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• Christophe Morisset & Antonio Peimbert
– [email protected][email protected]
Martes, Miercoles: 9h30:11h30
Jueves: 11h00:12h00
3 examenes (2/3)
~10 Tareas + 1 platica (= 2 tareas) (1/3)
1. Introducción
Condiciones físicas de Medio Interestelar
Fases del Medio Interestelar.
Halos de Galaxias
Medio Intergaláctico
Foresta de Lyman
Gas de Núcleos de Galaxias
Componentes de alta energí a: rayos cósmicos, rayos
2. Polvo interestelar
Propiedades radiativas del polvo
Composición y propiedades físicas del polvo
Formación y destrucción de granos
Hidrocarbonos poliaromáticos
3. Regiones H I
Estado de ionización
Calentamiento y enfriamiento
La línea de 21 cm
El polvo en las regiones H I
4. Regiones fotoionizadas
Regiones H~II y nebulosas planetarias
Esfera de Strömgren
Estructura del frente de ionización
Radiación difusa
Aproximación "on the spot"
Estado de ionización de los elementos pesados
Balance de energía
5. Espectro de Regiones HII y diagnósticos de
Líneas útiles para determinaciones de densidad,
temperatura y abundancias químicas
Corrección por extinción
Propiedades físicas a partir del espectro en radio
Temario 2
6. Nubes moleculares
Balance de energía
Líneas moleculares
Química de las nubes moleculares
Turbulencia y propiedades estadísticas de las nubes
Diagnósticos moleculares
7. Nubes en equilibrio
Teorema del virial
Soluciones hidrostáticas
El efecto del campo magnético
8. Dinámica del medio interestelar
Aplicabilidad de la mecánica de fluidos al medio
Ecuaciones de la dinámica de gases
Ondas de sonido
Teoría de Kolmogorov para turbulencia incompresible.
Espectro de -5/3 y cascada de energía.
Turbulencia astrofísica. Diferencias con la teoría de
forzamiento a escalas intermedias, compresibilidad.
9. Formación estelar
Criterio de Jeans
Colapso de una nube esférica
Acreción de una envolvente en rotación
10. Ondas de choque
Condiciones de salto
Zonas de relajamiento
Choque isotérmico
Ecuaciones para la zona post-choque
Ecuaciones para la ionización
Enfriamiento radiativo (curva de enfriamiento) y por
ionización colisional
Modelo mínimo: calentamiento y enfriamiento por
ionización de hidrógeno.
Efecto del campo magnético
11. Fenómenos dinámicos y su efecto en el medio
Expansión de regiones H II: expansión inicial del frente
de ionización, expansión dinámica, equilibrio final
Vientos estelares: isotérmico, presión de radiación
Burbujas de vientos estelares
Remanentes de supernova
Objetos Herbig-Haro y jets
• ~1800: W. Herschel, catalog of bright patches called
• 1864: Huggins, spectra of Andromeda (Sun-like) and
Orion (gaseous emission) nebulae. « Nebulium »
• 1895: Helium discovered on earth
• 1904: Hartmann: stationary Ca II lines in spectrum of
spectroscopic binary δ Ori : interstellar or circumstellar?
=>Discovery of ISM
• 1919: Barnard, catalog of dark nebulae : holes in stellar
distribution or obscuring matter?
