Download Matter Cycle in the Interstellar Medium (ISM)

Matter Cycle in the Interstellar
Medium (ISM)
Sandrine Bottinelli (IRAP)!
[email protected]
“The Interstellar Medium is anything not in stars”!
D. Osterbrock
1
Syllabus UE 45a
Note:!
• UE45a : Matter cycle in the ISM (Sandrine
Bottinelli, Katia Ferrière, Charlotte Vastel)!
• UE45b : Extragalactic physics (Roser Pello)
S. Bottinelli, 5 lectures
I.
II.
III.
IV.
Introduction!
Overview of the ISM!
Dust (formation, properties, composition)!
Molecular clouds, onset of star formation, shocks from molecular outflows
C. Vastel, 3 lectures
I.
II.
III.
Neutral gas / HI regions!
Ionized gas / HII regions!
Photo-dissociation regions
K. Ferrière, 2 lectures
I.
II.
III.
Large-scale shocks and dynamics: supernova remnants and super-bubbles,
and their impact on the ISM: turbulence, bubbles of hot gas, formation of
molecular clouds from atomic clouds!
Magnetic field (optical and IR polarization, Zeeman effect, Faraday rotation,
synchroton emission)!
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Cosmic-ray radiation
Textbooks, schedule, exam, etc
✤
Textbooks:!
✤
“The Interstellar Medium”, Lequeux!
✤
"The Physics of the Interstellar Medium", Dyson & Williams!
✤
“The Physics and Chemistry of the Interstellar Medium”, Tielens!
✤
“Physical Processes in the Interstellar Medium”, Spitzer!
✤
“Radiative Processes in Astrophysics”, Rybicki & Lightman!
✤
Schedule: see http://ezomp2.omp.obs-mip.fr/asep/index.php/Planning!
✤
Oral exam in january (23/01, TBC): present your analysis of a recent article
(chosen among a given list) and answer course questions.!
✤
Course notes available at:
http://userpages.irap.omp.eu/~sbottinelli/M2.html
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Chapter 1
Introduction
1.1 A few facts and some definitions !
1.2 Historical review of the ISM!
1.3 Matter cycle
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1.1. A few facts and some definitions
Structure of the Universe
Univers
Galaxie
Ionisé
Systèmes stellaires
Moléculaire
Milieu interstellaire
Atomique
5
1.1. A few facts and some definitions
The ISM in the Milky Way (MW)
✤
Molecular gas ~ atomic gas ~ 2×109 M⊙!
✤
Total ~ 4×109 M⊙ (1/10 of luminous matter in
stars)!
✤
Assume 2.4×10-24 g/H (local abundances)!
✤
⇒ total number of H nuclei (H, H+, H2) = 3.3×1066!
✤
ISM confined to disk of radius ~10 kpc and
thickness = ±100 pc!
✤
⇒ nH ~ 1.8 cm-3 (Earth’s atmosphere: 2.7×1019 cm-3)
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1.1. A few facts and some definitions
Stellar classification
FIG. 1.1 – Spectres d’étoiles montrant les absorptions dues au gaz autour de l’étoile
(ex. : celui présent dans l’atmosphère terrestre).
