Transcript Observing Star Formation

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, nearIR,
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:
13CO
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
Type of Region
FWHM
FWHM
Thermal
Jeans Jeans
Virial
Density Linewidth T Linewidth Size Length Mass
Mass
[ptcl/cc]
[km/s]
[K]
[km/s]
[pc]
[pc] [M suns] [M suns]
H I Cloud
Giant Molecular Cloud
Dark Cloud
Dense Core
5
50
3000
25000
9 100
7 30
2 15
0.5 10
1.95
0.77
0.54
0.44
400
200
5
0.2
58. 2
5.2
0.5
0.1
29177
402
18
3
3.4E+06
1.0E+06
2.1E+03
5
Spherical
Mass
[M suns]
4.1E+06
5.2E+06
4.8E+03
3
Jeans
Implied
Masses in
"Filling
Sphere
Factor"
[number of] [M vir/M sphere]
1.4E+02
1.3E+04
2.6E+02
~1
Mass>>Typical Stellar Masses for all
but Dense Cores
 Filling Factor Low for Molecular Clouds other
than Dense Cores
 Jeans
82%
20%
43%
~100%
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 C18O Map, 1.7 arcmin resolution
Columbia-Harvard “Mini”
AT&T Bell-Labs 7-m
0.6 pc
Wiseman 1995
NH3 Map, 8 arcsec resolution
VLA
“Clump” Mass Distribution
What is a clump?
Structure-Finding
Algorithms
Typical Stellar IMF
dN dM  M 2.50.3
+=dense
core
Salpeter 1955
Miller & Scalo 1979
What does the clump
“IMF” look like?
Ω
1.6
dN dM  M
y
v
x
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
 ~ R 0.5
Larson’s Laws
n ~ R 1
(Larson 1981)
GM
  2   T 2   NT 2
5R
2
2
B
v A2
2
 NT 

3
3 8 nmavg
 T 2  kT m
avg
If
 T 2  NT 2
Virial Theorem (G=K)
Non-thermal=Magnetic (K=M)
(Myers & Goodman 1988)
Sound speed
, then
15
 2
n
4 mavg G  R 
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 ... vA>>vS
• 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?
= 10 K
1
for T
K
9
8
7
6
L1251A, NH
1
3
(J, K)=(1,1)
9
Binned Hay st ack Data
8
v TA
7
-0.05 ± 0.05
Break in
slope at
~0.1 pc
6
5
4
18
L1251A, C
O (1, 0)
3
Binned FCRAO Data
v  TA
-0.4 ± 0.1
2
2
3
4
5
6
7 8 9
2
Non-Thermal Line Width [km/s]
Non-Thermal Line Width [km/s]
Line Width
for T
K
= 10 K
The Transition from Self-Similarity to Velocity Coherence
1
Ant enna Temperature, T A
5
4
3
2
5
6
7 8 9
2
3
[K]
5
Ant enna Temperature, T A [ K]
Radius
Goodman, Barranco, Heyer, & Wilner 1995,96
*low-mass!
4
0.1
6
7 8 9
What is Velocity Coherence?
narrower
FWHM
"core"
FWHM
wider
FWHM
"Velocity Coherent"
Core
"Chaff"...
Cumulatively Obeys
Larson's Laws
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?
.
1.2


-1
]
1.0
L1251E
0.8


0.6
c lo ud s ro t at io nally
L1082A
0.4
st ab iliz ed
ag ainst
f rag m ent at io n
~ no binaries due t o f ission
(G
ra
d
ie
n
t
*
R
)
[k
m
s
B35A

0.2
no binaries due t o f ragment at ion
0.0
0.4
0.5
Goodman et al. 1993
0.6
0.7
0.8
-1
 v [ km s ]
0.9
1.0
1.1

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
Polarization of Background Starlight
by Magnetically Aligned Grains
Background Star em its
Unpolarized Continuum
B
e
Least Likely
Orientation

Background Starlight
polarization gives planeof-the-sky field
 useful in low-density
regions

Most Likely
Orientation
(Partial)
Polarization
Observed

E
Thermal Dust Emission
 polarization
B
Š
Result: Observed E-vector is parallel to
plane-of-the-sky component of B .
is 90 degrees
to plane-of-the-sky field
 useful in high-density
regions
Using Polarimetry to Map Field Structure
A Truly Theoretical Set of Polarization Maps
Changes in the Efficiency of Polarization Along a Line of Sight
Dark Cloud,
Theory #1
Ambient ISMCloud EnvelopeDark Cloud Cloud EnvelopeAmbient ISM
e
(or)
Dark Cloud,
Theory #2
Background
Star
Observer
A =
1
5
>10
5
1 mag
"Dark Cloud"
is a Local
Density
Maximum
Along l.o.s.
Density
V
Polarization Efficiency
"Dark Cloud"
Polarization
Efficiency
Drops w/in
"Dark Cloud"
Dist ance Along Line-of-Sight
Polariztion [%]
Core
?
Polarization
May Show
NO Increase
with
Extinction!
A V [magnit udes]
Disk
+ Star
Result: "Dark Cloud" Affects the Extinction, but NOT the Polarization
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--
Jon Morse et al./HST
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 Field is Uniform
•Rotation Along B
•Outflow Along B
•Single Star Formed
•"External" Pressure Negligible
•Configuration Flattens as it Collapses
Astronomical Observation
Physics we Understand

B-field line
Site of
Star-Formation
Integrated Intensity
Contour
Shock
Front
(Color represents v elocity; sha ding density.)
Initial Conditions for Star-Formation
(Version 99)
Low-Mass Stars
High-Mass Stars
Dense Core with
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 (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)
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
wavenumber [cm-1]
10
10
10
8
10
6
10
4
10
2
10
0
10
-2
wavelength [Å]
10
10
10
0
0
-2
10
10
10
-4
10
10
4
10
6
10
8
10
10
10
12
cm-wave
16
sub-mm
mm-wave
18
Far-IR
X-ray
g-ray
10
Near-IR
2
2
20
4
10
10
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
10
10
8
6
4
2
0
-2
Energy [K]
10
10
Ultra-violet
Optical
10
-2
Energy [erg]
Energy [eV]
10
10
Frequency [Hz]
10
10
6
A Dense Core: L1489
Benson & Myers 1989
Optical Image
Molecular Line Map
A Dark Cloud: IC 5146
Near-IR Stellar Distribution
Lada et al. 1994
Molecular Line Map