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									Large Scale Simulations of
Reionization
Garrelt Mellema
Stockholm Observatory


Collaborators:
Ilian Iliev, Paul Shapiro, Marcelo Alvarez, Ue-Li Pen, Hugh Merz, LOFAR EoR Key Project team
Contents

   Reionization
   Simulations
   Some results
   WMAP1 versus WMAP3
   Secondary CMB Anisotropies

   Iliev et al. 2006, astro-ph/0512187
   GM et al. 2006, astro-ph/0603518
Reionization

   A view of the epoch when the
    first galaxies formed.
   Current observational data:
    WMAP Thomson optical depth,
    SDSS QSOs, TIGM from Lyα
    forest
   Future observational data:
    redshifted 21cm radiation
    (21CMA, LOFAR, MWA, SKA);
    direct view of HII regions
    (nature of sources) and IGM
    density field.
Simulations: Pro and Cons

   Reionization process is       Limited ranges
    complex:                       – mass resolution
    –   Source clustering          – spatial resolution
    –   HII region overlap         – number of sources
    –   Recombinations (n2)       Expensive
    –   Temperature effects        – Possible saves:
   Analytical models                     No temperature
                                           No helium
    cannot capture all of              

                                           Simple source
    these effects, numerical
                                       
                                           prescription
    models can.
Simulations: How?

   Our motivation: large scale simulations.
    – Observationally needed (~degree fields of view).
    – Theoretically needed (cosmic variance, size of HII regions, >>10
      Mpc).
   Approach:
    – PMFAST (Merz, Pen, Trac 2005) simulations (4.3 billion particles):
        Evolving density field             ΛCDM (WMAP)
        Collapsed halo list

        100/h and 35/h Mpc volumes (minimum halo masses 2.5x109
          and 108 M, respectively).
    – C2-Ray (GM et al. 2006) postprocessing (2033, 4063):
        Ionized hydrogen fraction
Simulations: Sources

   We have been working with stars as our sources of
    ionizing radiation.
   Assumptions:
    – M/L=const.
    – only atomically cooling halos contribute (M>108 M).
    – halos with M<109 M can be suppressed.
    – fixed photons/atom escaping (Iliev, Scannapieco & Shapiro
      2005): f = fSF x fesc x Nphoton.
   Choices used: f=2000 and 250.
   Other source models to be explored in the future.
Results: evolution

   Movie of density field and
    HII regions
   Green: neutral
   Red: Ionized

   Note: clustering &
    overlap.
   From z=20 to 10
    (WMAP3 parameters).
    Overlap expected at z~7.
                                 35/h Mpc
Importance of Large Scales

   From our (100/h Mpc)3
    volume we can analyze
    the reionization history
    of subvolumes.
   Large variations found,
    need at least volume of
    (30/h Mpc)3.
   Reionization is mostly
    inside-out.

                               Reionization histories for subvolumes
Statistics
                                                              Full density
   3D powerspectra:                                          HII density
    – Poisson noise at largest                                HI density
      scales
    – Clear peak at some (time-
      dependent) characteristic
      scale.
    – Resemble analytical work
      (Furlanetto et al. 2004a,b)
   The signal is strongly
    non-gaussian:
    – Numerical results do not      Furlanetto et al. 2004a
      resemble analytical inside-
      out, nor outside-in results
      (Furlanetto et al. 2004a,b)
Statistics

   3D powerspectra:                                          z=11.9   z=10.8
    – Poisson noise at largest                                              20/h Mpc
      scales                                                                10/h Mpc
    – Clear peak at some (time-                                              5/h Mpc
      dependent) characteristic
      scale.
    – Resemble analytical work
      (Furlanetto et al. 2004a,b)
   The signal is strongly
    non-gaussian:
                                    Furlanetto et al. 2004b
    – Numerical results do not
      resemble analytical inside-
      out, nor outside-in results
      (Furlanetto et al. 2004a,b)
LOS Reionization Histories

   From the
    simulations we
    can construct
    reionization
    histories along
    the line of sight.
   Will be used to
    prepare for the
    analysis of the
    LOFAR
    observations
    (2009)
What Cosmology?

   1st year WMAP versus 3 year WMAP:
    – τ: 0.17: to 0.09 (if instantanious, zreion: 16 to 11)
    – ns: 1.0 to 0.95, σ8: 0.9 to 0.74.
   Reionization happened later (good!), but structure
    formation also took longer.
   Alvarez et al. (2006): approximate scaling for
    simulations with similar types of sources:
    (1+z1)/(1+z3)≈1.4. Confirmed by new simulations.
WMAP1 versus WMAP3

   Identical simulations (100/h Mpc, f=250), differing
    only in cosmological parameters:


                              FM Band             WMAP1




                                        FM Band   WMAP3
Secondary CMB Anisotropies

   Patchy reionization is expected to imprint small
    scale anisotropies on the CMB signal through the
    kinetic Sunyaev-Zel’dovich effect.
   Several analytical estimates exist (Hu & Gruzinov
    98, McQuinn et al. 2005, Santos et al. 2006, Zahn
    et al. 2006), with large variation in strength and
    scales. Now the first numerical ones.
   Temperature variations given by LOS integral:
Sample kSZ map from patchy
reionization
   Sample kSZ map
    (100/h Mpc, f=250).
   Range of pixel values
    is DT/T=-10-5 to 10-5 , ~1°
    i.e. DT max/min are
    in the tens of mK at
    ~arcmin scales.


                                  ~1°
kSZ Power Spectra

   Power spectra peak at
    l~3000-5000, with a
    peak value ~1 μK.
   Instant reionization has
    order of magnitude less
    power for l~2000-8000,
    but same large-l
    behaviour.
   Uniform reionization
    has much less power on
    all scales.
Conclusions

   Large scale simulations needed for useful results.
   Reionization produces a clear signature in the nHI
    power spectra.
   WMAP3 results do not require different types of
    sources, but move reionization by a factor ~1.4 in
    (1+z).
   kSZ due to patchy reionization produces a signal of
    ~μK at l~3000-5000.

								
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