The Hydrogen Lyman-alpha line in emission

Transcription

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

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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