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Observing Star-FormationObserving Star-FormationFrom the Interstellar MediumFrom the Interstellar Medium
to Star-Forming Coresto Star-Forming CoresOn-Line Version, 1999On-Line Version, 1999
Alyssa A. GoodmanHarvard University
Department of Astronomy
http://cfa-www.harvard.edu/~agoodman
Observing Star Formation Observing Star Formation From the ISM to Star-Forming CoresFrom the ISM to Star-Forming Cores
HistoryThe Optical and Theoretical ISM
A Quick TourThe multi-wavelength ISM
What do we need to explain?Density/Velocity/Magnetic Field
Structure+
Initial Conditions for Star-Formation
History: Theory and Optical History: Theory and Optical ObservationsObservations
Theories of Cosmology + Stellar Evolution (c. 1925+)
•Stellar Population Continuously Replenished•Bright Blue Stars Very Young
Stars Illuminating Reflection Stars Illuminating Reflection Nebulae Should Be YoungNebulae Should Be Young
Optical Observations (c. 1900+)•Bright Nebulae Often Associated with Dark Nebulae
Perhaps Dark Nebulae are Sites Perhaps Dark Nebulae are Sites of Star-Formation?of Star-Formation?
...Theories of Star-formation prior to ~1970Jeans Instability
Galaxy
"Velocity Coherent" Dense Core
Young Stellar Object +Outflow
Stars
time
Self-Similar, Turbulent,"Larson's Law" Clouds
A Quick Tour A Quick Tour (based on (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 Important Distinction to Keep in MindMind
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.
Spectral Line Observations
Line-profile Fittingor
Channel Mapsor
Integrated Intensity Maps
Contour Mapor
Similar "2-D" Displayof 3-D information
Mountain Range
Orion:Orion:1313CO CO ChannelChannelMapsMaps
Bally 1987Bally 1987
887766
3 km s3 km s-1-1 5544
Molecular Outflows
FCRAO BIMA FCRAO+BIMA
Redshifted CO emission (Zhang et al. 1996)Blueshifted CO emission (Zhang et al. 1995)NH Half-Power Contour (Bachiller et al. 1993)3
L1157
0.1 pc
Jeans Mass, Virial Mass, Jeans Mass, Virial Mass, and Filling Factors in the and Filling Factors in the
ISMISMType of Region Density
FWHMLinewidth T
FWHMThermal
LinewidthSizeJeans
LengthJeansMass
VirialMass
SphericalMass
JeansMasses in
Sphere
Implied"FillingFactor"
[ptcl/cc] [km/s] [K] [km/s] [pc] [pc] [Msuns] [Msuns] [Msuns] [number of][Mvir/Msphere]
H I Cloud 5 9 100 1.95 400 58.2 29177 3.4E+06 4.1E+06 1.4E+02 82%Giant Molecular Cloud 50 7 30 0.77 200 5.2 402 1.0E+06 5.2E+06 1.3E+04 20%Dark Cloud 3000 2 15 0.54 5 0.5 18 2.1E+03 4.8E+03 2.6E+02 43%Dense Core 25000 0.5 10 0.44 0.2 0.1 3 5 3 ~1 ~100%
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 What do we need to explain?explain?
Self-similar Structure Self-similar Structure on Scales from 0.1 to 100 pc
“Clump” Mass Distribution Mass Distribution & Relation to IMF Rough Virial Equilibrium Virial Equilibrium in Star-forming regions Origin of “Larson’s Law” “Larson’s Law” Scaling Relations Density-Velocity-Magnetic Field Structure Cloud LifetimesLifetimes
Self-similar Structure on Scales from 100 pc to 0.1 pc...in Orion
65 pc3.5 pc 0.6 pc0.6 pc
Maddalena et al. 1986CO Map, 8.7 arcmin resolution
Dutrey et al. 1991C18O Map, 1.7 arcmin resolution
Wiseman 1995Wiseman 1995NHNH33 Map, 8 arcsec resolution Map, 8 arcsec resolution
Columbia-Harvard “Mini” AT&T Bell-Labs 7-m VLAVLA
“Clump” Mass Distribution
Ω
What is a clump? Structure-FindingAlgorithms
E. Lada 1992
+=dense core
CS (21)
Typical Stellar IMF
dN dM ∝ M−1.6
What does the clump “IMF” look like?