< 1900
>~ 1910
Spectral
Type
Fleming / Spectrum dominated
Secchi
Draper
by / type of object
I
A, B, C, D
Hydrogen Balmer
II
E, F, G, H,
I, K, L
Ca, Na
III
M
Wide bands
IV
N
Carbon stars
O
W-R stars, bright lines
P
Planetary Nebulae
Q
Other
∗
O
Atmospheric
Temperature
(K)
> 33, 000
Hydrogen
(Balmer)
Features
weak
B
A
10,500-30,000
7,500-10,000
medium
strong
F
G∗
K
6,000-7,200
5,500-6,000
4,000-5,250
medium
weak
v. weak
M
2,600-3,850
v. weak
Other Features
M/M⊙
R/R⊙
Ionized Helium (He+ ) sometimes in emission
Strong UV continuum
Neutral He absorption
H features maximum at A0
Some features of heavy elements, eg Ca+
20-60
9-15
3-18
2.0-3.0
3.0-8.4
1.7-2.7
1.1-1.6
0.9-1.05
0.6-0.8
1.2-1.6
0.85-1.1
0.65-0.80
0.08-0.5
0.17-0.63
+
Ca H&K, Na “D”
Ca+ , Fe
Strong molecules, eg CH, CN
Molecules, eg TiO
Very red continuum
Sun is G2V
H-R diagram
Les atmosphères des étoiles provoquent
des absorptions spécifiques :
(Herzsprung-Russell)
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Sub-division (0-5)
–
Main sequence
Ces absorptions ont été le premier critère de classification des étoiles :
III
IV
M
N
O
P
Q
Bandes larges
Etoiles carbones
Etoiles Wolf-Rayet, raies brillantes
Nébuleuses planétaires
Autres
1.1. A few facts and some definitions
Stellar classification
FIG. 1.2 – Diagramme de
Hertzsprung-Russell.
Depuis les années 1910, la classification se base sur la température et la luminosité des étoiles (cf.
diagramme H-R) :
Spectral
Type
∗
O
Atmospheric
Temperature
(K)
> 33, 000
Hydrogen
(Balmer)
Features
weak
B
A
10,500-30,000
7,500-10,000
medium
strong
F
G∗
K
6,000-7,200
5,500-6,000
4,000-5,250
medium
weak
v. weak
M
2,600-3,850
v. weak
Other Features
M/M⊙
R/R⊙
L/L⊙
Ionized Helium (He+ ) sometimes in emission
Strong UV continuum
Neutral He absorption
H features maximum at A0
Some features of heavy elements, eg Ca+
20-60
9-15
90,000-800,000
Main
Sequence
Lifetime
10-1 Myr
3-18
2.0-3.0
3.0-8.4
1.7-2.7
95-52,000
8-55
400-11 Myr
3 Gyr - 440 Myr
1.1-1.6
0.9-1.05
0.6-0.8
1.2-1.6
0.85-1.1
0.65-0.80
2.0-6.5
0.66-1.5
0.10-0.42
7-3 Gy
15-8 Gy
17 Gy
0.08-0.5
0.17-0.63
0.001-0.08
56 Gy
Ca+ H&K, Na “D”
Ca+ , Fe
Strong molecules, eg CH, CN
Molecules, eg TiO
Very red continuum
Sun is G2V
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1.1. A few facts and some definitions
Magnitude, extinction
✤
Hipparchus (-150 av. J-C): apparent magnitude = 1 for the brightest star, 6 for the
dimmest (to the naked eye)
✤
19th century: eye responds to the difference in
the logarithms of the brightness ⇒ scale in
which difference of one magnitude between
two stars implies constant ratio between their
brightness!
✤
Modern definition, a difference of 5 magnitudes
corresponds exactly to a factor 100 in intensity
(with the smallest magnitude corresponding to
the highest intensity) :
I2
= 100(m1 m2 )/5
I1
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1.1. A few facts and some definitions
Magnitude, extinction
, taille et de la longueur d’onde.
Extinction : characterized by extinction coefficient Qext = Qabs + Qsca (absorption
such
tinction+scattering),
Qext = Qabs +
Qdifthat
t.q. :! I = I0 exp( ng ⇥a2 Qext ⌥)
✤
✤ Measured
† : soit
as aAmagnitude
de magnitudes
le nombredifference:
de magnitudes
dû à l’extinction
Iλ,0
let Aλ the number of magnitudes due to gueur d’onde entre l’intensité non affectée, I ,0 , et celle observée,
extinction at a wavelength λ between Iλ,0 and Iλ (observed).!
