Measurement of 21 cm brightness fluctuations at z ~ 0.8 in   cross-correlation
  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 hours of radio integration time. The cross-correlation constrains Omega_HI b_HI r = [0.43 \pm 0.07 (stat.) \pm 0.04(sys.)] x 10^-3, where Omega_HI is the neutral hydrogen HI fraction, r is the galaxy-hydrogen correlation coefficient, and b_HI is the HI 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. 
K. W. Masui, E. R. Switzer, N. Banavar, K. Bandura, C. Blake, L.-M.   Calin, T.-C. Chang, X. Chen, Y.-C. Li, Y.-W. Liao, A. ...
astro-ph.CO astro-ph.GA