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Observing Star-Formation From the Interstellar Medium to Star-Forming Cores On-Line Version, 1999

Observing Star-Formation From the Interstellar Medium to Star-Forming Cores On-Line Version, 1999. Alyssa A. Goodman Harvard University Department of Astronomy http://cfa-www.harvard.edu/~agoodman. Observing Star Formation From the ISM to Star-Forming Cores. History

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Observing Star-Formation From the Interstellar Medium to Star-Forming Cores On-Line Version, 1999

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  1. Observing Star-FormationFrom the Interstellar Mediumto Star-Forming CoresOn-Line Version, 1999 Alyssa A. Goodman Harvard University Department of Astronomy http://cfa-www.harvard.edu/~agoodman

  2. Observing Star Formation From the ISM to Star-Forming Cores • History The Optical and Theoretical ISM • A Quick Tour The multi-wavelength ISM • What do we need to explain? Density/Velocity/Magnetic Field Structure+ • Initial Conditions for Star-Formation

  3. History: Theory and Optical Observations • Theories of Cosmology + Stellar Evolution (c. 1925+) • Stellar Population Continuously Replenished • Bright Blue Stars Very Young • Stars Illuminating Reflection Nebulae Should Be Young • Optical Observations (c. 1900+) • Bright Nebulae Often Associated with Dark Nebulae • Perhaps Dark Nebulae are Sites of Star-Formation? • ...Theories of Star-formation prior to ~1970 • Jeans Instability

  4. A Quick Tour (based on optical, near-IR, far-IR, sub-mm, mm- and cm-wave observations) (a.k.a. GMC or Cloud Complex)

  5. Important Distinction to Keep in Mind • Most theories apply to formation of Low-Mass Stars (e.g. the Sun) • Shu et al. inside-out collapse model • Formation of Massive (e.g. O & B) Stars may be physically different than low-mass case • Is triggering required? • Elmegreen & Lada proposal--effects of nearby stars? • Ionization differences?

  6. Spectral-Line Mapping Adds Velocity Dimension But remember... • Scalo's “Mr. Magoo” effect • Mountains do not move (much). Interstellar clouds do.

  7. 3 km s-1 4 5 Orion:13CO ChannelMaps 6 7 8 Bally 1987

  8. Molecular Outflows

  9. Jeans Mass, Virial Mass, and Filling Factors in the ISM • Jeans Mass>>Typical Stellar Masses for all but Dense Cores • Filling Factor Low for Molecular Clouds other than Dense Cores

  10. What do we need to explain? • Self-similar Structure on Scales from 0.1 to 100 pc • “Clump” Mass Distribution & Relation toIMF • Rough Virial Equilibrium in Star-forming regions • Origin of “Larson’s Law” Scaling Relations • Density-Velocity-Magnetic Field Structure • Cloud Lifetimes

  11. 3.5 pc 0.6 pc 65 pc Maddalena et al. 1986 CO Map, 8.7 arcmin resolution Dutrey et al. 1991 C18O Map, 1.7 arcmin resolution Wiseman 1995 NH3 Map, 8 arcsec resolution AT&T Bell-Labs 7-m VLA Columbia-Harvard “Mini” Self-similar Structure on Scales from 100 pc to 0.1 pc...in Orion

  12. +=dense core CS (21) “Clump” Mass Distribution Ω What is a clump? Structure-Finding Algorithms Typical Stellar IMF Salpeter 1955 Miller & Scalo 1979 What does the clump “IMF” look like? • CLUMPFIND (Williams et al. 1994) • Autocorrelations (e.g. Miesch & Bally 1994) • Structure Trees (Houlahan & Scalo 1990,92) • GAUSSCLUMPS (Stutzki & Güesten 1990) • Wavelets (e.g. Langer et al. 1993) • Complexity (Wiseman & Adams 1994) • IR Star-Counting (C. Lada et al. 1994) E. Lada 1992 E. Lada et al. 1991

  13. “Larson’s Law” Scaling Relations (1981) (line width)~(size)1/2 (density)~(size)-1 Curves assume M=K=G (Myers & Goodman 1988)

  14. Virial Equilibrium and Larson’s Laws Larson’s Laws (Larson 1981) Virial Theorem (G=K) Non-thermal=Magnetic (K=M) (Myers & Goodman 1988) Sound speed If , then so that virial equilibrium + either of Larson’s Laws gives other.

  15. Limiting Speed in Cold ISM is Alfvén Speed, not Sound Speed ... vA>>vS Rough Virial Equilibrium in Star-forming regions Rough Equipartition in ~all of Cold ISM M=K=G M=K • Uniform and/or Non-Uniform Magnetic Support? • Turbulent and/or Wavelike Magnetic Support?

  16. Density-Velocity-Magnetic Field Structure • Density Structure • appearance of ISM • algorithms • self-similarity* • Velocity Structure • self-similarity* • rotation • coherence Magnetic Field Structure Zeeman Observations polarimetry uniformity/non-uniformity *a.k.a. “Larson’s Laws”

  17. Velocity Structure • Velocity Coherent Dense Cores low-mass dense cores=end of self-similar cascade • Rotation detectable, but not very “supportive”

  18. Velocity Coherent Cores*Where does the self-similarity end? Break in slope at ~0.1 pc Line Width Radius Goodman, Barranco, Heyer, & Wilner 1995,96 *low-mass!

