21 cm FAST A Fast SemiNumerical Simulation of

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

Motivation • We know next to nothing about high-z --> ENORMOUS parameter space to explore • Dynamic range required is enormous: single star --> Universe • 21 cm observations are on LARGE scales • Cosmological numerical simulations are computationally expensive and don’t even approach the scales of 21 cm observations • Most relevant scales are in the linear to quasi-linear regime 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Philosophy Analytic Estimates Semi-Numerical Simulations (independent; 3 D realizations; FAST!) scale Hydrodynamical Numerical Simulations (+RT) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Philosophy Use the right tool for the job! Mesinger (2007) one size DOES NOT fit all! 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

21 cm. FAST • 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 Dex. M) • Run on arbitrarily large scales • Optimized for the 21 cm signal • Vary many independent free parameters; cover wide swaths of parameter space • Calibrated to hydrodynamic cosmological simulations 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

21 cm. FAST: 3 D realizations spin temperature LOS velocity gradient neutral fraction gas density 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

21 cm. FAST: 3 D realizations spin temperature LOS velocity gradient neutral fraction gas density Compare with hydro sims of Trac & Cen (2007); Trac+ (2008) - coupled hydro, DM, 5 freq. RT, Mmin~108 Msun, L=143 Mpc 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Density Fields 1. create linear density and velocity fields (like Nbody) 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 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

z=7 Density Fields, Pics 0. 19 Mpc cells 143 Mpc 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Density Fields, PDFs 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

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 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Ionization Fields (look Ma, no halos…) • Use excursion-set formalism (e. g. Furlanetto et al. 2004), and check if fcoll(Rfilter, x, z) > 1/ starting from some Rmax --> Rcell • Use evolved density field to compute fcoll • Set fractional ionization at last filter step • Include Poisson fluctuations in halo number when computing fcoll (see Zahn+ 2009, in preparation) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Ionization fields, stats power spectra PDFs (see Zahn+ 2009, in preparation) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Velocity Gradients, PDFs -nonlinear structure formation creates an asymmetric velocity gradient distribution! 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

How does this impact 21 cm 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 reionization 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Full comparison post heating (Ts>>T ) full sim 18. aug, 2009 Dex. M (MF 07) 21 cm. FAST Alba. Nova, Stockholm

Full comparison post heating (Ts>>T ) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Full comparison post heating (Ts>>T ) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

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 fcoll • 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 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Mean heating evolution 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Ts “weak” heating “strong” heating Ts >> T 1 Gpc 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Ts, power spectra 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

21 cm. FAST; publicly available (soon): download at http: //www. astro. princeton. edu/~mesinger • 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 Dex. M) • • Run on arbitrarily large scales No need to “run-down” a sim to a particular redshift Optimized for the 21 cm signal Vary many independent free parameters; cover wide swaths of parameter space • Calibrated to hydrodynamic cosmological simulations 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

in true marketing fashion, we also offer a “professional” version, with an even more pretentious title: Deus ex Machina (Dex. M) 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%20 ex%20 machina) but you will need lots of RAM to take advantage of added benefits, such as… 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Halo Finder Mesinger & Furlanetto (2007); Mesinger+ (2009, in preparation) z=8. 7 N-body halo field from Mc. Quinn et al. (2007) 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

Halo Finder Mesinger & Furlanetto (2007) without adjusting halo locations 18. aug, 2009 21 cm. FAST with adjusting halo locations Alba. Nova, Stockholm

Ionizing UV Flux Fields Mesinger & Dijkstra (2008) flux ∑ L(Mhalo)/r 2 e-r/ mfp 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

and maybe soon, absorption systems Crociani+ (2009, in preparation) mfp= x. HI=0. 72 x. HI=0. 45 x. HI=0. 18 x. HI=0 10 Mpc 20 Mpc 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm

PR Movie http: //www. astro. princeton. edu/~mesinger 250 Mpc 18. aug, 2009 21 cm. FAST Alba. Nova, Stockholm