Observing Star-Formation From the Interstellar Medium to Star-Forming Cores On-Line Version, 1999 Alyssa A. Goodman Harvard University Department of Astronomy

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

History: Theory and Optical Observations Theories of Cosmology + Stellar Evolution (c ) Stellar Population Continuously Replenished Bright Blue Stars Very Young  Stars Illuminating Reflection Nebulae Should Be Young Optical Observations (c ) 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

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)

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 Bally km s -1 54

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  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

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 CO Map, 8.7 arcmin resolution Dutrey et al 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

“Clump” Mass Distribution Ω What is a clump? Structure-Finding Algorithms E. Lada =dense core CS (2  1) Typical Stellar IMF What does the clump “IMF” look like? E. Lada et al 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

“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)

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.

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”

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

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?  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

Using Polarimetry to Map Field Structure

Taurus Ophiuchus Optical Polarization Maps of Dark Clouds 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

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

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

Initial Conditions for Star-Formation (Version 2000+)

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

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 Frequency [Hz] wavelength [cm] wavelength [  m] Energy [erg] wavelength [Å] Energy [eV] Energy [K] wavenumber [cm -1 ] OpticalNear-IR Far-IR cm-wave mm-wave sub-mm Ultra-violet X-ray  -ray m-wave

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

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