• 1913: Hess, discovers “Höhenstrahlung” in balloon
flights; cannot come from the Sun
• 1927: Clay, proves that “Höhenstrahlung” consist of high
energy charged particles : cosmic rays
=> ~1950: cosmic rays shown to consist of heavy
particles (protons, alfa particles)
• 1927: Bowen identify the « nebulium » emission lines as
forbidden Oxygen lines
• 1930: Trumpler, proof of interstellar extinction (distance
to open clusters is overestimated)
• 1933: Plaskett & Pearce, Ca II absorption is interstellar
(stronger for more distant stars)
• 1922 Heger: discovery of diffuse interstellar bands
• 1937 – 40: Swings & Rosenfeld, McKellar, Adams, first
small interstellar molecules (CH, CH+, CN)
• 1945: van de Hulst, prediction of H I 21 cm line
• 1949: Hall & Hiltner, correlation of polarization of starlight
with reddening : aligned grains : interstellar magnetic
field. Confirmed by discoveries of synchrotron radiation,
Faraday rotation and Zeeman splitting in 21 cm line
• 1960s: Discovery of soft X-ray background from hot,
ionized gas
1951: Ewen & Purcell, Oort & Muller, detection of 21 cm line
1950’s – 60’s: 21 cm maps => galactic disk contains 5x109 MO of
gas (=10% of disk mass) <n>=1 cm-3
1963: Weinreb, Townes et al.: interstellar OH masers
1968: NH3 (first polyatomic molecule)
1970: CO J = 1–0 emission at 2.6 mm (Penzias & Wilson!)
1970’s-1980’s: Galactic distribution of CO: distribution molecular vs
atomic gas
1970’s-now: Many new interstellar molecules found (>100); some
very exotic
1973: Carruthers, UV lines of H2 from rocket
1970’s – 80’s: Infrared astronomy (H2 infrared lines, small dust
particles, very large molecules)
1980’s – 90’s: Submillimeter astronomy (warm interfaces of
molecular clouds, cold protostellar regions)
The Impact of Space Astronomy
1973 – 80: Copernicus UV satellite
1983: IRAS
1990 – 91: COBE
1990 – now : HST
1995 – 98 : Infrared Space Observatory (ISO)
1999 – now: Chandra & XMM-Newton: X-rays
2000 – 2007: Far Ultraviolet Space Explorer (FUSE)
2003-2009+warm now: Spitzer Space Telescope
2009- : Herschel
General Properties of ISM
• Mostly confined to Galactic disk (little gas in
halo, as in elliptical galaxies)
• Enormous ranges in temperature and density
(T = 10 … 106 K, n = 10-3 … 106 cm-3)
• Even dense regions are “ultra-high vacuum”
(compare air at sea level n = 3.1019 cm-3)
• Very far out of thermal equilibrium => complex
processes (lots of interesting physics)
Regions of ISM Classified by
State of Hydrogen
• Hydrogen is by far the most abundant element (> 90 %
of atoms)
• Composition of ISM is similar to Solar System
• ISM regions characterized by state of hydrogen and
temperature; 5 kinds:
– Ionized atomic hydrogen (H+ or H II), Hot and Warm
– Neutral atomic hydrogen (H0 or H I), Cold and Warm
– Molecular hydrogen (H2)
• Regions are nearly pure (100 % H II, H I, or H2)
• Transition regions H II  H I  H2 are thin
H II Regions
Traditional H II regions surrounding early type stars
– T ~104 K, n ~0.1-104 cm-3, f small
– Heated and ionized by photons with hν>13.6 eV, λ<912 Å
– Cooled by forbidden lines of atoms +ions [OIII], [OII], [NII],….
– Observed by optical lines of atoms and ions, radio continuum,
– radio recombination lines
Coronal gas: very hot, tenuous gas pervading ISM (=HIM)
– T≥3x105 K, n ~ 0.003 cm-3, f ~0.6?
– Heated by shocks from SN and collisionally ionized
– Cooled by adiabatic expansion and X-ray emission
– Observed by X-ray emission, optical emission, non-thermal radio
emission, UV absorption lines of OVI
H II Regions (2)
Warm ionized gas: warm diffuse gas throughout ISM (=WIM = DIG)
– T 8000 K, nH ~0.25 cm-3, ne/nH ~0.7, f ~0.2?
– Heated and ionized by stray photons from O and B Stars
λ<912Å? Not clear...
– Cooled by forbidden lines of atoms and ions
– Observed by broad optical and radio recombination lines ( e.g.
