3.6, (4.5+5.8), 8.0 mm Spitzer MIPS 24, 70, 160 mm Rin = 5 pc Rin = 10 pc Rin = 20 pc Rin = 30 pc Rin = 45 pc Geometric Sequence with Rin increasing (pseudo-evolutionary sequence) Example: 90% clumpy, Rout=50pc, SFE=10% Johnson, Whitney, Indebetouw, & Wood submitted.

  16. Near-IR J, H, K Spitzer IRAC 3.6, (4.5+5.8), 8.0mm Spitzer MIPS 24, 70, 160mm Dependence on Viewing Angle Indebetouw, Whitney, Johnson, & Wood, ApJ 2006

  17. nFn[erg/s/cm2] black = smooth red = 99% clumpy l [mm] Variation with Clumpiness alone (averaged over all viewing angles) Shape of the infrared SED can vary significantly with clumpy fraction  We need to be very careful in our interpretation of IR observations!

  18. NGC7252: 8x107 M_sun NGC1569 NGC1705 NGC1569 NGC1705 DDO 165 IZW18 IC10 Weidner, Kroupa, & Larsen 2004 Is the formation of super star clusters special?

  19. What is the initial cluster luminosity function? Thermal radio sources in the Antennae a > -0.1 Whitmore & Zhang 2002 Extracted from Neff & Ulvestad 2000 • Linear resolution ~ 100pc • initial luminosity function compatible with a power-law

  20. What is the initial cluster luminosity function? Thermal radio sources in the He2-10 HST I-band a > -0.1 Probability < 10-35 from power law Resolution: radii ~4pc It appears that in at least some extreme cases cluster formation does not follow a power-law Kobulnicky & Johnson 1999, Johnson et al. 2000, Johnson & Kobulnicky 2003, Biswas & Johnson submitted

  21. What is going on here? He 2-10 Antennae Could be confusion, but this effect should be worse in the Antennae Could be statistics, but similar numbers (12 in Antennae, 7 in He2-10) Could be that for some reason low mass clusters aren’t radio sources, but we see these in other galaxies Could be that dwarf galaxies can isolate a “mode” of star formation

  22. Outstanding questions related to Massive Star Formation • Are there environmental differences betweenthe formation of small associations and massive clusters? e.g. Environmental requirements? Protostellar interactions? • How does the process of star formation vary between small associations and massive clusters? e.g. Star formation efficiency? • What is the role of metallicity in super star cluster formation as it relates to globular cluster formation in the early universe? e.g. Cooling, hardness of radiation field?

  23. SOFIA CARMA HERSCHEL ALMA SPITZER JWST 106 M proto cluster at 10 Mpc Looking toward the Future (IR - mm) ? There is a lot of work to do!

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