The Subaru Deep Field project

For many, the word Hawaii conjures visions of sun kissed beaches, magnificent tropical scenery or a respite from the harsher realities that accompany northern winters. But, for some with the interest, Hawaii also represents the finest location on our planet to ponder the mysteries of the heavens- perched almost 14,000 feet (4,200 meters) above sea level at the summit of a dormant volcano named Mauna Kea ("White Mountain") sits the world's largest astronomical observatory operated by eleven countries. On most clear nights, thirteen instruments scan the firmament in search of answers to humankind's most ponderous questions- what is the Universe that surrounds us, how did it begin and what is the true nature of our relationship with it.

Mauna Kea is a unique astronomical observing site because the mountain top pokes above most of the Earth's weather systems. This makes the atmosphere above the peak extremely dry and clear- the proportion of clear nights is among the highest in the world. The stability of the atmosphere above Mauna Kea also permits more detailed studies than are possible anywhere else from the surface of our planet- the stars seldom twinkle and appear nailed to the celestial vault. It's distance from city lights produces am exceptionally dark sky, allowing observation of the faintest galaxies that lie at the very edge of the observable Universe.

Many of the telescopes scattered across Mauna Kea's peak are among the largest optical instruments in the world. This is the home of the twin Keck telescopes- each gathers light with primary mirrors composed of 36 hexagonal segments that work together as a single piece of reflective glass spanning almost 33 feet (10 meters) in diameter. Nearby sits the Gillett (also known as the Gemini North) facility with its 26 foot (8.1 meter) mirror and the slightly larger Subaru telescope that employs a 27 foot (8.2 meter) diameter reflecting surface to detect and measure star light.

Operated by the National Observatory of Japan, the Subaru telescope is the second most powerful scope on the mountain and the fifth largest optical instrument in the world as of spring 2009. Since scientific observations commenced in the late nineteen-nineties, investigators have announced hundreds of discoveries using the Subaru's prodigious capabilities.

One of the initial results, produced shortly after the Subaru's first light, was a very deep near-infrared exposure that demonstrated the telescope's capabilities by capturing some of the most distant galaxies yet recorded in 2001, when it was released. However, armed with a more powerful camera, scientists soon decided to produce a new picture that would reach farther out and reveal an even earlier period of the Universe- one that would rival the most distant view seen by the Hubble Space Telescope.

The project, called the Subaru Deep Field (SDF), showcased the capabilities of ground based instruments and the Subaru, in particular. But, first, the project had to overcome restrictions imposed by the observatory's time allocation system to use the telescope.

Most research projects that require a large telescope must go through a competitive bidding process which limits time on the instrument to no more than a few nights during the upcoming year so that the scope is available for the greatest number of investigators. For example, astronomers are limited to just three nights every six months with the Subaru. However, the SDF team recognized that pooling observing nights among a large number of researchers would enable them to gather the extremely long exposure their project required. So, for thirty nights over a two year period, the SDF team produced an incredibly deep picture by accumulating a few images each night then digitally adding them together. This technique yielded a view that was equivalent to a single, almost, 50 hour exposure.

The SDF's goal was not limited to the identification of the most distant galaxies. The team also wanted to analyze and interpret the impact of early galaxies on the evolution of the universe. To help accomplish this, the SDF team developed a special filter that only permitted light with specific, narrow wavelengths to reach their detectors. These wavelengths matched the expected radiation emitted by galaxies close to the limits of observability- those that existed in the very early Universe. Other exposures also enabled the astronomers to gather light through traditional broadband filters.

The result was a mountain of data particularly when you consider Subaru's field of view- the telescope can see a portion of the sky that's about the size of the full moon! This is possible because of the telescope's low focal ratio (f/3) and the 80 mega-pixel images produced by the Suprime-Cam (Subaru Prime Focus Camera).    More »