In this letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in the WiggleZ Dark Energy Survey. The data span the redshift range 0.6 < z < 1 over two fields totaling ∼ 41 deg. sq. and 190 hr of radio integration time. The cross-correlation constrains Ω HI b HI r = [0.43 ± 0.07(stat.) ± 0.04(sys.)] × 10 −3 , where Ω HI is the neutral hydrogen (H I) fraction, r is the galaxy-hydrogen correlation coefficient, and b HI is the H I bias parameter. This is the most precise constraint on neutral hydrogen density fluctuations in a challenging redshift range. Our measurement improves the previous 21 cm cross-correlation at z ∼ 0.8 both in its precision and in the range of scales probed.

No abstract

The large-scale distribution of neutral hydrogen in the Universe will be luminous through its 21 cm emission. Here, for the first time, we use the auto-power spectrum of 21 cm intensity fluctuations to constrain neutral hydrogen fluctuations at z ∼ 0.8. Our data were acquired with the Green Bank Telescope and span the redshift range 0.6 < z < 1 over two fields totalling ≈ 41 deg 2 and 190 h of radio integration time. The dominant synchrotron foregrounds exceed the signal by ∼ 10 3 , but have fewer degrees of freedom and can be removed efficiently. Even in the presence of residual foregrounds, the auto-power can still be interpreted as an upper bound on the 21 cm signal. Our previous measurements of the cross-correlation of 21 cm intensity and the WiggleZ galaxy survey provide a lower bound. Through a Bayesian treatment of signal and foregrounds, we can combine both fields in auto-and cross-power into a measurement of Ω HI b HI = [0.62 +0.23 −0.15 ] × 10 −3 at 68% confidence with 9% systematic calibration uncertainty, where Ω HI is the neutral hydrogen (H I) fraction and b HI is the H I bias parameter. We describe observational challenges with the present data set and plans to overcome them.

The Giant Metrewave Radio Telescope Epoch of Reionization experiment is an ongoing effort to measure the power spectrum from neutral hydrogen at high redshift. We have previously reported an upper limit of (70 mK) 2 at wavenumbers of k ≈ 0.65 h Mpc −1 using a basic piecewise-linear foreground subtraction. In this paper we explore the use of a singular value decomposition to remove foregrounds with fewer assumptions about the foreground structure. Using this method we also quantify, for the first time, the signal loss due to the foreground filter and present new power spectra adjusted for this loss, providing a revised measurement of a 2σ upper limit at (248 mK) 2 for k = 0.50 h Mpc −1 . While this revised limit is larger than previously reported, we believe it to be more robust and still represents the best current constraint on reionization at z ≈ 8.6.