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An intensity map of hydrogen 21-cm emission at redshift z ≈ 0.8

Image Credit: Chang et al.

A cross-correlation measurement of 21-cm emission measured by the Green Bank Telescope, and the optical galaxies measured by the DEEP2 galaxy survey.

At redshifts around unity, we have recently reported a cross-correlation measurement of 21- cm emission measured by the Green Bank Telescope, and the optical galaxies measured by the DEEP2 galaxy survey. The redshifts of the cross-correlation is at 0.5 < z < 1.1, and at the mean redshift of 0.8, we have reported a HI-optical cross-correlation amplitude that yields constraints on the neutral hydrogen mass content at z=0.8 and its bias factor on 10 h^-1 Mpc comoving scales. (Chang et al., 2010, Nature, 466, 463)This is the highest redshift detection of neutral hydrogen, and opens up a promising window for using 21-cm as tracers of the matter distribution, and eventually as a powerful tool for measuring the Baryon Acoustic Oscillation (BAO) features, shedding light on properties of dark energy.