I ,0
ude, on peut donc écrire :
= 100A /5 = 10A /2.5 , d’où
I ,0
I
✤ From the definition of the magnitude, we have : ✓
◆
= 100A /5 = 10A /2.5
⇥ I
I
hence! A = 2.5I log
I ,0
A = 2.5 log
(1.7)
I ,0
✤ Moreover, we also define the optical depth τ such that:
I
= I ,0 e ⌧
λ
lation :
By combining
the previous equations, we get :
I
⇤
=e ,
(1.8)
⌧
I ,0
A = 2.5 log(e
) = 2.5⌧ ⇥ log e = 1.086⌧
Iλ
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1.1. A few facts and some definitions
Distance determination in the ISM
Recall : stellar distances determined by the parallax or by comparison
between apparent and absolute magnitudes (determined from the spectral
type).
✤
✤
Parallax method first used by Friedrich Wilhelm Bessel in 1838 for the
binary star 61 Cyg. D=1AU/tan θ ≈ 1/θ AU!
✤
Parsec (pc) = distance for which the annual parallax is 1 arcsec (1/3600 of a
degree) ; e.g. Proxima Centauri has D=1/p(“)=1/0.76=1.32pc!
✤
Except for a few cases, method impossible to use for distance
determination of the ISM!
✤
For dark (absorbing) clouds, can use extinction method
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1.1. A few facts and some definitions
Distance determination in the ISM
✤
Kinematic distance: determined from the radial velocity of the clouds,
obtained from spectroscopic absorption or emission lines:
✤
galactic disk rotation is not that of a solid body
(same angular velocity, linear velocity ➚ with
radial distance) but it is a differential rotation
(angular velocity ➘ with radial distance) ⇒ all
points along the line of sight have a different
radial velocity.!
✤
origin = point close to the Sun, which has a
circular orbit and velocity equal to the mean
velocity of stars in the solar neighborhood
(around 10-20pc)!
✤
neighboring stars appear stationary w.r.t Sun
hence the name “Local Standard of Rest” (LSR)
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1.1. A few facts and some definitions
Units, abbreviations
✤
✤
“cgs” units (centimeters, grams, seconds) frequently used (instead of
“mks” ⇔ S.I. : meters, kilograms, seconds)!
✤
cf. handout for equivalences!
✤
moreover, use of “practical” or “historical” units (e.g., km/s for
velocities, cm-1 for energies) ⇒ take great care with calculations!!
Abbreviations for wavelength ranges: NIR (near infra-red), MIR (mid
infra-red), FIR (far infra-red), FUV (far ultra-violet), submm (submillimeter)
10-4nm
γ-rays
ν (GHz)
1nm
X-rays
200nm
FUV
380nm
UV
VIS
780nm
5(m 30(m
NIR
MIR
200(m
FIR
1mm
submm
mm
1cm
cm/
radio
λ
13
1.2. Historical review of the ISM:
Before the 1900s
✤
Herschel & cie realized that the MW is not just stars in vacuum.!
✤
Bright nebulae : “clouds” of gas that do not resolve into stars (when
viewed with a telescope). 3 categories :
diffuse nebulae (e.g.
reflection nebulae)
planetary nebulae
About reflection nebulae: spectrum of the
Pleiades Nebula by Vesto Slipher (Lowell Obs.)
➙ replica of stellar spectra ⇒ concluded there
must be reflection by “small particles”
filamentary nebulae
About planetary nebulae: Herschel
called these spherical clouds planetary
nebulae because they were round like
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the planets.
1.2. Historical review of the ISM:
Before the 1900s
✤
Dark nebulae: originally thought to be holes in the star clouds ; later
recognized to be dark clouds of obscuring material seen in silhouette
against rich star fields. Especially prominent in the brightest regions of the Milky Way (e.g.,
the Great Rift in Cygnus or the Coal Sack in the Southern Milky Way)!
!
!
!
✤
In general, these were viewed as isolated entities in otherwise mostly
empty space, and not as a manifestation of a general ISM.
15
1904ApJ....19..268H
1904ApJ....19..268H
1.2. Historical review of the ISM:
Early 1900s
✤
1st observational evidence of the existence ISM came from spectroscopic
observations of binary stars: revealed presence of narrow stationary
lines. ✤
1st identified lines = Ca+ in the
spectrum of δ Ori (Hartmann,
1904) ➙ absorption by a cloud of
ionized Ca lying between Earth
and the star system.
