PhD_04

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L 1 Pre-collapse phase observational evidence
Background image courtesy J. Hester P. Scowen,
NASA/HST/WFPC2, Gaseous Pillars in M 16
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L 1 Pre-collapse phase observational evidence
Stahler and Palla The Formation of
Stars Chapters 1, 2, 3, 4
Background image courtesy J. Hester P. Scowen,
NASA/HST/WFPC2, Gaseous Pillars in M 16
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Why must stars form?
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ms lifetimes nuclear times
tTrapezium cluster qn Ori
tSun
tBigBang
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Where do stars form?
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For how long do stars form?
How much of the total mass of a galaxy is turned
into stars? And locked
there? ISM course (fraction of H II, H I, H2,
XYZ, grains, CDM...)
Stellar Evolution II
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Global Concepts (galactic scales, spatial and
temporal)
IMF Initial Mass Function SFR Star
Formation Rate SFE Star Formation Efficiency
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Local Concepts (cloud scales, spatial and
temporal)
GMCs to
cores
IMF Initial Mass Function SFR Star
Formation Rate SFE Star Formation Efficiency
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In General
What Form ? What Value ? What Time
Dependence ?
IMF Initial Mass Function SFR Star
Formation Rate SFE Star Formation Efficiency
MASS is a central issue here
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The best review article is that by John Scalo
(1986) The Stellar Initial Mass
Function Fundamentals of Cosmic Physics, Vol.
11, pp. 1-278 See also the updates Scalo 1998,
ASP Vol. 142, pp. 201-236
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L 1 Pre-collapse phase observational evidence
Home Work for every one
Give accountance of how to determine
empirically basic parameters (1) How does one
determine Distances D to
clouds (2) How does one determine Mass
M of clouds (3) How does one
determine Extinction AV in
clouds (4) How does one determine Pressure
P in clouds (5) How does one
determine Rotation W of
clouds (6) How does one determine Ages
t of clouds
What are the Uncertainties ?
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Interstellar Clouds 1. some Historical Milestones
1784 Visual Eye (optical) Herschel, in Construction of the Heavens holes in the sky
1918 Imaging (optical) Curtis, PASP 30, 65, dark nebulae
1937 1st detection CH (optical) Swings Rosenfeld, ApJ 86, 483
1941 1st detection CH (optical) Douglas Herzberg, ApJ 94, 381
1951 1st detection H I (21 cm) Ewen Purcell, Nature 168, 356
1963 1st detection OH (18 cm) Weinreb et al., Nature 200, 829
1965 1st detection CMB (7.3 mm) Penzias Wilson, ApJ 142, 419
1970 1st detection CO (2.6 mm) Wilson et al. , ApJ 161, L 43
1983 multimode MIR - FIR IRAS sky survey
1989 multimode NIR - mm COBE sky survey
1995 multimode NIR FIR ISO observatory
2003 multimode MIR - FIR Spitzer Space Telescope
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Interstellar Molecular Clouds 2. Galactic
Distribution
Visual Obscuration CO emission Distribution
cf. also H I IRAS 100 mm Cosmic Rays/g et cetera
CO (J 1- 0) Integrated Line
Intensity Dame, Hartmann Thaddeus, 2001, ApJ
547, 792
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Interstellar Molecular Clouds 2. Galactic
Distribution
Completeness ?
CO (J 1- 0) Integrated Line Intensity
(K km s-1) Dame, Hartmann Thaddeus, 2001, ApJ
547, 792
Units ?
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Interstellar Molecular Clouds 2. Galactic
Distribution
CO (J 1- 0) Radial
Velocity (LSR) Dame, Hartmann Thaddeus, 2001,
ApJ 547, 792
Define !
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Eup/kB 5.5 K
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Interstellar Molecular Clouds 3. Solar
Neighbourhood (within 1 kpc)
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Interstellar Molecular Clouds 3. Solar
Neighbourhood (within 1 kpc)
empty? Liseau et al. 1992 AA 265, 577
What is Goulds Belt ?
cf. also OB associations de Zeeuw et al. 1999, AJ
117, 354
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Interstellar Molecular Clouds 3. Solar
Neighbourhood (within 1 kpc)
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Interstellar Molecular Clouds 3. Solar
Neighbourhood (within 1 kpc)
Scale Height, H 75 pc
Molecular Mass, M 4 106 Mo
Surface Density, S 1 Mo pc-2
Mass Density, r(z0) 7 10-3 Mo pc-3
Particle Density, n(z0) 0.1 H2 cm-3

• Most in
• GMCs
• total mass
• H I H2
• times x
• x 2 - 4
• Blitz 1993
• Dame 1993

All clouds M (H2)
CO (J 1- 0) Dame et al. 1987, ApJ 322, 706
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Interstellar Molecular Clouds 4. Individual
Clouds (Solar Neighbourhood)
Type R (pc) n (cm-3) M (Mo) Dv (km s-1) T (K) Cores and Stars
Diffuse 0.3 3 30 500 0.5 100 0.7 1.5 10 ? Low-mass
Dark 3 10 102 3 103 4 1 3 10 Low-mass
Giant 20 100 10 300 105 6 5 15 10 -20 Massive and Low-mass

