1. 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

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 )
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 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)
Point out that velocity coherence may only apply in low-mass star-forming regions!!!
(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 Channel Maps 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 to IMF
Rough Virial Equilibrium in Star-forming regions
Origin of “Larson’s Law” Scaling Relations
Density-Velocity-Magnetic Field Structure
Cloud Lifetimes

11. 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

12. “Clump” Mass DistributionΩ
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

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
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. 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?

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
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”

17. Velocity Structure Velocity Coherent Dense Cores Rotation
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 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.

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
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.

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

27. 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

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. 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

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

32. 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)

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 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]

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

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