Simulations of next generation radio interferometers for observing 21cm tomography

A rich variety of cosmological processes have imprinted large-scale spatial fluctuations in the universe. Measuring these fluctuations is the primary tool for testing cosmological models and determining cosmological parameters. The emission from neutral hydrogen at 21 cm is a powerful probe of fluctuations from redshift 0 to as high as ~200. By mapping the three-dimensional 21 cm intensity field with 10 arc-minute resolution, for example, it may be possible to determine precisely the equation of state of the dark energy by measuring the expansion history throughout the transition from deceleration to acceleration. To measure these signals a new class of radio interferometers is being developed. These interferometers contain hundreds to thousands of elements and have bandwidths as large as an octave or more. Optimizing these instruments presents a number of technical challenges.

We propose to develop general-purpose software to model systematic effects in interferometers to address three important issues facing interferometers consisting of hundreds to thousands of antennas. First, we will develop calibration algorithms, which require measuring the complex beam gain of each element as a function of frequency. Second, we will develop analysis techniques for large "data cubes" for removing foreground sources and recovering cosmological power spectra. Third, we will extend our simulation techniques for modelling and controlling systematic effects.

Here we show a simulated 21cm sky cube of 1474×1474×810 Mpc^3 in Fourier space, covering a 30 degree × 30 degree sky patch (X-Y plane) and spanning a 736-864 MHz frequency range (Z direction), corresponding to z=0.77 and Δz=0.28. The three ring-like structures clearly indicate the Baryon Acoustic Oscillations (BAO) imprinted in the neutral hydrogen density field by acoustic waves travelling in the plasma of the early universe.

Simulated Stokes visibilities
Simulated 3-D 21cm visibilities for interferometric observation in arbitrary units.