Average Property Depends On Molecular Tracer ?
is there a potential problem?
CO (J 1- 0) Myers 1991, in Molecular Clouds,
James Millar (eds.), p. 1
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Interstellar Molecular Clouds 5. Dense Cores
(Solar Neighbourhood)
Type R (pc) n (cm-3) M (Mo) Dv (km s-1) T (K) Cores and Stars
Low-Mass 0.05 0.2 104 5 0.3 10 0.2 0.4 10 T Tauri
Massive...
Large 0.3 0.6 104 5 30 - 104 1 2 10 30 OB
Small 0.01 0.03 106 7 0.3 300 1 3 30 100 OB
NH3 (J,K 1,1) Myers 1991, in Molecular
Clouds, James Millar (eds.), p. 1
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Interstellar Dark Clouds and Cores 6a. Selection,
optical
Barnard 1927, Univ. Chicago Press
Catalogue of 349 dark objects in the sky Bok
Reilly 1947, ApJ 105, 255
Globules size 5 arcsec to 60 arcsec Lynds
1962, ApJS 7, 1
DCs 1802 north of d - 33o Hartley et al.
1986, AAS 63, 27 DCs 1101
south of d - 33o Clemens Barvainis, 1988,
ApJS 68, 257 lt10 248 north of d - 33o
observational selection effects ?
more references from RL upon request
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Interstellar Dark Clouds and Cores 6a. Selection,
optical
Off the galactic plane few background stars
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Interstellar Dark Clouds and Cores 6a. Selection,
optical
Optical selection based on optical obscuration
extinction
most widely used is (0.3 to 10 mm)
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Interstellar Dark Clouds and Cores 6a. Selection,
optical
Optical selection based on optical obscuration
Dependence on what physics ? Rieke Lebofsky
curve applicable where ? Is A(l) a function of
the time, i.e. A(l, t) ?
Example White et al. 2000, AA 364, 741
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Interstellar Dark Clouds and Cores 6a. Selection,
optical
l 0.55 mm AV gt 100 mag ! ! !
kext kabs ksca
Optical photographic plates CCD images AV ltlt
100m N(H) AV saturation N(H) AV
calibration ?
gas mass vs dust mass normal mg/md 100
How well established ?
How relate AV and N(H2) ?
White et al. 2000, AA 364, 741
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Interstellar Dark Clouds and Cores 6b.
Observations, molecular lines
Benson Myers 1989, APJS 71, 89 119
Barnard/Lynds objects NH3 (1,1) Clemens et
al. 1991, APJS 75, 877 248
Clemens/Barvainis cores CO (2-1) Bourke et
al. 1995, MNRAS 276, 1067 169 Hartley et al.
cores NH3 (1,1), (2,2) Lemme et al. 1996, AA
312, 585 237 Clemens/Barvainis NH3 (1,1),
(2,2)
6b. Observations, dust continuum
Launhardt Henning 1997, AA 326, 329 59
CB 1.3 mm Osterloh et al. 1997, ApJS 110, 710
31 CB 1.3 mm Shirley et al. 2000, ApJS 131,
249 21 L CB 450 mm 850 mm Visser et al.
2001, AJ 124, 2756 42 CB L 850 mm
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In extragalactic applications, one uses CO and
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Interstellar Dark Clouds and Cores 6c.
Observational Results
1. See slide 23 (Myers schematic
presentation of core properties) 2. In addition
Cores with/without associated IRAS
source(s)
observational selection effects ?
IRAS sources are cold how cold ? and why ?
mean aspect ratio 2, but prolate? oblate? gt 50
of MB cores have IRAS source no difference
globules / embedded cores
Spitzer fraction of starless cores ?
Core with IRAS source without IRAS source
broader lines narrow / thermal widths
larger size smaller
more evolved ? younger ?
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Summary Molecular Probes of Tkin and n(H2)
n(H2)
ten orders of magnitude
two orders
Tkin
Genzel 1990, in The Physics of Star Formation
and Early Stellar Evolution, Lada Kylafis
(eds.), NATO ASI 342, p.155 - 219
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Genzel 1990, in The Physics of Star Formation
and Early Stellar Evolution, Lada Kylafis
(eds.), NATO ASI 342, p.155 - 219
Tkin
n(H2)
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Interstellar Dark Clouds and Cores 7. Rotation
Cloud dv/dr (km s-1 pc-1) j (km s-1 pc) Reference
Rosette 0.18 47 Blitz Thaddeus 1980
Mon R 1 0.20 45 Blitz 1978
W 3 0.30 27 Thronson et al. 1985
Orion 0.10 74 Kutner et al. 1977