H166α) and pulsar dispersion measures. Some [NII] and [OIII]
H I Regions
Cold neutral clouds: HI clouds throughout ISM (=CNM)
T~80 K, nH~ 40 cm-3, f=0.025, ne/nH~10-4
Heated by UV photons with λ>912 Å through p.e. effect
Cooled by [CII] fine-structure emission at 157µm
Observed by HI 21cm emission + absorption, optical and UV
absorption lines of atoms ( e.g. Na)
Warm neutral gas: warm diffuse gas throughout ISM (=WNM)
– T ~8000 K, nH ~ 0.4 cm-3, ne/nH ~ 0.15, f ~ 0.1-0.5?
– Heated + partly ionized by soft X-rays
– Cooled by atomic lines
– Observed by HI 21 cm emission
H2 Regions
• Diffuse molecular clouds: includes translucent and high
latitude clouds
T ~ 0-80 K, nH ~100-103 cm-3, ne/nH ~10-4, f ~0.01
Heated by UV photons with λ>912 Å through p.e. effect
Cooled by [C II] fine-structure emission
Observed by HI21 cm emission, CO mm emission, optical +
UVabsorption lines, IRAS 100 µm
• Dense molecular clouds: dark clouds +GMCs
T ~10-100 K, nH ~103-106 cm-3, ne/nH ~10-6, f ~0.0005
Heated by cosmic rays +newborn stars
Cooled by mm emission from molecules such as CO
Observed by mm lines from molecules, FIR and submm
continuum emission from dust
Other Ingredients of ISM
• Heavier elements
– He (= 10 %)
– C, N, O (= “cosmic” abundances)
– Si, Ca, Fe (depleted onto grains)
• Grains ( 0.1 µm size, silicates or carbonaceous material,
= 1% by mass of ISM)
• Star light
• Combined light of bright stars produces average
interstellar radiation field
• X-rays, cosmic rays
• Magnetic fields
The local ISM (within ~200 pc from
the Sun)
Interstellar absorption lines towards nearby stars
=> very little neutral matter within 100 pc of the Sun, N(H) ≤
1019 H atoms cm–2
Confirmed by polarization data n< 0.3 cm–3
Soft X-ray emission mostly of local origin
OVI absorption lines also indicate that there is a lot of hot
gas locally
=> The Sun is inside a “local bubble” of hot, ionized
3 phases model with fountains
Purple= mol. Clouds || Solid green= cold H I clouds || Hatched green= warm H I || Hatched green on yellow =
diffuse warm H II || Orange= Hotter gas with OVI || Red=Hot gas emitting X-rays|| Blue= star
Why is ISM not in Thermal
Thermal equilibrium requires “detailed balance”, i.e., each process
occurs as often as the inverse process
This is frequently not true in ISM, e.g., collisional excitation is
followed by radiative decay (because of low density)
Example: O2+ = OIII in HII region
The interstellar radiation field is far from thermal equilibrium : peak
at 2000Å => Tcolor=104 K, but energy content ~1 eV cm-3 => 3 K
Energy Densities in Local ISM
Observations: images and
• From radio, cm, IR, Visible, UV to X-rays.
• Spectroscopy: art of giving values to
ISM = filter
ISM = filter
 Bubbles of ionized material blown by fast stellar winds
are frequently observed in the ISM
S 308
X-ray Detections of Hot Gas in PNe
Hen 3-1475
NGC 40
NGC 3242
NGC 7009
NGC 2392
NGC 6543
NGC 7026
NGC 7027
Mz 3
X-ray Detections of Hot Gas in PNe
Central Cavity
Swept-up AGB Wind
AGB Wind (!)
Chandra 0.2-1.5 keV X-rays
Chu et al. (2001)
X-ray emission within a
sharp central cavity
Also unexpected hard
X-ray source at the
central star
(Guerrero et al. 2001)
Movies: Orion, Herschel
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