Astronomy 405 Solar System and ISM
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Astronomy 405Solar System and ISM
Lecture 22
ISM - What is diffuse matter?
March 16, 2013
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What’s out there? What physical descriptions?
In the interstellar medium (ISM), we do not worry aboutdark matter or dark energy at scales of pc to kpc.( 1 pc = 3.08 x 1016 m)
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Planck Function (Carroll & Ostlie, p.73)
or
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What’s out there? What physical descriptions?
In the interstellar medium (ISM), we do not worry aboutdark matter or dark energy at scales of pc to kpc.( 1 pc = 3.08 x 1016 m)
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Saha Equation (Carroll & Ostlie, p.214)
Ionization stages i and i+1
i : ionization energy of the ionization stage i
Z: partition function; g: statistical weight
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What’s out there? What physical descriptions?
In the interstellar medium (ISM), we do not worry aboutdark matter or dark energy at scales of pc to kpc.( 1 pc = 3.08 x 1016 m)
![Page 7: Astronomy 405 Solar System and ISM](https://reader036.fdocuments.in/reader036/viewer/2022081603/5681452e550346895db1f559/html5/thumbnails/7.jpg)
Maxwell-Boltzmann Distribution (Carroll & Ostlie, p.206)
Number of particles with velocities within v to v+dv
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Boltzmann Equation (Carroll & Ostlie, p.212)
g: statistical weightE: energy
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In the interstellar medium (diffuse matter),densities are so low and interactionsbetween radiation and matter and collisionsbetween particles are so infrequent thatthermal equilibrium is no longer valid.
Radiation and matter need to be consideredseparately.
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IonizationIonization can be carried out by absorbing a photonor through collision with another particle.
The ionization state is determined by balancingthe number of ionizations and the number ofrecombinations.
ExcitationSimilarly, excitation is carried out by photon or collision.Boltzmann equation is applicable at high energy levelswhen densities are high.
What is the “temperature” then?You can count on electrons establishing Maxwell-Boltzmann distribution very quickly. Therefore,electron temperatures or kinetic temperatures are used.
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MCPS (UBVI) s
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MCPS Zaritsky & Harris
2MASS (JHK)
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MCPS Zaritsky & Harris
2MASSSAGE (3.6, 4.5, 5.8, 8.0, 24 m)
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MCELS (H, [O III], [S II])
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MCELSROSAT (X-ray, 0.1-2.4 keV)
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MCELSROSAT
Fermi (gamma-ray)
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ATCA+Parkes (H I)
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ATCA+Parkes NANTEN (CO)
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ATCA+Parkes (H I)NANTEN
MAGMA (PI: Wong; 10 pc resolution)
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Radiation FieldRadio -- thermal emission from ionized gas, line emission from molecular, atomic, ionized gas
Far-IR -- luke-warm dust emission
Near-IR -- emission from cool stars, warmer dust emission
Optical -- star light (OBAFGKM) line emission from ionized ISM
X-ray -- emission from hot plasma > 106 K
Gamma-ray -- supernovae, accreting compact objects (BH, NS binaries) cosmic rays interacting with ISM