typical GMC lt 0.05 lt15 various Blitz 1980

typical DC 1.5 3 10-3 Goodman et al. 1993
for q 0.5 and j J/ M q R2 W

j(sol sys) 5 10-7 km s-1 pc
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Interstellar Dark Clouds and Cores 8a. Magnetic
Fields spectral lines
Region Method Bobs (mG)
Intercloud Medium Faraday rotation 5
Diffuse Cloud Zeeman H I 7
Dark Cloud Zeeman H I 5 - 10
Zeeman OH 20 - 30
GMC Zeeman H I 10
Massive Core Zeeman OH 100 - 103
Maser Spots Zeeman H2O 104
Table adapted from Myers 1991
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Interstellar Dark Clouds and Cores 8a. Magnetic
Fields spectral lines
Zeeman OH 18 cm Bourke et al. 2001, ApJ 554,
916
Zeeman OH 18 cm
Crutcher 1999, ApJ 520,706
1665, 1667 MHz
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Interstellar Dark Clouds and Cores 8a. Magnetic
Fields spectral lines
Spatial Scale
Crutcher 1999
Mass Scale
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Interstellar Dark Clouds and Cores 8b. Magnetic
Fields continuum
e.g., 800 mm map of linear polarisation
How ?
see also Ward-Thompson et al. 2000, ApJ 537, L
135 3 L Wolf et al. 2003, ApJ 592, 233 3 CB

(3 CB)
give also B-field strength 257 mG
Holland et al. 1996, AA 309, 267
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Interstellar Dark Clouds and Cores 9. Time Scales
- Ages
cf. slide 18 cross communication (dP) at the
signal speed cs DC 10 40 Myr GMC 10
100 Myr Blitz 1993 and Elmegreen 1993
30 40 Myr
Correct ?
Cloud Age Method Reference gt20 Myr OB
n(stellar generations) gt 1 Blaauw 1964, ARAA 2,
213 gt10 Myr 34 open clusters/clouds Leisawitz et
al. 1989, ApJS 70, 731
what are G and m and what values do they take?
star forming lifetime
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Interstellar Dark Clouds and Cores 9. Time Scales
- Ages
Recent assessments suggest low ages,
O(Myr) Elmegreen 2000, ApJ 539, 342 Hartmann et
al. 2001, 562, 852 Visser et al. 2002, AJ 124,
2756 or ? Tassis Mouschovias 2004, ApJ 616,
283 Tassis et al., 2006, ApJ 646, 1043 ...
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Pre-collapse stages in regions of high-mass
star formation
Theoretical Expectation and Observational
Evidence for

• Schematically
• low-mass stars M 0.08 - 1.5 Mo
• intermediate-mass stars M 1.5 3 Mo
• high-mass stars M gt 3 Mo

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Interstellar Clouds 10. Structure
10 pc
0.1 pc
0.01 pc
Genzel 1990, in The Physics of Star Formation
and Early Stellar Evolution, Lada Kylafis
(eds.), NATO ASI 342, p.155 - 219
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Interstellar Clouds 10. Structure
continuous
power laws
structure
clumps
inhomogeneous
fractals
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Interstellar Clouds 10a. Continuous Structure

continuum
Motte et al. 1998, AA 336, 150
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Interstellar Clouds 10b. Inhomogeneous Structure

continuum
See also 850 mm map by Johnstone et al. 2000, ApJ
545, 327
Motte et al. 1998, AA 336, 150
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Interstellar Clouds 10b. Inhomogeneous Structure
Observational evidence from spatial distribution
of FIR/submm lines Neutral Carbon C I 609
mm Ionised Carbon C II 157 mm
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• Oph (L1688) in C I 609 mm, C II 157 mm and
  13CO 2.7 mm
• Kamegai et al. 2003, ApJ 589, 378

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Interstellar Clouds 10b. Inhomogeneous Structure
Observational evidence from spatial distribution
of FIR/submm lines Neutral Carbon C I 609
mm Ionised Carbon C II 157 mm
External UV radiation penetrates to large
depths (e.g., Swiss cheese model)
clump interclump contrast gt 100 to 102
in density
lt 10-1 to 10-2 in mass
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• L 1 conclusions
• Stars are formed throughout the Galaxy today
• The natal material has been identified as
  interstellar molecular clouds
• Pre-natal sites have been identified both as
  clumps/cores in molecular
• cloud complexes and in isolated
  globules they appear fragmented
• Both embedded and isolated clumps exhibit the
  same properties
• These inhomogeneties appear dense, cold and
  magnetised
• Their rotation rates are small (but angular
  momenta relatively large)

• L 1 open questions
• How do cores/clumps form and what are their
  lifetimes ?
• How do globules form and what are their
  lifetimes ?
• What are the detailed physics and chemistry of
  these structures ?
• What is the fraction of forming stars ? and
  forming
• at what rate ?
• with what efficiency ?
• what is the resulting IMF ? (inc. BDs and
  free-floating planets)
• how is ang. momentum re-distributed/lost from the
  system ?