Spitzer’s Chapter
on Star Formation
Alyssa A. Goodman
Harvard-Smithsonian
Center for Astrophysics
Physical Processes in the Interstellar Medium (Spitzer 1978)
13.3 Gravitational Condensation and Star Formation
“The detailed analysis of star formation is
a complex topic, as well as a somewhat
uncertain one.”
Since “Spitzer,” The Book
large-scale molecular-line mapping (1980’s-now)
IRAS (1983); HST (1990-now); Chandra (1999-now); ISO (1997-8)
wide-field ground-based IR imaging (1990’s -now)
interferometric & A.O. imaging (1980’s-now)
sub-mm imaging (1990’s-now)
realistic 3D numerical simulations (1990’s/soon-)
ISM to IMF
Galaxy
Molecular Cloud Complex
Star-Forming “Globule”
Circumstellar
Disk+Outflow
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Extrasolar System
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Star Cluster
Star-Forming “Globule”
Number of Stars of each Mass
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?
Stellar Mass
(Realistic?)
3D Numerical
Simulations
•MHD turbulence gives “t=0”
conditions; Jeans mass=1
M
•50 M, 0.38 pc, navg=3 x
105 ptcls/cc
•forms ~50 objects
•T=10 K
•SPH, no B or , 
•movie=1.4 free-fall times
Bate, Bonnell & Bromm 2002
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Cinepak decompressor
are needed to see this picture.
Physical Processes in the Interstellar Medium (Spitzer 1978)
Chapter 13: Gravitational Motion
The very last paragraph of Spitzer’s book (end of 13.3) reads:
We conclude that the reduction of magnetic field
made possible by plasma drift (ambipolar
diffusion) is unimportant during the free-fall time.
If magnetic forces, combined perhaps with
centrifugal forces, maintain a cloud or fragment in
hydrostatic equilibrium, [ambipolar diffusion] can
significantly reduce the magnetic flux, permitting
gradual contraction and possibly the resumption of
free fall when the flux has fallen to a sufficiently
low value (Nakano, 1976).
ISM to IMF
Unmagnetized Turbulent Fragmentation
Turbulent Fragmentation
+ Competitive/Bondi-Hoyle Accretion
Role of a “Core”
“Squeezed” Ambipolar Diffusion/
Turbulent Fragmentation leading to A.D.
Role of Interactions
~107 yr Ambipolar Diffusion
~105 yr Free Fall Time
See also Ballesteros-Paredes, Vazquez-Semadeni et al.; Ostriker, Stone & Gammie;
Klein, McKee, Krumholz et al. ; Tilley & Pudritz; Hartmann & Burkert & more
Shu et al.;
Mouschovias
et al.
Li &
Nakamura
Padoan et al.
MacLow &
Klessen
Bate et al.;
Padoan et al.
(Newton)
Can this
happen…
Cores form by
Ambipolar Diffusion
Shu, Adams & Lizano 1987
…inside this?
Bondi-Hoyle Accretion, not (Purely) Disk Accretion?
Padoan et al. 2004 (astro-ph, Nov. 8)
ISM to IMF
Turbulent Fragmentation
+ Competitive/Bondi-Hoyle Accretion
~105 yr Free Fall Time
Role of a “Core”
Turbulent Fragmentation leading to A.D.
Role of Interactions
~107 yr Ambipolar Diffusion
How Should this Picture Look?
Star Formation in Space & Time
10000
1000
Time [Myr]
100
Crossing
Time
10
0.1 km s
-1
1
1 km s
-1
0.1
10 km s
-1
0.01
-1
100 km s
100,000 years
to escape a 0.1 pc
dense core at
1 km s-1
0.001
0.1
1
10
Scale [pc]
100
1000
Star Formation in Space & Time
10000
1000
Time [Myr]
100
Crossing
Time
10
0.1 km s
-1
1
1 km s
-1
0.1
10 km s
-1
0.01
-1
100 km s
5 Myr
to escape a
(7 pc) dark cloud
at the sound speed
0.001
0.1
1
10
Scale [pc]
100
1000
Star Formation in Space & Time
10000
1000
Time [Myr]
100
Crossing
Time
10
0.1 km s
-1
1
1 km s
-1
0.1
10 km s
-1
0.01
-1
100 km s
0.001
0.1
1
10
Scale [pc]
100
1000
10 Myr
to escape a
whole GMC
at 10 km s-1
PV Ceph:
Speeding
at 22 km/s
Goodman & Arce 2004
Optical Image of NGC 7023
Dust Emission Map
10 pc in 500,000 yr (@20 km/s)
“Exit wound”
Tom Licha, 2002
PV Ceph:
Speeding
at 22 km/s
Goodman & Arce 2004
NGC 7023
PV Ceph
Spitzer’s Forté
HH 46-47 flow poking out of a globule, optical (DSS)
Spitzer Infrared Image: A. Noriega-Crespo (SSC/Caltech)
How Fast is the Source of HH46-47 Moving?
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Image from Stanke, McCaughrean & Zinnecker, 1999
CO flow: Chernin & Masson 1991
HST image: Heathcote et al. 1996
How Fast is the Source of HH46-47 Moving?