E. Lada et al. 1991
v
y
x
•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 1955Miller & Scalo 1979
dN dM∝ M−2.5±0.3
““Larson’s Law” Larson’s Law” Scaling RelationsScaling Relations (1981)(1981)
(line width)~(size)1/2 (density)~(size)-1
Curves assume M=K=G (Myers & Goodman 1988)
GM
5 R
= σ2
= σ T2
+ σ N T2
σ N T
2=
2
3
B2
8 π nm a v g
=v
A2
3
σ T
2= kT
m a v g
Virial Equilibrium and Larson’s Laws
Virial Theorem (G=K)
Non-thermal=Magnetic (K=M)(Myers & Goodman 1988)
Sound speed
If σT
2< < σ
N T2 , then
Larson’s Laws (Larson 1981)
σ ~ R0 . 5
n ~ R− 1
so that virial equilibrium + either of Larson’s Laws gives other.
n =15
4 π m a v g G
σ
R
⎛
⎝
⎞
⎠
2
Rough Virial Equilibrium in Star-forming regions
M=K=GRough Equipartition in ~all of Cold
ISMM=K
Limiting Speed in Cold ISM is Limiting Speed in Cold ISM is Alfvén Speed, not Sound Alfvén Speed, not Sound Speed ... vSpeed ... vAA>>v>>vSS
• Uniform and/or Non-Uniform Magnetic Support?
• Turbulent and/or Wavelike Magnetic Support?
Density-Velocity-Magnetic Field Structure
Density Structureappearance of ISM
algorithmsself-similarity*
Velocity Structureself-similarity*
rotationcoherence
Magnetic Field StructureZeeman Observations
polarimetryuniformity/non-uniformity
*a.k.a. “Larson’s Laws”
Velocity StructureVelocity Structure
Velocity Coherent Dense CoresVelocity Coherent Dense Coreslow-mass dense cores=end of self-similar cascade
Rotation Rotation detectable, but not very “supportive”
Velocity Coherent Cores*Where does the self-similarity end?
*low-mass!
The Transition from Self-Similarity to Velocity Coherence
A
2 3 4 5 6 7 8 91
2
Antenna Temperature, TA [K]
2
3
4
5
6
7
8
91
L1251A, C18
O (1,0)
Binned FCRAO Data
Δv ∝ TA-0.4 ± 0.1
2
3
4
5
6
7
8
91
5 6 7 8 90.1
2 3 4 5 6 7 8 9
, Antenna Temperature T [ ]K
1251 , L A NH 3 ( , )=(1,1)J K
Binned Haystack Data
Δv ∝TA-0.05 ± 0.05
Goodman, Barranco, Heyer, & Wilner 1995,96
Radius
Lin
e W
idth Break in
slope at~0.1 pc
What is Velocity Coherence?
"Velocity Coherent"Core
narrowerFWHM
widerFWHM
"Chaff"... Cumulatively Obeys
Larson's Laws
"core"FWHM
Similar “Transition” Found in Spatial Distribution of Stars
(Larson 1995)
Surface Density of Stellar Companions as a Function of Angular Separation in Taurus-Auriga
break in slope at ~0.04 pc
"Velocity Coherent" Regime
"Turbulent " Regime
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
.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.11.00.90.80.70.60.50.4
Δv [km s-1 ]
L1082A
L1251E
B35A
β=0.44
β=0.20
β=0.02
Goodman et al. 1993
Magnetic Field StructureLarge-scale field in Spiral Galaxies
follows arms, mostly in planePolarization of Background Starlight
“not all grains are created equal”not useful for cold dense regions
Polarization of Emitted Grain Radiationpotentially useful for dense regions
Field Uniformity/Non-Uniformity
Using Polarizationto 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
≤
Background Star emitsUnpolarized Continuum
Result: Observed -vector is parallel to plane-of-the-sky component of .
EB
B
ee
Most LikelyOrientation
Least Likely Orientation
Polarization of Background Starlightby Magnetically Aligned Grains
E
B
(Partial) Polarization Observed
Using Polarimetry to Map Field StructureUsing Polarimetry to Map Field Structure
e
Dark CloudAmbient ISM Ambient ISMCloud Envelope
1A = V
5 >10 5 1mag
Changes in the Efficiency of Polarization Along a Line of Sight
A V
[magnitudes]
Polariztion [%]?
