Observing StarFormation From the Interstellar Medium to StarForming

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

A Quick Tour (based on optical, near. IR, far-IR, sub-mm, mm- and cm-wave observations) (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.

Orion: 13 CO Channel Maps 3 km s-1 4 5 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 3. 5 pc 65 pc Maddalena et al. 1986 Dutrey et al. 1991 CO Map, 8. 7 arcmin resolution C 18 O Map, 1. 7 arcmin resolution Columbia-Harvard “Mini” AT&T Bell-Labs 7 -m 0. 6 pc Wiseman 1995 NH 3 Map, 8 arcsec resolution VLA

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

“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 (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.

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?

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”

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

Line Width Velocity Coherent Cores* Where does the self-similarity end? Break in slope at ~0. 1 pc 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

Is Rotation Important? � � � Goodman et al. 1993 Rotation Detectable in Dense Cores Important in Fragmentation, but not in support ~0. 02

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

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+

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

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

Density-Velocity-Magnetic Field Structure

Initial Conditions for Star-Formation (Version 99) Low-Mass Stars High-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 � 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 (Cf. A) E. Lada (U. Maryland) E. Ladd (UMASS/FCRAO) S. Kenyon (Cf. A) D. Mardonnes (Cf. A) S. Mohanty (U. Arizona) P. Myers (Cf. A) M. Pound (UC Berkeley) M. Sumner (Cf. A) M. Tafalla (Cf. A) D. Whittet (RPI) D. Wilner (Cf. A)

What now? � Apply “measures” of n, v, & B structure to observations & (physical) simulations � � see Adams, Anderson, Bally, Blitz, de. Geus, Dickman, Dubinski, Elmegreen, Falgarone, Fatuzzo, Fuller, Gammie, Gill, Goldsmith, M. Hayashi, Henriksen, Heyer, Houlahan, Jog, Kannappan, Kleiner, H. Kobayashi, La. Rosa, Langer, Larson, Magnani, Mc. Kee, 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 0 10 -2 wavelength [Å] 10 10 10 0 -2 10 10 -4 10 2 10 4 10 6 10 8 10 10 10 12 20 16 cm-wave 18 Far-IR X-ray g-ray 10 sub-mm mm-wave 10 10 Near-IR 2 0 10 10 14 10 12 10 10 10 -6 10 8 10 10 m-wave -10 10 -8 10 -6 10 -4 10 -2 10 0 10 2 10 4 wavelength [cm] 10 -6 10 -4 10 -2 10 0 10 2 10 wavelength [ m] 4 10 6 10 8 -6 10 -8 10 -10 10 -12 -14 -16 -18 10 10 10 8 6 4 2 0 -2 Energy [K] 10 10 10 Ultra-violet Optical 10 4 -2 Energy [erg] Energy [e. V] 10 10 Frequency [Hz] 10 10 6

A Dense Core: L 1489 Benson & Myers 1989 Optical Image Molecular Line Map

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