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Lyman-alpha Emitters in the Local Universe

Lyman-alpha Emitters in the Local Universe. Atelier MUSE – Toulouse, 19 mars 2009. Hakim ATEK Daniel Kunth, Matthew Hayes, Claus Leitherer, J. Miguel Mas-Hesse, Göran Östlin, Artashes Petrosian, Daniel Schaerer, Anne Verhamme. The Lyman-alpha Puzzle. Early observations with IUE:

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Lyman-alpha Emitters in the Local Universe

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  1. Lyman-alpha Emitters in the Local Universe Atelier MUSE – Toulouse, 19 mars 2009 Hakim ATEK Daniel Kunth, Matthew Hayes, Claus Leitherer, J. Miguel Mas-Hesse, Göran Östlin, Artashes Petrosian, Daniel Schaerer, Anne Verhamme Hakim ATEK

  2. The Lyman-alpha Puzzle • Early observations with IUE: • Ly was not detected in many cases • A damped absorption was observed instead • When detected, Ly was well below the theoritical value • predicted by recombination theory Which factors are actually driving the visibility of Lyman-alpha emission in star-forming galaxies ? This question will remain unclear after the IUE era … Hakim ATEK

  3. Giavalisco et al. (1996) The Lyman-alpha Puzzle • Attempts to solve the puzzle 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) Hakim ATEK

  4. New Insight with HST/GHRS 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 Hakim ATEK

  5. New Insight with HST/GHRS • Similar results by Thuan and Izotov (1997) : Low metallicity BCGs SBS 0335-052 & Tol 65 A prominent Ly emission was found in a more metallic and dusty starburst Haro 2 Lequeux et al. 1995 Hakim ATEK

  6. GHRS Sample of BCGs: The Role of Kinematics • 8 local BCGs: 4 Ly emitters, 4 absorbers • In all Ly emitters the neutral, metallic absorption lines were blueshifted by 100-400 km/s. • In the damped systems, the neutral absorptions were always at the systemic velocities • All Ly emission lines showed a clear • P Cyg profile, indicating the presence of an expanding shell of neutral gas. •  The profiles could be well fitted assuming the measured expansion velocity Kunth et al. 1998 Hakim ATEK

  7. Lyman Break Galaxies Shapley et al. 2003 Lyman Break Galaxies: have P-Cyg profiles superwinds of neutral gas at z ~ 3 : outflows are ubiquitous Only 25% of the LBG sample show Lya in emission !! Hakim ATEK

  8. HST/STIS: Spatial Analysis • Long slit spectroscopy with STIS To map the kinematics of the neutral gas In 3 galaxies: Mas-Hesse et al. (2003) • Ly emission extends over more • than 10” (~1 kpc) • Large expanding shell in 2 cases with • An ionised front in IRAS 08+65 associated • With a secondary Ly emission • No leaking photons from IZw 18 over the • whole slit • The visibility of Lya might be driven mostly • by the neutral gas distribution (porosity) • and kinematics Hakim ATEK

  9. Emission “Absorption” HST/ACS Imaging of Local Starburst Galaxies • Need to map the diffuse Lya emission: complementary to UV-bright targeted spectroscopic studies • Resonant scattering Emission and absorption at small scale • To infer the relative importance of the factors regulating the detectability of Lya emission Kunth et al. 2003 Haro 2 (STIS) Haro 11 (ACS) Hakim ATEK

  10. -20 7.9 -17 7.3 -21 8.7 -15 7.6 -21 8.8 -19 7.9 HST/ACS Imaging : Pilot Study 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 and metallicity - dust • Preliminary results: - Complex emission + absorption - Lya emission with no continuum counterpart - Global damped absorption Continuum subtraction issue MB Z HST / ACS / F550M Hakim ATEK

  11. Haro 11 SBS 0335 IRAS 08 Tol 65 NGC 6090 ESO 338 F122M F140LP HST/ACS Imaging: SBC Observations  = -2  = 0  = +1 Hakim ATEK