Polarization May Show
NO Increase with
Extinction!
Density
Distance Along Line-of-Sight
Polarization Efficiency
Polarization Efficiency Drops w/in
"Dark Cloud"
"Dark Cloud" is a Local Density
Maximum Along l.o.s.
Cloud Envelope
Background Star Observer
Result: "Dark Cloud" Affects the Extinction, but NOT the Polarization
"Dark Cloud"
(or)
Disk + Star
Core
Dark Cloud, Theory #2
Dark Cloud, Theory #1
A Truly Theoretical Set of Polarization Maps
Tau
rus
Ophiuchus
Optical Polarization Maps of Dark Clouds
Figure from PPIII--Heiles et al. 1993
Magnetic Field Structure: Emission Polarimetry
100 m KAOdust emissionobservations
Hildebrand, Davidson,
Dotson, Dowell,Novak, Platt,Schleuning
et al. 1996+
Cloud Lifetimes
•Evaporation-- Evaporation-- The Fate of Many Unbound Clouds, i.e. K>>G)•Collisions--Collisions--Accretion/Tidal Stripping •StellarStellar Winds--Winds--
Steady Spherical Winds & PNeBipolar Outflows Supernovae
Cloud Formation
Star-Formation
Cloud Destruction
Jon Morse et al./HST
The Effects of a Previous Generation of StarsThe Effects of a Previous Generation of Stars
Tóth, et al. 1995
They giveth... ...and they taketh away.
Hester & Scowen 1995
Density-Velocity-Magnetic Field Structure
Physics we Understand
Astronomical Observation
B-field lineIntegrated Intensity Contour
Shock Front
Site of Star-Formation
•Initial Field is Uniform•Rotation Along B•Outflow Along B•Single Star Formed•"External" Pressure Negligible•Configuration Flattens as it Collapses
(Color represents velocity; shading density.)
ω
Initial Conditions for Star-Initial Conditions for Star-FormationFormation(Version 99)(Version 99)
Low-Mass StarsDense Core with
R~0.1 pc T~10 K n~2 x 104 cm-3
Δv~0.5 km s-1
B~30 G ~a few forming
stars/core not much internal
structure
High-Mass StarsDense Core with
R~0.5 pc T~40 K n~106 cm-3
Δv~1 km s-1
B~300 G ~many tens of
forming stars/core (some high- and some low-mass)
much internal structure
SNRStellar WindsRadiation Pressure(Ionization)
Outflows
Magnetic Fields+MHD Waves
Gravity
Thermal Pressure
Rotation
"Turbulence"
Initial Conditions for Star-FormationInitial Conditions for Star-Formation(Version 2000+)(Version 2000+)
Thanks to: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-FormationObserving Star-FormationFrom the Interstellar MediumFrom the Interstellar Medium
to Star-Forming Coresto Star-Forming Cores
What now?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 PleiadesThe Pleiades
Photo: Pat Murphy
Bright Nebula: OrionBright Nebula: Orion
Photo: Jason Ware
Dark Nebula: The HorseheadDark Nebula: The Horsehead
Photo: David Malin
The Electromagnetic SpectrumThe Electromagnetic Spectrum
1020
1018
1016
1014
1012
1010
108
Frequency
[H
z]
10-10
10-8
10-6
10-4
10-2
100
102
104
wavelength [cm]
108
106
104
102
100
10-2
10-4
10-6
wavelength [m]
10-18
10-16
10-14
10-12
10-10
10-8
10-6
En
erg
y [e
rg]
1012
1010
108
106
104
102
100
10-2
wavelength [Å]
10-6
10-4
10-2
100
102
104
106
Energ
y [
eV
]
1010
108
106
104
102
100
10-2
Energ
y [K
]10
1010
810
610
410
210
010
-2
wavenumber [cm-1]
Opti
cal
Near-
IR
Far-
IR
cm-w
ave
mm
-wave
sub-m
m
Ult
ra-v
iole
t
X-r
ay-ray
m-wave
A Dense Core: L1489A Dense Core: L1489
Optical Image Molecular Line Map
Benson & Myers 1989
A Dark Cloud: IC 5146A Dark Cloud: IC 5146
Molecular Line Map
Near-IR Stellar Distribution
Lada et al. 1994