1. 1a.Introduction 1b.PopIII stars and galaxies --> « top down » theoretical approach 2.,3a.Ly  physics and astrophysics 3.b,4.Distant/primeval galaxies: - observational searches - current knowledge about high-z galaxies --> « bottom up » observational approach and confrontation with theory Outline of the lectures

2. Outline of Part 2+3a Ly  physics and astrophysics ISM emission Ly  : the observational « problem » Lessons from local starbursts Ly  radiation transfer (+dust) Lessons from Lyman Break Galaxies Ly  trough the InterGalactic Medium Ly  from sources prior to reionisation Ly  Luminosity Function and reionisation

3. Ly  Emission Galaxies with intense star formation (starbursts): Intense UV radiation, ionising flux (>13.6 eV), and emission lines from HII regions and diffuse ionised ISM  H, He recombination lines, [semi-]forbidden metal lines …  case B: L(Ly , H , …) = c l * Q H and I(Ly  )/I(Hn) = c(T,n e ) 2/3 of recombinations lead to emission of 1 Lya photon (cf. lectures G. Stasinska)

4. Ly  Emission At (very) low metallicity: strong/dominant Ly  ! since increased ionising flux from stellar pops. dominant cooling line (few metals) emissivity increased by collisional excitation (higher nebular temperature, Te) --> up to ~10% of Lbol emitted in Ly  ! ==> potentially detectable out to highest redshifts!! …searches unsuccessful until 1990ies --> Part 3 Partridge & Peebles (1967)

5. GENERAL: fate of Ly  photons scattering until escape--> Ly  halo Ly  destruction by dust destruction through 2 photon emission (only in HII region) Ly  - the «problem » Observable UV (>912 Ang): galaxies optically thin However, very rapidly optically thick in Ly  line (N HI >~ 10 13 cm -2 ) --> Radiation transfer within the galaxy determines the emergent line profile and Ly  « transmission » ! Furthermore: dust may destroy Ly  photons Ly  TRANSFER 0 E_B-V 0.1 Ly  escape fraction {

6. The Ly  puzzle(s) in nearby starbursts 1980-90ies: several searches for Ly  emission from z~2-3 primordial galaxies unsuccesful --> 1 or 2 puzzles: small number of galaxies and/or lower Ly  emission? IUE satellite: UV spectra of nearby starbursts (Ly  ) + optical spectra (H ,H  ) ==> 1) extinction corrected I(Ly  )/I(H  ) << case B Ly  : THE « OBSERVATIONAL » PROBLEM Valls-Gabaud (1993) Terlevich et al. (1993) (Meier & Terlevich 1981, Hartmann et al. 1984, Deharveng et al. 1986,… Giavalisco et al. 1996)

7. The Ly  puzzle(s) in nearby starbursts 1980-90ies: several searches for Ly  emission from z~2-3 primordial galaxies unsuccesful --> 1 or 2 puzzles: small number of galaxies and/or lower Ly  emission? IUE satellite: UV spectra of nearby starbursts (Ly  ) + optical spectra (H ,H  ) ==> 1) extinction corrected I(Ly  )/I(H  ) << case B and W(Ly  ) smaller than expected (synthesis models) ==> 2) no trend with metallicity (O/H) Ly  : THE « OBSERVATIONAL » PROBLEM Possible explanations: -dust (Charlot & Fall 1993) (but 2!) -With « appropriate » (metallicity-dependent) extinction law no problem. Also underlying stellar Ly  absorption (Valls-Gabaud 1993) -Inhomogeneous ISM geometry primarily determining factor, not dust (Giavalisco et al. 1996) -Short « duty cycle » of SF may explain small number of Ly  emitters

8. The Ly  puzzle(s) in nearby starbursts Possible explanations for individual objects: -dust ? -With « appropriate » (metallicity-dependent) extinction law no problem. Also underlying stellar Ly  absorption RULED out as SOLE explanations by IZw18, SBS 0335-052 (most metal poor stabursts known) which show no Ly  emission !! -Inhomogeneous ISM geometry primarily determining factor, not dust OK, but quantitatively ? Ly  : THE « OBSERVATIONAL » PROBLEM Kunth et al. (1994)

9. The Ly  puzzle(s) in nearby starbursts Detection of (neutral gas) outflows in 4 starbursts with Ly  in emission -metallicities 12+log(O/H)~8.0…8.4..solar -E B-V ~ 0.1 - 0.55 ==> outflows, superwinds main crucial/determining factor for Ly  escape!? Ly  :LESSONS FROM LOCAL STARBURST Kunth et al. (1998)

10. Ly  :LESSONS FROM LOCAL STARBURST Hayes et al. (2005) Ly  line image (cont.subtracted) 2-3 D studies of Ly  in nearby starbursts ACS/HST imaging in Ly  + narrow continuum filter WFPC2/HST images in 5 other filters --> stellar population, UV slope … ==> Diffuse Ly  emission seen ! Contains 2/3 of total flux in large aperture (IUE…) --> confirmation of Ly  resonant scattering halo * different regions: different H  kinematics --> but no constraint on HI kinematics at this spatial scale (requires SKA)!

11. 2-3 D studies of Ly  in nearby starbursts Imaging (ACS)+ kinematics (H  Integral Field, Ly  long-slit STIS) ESO 350-IG038: knots B + C: similar, high extinction  one shows emission other not. Kinematics, NOT DUST, dominant SBS 0335-052: only absorption seen. If dust affects Ly , it must do so at even small scale (1 pixel ~ 6- 9 pc!) Ly  :LESSONS FROM LOCAL STARBURST Kunth et al. (1998) Kunth et al. (2003)

12. 2-3 D studies of Ly  in nearby starbursts Diversity of line profiles explained by evolutionary sequence of staburst driven supershells / superwind? Ly  :LESSONS FROM LOCAL STARBURST Tenorio-Tagle et al. (1999) Mas-Hesse et al. (2003) 1 2 4 1 2 3, 4 5,6 M82

13. Lessons from nearby starbursts W(Ly  ) and Ly  /Hb < case B prediction ! No clear correlation of Ly  with metallicity, dust, other parameters found. Strong variation of Ly  observed within a galaxy Ly  scattering « halo » observed Starbursts show complex structure (super star clusters + diffuse ISM); outflows ubiquitous Ly  affected by: ISM kinematics ISM (HI) geometry Dust Precise order of importance unclear!  Quantitative modeling including known constraints (stars, emitting gas, HI, dust + kinematics) with 3D radiation transfer model remains to be done Ly  :LESSONS FROM LOCAL STARBURST

14. Ly  transfer: basics Ly  TRANSFER: THE ESSENTIALS Verhamme, Schaerer, Masseli (2006) Cross section in atoms frame Optical depth taking Maxwellian velocity distr. into account Ly  optical depth (in convenient units)  ~1 at line center for N H =3.10 13 cm -2 (and T=10 4 K) Line absorption profile (Voigt)

15. Ly  transfer: basics Ly  TRANSFER: THE ESSENTIALS From Hubeny  >> 1 at line center for N H >3.10 13 cm -2 (and T=10 4 K) Very large number of scatterings required to escape. E.g. N H =10 20 --> N scatt ~ 10 7 for static slab BUT: velocity fields or inhomogeneous medium can ease escape (Ly  ) line scattering NOT a random walk: - walk in coupled spatial and frequency space - transport dominated by excursions to line wing! --> lower opacity --> longer mean free path