A METHOD TO EXTRACT THE ANGULAR POWER SPECTRUM OF THE EPOCH OF REIONIZATION FROM LOW-FREQUENCY RADIO INTERFEROMETERS

The redshifted 21 cm signal of neutral hydrogen from the epoch of reionization (EoR) is extremely weak and its first detection is therefore expected to be statistical with first-generation low-frequency radio interferometers. In this Letter, we propose a method to extract the angular power spectrum of the EoR from the visibility correlation coefficients p sub(ij)(u, [upsilon]), instead of the visibilities V sub(ij)(u, [upsilon]) measured directly by radio interferometers in conventional algorithm. The visibility correlation coefficients are defined as p sub(ij)(u, [upsilon]) = V sub(ij)(u, [upsilon])/[radical]V sub(ii)V sub(jj) by introducing the autocorrelation terms V sub(ii) and V sub(jj) such that the angular power spectrum C sub(l) can be obtained through C sub(l) = (ProQuest: Formulae and/or non-USASCII text omitted) independently of the primary beams of antennas. This also partially removes the influence of receiver gains in the measurement of C sub(l) because the amplitudes of the gains cancel each other out in the statistical average operation of [left angle bracket]p sub(ij)(u, [upsilon]) super(2)[right angle bracket]. We use the average system temperature T sub(0) as a calibrator of C sub(l), which is dominated by the Milky Way and extragalactic sources in the frequency range that we are interested in, below 200 MHz. Finally, we demonstrate the feasibility of this novel method using the simulated sky maps as targets and the 21 CentiMeter Array (21CMA) as interferometer.