Black: FUSE observation of LB3459; blue: synthetic stellar spectrum;
red: synthetic stellar spectrum+ISM (Fleig et al. 2008)
16
1919ApJ....49....
1.2. Historical review of the ISM:
Early 1900s
Barnard (1919): proximity of dark/bright regions
➙ obscuring matter rather than vacuum, blocking light from more distant stars.!
✤
Survey of atomic absorption lines convinced astronomers that the space between
stars was filled with interstellar gas, transparent in the visible, except for a few
spectral lines arising from atomic ground states. (but this could not explain the
dark clouds catalogued by Barnard.)
Diameter
1930PASP...42..214T
✤
distance
4000
✤
Trumpler effect (1930): apparent diameter of
star cluster ↘ more slowly than their
luminosity ➙ extinction and reddening of
light due to small solid particles (dust
grains) mixed with gas.
No absorption
Absorption of
0.7mag/1000pc
1000
1000
4000
Photometric
distance
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1.2. Historical review of the ISM:
Early 1900s
✤
At the end of the 1930s:!
✤
ISM viewed as homogenous and diffuse, pervading space with a nearly
constant density. High-resolution spectroscopy of stationary lines ➙ complex structure: many
narrower line components with different radial velocities. ISM is clumpy and structured into clouds.!
✤
Discovery of the 1st molecules : CH (1937), CN (1940)
CN
CH
18
1.2. Historical review of the ISM:!
1940s
✤
Strömgren sphere: Bengt Strömgren ➙ bright diffuse nebulae with strong line
emission = regions of photo-ionized gas surrounding hot stars. These idealized
“Strömgren spheres” are at the heart of our modern theory of ionized nebulae.!
✤
3 types of ionized nebulae: !
Introduction to the Interstellar Medium
Regions) for the specific objects. Long-established practice and tradition, however, mean that we are
generally stuck with the confusion. Beware.
i. H II regions (= “classical” diffuse nebulae ) : characterized by intense line
At least three basic kinds of ionized nebulae are recognized in the ISM. Note that these are generally
isolated
objects, and not to be(hν
confused≥
with
the ionized phasesfrom
of the generalthe
ISM that we will
emission ; gas heated and ionized by UV
photons
13.6eV)
discuss later.
atmospheres of embedded O,B stars.
H Regions are the classical Fdiffuse nebulae) described by Herschel and others that show strong
II
emission-line spectra. These are regions of interstellar gas heated and ionized by UV (h
photons from the atmospheres of embedded O and B stars.
Nomenclature : spectroscopically, H II refers to ionized hydrogen
(H+), which can be present in a number of unrelated objets. The
term “H II regions” specifically refers to the bright diffuse nebulae
described here. H+ is not confined to discrete regions, but is
observed in the entire ISM; in fact, ~ 90% of H+ in the MW is
outside classical H II regions : it is the WIM (warm ionized
medium). (So it is not because there is some H+ that it is an H II
region.)
13.6eV)
19
1.2. Historical review of the ISM:!
1940s
✤
3 types of ionized nebulae (ctd): !
ii. planetary nebulae (PN) : UV photo-ionized
ejected stellar envelopes surrounding hot
remnant stellar core (white dwarf) !
!
‣
Note : H II regions and PN = similar
manifestation of 2 different processes
(stellar birth vs stellar death)
iii. SuperNova Remnants (SNRs): regions ionized by the passage of a blast
wave from SN explosion; differ from the previous 2 by the source of ionizing
photons and the additional heating mechanism.
20
Supernova Remnants (SNRs). These are regions ionized by the passage of a blast wave fro
supernova explosion through the ISM (either Type I or Type II supernovae). They differ from
regions and PNe in the source of ionizing photons and the additional mechanical heating due
hydrodynamical shockwave. Two basic types of SNRs are recognized:
1.2. Historical review of the ISM:!
1940s
Young SNRs (e.g., Crab Nebula) are photoionized by UV synchrotron radiation emitted by
relativistic electrons accelerated by the central pulsar. These are often called JPlerionsK (liter
Introduction
the Interstellar
Medium
crab-like)toafter
the prototype
Crab Nebula in Taurus (remnant of SN1054).
