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AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University.

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Presentation on theme: "AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University."— Presentation transcript:

1 AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University Mesinger, Cen, & Furlanetto (2009), in preparation

2 AlbaNova, Stockholm 18. aug, 200921cmFAST Motivation We know next to nothing about high-z --> ENORMOUS parameter space to explore Dynamic range required is enormous: single star --> Universe 21cm observations are on LARGE scales Cosmological 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 regime

3 AlbaNova, Stockholm 18. aug, 200921cmFAST Philosophy scale Hydrodynamical Numerical Simulations (+RT) Semi-Numerical Simulations (independent; 3D realizations; FAST!) Analytic Estimates

4 AlbaNova, Stockholm 18. aug, 200921cmFAST Philosophy Use the right tool for the job! one size DOES NOT fit all! Mesinger (2007)

5 AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST Portable 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) Run on arbitrarily large scales Optimized for the 21cm signal Vary many independent free parameters; cover wide swaths of parameter space Calibrated to hydrodynamic cosmological simulations

6 AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST: 3D realizations neutral fraction gas density LOS velocity gradient spin temperature

7 AlbaNova, Stockholm 18. aug, 200921cmFAST 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 Mpc

8 AlbaNova, Stockholm 18. aug, 200921cmFAST Density Fields 1.create 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 field OR 1. scale ICs using linear growth factor

9 AlbaNova, Stockholm 18. aug, 200921cmFAST Density Fields, Pics z=7 0.19 Mpc cells 143 Mpc

10 AlbaNova, Stockholm 18. aug, 200921cmFAST Density Fields, PDFs

11 AlbaNova, Stockholm 18. aug, 200921cmFAST Density Field, power spectra -Collapse of gas is delayed with respect to DM -Then Jeans smoothing, which depends on uncertain ionization + heating history Note scales

12 AlbaNova, Stockholm 18. aug, 200921cmFAST Ionization Fields Use excursion-set formalism (e.g. Furlanetto et al. 2004), and check if f coll (R filter, 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 Include Poisson fluctuations in halo number when computing f coll (look Ma, no halos…) (see Zahn+ 2009, in preparation)

13 AlbaNova, Stockholm 18. aug, 200921cmFAST Ionization fields, stats PDFs power spectra (see Zahn+ 2009, in preparation)

14 AlbaNova, Stockholm 18. aug, 200921cmFAST Velocity Gradients, PDFs -nonlinear structure formation creates an asymmetric velocity gradient distribution!

15 AlbaNova, Stockholm 18. aug, 200921cmFAST How does this impact 21cm power spectra? dimensional ratiodimensionless 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 reionization

16 AlbaNova, Stockholm 18. aug, 200921cmFAST Full comparison post heating (T s >>T  ) full simDexM (MF07)21cmFAST

17 AlbaNova, Stockholm 18. aug, 200921cmFAST Full comparison post heating (T s >>T  )

18 AlbaNova, Stockholm 18. aug, 200921cmFAST Full comparison post heating (T s >>T  )

19 AlbaNova, Stockholm 18. aug, 200921cmFAST Including X-ray heating and Ly  pumping Numerically integrate outward/back in time, summing the received photons Number density of sources is computed by conditional f coll Similar to Pritchard & Furlanetto (2007) & Santos+ (2008), but –Do not resolve individual sources; use fcoll –Work in the frame of gas elements, so deal with heating & coupling locally, not globally

20 AlbaNova, Stockholm 18. aug, 200921cmFAST Mean heating evolution

21 AlbaNova, Stockholm 18. aug, 200921cmFAST TsTsTsTs “weak” heating“strong” heating T s >> T  1 Gpc

22 AlbaNova, Stockholm 18. aug, 200921cmFAST T s, power spectra

23 AlbaNova, Stockholm 18. aug, 200921cmFAST 21cmFAST; publicly available (soon): Portable 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) Run on arbitrarily large scales No need to “run-down” a sim to a particular redshift Optimized for the 21cm signal Vary many independent free parameters; cover wide swaths of parameter space Calibrated to hydrodynamic cosmological simulations download at http://www.astro.princeton.edu/~mesinger

24 AlbaNova, Stockholm 18. aug, 200921cmFAST Deus ex Machina (DexM) Etymology: New Latin Literally: "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)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…

25 AlbaNova, Stockholm 18. aug, 200921cmFAST Halo Finder Mesinger & Furlanetto (2007); Mesinger+ (2009, in preparation) z=8.7 N-body halo field from McQuinn et al. (2007)

26 AlbaNova, Stockholm 18. aug, 200921cmFAST Halo Finder Mesinger & Furlanetto (2007) without adjusting halo locationswith adjusting halo locations

27 AlbaNova, Stockholm 18. aug, 200921cmFAST Ionizing UV Flux Fields Mesinger & Dijkstra (2008) flux   ∑ L(M halo )/r 2 e -r/ mfp

28 AlbaNova, Stockholm 18. aug, 200921cmFAST and maybe soon, absorption systems Crociani+ (2009, in preparation) x HI =0.72x HI =0.45x HI =0.18x HI =0 mfp= 10Mpc 20Mpc

29 AlbaNova, Stockholm 18. aug, 200921cmFAST PR Movie http://www.astro.princeton.edu/~mesinger 250 Mpc

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