1. On the implications for the Lya line of an inhomogeneous, dusty medium
– also: modelling Lya emission from a damped Lya system
With:
Florent Duval, OKC;
Göran Östlin, OKC, &
Daniel Schaerer, Genève/Toulouse
Peter Laursen, Corsica, 2011
Oskar Klein Centre | Inst. för Astronomi | Stockholms Universitet

2. Lyman a radiative transferHI

3. Ly escape Analytical attempt (Neufeld 1990)
T = 104, NHI = 1019, E(B–V) = 0.1
Already for high --- but realistic --- dust and gas optical depths, the analytical solution implies that ~none of the Lya radiation should be able to escape
Gas density and temperature
Dust density and cross-section

4. Ly escape – Why does Ly escape after all? Outflow?
Various scenarios has been invoked:
The fact that Lyα line profiles are often seen to exhibit a P Cygni-like profile has led to the suggestion that high-velocity outflows of gas are needed to enable escape (Kunth et al. 1998; Östlin et al. 2008; Atek et al. 2008).
However, at high redshifts many galaxies are still accreting matter, which should result in an increased blue peak. Since this is rarely observed, the shape could be caused by other mechanisms, e.g. IGM absorption.
Kunth et al. (1999);
Verhamme et al. (2006);
Östlin et al. (2008)

5. Ly escape – Why does Ly escape after all? Ionized cones +
viewing angle?
Various scenarios has been invoked:
Ionizing UV radiation could create “cones” of low neutral hydrogen density emanating from the star-forming regions through which the Lyα can escape (Tenorio-Tagle et al. 1999; Mas-Hesse et al. 2003).
Even without these ionized cones, scattering effects alone may cause an anisotropic escape of the Lyα (Laursen & Sommer-Larsen 2007).
Tenori-Tagle et al. (1999);
Mas-Hesse et al. (2003)

6. Ly escape – Why does Ly escape after all? Multiphase medium?
Neufeld (1991);
Hansen & Oh (2006)
Multiphase medium?
Various scenarios has been invoked:
In a multi-phase medium, the dust is locked up in cold clouds so that the photons primarily travel in an ionized, dustless medium (Neufeld 1991; Hansen & Oh 2006). Since continuum radiation travels through the cloud, it would be attenuated more by the dust.
This could explain the high Lyα equivalent widths occasionally observed in in LAEs (e.g. Malhotra & Rhoads 2002; Rhoads et al. 2003; Shimasaku et al. 2006).

7. Equivalent width
Definition:
EW boost: EWobserved / EWintrinsic

8. Citation rate

9. Numerical approch
MOCALATA

10. From ideal to semi-realistic
• ICM density
• Outflow velocity
• Dust contents
• Emission site
• Cloud velocity dispersion

11. From ideal to semi-realistic

12. From ideal to semi-realistic
• Density contrast threshold:
nHI,ICM / nHI,cl ~ 10–4

13. From ideal to semi-realistic
• Density contrast threshold:
nHI,ICM / nHI,cl ~ 10–4
• Cloud velocity dispersion
threshold: sV,cl ~ 50 km s–1

14. From ideal to semi-realistic
• Density contrast threshold:
nHI,ICM / nHI,cl ~ 10–4
• Cloud velocity dispersion
threshold: sV,cl ~ 50 km s–1
• Expansion velocity
threshold: Vexp ~ 50 km s–1

15. Modeling a damped Lyman a emitter
With:
P. Noterdaeme,
P. Petitjean,
M.-J. Maureira,
S. D. Vergani,
C. Ledoux,
J. P. U. Fynbo,
S. López
and R. Srianand

16. Modeling a damped Lyman a emitter
• NHI = cm–2

17. Modeling a damped Lyman a emitter
• NHI = cm–2
• E(B–V) = 0.04

18. Modeling a damped Lyman a emitter
• NHI = cm–2
• E(B–V) = 0.04
• Impact parameter ~ 1 kpc

19. Modeling a damped Lyman a emitter
• NHI = cm–2
• E(B–V) = 0.04
• Impact parameter ~ 1 kpc
• SFR ~ 20–25 M yr–1
• FLya = 14.3 × 10–17 erg s–1 cm–2
• fesc, Lya = 0.2

20. Modeling a damped Lyman a emitter
• NHI = cm–2
• E(B–V) = 0.04
• Impact parameter ~ 1 kpc
• SFR ~ 20–25 M yr–1
• FLya = 14.3 × 10–17 erg s–1 cm–2
• fesc, Lya = 0.2
• Red and blue part of the
spectrum spatially
detached

21. Semi-realistic modelling
• NHI = cm–2
• E(B–V) = 0.04
• Impact parameter ~ 1 kpc
• SFR ~ 20–25 M yr–1
• FLya = 14.3 × 10–17 erg s–1 cm–2
• fesc, Lya = 0.2
• Red and blue part of the
spectrum spatially
detached
• Metallicity: [Zn/H] = -1.1
• Depletion patterns:
[Zn/Fe] = 0.72,
[Zn/Cr] = 0.49,
[Zn/Mn] = 0.79,
[Zn/Ni] = 0.61

22. Semi-realistic modelling