Supernova Remnants (SNRs). These are regions ionized by the passage of a blast wave f
supernova explosion through the ISM (either Type I or Type II supernovae). They differ fr
regions and PNe in the source of ionizing photons and the additional mechanical heating du
hydrodynamical shockwave. Two basic types of SNRs are recognized:
Young SNRs (e.g., Crab Nebula) are photoionized by UV synchrotron radiation emitted by
relativistic electrons accelerated by the central pulsar. These are often called JPlerionsK (lit
crab-like) after the prototype Crab Nebula in Taurus (remnant of SN1054).
✤
3 types of ionized nebulae (SNRs, ctd): !
✤
young SNRs (e.g. Crab Nebula) : photo-ionized by synchrotron radiation emitted by relativistic e− accelerated by the central pulsar !
Figure I-4: Crab Nebula, young SNR (AD1054). [Credit: VLT Kueyen+FORS2]
Old SNRs (e.g., Cygnus Loop), which are photoionized by X-rays emitted from dense coolin
regions collisionally heated to 105 6K by the passage of the supernova blast wave through the
ISM. Most of the gas in the remnants has been plowed up by the shock, and we see the cooli
where the gas has reached temperatures of ~104 K (where line emission is most efficient as w
see later).
✤
old SNRs (e.g., Cygnus Loop) : photo-ionized by Old SNRs (e.g., Cygnus Loop), which are photoionized by X-rays emitted from dense coo
X-rays emitted by cooling of dense regions heated
regions collisionally heated to 10 K by the passage of the supernova blast wave through t
ISM. Most of the gas in the remnants has been plowed up by the shock, and we see the coo
5−6
to 10 K by collisions due to the passage of a shock
where the gas has reached temperatures of ~10 K (where line emission is most efficient as
see later).
wave from the SN in the ambient ISM. !
Figure I-4: Crab Nebula, young SNR (AD1054). [Credit: VLT Kueyen+FORS2]
5 6
4
!
✤
Figure I-5: The Cygnus Loop, an old SNR. This image shows emission from the
shockwaves impinging on the ambient ISM (sharp filaments). [Credit/Copyright:
Jerry Lodriguss, www.astropix.com]
Strömgren’s work led to the recognition that the spectra of photo-ionized regions
contained a number of important diagnostics of the physical state of the gas
(density, temperature, abundances, etc), which is now a major research field.
I-5
Figure I-5: The Cygnus Loop, an old SNR. This image shows emission from the
shockwaves impinging on the ambient ISM (sharp filaments). [Credit/Copyright:
Jerry Lodriguss, www.astropix.com]
I-5
21
1.2. Historical review of the ISM:!
1950s-1970s
✤
Line emission from cold (10K) neutral hydrogen atoms at 21-cm via hyperfine atomic transitions in the ground state predicted in 1945 by van de Hulst, and first detected in 1951 by Ewen and Purcell at Harvard (followed 6 weeks later by the Dutch astronomers Muller and Oort) Cold H I clouds = majority of the total mass of the ISM.!
✤
This discovery initiated the era of radio-wavelength studies of the ISM, and was
the beginning of using the ISM to trace out Galactic structure. !
✤
cm: OH @ 18cm (Weinreb et al. 1963), NH3 @ 1.25cm (Cheung et al. 1968),
H2O @ 1 cm (22 GHz) (Cheung et al. 1969)!
✤
mm: CO @ 2.7 mm (Wilson, Jefferts & Penzias 1970) !
✤
UV (space): H2 in 1970!
✤
>130 molecules detected: http://www.astro.uni-koeln.de/cdms/molecules
22
1.3. Matter cycle
Diffuse
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1.3. Matter cycle
24
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