Department of Astronomy 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 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

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

A Quick Tour (based on optical, near-IR, far-IR, sub-mm, mm- and cm-wave observations) Point out that velocity coherence may only apply in low-mass star-forming regions!!! (a.k.a. GMC or Cloud Complex)

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?

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

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

Molecular Outflows

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

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

Self-similar Structure on Scales from 100 pc to 0.1 pc...in Orion J. Wiseman Figure, cleaned up, gets inserted on this page 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 Columbia-Harvard “Mini” AT&T Bell-Labs 7-m VLA

“Clump” Mass Distribution Ω What is a clump? Typical Stellar IMF Structure-Finding Algorithms +=dense core CS (21) Salpeter 1955 Miller & Scalo 1979 What does the clump “IMF” look like? CLUMPFIND, etc. story goes here, on left LADA, Blitz, Miesch & Scalo, etc. go on right Lifetime discussion cannot be separated from clump mass spectrum! 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

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

Virial Equilibrium and Larson’s Laws 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.

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 ... vA>>vS Uniform and/or Non-Uniform Magnetic Support? Turbulent and/or Wavelike Magnetic Support?

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 Density Structure Morphology self-similarity prevalence of prolate structures to core scales Analysis of Density Structure Structure Trees, Wavelets, IR Star-Counting No Preferred Scale between ~GMC and “dense core core” *a.k.a. “Larson’s Laws”

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

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!

What is Velocity Coherence?

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 Larson concludes: Slope on large scales (>0.04 pc) characterizes "turbulence" in ISM and fractal distribution of material on large scales. Slope on small scales (<0.04 pc) characterizes "Jeans instability," or the fragmentation of self-gravitating clumps. Our Interpretation: "Larson's Laws" (A.A.. self-similarity/fractal nature of ISM) ultimately gives behavior on scales >>0.04 pc. Small scale (<<0.1 pc) power spectrum is due to breakup of velocity-coherent clumps.

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

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

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 Larson concludes: Slope on large scales (>0.04 pc) characterizes "turbulence" in ISM and fractal distribution of material on large scales. Slope on small scales (<0.04 pc) characterizes "Jeans instability," or the fragmentation of self-gravitating clumps. Our Interpretation: "Larson's Laws" (A.A.. self-similarity/fractal nature of ISM) ultimately gives behavior on scales >>0.04 pc. Small scale (<<0.1 pc) power spectrum is due to breakup of velocity-coherent clumps.

Using Polarimetry to Map Field Structure

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

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

Steady Spherical Winds & PNe Cloud Lifetimes Cloud Formation Star-Formation Cloud Destruction Evaporation-- The Fate of Many Unbound Clouds, i.e. K>>G) Collisions--Accretion/Tidal Stripping Stellar Winds-- Lifetime discussion cannot be separated from clump mass spectrum! Steady Spherical Winds & PNe Bipolar Outflows Supernovae

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

Density-Velocity-Magnetic Field Structure

Initial Conditions for Star-Formation (Version 99) 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 2000+)

Observing Star-Formation From the Interstellar Medium to 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)

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

The Pleiades Photo: Pat Murphy

Bright Nebula: Orion Photo: Jason Ware

Dark Nebula: The Horsehead Photo: David Malin

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

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

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