  12. HST/ACS Imaging Continuum subtraction technique Hakim ATEK

  13. FUV H Ly HST/ACS Imaging Results: Haro 11 • Net Ly emitter • Ly does NOT resemble FUV • Ly does NOT resemble H • 90% of flux in diffuse compnt. • (Hayes et al. 2007a; Östlin et al. 2007) Hakim ATEK

  14. FUV H Ly HST/ACS Imaging Results: ESO 338-04 • Net Ly emitter • Ly largely symmetric around one knot • Ly uncorrelated with H Hakim ATEK

  15. FUV H Ly HST/ACS Imaging Results: SBS 0335-052 • Net Ly absorber • Ring-like Ly leakage • Ha follows FUV tightly • Lya almost exact mirror Hakim ATEK

  16. FUV H Ly HST/ACS Imaging Results: IRAS 08+65 • Strong nuclear emission • Diffuse component Hakim ATEK

  17. FUV H Ly HST/ACS Imaging Results: NGC 6090 • Strong + diffuse Lya from NE core • Weak diffuse surrounding SW • Brightest Ha region not the brightest in Lya Hakim ATEK

  18. The Role of Dust in Lya Obscuration: Haro 11 • 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 Neufeld, 1991 Hakim ATEK

  19. The Role of Dust in Lya Obscuration: IRAS 08+65 • Spread Lyemission over the extinction range • No correlation EW(Ly) EW(H) • Ly/Hindependent of the extinction • Role of the gas kinematics Hakim ATEK

  20. The Role of Dust in Lya Obscuration: SBS 0335 • Absoprtion correlates with extinction • Role of the static column density • EW(Ly) declines with the dust content Hakim ATEK

  21. HST/ACS Imaging Results • Escape fraction decreases with dust No clear correlation between EW(Ly) and dust • Different evolutionnary effects :  mixed effects: EW(lya) should be not correlated with age Hakim ATEK

  22. HST/ACS Imaging Results • 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 ! Atek et al. 2008 Hakim ATEK

  23. A young, metal- and dust-poor galaxy shows a strong damped absorption !! • - Profile well fitted with a shell model using observational constraints on Hi column density and dust • Considering observer’s sight-line and N(H)=4x10^21 cm-2 damped absorption is reproduced with NO DUST E(B-V) = 0 • Lya absorbers : with static and high N(Hi) only a small amount of dust is needed to suppress Lya emission • Lya emitters : in presence of outflows high N(Hi) and high dust content is needed. Lya from emission to absorption (atek et al. 2009a)

  24. Radiation transport of Lya explains the observed profile variations across the galaxy Lya from emission to absorption

  25. MUSE Prospects LAEs number density • Need to observe galaxies at higher redshift •  Is the evolution of fesc ratio always related to the dust content ? • Lya variations at a small scale • Emission/absorption usually not local • Variety of profiles (The case of P Cygni) • High spatial resolution needed • (AO, space facilities) • IFU mode capabilities with high sampling • Investigate spectroscopically the ISM kinematics • complementary to GALEX sample at z ~ 0.3 (atek et al. 2009b) Verhamme et al 2008 Hakim ATEK

  26. LAEs number density LAEs number density Le Delliou et al. (2005) • Discrepancy between models and observations • now less severe: • Past: • Completeness limit (instr. Sensitivity) • Radiation transfer effects • Now: • New instrumental capabilities • and detection techniques and • new models seem to converge • with actual • observations • BUT models assumptions • still too simple e.g : • using a constant escape fraction … Nagamine et al. (2008) Hakim ATEK

  27. Summary • Reliability of Lya emission as a COSMOLOGICAL TOOL ? • 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 • Low escape fractions (< 15%) -- dust corrections fail • New routes to SFR(Lya) calibration !! Demonstrates the need for a detailed, statistically significant investigation !! Instrinsic Emission Radiation Transfer Hakim ATEK

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