21cmFAST 21cmFAST A Fast SemiNumerical Simulation of the HighRedshift 21cm Signal Andrei Mesinger Princeton University Mesinger Furlanetto amp Cen 2010 18 mar 2010 21cmFAST ID: 615766
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Slide1
18. mar, 2010
21cmFAST
21cmFASTA Fast, Semi-Numerical Simulationof the High-Redshift 21cm Signal
Andrei MesingerPrinceton University
Mesinger,
Furlanetto
,
&
Cen
(2010)Slide2
18. mar, 2010
21cmFAST
MotivationWe know next to nothing about high-z --> ENORMOUS parameter space to explore
Dynamic range required is enormous: single star --> Universe21cm observations are on LARGE scalesCosmological numerical simulations are computationally expensive and don’t even approach the scales of 21cm observations
Most relevant scales are in the linear to quasi-linear regimeSlide3
18. mar, 2010
21cmFAST
Philosophy
scale
Hydrodynamical Numerical Simulations (+RT)
Semi-numerical
Simulations
(
independent
3D
realizations;
FAST!
)
Analytic EstimatesSlide4
18. mar, 2010
21cmFAST
21cmFASTPortable and FAST! (if it’s in the name, it must be true…)A realization can be obtained in ~ minutes on a single CPU
Does not require lots of RAM (unlike DexM; Mesinger & Furlanetto 2007)Run on arbitrarily large scales
Optimized for the 21cm signalVary many independent free parameters; cover wide swaths of parameter spaceCalibrated to hydrodynamic cosmological simulationsPublically available!Slide5
18. mar, 2010
21cmFAST
21cmFAST: 3D realizations
neutral fraction
gas density
LOS velocity gradient
spin temperatureSlide6
18. mar, 2010
21cmFAST
21cmFAST: 3D realizations
neutral fraction
gas density
LOS velocity gradient
spin temperature
Compare with hydro sims of
Trac & Cen (2007); Trac+ (2008)
- coupled hydro, DM, 5 freq. RT, M
min
~10
8
M
sun
, L=143 MpcSlide7
18. mar, 2010
21cmFAST
Density Fieldscreate linear density and velocity fields (like N-body)
2. perturb linear density field using first-order displacement vectors (Zel’Dovich 1970)3. recreate
evolved velocity field corresponding to the evolved density fieldOR
1. scale ICs using linear growth factorSlide8
18. mar, 2010
21cmFAST
Density Fields, Pics
z=7
0.19 Mpc cells
143 MpcSlide9
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21cmFAST
Density Fields, PDFsSlide10
18. mar, 2010
21cmFAST
Density Field, power spectra
Collapse of gas is delayed with respect to DMJeans
smoothing, which depends on uncertain ionization + heating history
Note scalesSlide11
18. mar, 2010
21cmFAST
Ionization FieldsUse excursion-set formalism (e.g.
Furlanetto et al. 2004), and check if fcoll(Rfilter,
x, z) > 1/
starting from some
R
max
-->
R
cell
Use evolved density field to compute
f
coll
Set fractional ionization at last filter
step from
subgrid
sources
If desired, include Poisson fluctuations in halo number when computing
f
coll
(look Ma, no halos…)
(see
Zahn
+
2010)Slide12
Pics
18. mar, 2010
21cmFAST
McQuinn+ (2007)
Trac & Cen
(2007)
21cmFAST
see
Zahn
+ (2010)
FFRT-SSlide13
Ionization Fields, PDFs
18. mar, 2010
21cmFAST
0.56 Mpc cellsSlide14
Ionization Fields, power spectra
18. mar, 2010
21cmFASTSlide15
18. mar, 2010
21cmFAST
Velocity Gradients, PDFs
-nonlinear structure formation creates an asymmetric velocity
gradient distribution! Slide16
18. mar, 2010
21cmFAST
How does this impact 21cm power spectra?
dimensional ratio
dimensionless ratio
enhanced power in excess of the geometric (Kaiser) effect
(e.g. Barkana & Loeb 2005)
Ionized bubbles quickly erase the boosts from velocity gradients on moderate to large scales
Mean signal is
smaller
due to velocity gradients late in reionization:
inside-out reionizationSlide17
18. mar, 2010
21cmFAST
Full comparison post heating (Ts>>T)
full sim
DexM (MF07)
21cmFASTSlide18
18. mar, 2010
21cmFAST
Full comparison post heating (Ts>>T)Slide19
18. mar, 2010
21cmFAST
Full comparison post heating (Ts>>T)Slide20
18. mar, 2010
21cmFAST
Including X-ray heating and Ly pumpingNumerically integrate outward/back in time, summing the received photons
Number density of sources is computed by conditional fcoll, again bypassing halo finderSlide21
Global evolution
18. mar, 2010
21cmFASTSlide22
Cool Movie
18. mar, 2010
21cmFAST
http://www.astro.princeton.edu/~mesinger/Movies/delT.movSlide23
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21cmFAST
21cmFAST; publicly available (Mon):Portable and FAST! (if it’s in the name, it must be true…)
A realization can be obtained in ~ minutes on a single CPUDoes not require lots of RAM (unlike DexM)Run on arbitrarily large scalesNo need to “run-down” a sim to a particular redshiftOptimized for the 21cm signalVary many independent free parameters; cover wide swaths of parameter spaceCalibrated to hydrodynamic cosmological simulations
download at http://www.astro.princeton.edu/~mesingerSlide24
18. mar, 2010
21cmFAST
Deus ex Machina (DexM)
Etymology: New LatinLiterally: "God from a Machine", translation of Greek theos ek mechanes- a person or thing that appears unexpectedly and provides a contrived solution to an apparently insoluble difficulty
(http://www.merriam-webster.com/dictionary/deus%20ex%20machina
)
in true marketing fashion, we also offer a “professional” version,
with an even more pretentious title:
but you will need lots of RAM to take advantage
of added benefits, such as…Slide25
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21cmFAST
Halo Finder
Mesinger & Furlanetto (2007); Mesinger+ (2009, in preparation)
z=8.7 N-body halo field from
McQuinn et al. (2007)Slide26
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21cmFAST
Halo FinderMesinger & Furlanetto (2007)
without adjusting halo locations
with adjusting halo locationsSlide27
18. mar, 2010
21cmFAST
Ionizing UV Flux Fields
Mesinger & Dijkstra (2008)
flux
∑ L(M
halo
)/r
2
e
-r/
mfpSlide28
18. mar, 2010
21cmFAST
and maybe soon, absorption systems
Crociani+ (2009, in preparation)
xHI=0.72
x
HI
=0.45
x
HI
=0.18
x
HI
=0
mfp=
10Mpc
20MpcSlide29
18. mar, 2010
21cmFAST
PR Movie
http://www.astro.princeton.edu/~mesinger
250 Mpc