Simulations of Ly emission fluorescence cooling galaxies H
- Slides: 30
Simulations of Lyα emission: fluorescence, cooling, galaxies Hα UV Lyα ESO 338–IG 04 Östlin et al. 2009 Jordi Miralda Escudé ICREA University of Barcelona, Catalonia Berkeley, 9 -2 -2010 Collaborators: Juna Kollmeier, Zheng David Weinberg, Neal Katz, Romeel Dave Renyue Cen, Hy Trac Andy Gould
Exploring reionization with the highest redshift objects • Lyα galaxies • Quasars Iye et al. 2006 White et al. 2003 • Gamma-ray burst afterglow: fireball shots? Tanvir et al. 2009
Can we observe the IGM in 3 D? Santos et al. 2008 • 21 cm, epoch of reionization. • Extended Lyα emission? This can be done at lower redshift. Rauch et al. 2008
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.
Lyα blobs: large emission region outside of a starforming galaxy Matsuda et al. 2010 Yang et al. 2009
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 anisotropic. • Cooling gaseous halos: better for blobs of L < 1042 erg/s (1011 MSun of gas emitting 10 Lyα photons over 3· 108 years).
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/cm 2/s/Hz/sr. • Surface brightness of optically thick Lyman limit system: ~ 0. 5 Jν νHI/β • Observed surface brightness: ~ 10 -17 erg/cm 2/s/arcsec 2 / (1+z)4
Lyα Radiative Transfer: how to compute a Lyα image from any distribution of gas and emission? with Zheng Lyα line ? surface brightness frequency change H atom rest frame H laboratory frame • a large number of scatterings • frequency change after each scattering
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 Lyα
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 y The code outputs IFU-like data cube, which can be used to obtain Lyα image and 2 D spectra. λ x Application: z~3 fluorescent Lyα emission from cosmic structure: Kollmeier et al. 2009 Image Courtesy: Stephen Todd & Douglas Pierce-Price
Fluorescence of the background in an SPH simulation Kollmeier et al. 2009
Spectra of the fluorescent emission
Fluorescence in the presence of a luminous quasar
Scattering of Lyα photons from star-forming galaxies and other luminous sources • 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. Absorption profile of a neutral medium in Hubble expansion.
Observation of the spectrum of GRB 050904 The absorption is due to local hydrogen with column density NHI = 1021. 6 cm-2 Totani et al. 2006
Lyα emitting galaxies: the damped IGM absorption becomes a probe to the late stages of reionization. • The clustering of Lyα emitters increases owing to a patchy reionization structure. • An accurate radiative transfer calculation is required. Mc. Quinn et al. 2007
Lyman-alpha Radiative Transfer applied to galaxy sources placed in a simulation at z=5. 7 (with Cen, Trac): example of one halo
Shift in the Lyα Line Peak
Intrinsic and Apparent Lyα Luminosity
Comparison with Observation Lyα Equivalent Width Distribution • dust extinction? • age of stellar population? • gas density? • gas kinematics? Ando et al. 2006 deficit of UV bright, high Lyα EW sources Ouchi et al. 2008
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
A Simple Model of LAEs morphology Lyαluminosity spectra neutral gas distribution Intrinsic Lyαemissi on Lyαline profile Apparent Lyαemissi on Radiative Transfer LyαLF UV LF LyαEW clustering radiative transfer as the single factor in transforming the intrinsic properties of Lyα emission to observed ones ✦ ✦ natural interpretation of observations ✦ high predictive power . . .
Effect on clustering of Lyα emitters.
Correlation functions
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.
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.
Apparent Lyα Luminosity Function
Comparison with Observation Lyα Luminosity Function offset in Lyα luminosity ✴ SFR ✴ IMF ✴ intrinsic line width
Comparison with Observation UV Luminosity Function Broad distribution of apparent Lyα luminosity at fixed intrinsic (UV) luminosity
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