Emission Lyα dans les galaxies starburst

Transcription

1 Emission Lyα dans les galaxies starburst D. Kunth, D. Schaerer; M. Hayes; G. Ostlin, J.M. Mas-Hesse; A. Verhamme; C. Leitherer; A. Petrosian Institut d'astrophysique de Paris Atelier MUSE Lyon, 7- Lyα Workshop - October 15, 2007

2 Lyα physics Production in HII regions Resonant scattering HI kinematics and distribution Dust Geometry & sight-line Lyα path length to escape greatly increased Sees more dust High-z : F(Lyα) SFR EW(Lyα) Evolution, Stellar population SFR(Lyα) vs SFR(UV)? Calibration, Reddening correction What fraction of Lyα actually escapes from the starburst? Through which mechanisms Lyα photons escape?

3 The observational puzzle Weaker Lya emission than predicted Attenuation by dust : Only very early starbursts are detectable? - Lya NOT correlated with dust - Lya emission, even after extinction correction, is still below CASE B Charlot & Fall (1993) Giavalisco et al. (1996) Case B

4 The observational puzzle Very low metallicity and dust deficient galaxies does not show Lya in emission but a broad damped absorption profile IZw18 the most metal-poor galaxy known IZw18 [O/H] =-1.66 W Lyα <- 30Å

5 Results from local starbursts Mas-Hesse et al. (2003) No clear correlation seen between the Lya profile and the dust or metallicity. There are clear hints indicating the important role of the ISM kinematics IS lines velocity offset Lya visibility driven by the kinematics configuration and the density of the neutral gas

6 Lyα Imaging of local starbursts 1216Å 1500Å Haro11 SBS0335 IRAS08 Tol65 NGC6090 ESO338 LBCG BCG Starburst BCD LIRG LBCG 6 targets HST ACS/SBC GO 9470 cy. 11 F122M : Lyα F140LP : cont. Kunth et al. 03 β=-2 β=0 Continuum Subtraction problem β=+1

7 Lyα Imaging of local starbursts Continuum subtraction technique Stellar population modelling: HST imaging at 1500Å, 2200Å, U, B, medium V, Hα, and I Age and E(B-V) non-degenerate sample β and Balmer/4000Å break But 4000Å break affected by nebular gas and underlying population Use Hα to control nebular emission Fit age and reddening pixel-by-pixel Hayes et al. (2005)

8 Haro 11 Blended Emission and Absorption Systems Hα Lyα A E(B-V) smooth B C Lyα + FUV contours Lyα largely uncorrelated with Hα Lyα seen in only one star-forming knot Lyα photons emerge from the dustiest region Large diffuse Lyα halo

9 Haro 11 Diffuse emission component independent of the dust Emission from knot C with E(B-V) ~ 0.48 Absorption from knot A with E(B-V) ~ 0.2 EW(Lyα) vs EW(Hα) Lyα/Hα above the theoretical value (8.7 case B extinction corrected) enhanced Lyα emission

10 Haro 11 Neufeld 1991 The case of multi-phase ISM : (HI dusty clumps embedded in ionised medium) Lya photons resonantly scatters and reflects on the clouds and escape Non-resonant photons go through the clouds and increase their probability to be destroyed by dust Thanks to the resonance scattering, Lya photons see less dust than non-resonant photons.

11 ESO 338 Hα Lyα E(B-V) smooth Lyα uncorrelated with Hα Lyα morphology does not follow the dust distribution Dust loosely follows Hα morphology Diffuse Lyα emission Lyα + FUV contours

12 ESO 338 Blended emission and absorption at same extinction EW(Lyα) declines with E(B-V) Spread EW(Hα) Lyα/Hα above case B (green) and tends to decrease with dust

13 NGC 6090 Pure Emission Systems Hα Lyα E(B-V) smooth Lyα + FUV contours Lyα morphology similar to Hα Brightest Hα region not the brightest in Lyα Diffuse Lyα emission

14 NGC 6090 Pure emission supeinmposed on diffuse componenet Low EW(Lyα) for direct emission Lyα/Hα follows the theoretical value in central emission regions (independent of the extinction)

15 IRAS 08 Hα Lyα E(B-V) smooth Lyα + FUV contours Hα more extended than Lyα emission Diffuse Lyα emission

16 IRAS 08 Spread Lyα emission over the extinction range No correlation EW(Lyα) EW(Hα) Lyα/Hα independent of the extinction Role of the gas kinematics

17 SBS 0335 Damped Absorption Systems Hα Lyα E(B-V) smooth Lyα + FUV contours Lyα absorption associated with Hα emission Lyα independent of the extinction Dust losely follows Hα morphology Diffuse Lyα emission

18 SBS 0335 Absoprtion correlates with extinction Role of the static column density EW(Lyα) declines with the dust content

19 Tololo 65 Hα Lyα E(B-V) smooth No direct Lyα escape despite Hα emission Dust losely follows Hα morphology Weak diffuse Lyα emission Lyα + FUV contours

20 Tololo 65 Diffuse component No correlation seen according to the extinction

21 Global Properties Lyα/Hα is still well below the CASE B level for all galaxies Escape fraction does not exceed 12% No clear trends between EW(Lyα) and the extinction (similar to Giavalisco et al. 1996)

22 Global Properties Different evolution obetween EW(Lyα) and EW(Hα) Evolutinary (age ) effects? Reddening correction?

23 Summary and future issues Different escape mechanisms : Direct or diffuse emission Emission through outflowing medium Scattering into inhomogenous ISM Scattering halo emission (ubiquitous) higher than case B recombination level in some regions Lyα emission extends to E(B-V) ~ 1 Dust is apparently not the main regulator of Lyα escape HI distribution and kinematics might play a more significant role Pilot study. Six galaxies only not statistically significant, but Complexity of the radiative transfer of Lyα photons should prompt us to consider physical quantities derived from Lyα alone with caution.

24 Summary and future issues Need to observe galaxies at higher redshift Is the evolution of the Lya/Ha 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

25 NACO Imaging of ESO 338 Brγ online HST Hα Brγ continuum-subtracted Hα / Brγ

26 Lyman α Team Daniel Kunth & Hakim Atek (IAP, France) Daniel Schaerer & Anne Verhamme (Observatoire de Genève, Switzerland) Göran Östlin & Matthew Hayes (Stockholm obsevatorium, Sweden) J. Miguel Mas-Hesse (LAEFF, Spain) Claus Leitherer (STScI, USA) Artashes petrosian (Buyrakan observatory, Armenia)