The Hydrogen Lyman-alpha line in emission
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1 Lyman 1904 The Hydrogen Lyman-alpha line in emission Fabrizio Arrigoni Battaia
2 Most of these slides use materials from:
3 Relative contributions to Universal energy/mass density
4 The Hydrogen Lyman- a line Lya (2p - > 1s) à Å or 10.2 ev Selection rules (electric dipole approx.)
5 1892 Victor Schumann 1896
6
7
8 Schmidt 1963 QSO s discovery 1965 Lya in 3C 9 (z=2.012) Chronicle of Lya Observations (extragalactic) Partridge 1974 Davis&Wilkinson 1974 IUE satellite s CCDs advent low- z AGN (Fosbury+1982; Ferland&Osterbrock 1985) Partridge&Peebles 1967 Spinrad+1985 Lya in HzRGs Are young galaxies visible? Hu&Cowie Steidel Hu&Cowie Lowenthal (and many more) Møller&Warren+1993 Lya from DLA 1990s HST time begins e.g., Bahcall Heckman Bergeron meter class telescope era begins Hu&McMahon+1996 LAEs z~4.5 Pentericci+2000 Lya imaging around HzRGs Steidel+2000 Lya imaging of protocluster
9 The Hydrogen Lyman- a line Lya (2p - > 1s) à Å or 10.2 ev Selection rules (electric dipole approx.)
10 The Hydrogen Lyman- a line Lya (2p - > 1s) à Å or 10.2 ev A (2p- >1s) = 6.248e+08 s - 1 Selection rules (electric dipole approx.)
11 The Hydrogen Lyman- a line Lya (2p - > 1s) à Å or 10.2 ev A (2p- >1s) = 6.248e+08 s - 1 A (3p- >2s) = e+07 s - 1 Selection rules (electric dipole approx.)
12 Lya emission mechanisms: collisions and recombination
13 Lya emission mechanisms: collisions Hydrogen atom excited at the expenses of kinetic energy of free electrons.
14 Lya emission mechanisms: collisions Hydrogen atom excited at the expenses of kinetic energy of free electrons.
15 Lya emission mechanisms: collisions Hydrogen atom excited at the expenses of kinetic energy of free electrons C(T ) / exp T Black+1981
16 Fraction of cooling in Lya Lya emission mechanisms: collisions
17 collisional excitation Lya emission mechanisms: collisions Cooling rate for primordial gas (CIE assumption) T sets ionization state collisional Ionization of H collisional excitation of HeII
18 Lya emission mechanisms: recombination Recombination of free proton and electron + radiative cascades to the ground state à Lya line
19 Lya emission mechanisms: recombination Recombination of free proton and electron + radiative cascades to the ground state à Lya line
20 Lya emission mechanisms: recombination Recombination of free proton and electron + radiative cascades to the ground state à Lya line
21 Lya emission mechanisms: recombination Recombination of free proton and electron + radiative cascades to the ground state à Lya line Case A: medium optically thin at all photon frequencies Case B: medium opaque to all Lyman series photons and to ionizing photons from direct recombination to ground state. On the spot approx.
22 Lya emission mechanisms: recombination
23 Lya emission mechanisms: recombination P(Lya )=0.68 at T=10 4 K
24 Lya radiative transfer: the radiative transfer equation
25 Lya radiative transfer: the radiative transfer equation emission
26 Lya radiative transfer: the radiative transfer equation emission absorption
27 0 = N HI Lya radiative transfer: absorption Line center/resonance Off line center
28 Lya radiative transfer: the radiative transfer equation emission absorption ``destruction
29 Lya radiative transfer: ``destruction Dust can absorb Lya photons. The dust grains increase their temperature and re- radiate at longer wavelengths. (dust cross- section basically constant) Molecular Hydrogen has two vibrational transitions close to Lya resonance (at 99 km/s and 15 km/s) 2g - photons emission : collisional mixing of 2p and 2s states
30 2g emission 2g (2s - > 1s) Selection rules (electric dipole approx.) A (2p- >1s) = 6.248e+08 s - 1 A (2s- >1s) = 8.23 s - 1
31 Lya radiative transfer: ``destruction Dust can absorb Lya photons. The dust grains increase their temperature and re- radiate at longer wavelengths. (dust cross- section basically constant) Molecular Hydrogen has two vibrational transitions close to Lya resonance (at 99 km/s and 15 km/s) 2g - photons emission : collisional mixing of 2p and 2s states Other minor processes, e.g. Lya photons can photoionize hydrogen atoms not in the ground state;.
32 Lya radiative transfer: the radiative transfer equation emission absorption ``destruction scattering
33 Lya radiative transfer: scattering Following absorption, re- emission occurs instantly à ``scattering
34 Lya radiative transfer: scattering Following absorption, re- emission occurs instantly à ``scattering Lya scattering is a double diffusion process
35 Lya scattering is a double diffusion process x = vth/c
36 Lya radiative transfer: scattering x = v th /c Probability Distribution Function R(x out x in ) or redistribution functions
37 Lya radiative transfer: through an uniform, static gas cloud
38 Lya radiative transfer: through an uniform, static gas cloud Orsi+2012 Analytic solutions available: Harrington 1973; Neufeld 1990; Dijkstra+2006
39 Lya radiative transfer: through uniform, expanding or contracting gas cloud Laursen+2009
40 Lya radiative transfer: through uniform, expanding or contracting gas cloud Laursen+2009
41 Lya radiative transfer: dust Laursen+2009
42 You can find the videos at Gronke+2017
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