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