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The Regulation of Lyman-alpha Emission in Star Forming Galaxies

The Regulation of Lyman-alpha Emission in Star Forming Galaxies. Hakim ATEK Daniel Kunth, Daniel Schaerer, Matthew Hayes, Anne Verhamme, Göran Östlin, J. Miguel Mas-Hesse, Claus Leitherer, Artashes Petrosian.

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The Regulation of Lyman-alpha Emission in Star Forming Galaxies

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  1. The Regulation of Lyman-alpha Emission in Star Forming Galaxies Hakim ATEK Daniel Kunth, Daniel Schaerer, Matthew Hayes, Anne Verhamme, Göran Östlin, J. Miguel Mas-Hesse, Claus Leitherer, Artashes Petrosian Understanding LAEs , Heidelberg, October 6, 2008

  2. Hakim ATEK Giavalisco et al. (1996) Lya regulation: early controversies • Hypotheses under consideration in the early 90’s: -- LyNOTcorrelated with dust -- Ly emission, even after extinction correction, is still below CASE B • Attenuation by dust : • Only very early starbursts are detectable ? Charlot & Fall (1993)

  3. The case of IZw 18 High resolution spectroscopy with HST/GHRS of local BCGs: • First results by Kunth et al. (1994) : Very low metallicity and dust deficient galaxy IZw 18 : • A prominent Ly emission is expected for a young unevolved starburst IZw18 [O/H] =-1.66 WLy <- 30Å Suprisingly, a strong damped absorption is observed Heidelberg, October 6, 2008 Hakim ATEK

  4. -20 7.9 -17 7.3 -21 8.7 -15 7.6 -21 8.8 -19 7.9 Pilot study: the galaxy sample MB Z Kunth et al. 2003 • 6 selected local galaxies : -0.009 < z < 0.029 • - 40 orbits in total • - 0.03” sampling • span a range of : - Lya morphology and profiles - Luminosity - Dust and metallicity HST / ACS / F550M Heidelberg, October 6, 2008 Hakim ATEK

  5. Results: Haro 11 • Lya and Ha vs. dust distribution : • Lya does not resemble Ha nor FUV image • Blended emission and absorption • Lya seen only in knot C • Lya radiation escapes from the dustiest region • Why dust is not the main regulatory factor ? Heidelberg, October 6, 2008 Hakim ATEK

  6. Lya regulation factors Atek et al. 2008 • Diffuse emission component independent • of the dust • Emission from knot C with E(B-V) ~ 0.4 • Absorption from knot A with E(B-V) ~ 0.2 • EW(Ly) vs EW(H) • Ly/Habove the theoretical value • (8.7 case B extinction corrected) •  EnhancedLy/Hratio !! Heidelberg, October 6, 2008 Hakim ATEK

  7. Lya regulation factors: multi-phase medium Neufeld, 1991 Thanks to their resonant nature Lya photons “feel” less dust attenuation (see also Hansen & Oh 2006, Finkelstein et al. 2008) Heidelberg, October 6, 2008 Hakim ATEK

  8. Results: IRAS 08 • Lya and Ha vs. dust distribution : • Nuclear and symmetrical Lya emission • No sign of strong absorption • Lya does not follow the dust distribution • Morphology • Dust doesn't seem to play a major role … Heidelberg, October 6, 2008 Hakim ATEK

  9. Lya regulation factors • Spread Lyemission over the extinction range • No correlation EW(Ly) EW(H) • Ly/Hindependent of the extinction • The role of gas kinematics Heidelberg, October 6, 2008 Hakim ATEK

  10. Results: SBS 0335-052 • Lya and Ha vs. dust distribution : • Lyα absorption associated with Hα emission • Lyα absorption coincident with dusty region • Why dust is now important for Lya obscuration ? Heidelberg, October 6, 2008 Hakim ATEK

  11. Lya regulation factors • Absorption correlates with extinction • EW(Ly) declines with the dust content •  Role of the static neutral gas Heidelberg, October 6, 2008 Hakim ATEK

  12. Lya regulation factors • Lya escape is multi-parameter process : • Intrinsic EW(Lya) (age, mass) • Line broadening • Static HI coverage: Lya greatly attenuated by dust • Out flowing HI gas: effect of dust is reduced • Multi-phase medium: Lya escape if favored Instrinsic Emission Radiation Transfer • No correlation between EW(Lya) and dust content (amongst many param.) • Different from high-z results (e.g. Shapley et al. 2003, Pentericci et al. 2007) • statistically limited sample Heidelberg, October 6, 2008 Hakim ATEK

  13. Lya regulation factors • Different evolutionnary effects :Superwinds formation ? ISM morphology ? • Statistical sample is needed (see e.g. Verhamme et al. 2008) Heidelberg, October 6, 2008 Hakim ATEK

  14. Star Formation Rate calibration • Star Formation Rate calibration: What fraction of Ly photons actually escape from the starburst ? simple dust correction of Ly luminosity fails to recover the intrinsic SFR ! Heidelberg, October 6, 2008 Hakim ATEK

  15. Summary • Different escape mechanisms : Direct or diffuse emission Emission through outflowing medium Scattering into inhomogenous ISM • Low escape fractions (< 10%) -- dust corrections fail • When H strongest (starburst youngest) Ly weakest • Dust correction fails to reconcile SFR indicators • Dust is not always the main extinction parameter • HI kinematics and ISM morphology may play a more significant role Heidelberg, October 6, 2008 Hakim ATEK

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