Len Cowie and Esther Hu: At the Cosmic Frontier

Esther Hu and Len Cowie study the most distant galaxies in the Universe, from a time when the first galaxies were beginning to light up the cosmos, about 800 million years after the Big Bang. Such light, having traveled for 13 billion years, provides a unique window into how the first galaxies originated.

For several hundred million years after the Big Bang, the Universe was in a Dark Age when ubiquitous neutral gas prevented the high-energy ultraviolet light produced by newborn massive stars from traveling freely through space. The Universe became opaque and unobservable. But the gravitational collapse of the denser parts of the Universe then led to the formation of stars, galaxies and quasars, and the resulting ultra-violet radiation caused the Universe to become highly ionized and transparent, revealing the distant Universe observed today through optical and infrared telescopes.

In 2016, Hu and Cowie led a team that discovered the most luminous galaxy ever detected during this period, which is known as the “Epoch of Reionization.” COSMOS Lyman Alpha 1, or COLA 1, was found during a wide-area search of a region of sky known as the COSMOS field using the Hyper-Suprime-Cam imaging camera on the Subaru 8-meter telescope on Maunakea. The galaxy’s enormous distance was confirmed from the redshift of a prominent emission line (The Lyman Alpha line of neutral hydrogen) that signals the presence of very distant galaxies.

“Our discovery in 2016 of the  galaxy called COLA-1, the most distant luminous galaxy detected during this early period, gives us a unique look at a galaxy in this important stage of the evolution of the universe.” — Esther Hu