# Galaxy redefines reionization epoch

22 April 2002

Lyman alpha emission has been detected from a galaxy of redshift z = 6.56. If confirmed, this discovery pushes back the limits of when reionization could have occurred in the early universe.

The distant galaxy was detected as its luminosity was increased by gravitational lensing from the cluster Abell 370. It is the first galaxy to be detected with z > 6. Quasars have now been detected out to z = 6.28.

Initial observations of continuum emission using the Keck II telescope in Hawaii were followed up with spectroscopic analysis using the Subaru telescope, also in Hawaii. The authors say that whereas discriminating Lyman alpha emitters from lower redshift objects can be difficult at low redshifts, at high redshifts their signature becomes so extreme that misidentification is very unlikely.

The detection of a galaxy at this redshift suggests observations have not yet reached the redshift of reionization. Pre-reionization, neutral gas would block out emission of this kind.

E Hu et al. 2002 Astrophys. J. Lett. 568 L75.