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Counting All The Light In Deep Space

To best observe distant parts of our Universe, we need to look as far as possible away from the plane of our own Galaxy to avoid the interstellar dust and great myriad of stars that comprise the Milky Way. The island of Hawaii where Subaru Telescope is located is well situated for making these kinds of observations as the North Galactic Pole (as far away as you can get from the plane of our Galaxy) passes nearly directly overhead. This is where the influence of the atmosphere is smallest and the number of hours available for observing is relatively large. The Subaru Telescope has plans to observe a one-degree wide field near the North Galactic Pole called the "Subaru Deep Field" to study in great detail the contents of this distant part of our Universe.
Hilo - May 20, 2001
A team of astronomers from the National Astronomical Observatory of Japan, the University of Tokyo, and Kyoto University has completed a careful analysis of a very deep image taken at near-infrared wavelengths.

The "Subaru Deep Field" (SDF) was observed soon after the first light of Subaru Telescope, and subsequent study has revealed that the galaxies detected in the image account for more than 90% of all the galactic light in the Universe.

This is a higher fraction than that of the optical Hubble Deep Field images, and the SDF is therefore the deepest image of the Universe ever taken.

The SDF was imaged at a wavelength of 2.1 microns (Figure 1), and detected some of the faintest galaxies ever observed, down to a magnitude of 24.5.

The team used their models of galaxy evolution to predict how many faint galaxies would be missed in deep images, and discovered that the galaxies they detected in the SDF image accounted for more than 90% of the total near-infrared light from all the galaxies in the Universe along this line of sight (Figure 2). Subaru is now seeing almost to the edge of the Universe and very little extra light from fainter galaxies would be seen using more sensitive observations.

Although the Subaru observations can account for almost all of the light emitted by galaxies in the Universe, measurements from satellites have revealed that the total amount of extragalactic background light (Figure 3) is 3 times larger.

It was previously believed that all the near-infrared extragalactic light came from discrete galaxies (Figure 4); but these latest observations reveal that there is a great deal of light unaccounted for, which cannot be due to normal galaxies. Resolving this discrepancy will be an important challenge for future astronomy.

These results are published in the April 1 issue of the Astrophysical Journal Letters.

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Distant Nebulae Pumping Out Brown Dwarfs By The Hundreds
Mauna Kea - Feb. 13, 2001
Subaru Telescope has successfully taken a sharp and deep infrared image of the star-forming region, S106, creating a stunning image from across. In addition, many objects with masses less than that of an ordinary star have been discovered in this region.

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