  19. What is Velocity Coherence?

  20. Similar “Transition” Found in Spatial Distribution of Stars • Large-scales (>0.1 pc) characterized by cloud mass distribution (fractal, turbulent) • Small-scales (<0.1 pc) characterized by fragmentationof cores & Jeans instability

  21. Is Rotation Important? • Rotation Detectable in Dense Cores • Important in Fragmentation, but not in support • ~0.02 Goodman et al. 1993

  22. Magnetic Field Structure • Large-scale field in Spiral Galaxies • follows arms, mostly in plane • Polarization of Background Starlight • “not all grains are created equal” • not useful for cold dense regions • Polarization of EmittedGrain Radiation • potentially useful for dense regions • Field Uniformity/Non-Uniformity

  23. Using Polarizationto Map Magnetic Fields • Background Starlight • polarization gives plane-of-the-sky field • useful in low-density regions • Thermal Dust Emission • polarization is 90 degrees to plane-of-the-sky field • useful in high-density regions

  24. Using Polarimetry to Map Field Structure

  25. Optical Polarization Maps of Dark Clouds Taurus Ophiuchus Figure from PPIII--Heiles et al. 1993

  26. Magnetic Field Structure: Emission Polarimetry 100 m KAO dust emission observations Hildebrand, Davidson, Dotson, Dowell, Novak, Platt, Schleuning et al. 1996+

  27. Cloud Formation Cloud Destruction Star-Formation Cloud Lifetimes • Evaporation-- The Fate of Many Unbound Clouds, i.e. K>>G) • Collisions--Accretion/Tidal Stripping • StellarWinds-- Steady Spherical Winds & PNe Bipolar Outflows Supernovae

  28. The Effects of a Previous Generation of Stars They giveth... ...and they taketh away. Tóth, et al. 1995 Hester & Scowen 1995

  29. Density-Velocity-Magnetic Field Structure

  30. Low-Mass Stars Dense Core with R~0.1 pc T~10 K n~2 x 104 cm-3 v~0.5 km s-1 B~30 G ~a few forming stars/core not much internal structure High-Mass Stars Dense Core with R~0.5 pc T~40 K n~106 cm-3 v~1 km s-1 B~300 G ~many tens of forming stars/core (some high- and some low-mass) much internal structure Initial Conditions for Star-Formation(Version 99)

  31. Initial Conditions for Star-Formation(Version 2000+)

  32. Observing Star-FormationFrom the Interstellar Mediumto Star-Forming Cores Thanks to: J. Barranco (UC Berkeley) P. Bastien (U. Montreal) P. Benson (Wellesley) G. Fuller (Manchester) T. Jones (U. Minnesota) C. Heiles (UC Berkeley) M. Heyer (UMASS/FCRAO) R. Hildebrand (U. Chicago) S. Kannappan (CfA) E. Lada (U. Maryland) E. Ladd (UMASS/FCRAO) S. Kenyon (CfA) D. Mardonnes (CfA) S. Mohanty (U. Arizona) P. Myers (CfA) M. Pound (UC Berkeley) M. Sumner (CfA) M. Tafalla (CfA) D. Whittet (RPI) D. Wilner (CfA)

  33. What now? • Apply “measures” of n, v, & B structure to observations & (physical) simulations • see Adams, Anderson, Bally, Blitz, deGeus, Dickman, Dubinski, Elmegreen, Falgarone, Fatuzzo, Fuller, Gammie, Gill, Goldsmith, M. Hayashi, Henriksen, Heyer, Houlahan, Jog, Kannappan, Kleiner, H. Kobayashi, LaRosa, Langer, Larson, Magnani, McKee, Miesch, Myers, R. Narayan, E. Ostriker, J. Ostriker, T. Phillips, Pérault, Pouquet, Pudritz, Puget, Scalo, Stone, Stutzki, Vázquez-Semadeni, Williams, Wilson, Wiseman, Zweibel... • Measure B-field structure in more detail • dense regions:ISO, SOFIA, “PIREX” • Zeeman observations in high-density gas

  34. The Pleiades Photo: Pat Murphy

  35. Bright Nebula: Orion Photo: Jason Ware

  36. Dark Nebula: The Horsehead Photo: David Malin

  37. The Electromagnetic Spectrum wavenumber [cm-1] 10 8 6 4 2 0 -2 10 10 10 10 10 10 10 wavelength [Å] -2 0 2 4 6 8 10 12 10 10 10 10 10 10 10 10 6 10 -6 10 10 20 10 10 g -ray X-ray 4 8 10 -8 10 18 Near-IR 10 Ultra-violet Far-IR Optical sub-mm 10 mm-wave cm-wave 2 6 -10 10 10 16 10 10 Energy [eV] 0 4 -12 10 Frequency [Hz] 10 14 10 10 Energy [erg] Energy [K] -2 2 10 -14 10 12 10 10 -4 0 -16 10 10 10 10 10 -6 -2 -18 10 10 8 10 m-wave 10 -10 -8 -6 -4 -2 0 2 4 10 10 10 10 10 10 10 10 wavelength [cm] -6 -4 -2 0 2 4 6 8 10 10 10 10 10 10 10 10 wavelength [mm]

  38. A Dense Core: L1489 Benson & Myers 1989 Optical Image Molecular Line Map

  39. Molecular Line Map A Dark Cloud: IC 5146 Near-IR Stellar Distribution Lada et al. 1994

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