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Image from Stanke, McCaughrean & Zinnecker, 1999
CO flow: Chernin & Masson 1991
HST image: Heathcote et al. 1996
Substituting Spatial Statistics
for Temporal Sampling
Distribution of Stars
Current
Positions
Easiest
IR-radio surveys (e.g. Spitzer
c2d, GLIMPSE)
Masses
Pretty
hard
(IR) luminosity-mass relations
Ages
Very hard IR spectroscopy of PMS stars
(models??)
Outflow properties
Velocities
Very, very Proper motion: needs future
hard
technology in most cases
Radial Velocity: nearing
feasibility with IR spectroscopy
Stellar “Age”
from
Spitzer
Spitzer Colors
Class I Models
Classes
I
<1 Myr
(major disk)
II
1 to 10 Myr
(some disk)
III
older TTS
(almost no disk)
Class II Regime
Class III
Allen et al. 2004; see also Whitney et al. 2003,4
Distribution of Gas & Dust
Column
Density
Easiest,
but…
NIR or MIR extinction mapping is
best (see COMPLETE)
Masses
Pretty
hard
Describing 3D geometry a problem
& emission-to-mass conversion
is uncertain (gas & dust chemistry)
Time
Evolution
Very hard Even with velocities from molecular
3D
velocity
field
Very, very Proper motion: impossible w/o
masers
hard
lines, gravitational binding energy
uncertain
Radial Velocity: easy, but hard to
define “features”
Optical
Near-Infrared
The Value of Coordinated Observations: B68
Optical
Image
Dust Emission
C18O
Coordinated Molecular-Probe Line, Extinction &
Thermal Emission Observations of Barnard 68
This figure highlights the work of João Alves and his
collaborators. The top left panel shows a deep VLT image
(Alves, Lada & Lada 2001). The middle top panel shows
the 850 m continuum emission (Visser, Richer & Chandler
2001) from the dust causing the extinction seen optically.
The top right panel highlights the extreme depletion seen at
high extinctions in C18O emission (Lada et al. 2001). The
inset on the bottom right panel shows the extinction map
derived from applying the NICER method applied to NTT
near-infrared observations of the most extinguished portion
of B68. The graph in the bottom right panel shows the
incredible radial-density profile derived from the NICER
extinction map (Alves, Lada & Lada 2001). Notice that the
fit to this profile shows the inner portion of B68 to be
essentially a perfect critical Bonner-Ebert sphere
NICER
Extinction
Map
Radial Density
Profile, with Critical
Bonnor-Ebert
Sphere Fit
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Perseus
Ophiuchus
Serpens
The
COordinated
Molecular
Probe
Line
Extinction
Thermal
Emission
Survey
COMPLETE
Alyssa A. Goodman, Principal Investigator (CfA)
João Alves (ESO, Germany)
Héctor Arce (AMNH)
Paola Caselli (Arcetri, Italy)
James DiFrancesco (HIA, Canada)
Jonathan Foster (CfA, PhD Student)
Mark Heyer (UMASS/FCRAO)
Helen Kirk (HIA, Canada)
Di Li (CfA)
Doug Johnstone (HIA, Canada)
Jaime Pineda (CfA, PhD student)
Naomi Ridge (CfA)
Scott Schnee (CfA, PhD student)
Mario Tafalla (OAN, Spain)
Tom Wilson (ESO, Germany)
H
W(13CO)
2MASS/NICER
Extinction
H- emission,WHAM/SHASSA Surveys (see Finkbeiner 2003)
IRAS Ndust
Implied Column Density Distributions and lognormal Fits
(Perseus COMPLETE data)
140
log normal fit to
2MASS column density
(all panels)
120
Number
100
60
40
20
2M ASS/NICER
0
140
120
100
Number
What is the True
Distribution of
Star-Forming
Material in
Molecular Clouds?
80
80
60
40
13
CO
20
0
140
Goodman, Ridge & Schnee 2005
120
Number
100
80
60
40
IRAS
log normal fit to
IRAS column density
20
0
-1.0
-0.5
0.0
0.5
Log (Equiv alent A
V [ mag] )
1.0
Class II
L1688 class II
Sources are
widely
distributed
NB:
require
detections in all
4 IRAC bands
Slide courtesy of
Lori Allen (c2d +
IRAC GTO data)
Class I
L1688 class II
sources
are
clustered
peak surface
density is a
few x 102/pc2
Slide courtesy of
Lori Allen (c2d +
IRAC GTO data)
C18O
L1688 class II
integrated
intensity
Class I
sources are
primarily
concentrated
along
molecular gas
ridge
Slide courtesy of
Lori Allen (c2d +
C18O map courtesy D. Li IRAC GTO data)
Physical Processes in the Interstellar Medium (Spitzer 2004!)
13.3 Gravitational Condensation and Star Formation
“The detailed analysis of star formation is a
complex topic, as well as a somewhat
uncertain one. It is only since the advent of
sensitive infrared telescopes that we can peer
inside the dark dusty regions where stars
form to see the youngest stars. By combining
measures of the stellar spatial and age
distributions with measures of the gas and
dust temperature, density, and compositional
distributions, stellar and gas velocities, and
magnetic field topology, one can test
statistically-oriented but predictive theories of
the production of stars over time.”