A team of astronomers using the Subaru Telescope’s Suprime-Cam to perform the Subaru Ultra-Deep Survey for Lyman-alpha Emitters have looked back more than [z=7] to find 7 early galaxies that appeared quite suddenly within 700 million years of the Big Bang. The team, led by graduate student Akira Konno and Dr. Masami Ouchi (Associate Professor at the University of Tokyo’s ICRR) was looking for a specific kind of galaxy called a Lyman-alpha emitter (LAE), to understand the role such galaxies may have played in an event called “cosmic reionization”.

The team looked at distant galaxies that primarily emit Lyman-alpha radiation, “Lyman-alpha emitters” or LAE, and saw fewer than expected, further back in time. There’s an apparent sudden cutoff at that redshift. The redshift corresponds to a distance and time in history that’s model dependent. The standard big bang model would put this at about 13.1 billion years and only 700 million years after the big bang itself. The cosmological-history implication is that these galaxies “suddenly” appear.

One thing is pretty certain. A cosmological redshift of seven indicates the universe was about 1/8 it’s current size at the time the light they observed was emitted. That’s 1 / (z + 1).

According to the team’s analysis, one reason that LAEs appeared very quickly is cosmic reionization. LAEs in the epoch of cosmic reionization became darker than the actual luminosity due to the presence of the neutral hydrogen fog. In the team’s analysis of their observations, they suggest the possibility that the neutral fog filling the universe was cleared about 13.0 billion years ago and LAEs suddenly appeared in sight for the first time.”

“However, there are other possibilities to explain why LAEs appeared suddenly,” said Dr. Ouchi, who is the principal investigator of this program. “One is that clumps of neutral hydrogen around LAEs disappeared. Another is that LAEs became intrinsically bright. The reason of the intrinsic brightening is that the Lyman-alpha emission is not efficiently produced by the ionized clouds in a LAE due to the significant escape of ionizing photons from the galaxy. In either case, our discovery is an important key to understanding cosmic reionization and the properties of the LAEs in early universe.”

Subaru Telescope detects sudden appearance of galaxies in the early universe at phys.org
Press release from ICRR
PDF of paper “Accelerated Evolution Of The Lyα Luminosity Function At z >~ 7 Revealed By The Subaru Ultra-Deep Survey For Lyα Emitters AT z = 7.3”