Astrophys. J. 700, 20–48 (2009)

The details of reionization — in which radiation from the Universe's first stars and galaxies ripped apart atomic hydrogen left over from the Big Bang — matter greatly to astronomers. One class of galaxy, comprising those enshrouded in glowing hydrogen gas, is thought to have been important in reionization. But the earliest examples of these are hard to detect because they are so distant.

Using the 10-metre Keck telescopes in Hawaii, Brian Lemaux of the University of California, Davis, and his colleagues found a surprising number of gas-blanketed galaxies in a small patch of sky from a time when the Universe was 1.2 billion to 1.8 billion years old. Even the dimmer galaxies had significant rates of star formation, suggesting that this class plays a crucial part in reionization.