Simulations of Lya emission: fluorescence, cooling, galaxies

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Simulations of Lya emissionfluorescence,
cooling, galaxies
Ha UV Lya
Östlin et al. 2009
ESO 338IG04
CollaboratorsJuna Kollmeier, Zheng
ZhengDavid Weinberg, Neal Katz, Romeel Dave
Renyue Cen, Hy Trac Andy Gould
Jordi Miralda Escudé ICREAUniversity of
Barcelona, CataloniaBerkeley, 9-2-2010
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Exploring reionization with the highest redshift
objects

• Lya galaxies

• Quasars

Iye et al. 2006
White et al. 2003

• Gamma-ray burst afterglow

fireball shots?
Tanvir et al. 2009
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Can we observe the IGM in 3D?
Santos et al. 2008

• 21 cm, epoch of reionization.
• Extended Lya emission? This can be done at lower
  redshift.

Rauch et al. 2008
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Possible origin of extended Lya

• Star-forming galaxies the ionizing photons from
  stars ionize the surrounding interstellar or
  intergalactic gas, which emits Lya by
  recombinations.
• Radiative cooling infalling gas is heated during
  dissipational galaxy formation, emitting Lya
  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 Lya.
• Scattering Lya forest systems scatter the
  continuum UV background radiation when it
  redshifts to the Lya line.

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Lya blobs large emission region outside of a
star-forming galaxy
Matsuda et al. 2010
Yang et al. 2009
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Physical properties and abundance of Lya blobs

• Abundance 310-6 Mpc-3, luminosity L gt 1043
  erg/s, size 30 kpc.
• The luminosity implies 1054 recombinations/second.
  
• The minimum gas density required is 0.1 cm-3
  104 ?mean,
  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 gt
  1044 erg/s. When it is not seen, it is probably
  obscured and anisotropic.
• Cooling gaseous halos better for blobs of L lt
  1042 erg/s (1011 MSun of gas emitting 10
  Lya photons over 3 108 years).

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Expected Lya surface brightness from fluorescence
of the ionizing background
Hogan Weymann 1987 Gould Weinberg 1996

• Measured intensity of the ionizing background
  J? 310-22 erg/cm2/s/Hz/sr.
• Surface brightness of optically thick Lyman limit
  system 0.5 J? ?HI/ß
• Observed surface brightness
  10-17 erg/cm2/s/arcsec2 / (1z)4

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Lya Radiative Transfer how to compute a Lya
image from any distribution of gas and emission?
with Zheng Zheng
Lya line
?
surface brightness frequency change

• a large number of scatterings
• frequency change after each scattering

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Monte Carlo Code for Lya 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
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• 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 Lya image and 2D spectra.
Application z3 fluorescent Lya emission from
cosmic structure Kollmeier et al. 2009
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Fluorescence of the background in an SPH
simulation
Kollmeier et al. 2009
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Spectra of the fluorescent emission
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Fluorescence in the presence of a luminous quasar
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Scattering of Lya 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
  Lya system from the intergalactic absorption.

Absorption profile of a neutral medium in Hubble
expansion.
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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
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Lya emitting galaxies the damped IGM absorption
becomes a probe to the late stages of
reionization.

• The clustering of Lya emittersincreases owing to
  a patchy reionization structure.
• An accurate radiative transfer calculation is
  required.

• McQuinn et al. 2007

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Lyman-alpha Radiative Transfer applied to galaxy
sources placed in a simulation at z5.7 (with
Cen, Trac) example of one halo
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(No Transcript)
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Shift in the Lya Line Peak
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Intrinsic and Apparent Lya Luminosity
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Comparison with Observation Lya
Equivalent Width Distribution

• dust extinction?
• age of stellar population?
• gas density?
• gas kinematics?

deficit of UV bright, high Lya EW sources
Ouchi et al. 2008
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Comparison with Observation Lya
Equivalent Width Distribution
Observational effect of small survey volume
decreasing UV LF towards high UV luminosity
decreasing EW
distribution at fixed UV luminosity
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A Simple Model of LAEs
Intrinsic Lyaemission
Apparent Lyaemission

• radiative transfer as the single factor in
  transforming the intrinsic
• properties of Lya emission to observed ones
• natural interpretation of observations
• high predictive power

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Effect on clustering of Lya emitters.
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Correlation functions
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Angular correlation function
Large effects on the angular correlation
function are induced by the special selection of
Lya emitters depending on the radiative transfer
in their intergalactic environment.
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Conclusions

• We expect the sky background to contain a
  detailed map of Lya 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. Lya
  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 Lya 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 Lya emitting galaxies may provide a
  powerful probe to the structure of the reionized
  intergalactic medium, but modelling the radiative
  transfer is fundamental.

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Apparent Lya Luminosity Function
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Comparison with Observation Lya Luminosity
Function

• offset in Lya luminosity
• SFR
• IMF
• intrinsic line width

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