1. 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

2. Observing Star Formation From the ISM to Star-Forming Cores  History History The Optical and Theoretical ISM  A Quick Tour A Quick Tour A Quick Tour The multi-wavelength ISM  What do we need to explain? What do we need to explain? What do we need to explain? Density/Velocity/Magnetic Field Structure+  Initial Conditions for Star-Formation Initial Conditions for Star-Formation 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 NebulaeBright Dark  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, optical, near- IR,optical, near- IR, far-IR, sub-mm, mm- and cm-wavefar-IR, sub-mm, mm- and cm-wave observations) far-IR, sub-mm, mm- and cm-wave (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. Orion: 13 CO Channel Maps Bally 1987 876 3 km s -1 54

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  Self-similar Structure on Scales from 0.1 to 100 pc Mass Distribution  “Clump” Mass Distribution & Relation to IMF Virial Equilibrium  Rough Virial Equilibrium in Star-forming regions “Larson’s Law”  Origin of “Larson’s Law” Scaling Relations  Density-Velocity-Magnetic Field Structure Lifetimes  Cloud Lifetimes

11. Self-similar Structure on Scales from 100 pc to 0.1 pc...in Orion 65 pc 3.5 pc 0.6 pc Maddalena et al. 1986 CO Map, 8.7 arcmin resolution Dutrey et al. 1991 C 18 O Map, 1.7 arcmin resolution Wiseman 1995 NH 3 Map, 8 arcsec resolution Columbia-Harvard “Mini” AT&T Bell-Labs 7-mVLA

12. “Clump” Mass Distribution Ω What is a clump? Structure-Finding Algorithms E. Lada 1992 +=dense core CS (2  1) Typical Stellar IMF What does the clump “IMF” look like? E. Lada et al. 1991 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) Salpeter 1955 Miller & Scalo 1979

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

15. Rough Virial Equilibrium in Star-forming regions M=K=G Rough Equipartition in ~all of Cold ISM M=K Limiting Speed in Cold ISM is Alfvén Speed, not Sound Speed... v A >>v S 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? *low-mass! Goodman, Barranco, Heyer, & Wilner 1995,96 Radius Line Width Break in slope at ~0.1 pc

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 fragmentation of 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 Emitted Grain Radiation  potentially useful for dense regions Field Uniformity/Non-Uniformity

23. Using Polarization to 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. Taurus Ophiuchus Optical Polarization Maps of Dark Clouds 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 Lifetimes Evaporation--Evaporation-- The Fate of Many Unbound Clouds, i.e. K>>G ) Collisions--Collisions-- Accretion/Tidal Stripping StellarWinds--Stellar Winds-- Steady Spherical Winds & PNe Bipolar OutflowsSupernovae Cloud Formation Star-Formation Cloud Destruction

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

29. Density-Velocity-Magnetic Field Structure

30. Initial Conditions for Star-Formation (Version 99) Low-Mass Stars Dense Core with  R~0.1 pc  T~10 K  n~2 x 10 4 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~10 6 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

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

32. 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) Observing Star-Formation From the Interstellar Medium to Star-Forming Cores

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 10 20 10 18 10 16 10 14 10 12 10 8 Frequency [Hz] 10 -10 10 -8 10 -6 10 -4 10 -2 10 0 2 4 wavelength [cm] 10 8 6 4 2 0 -2 10 -4 10 -6 wavelength [  m] 10 -18 10 -16 10 -14 10 -12 10 -10 10 -8 10 -6 Energy [erg] 10 12 10 8 6 4 2 0 -2 wavelength [Å] 10 -6 10 -4 10 -2 10 0 2 4 6 Energy [eV] 10 8 6 4 2 0 -2 Energy [K] 10 8 6 4 2 0 -2 wavenumber [cm -1 ] OpticalNear-IR Far-IR cm-wave mm-wave sub-mm Ultra-violet X-ray  -ray m-wave

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

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