Simulations of Ly α emission: fluorescence, cooling, galaxies

1. Simulations of Lyα emission:fluorescence, cooling, galaxies Hα UV Lyα ESO 338–IG04 Östlin et al. 2009 Collaborators:Juna Kollmeier, Zheng ZhengDavid Weinberg, Neal Katz, Romeel Dave Renyue Cen, Hy Trac Andy Gould Jordi Miralda Escudé ICREAUniversity of Barcelona, CataloniaBerkeley, 9-2-2010

2. Lyα galaxies Exploring reionization with the highest redshift objects • Quasars Iye et al. 2006 White et al. 2003 • Gamma-ray burst afterglow: fireball shots? Tanvir et al. 2009

3. Can we observe the IGM in 3D? Santos et al. 2008 • 21 cm, epoch of reionization. • Extended Lyα emission? This can be done at lower redshift. Rauch et al. 2008

4. Possible origin of extended Lyα • Star-forming galaxies: the ionizing photons from stars ionize the surrounding interstellar or intergalactic gas, which emits Lyα by recombinations. • Radiative cooling: infalling gas is heated during dissipational galaxy formation, emitting Lyα after collisional ionization or line excitation. • Fluorescence of the ionizing background: dense Lyman limit systems in the intergalactic medium are ionized by distant sources and recombine to emit Lyα. • Scattering: Lyα forest systems scatter the continuum UV background radiation when it redshifts to the Lyα line.

5. Lyα blobs: large emission region outside of a star-forming galaxy Matsuda et al. 2010 Yang et al. 2009

6. Physical properties and abundance of Lyα blobs • Abundance: ~ 3·10-6 Mpc-3, luminosity L > 1043 erg/s, size ~ 30 kpc. • The luminosity implies 1054 recombinations/second. • The minimum gas density required is 0.1 cm-3 ~ 104 ρmean, for the size of 30 kpc and no clumping, with a total mass of 1011 MSun. • These atoms must be ionized every ~ 106 years to keep them emitting. • The ionizing source should be a quasar with LUV > 1044 erg/s. When it is not seen, it is probably obscured and anisotropic. • Cooling gaseous halos: better for blobs of L < 1042 erg/s (1011 MSun of gas emitting 10 Lyα photons over 3· 108 years).

7. Expected Lyα surface brightness from fluorescence of the ionizing background Hogan & Weymann 1987; Gould & Weinberg 1996 • Measured intensity of the ionizing background: Jν ~ 3·10-22 erg/cm2/s/Hz/sr. • Surface brightness of optically thick Lyman limit system: ~ 0.5 JννHI/β • Observed surface brightness: ~ 10-17 erg/cm2/s/arcsec2 / (1+z)4

8. H H laboratory frame atom rest frame Lyα Radiative Transfer: how to compute a Lyα image from any distribution of gas and emission? with Zheng Zheng Lyα line ? surface brightness frequency change • a large number of scatterings • frequency change after each scattering

9. Lyα Monte Carlo Code for Lyα Radiative Transfer 1. Initialization of the photon 2. determine the spatial location of the scattering 3. choose the velocity of the atom that scatters the photon 4. scattering in the rest frame of the atom: new frequency and direction 5. repeat 2-5 until escape Zheng & Miralda-Escudé 2002

10. y λ x Image Courtesy: Stephen Todd & Douglas Pierce-Price • The code can be applied to systems with arbitrary • gas geometry • gas emissivity distribution • gas density distribution • gas temperature distribution • gas velocity distribution well suited for applying to cosmological simulation outputs The code outputs IFU-like data cube, which can be used to obtain Lyα image and 2D spectra. Application: z~3 fluorescent Lyα emission from cosmic structure: Kollmeier et al. 2009

11. Fluorescence of the background in an SPH simulation Kollmeier et al. 2009

12. Spectra of the fluorescent emission

13. Fluorescence in the presence of a luminous quasar

14. Scattering of Lyα photons from star-forming galaxies and other luminous sources Absorption profile of a neutral medium in Hubble expansion. • The damped wing of the Gunn-Peterson trough indicates that a source is being seen behind atomic intergalactic medium • We may observe this on the spectrum of a fireball shot. • Only a fraction of the intergalactic medium should be neutral, and this fraction will vary widely among different lines of sight. • Main challenge: separating the host galaxy damped Lyα system from the intergalactic absorption.

15. Observation of the spectrum of GRB050904 The absorption is due to local hydrogen with column density NHI = 1021.6 cm-2 Totani et al. 2006

16. Lyα emitting galaxies: the damped IGM absorption becomes a probe to the late stages of reionization. McQuinn et al. 2007 • The clustering of Lyα emittersincreases owing to a patchy reionization structure. • An accurate radiative transfer calculation is required.

17. Lyman-alpha Radiative Transfer applied to galaxy sources placed in a simulation at z=5.7 (with Cen, Trac): example of one halo

19. Shift in the Lyα Line Peak

20. Intrinsic and Apparent Lyα Luminosity

21. Ando et al. 2006 Comparison with Observation Lyα Equivalent Width Distribution • dust extinction? • age of stellar population? • gas density? • gas kinematics? deficit of UV bright, high Lyα EW sources Ouchi et al. 2008

22. Comparison with Observation Lyα Equivalent Width Distribution Observational effect of small survey volume decreasing UV LF towards high UV luminosity + decreasing EW distribution at fixed UV luminosity

23. Lyαluminosity neutral gas distribution morphology spectra Radiative Transfer LyαLF Lyαline profile UV LF LyαEW clustering ... A Simple Model of LAEs Intrinsic Lyαemission Apparent Lyαemission • radiative transfer as the single factor in transforming the intrinsic • properties of Lyα emission to observed ones • natural interpretation of observations • high predictive power

24. Effect on clustering of Lyα emitters.

25. Correlation functions

26. Angular correlation function Large effects on the angular correlation function are induced by the special selection of Lyα emitters depending on the radiative transfer in their intergalactic environment.

27. Conclusions • We expect the sky background to contain a detailed map of Lyα emission from the intergalactic medium. • Detecting fluorescence from the ionizing background requires even greater depths than achieved so far. Fluorescence in the vicinity of quasars should more easily be detectable now. Lyα blobs likely are particular cases of high gas density near luminous quasars; we expect the lower luminosity ones to arise from cooling in galactic halos. • The Lyα emission of star-forming galaxies is greatly affected by scattering in their surrounding medium. This can result in: • The wide distribution of equivalent widths in galaxies of different UV luminosity. • A greatly enhanced correlation function along the line of sight, and projected angular correlation function. • These Lyα emitting galaxies may provide a powerful probe to the structure of the reionized intergalactic medium, but modelling the radiative transfer is fundamental.

28. Apparent Lyα Luminosity Function

29. Comparison with Observation Lyα Luminosity Function • offset in Lyα luminosity • SFR • IMF • intrinsic line width

30. Comparison with Observation UV Luminosity Function Broad distribution of apparent Lyαluminosity at fixed intrinsic (UV) luminosity