Summary of Scientific Results – 2004
The outstanding qualities of the Subaru Telescope, including a wide field-of-viewand sophisticated detection instruments, continue to attract astronomers fromaround the world to study the inner and outer portions of the cosmos. New
discoveries are frequently being made that change our fundamental
understanding of the Universe and its many components. Subaru leads the way
into exploring these new-found frontiers.
Most people think that with a large 8.2m telescope, all of the astronomical
research focuses on objects very, very far away. Subaru does like to study thecosmos as far back in time as possible, but we also like to take a new look at
familiar neighbors in our Solar System. Comet LINEAR was expected to be avery bright comet as it approached Earth in May 2004, and, as such, was aconvenient target for further inspection. Observations of the comet discovered
water ice grains in its coma, the second discovery of water ice in any comet.
This is significant because cometary nuclei are thought to be remnants ofplanetary sources that existed in the early Solar System. Just a little furtheraway, Subaru obtained the first infrared spectrum of two of Jupiter’s small innermoons. The data shows that Amalthea and Thebe formed in a low temperatureenvironment, and may be two of the few remaining pieces of the material thatformed the Galilean moons. Just past Jupiter is another colossal planet, Saturn.
Subaru focused its gaze onto Saturn’s giant moon of Titan to measure the distantwinds raging on that strange world. In support of NASA’s Cassini mission,
Subaru acquired the direction and speed of winds on Titan to better understandthe dynamics of its atmosphere before a robotic Huygen probe would be sentplunging into it.
An area of study for Subaru is the Milky Way galaxy and its inhabitants. One
such resident is Beta Pictoris, the first star for which a circumstellar dust disc wasdiscovered. At approximately 62 light years away, Beta Pictoris is surprisingly
close and a nice known target to study. Japanese astronomers discovered small
amorphous silicate grains in ring-like locations around the star. The teamconcluded that the grains are replenished by the collisions of planetesimals. Justa little further away in the constellation Auriga, another team of Japanese
astronomers studied a protoplanetary disc surrounding star AB Aurigae using a
super sharp resolution of 0.1 arcsecs. They discovered that the planetarynursery is not a featureless and smooth place, but a place where gas and dust
swirl in a complex spiral pattern. This discovery evoked many theories andproduced new goals into determining how the spiral structure formed and if
planets can form in the spiral arms.
Two studies this year looked into dwarf irregular galaxies, one (Sextans A) foundin the Antila-Sextans Group and the other (Leo A) found in our Local Group.
Sextans A is located about 5 million light years away and has a mass of about

100 million stars, about one thousandth of the Milky Way. The oddness of thegalaxy is found in the presence of a comparatively large amount of gas and dust
for such a small galaxy and a high concentration of hydrogen gas. Leo A is an
isolated and extremely gas rich dwarf irregular galaxy with a mass of 0.01% of
the Milky Way. Astronomers are attempting to understand galaxy formation, anda deep imaging view of Leo A found for the first time that even small galaxies
have a complex structure, indicating a complex history. As we discuss galaxy
sizes, shapes, and their formation, this year Subaru also witnessed a large
galaxy devouring a small companion galaxy. Gravity from a large ellipiticalgalaxy is tidally tearing apart a nearby dwarf galaxy as it becomes stretched andthinned over 500 thousand light years. Eventually the stars and other material ofthe dwarf galaxy will be consumed by the larger galaxy.
One of the larger on-going projects at Subaru is the Subaru/XMM-Newton Deep
Survey (SXDS), which provides a comprehensive characterization andpopulation census of galaxies from the early Universe to the present. Thesurvey area is 1.3 square degrees, which corresponds to a piece of the Universe
150 million times 150 million light years in area in the Universe 5 to 13 billion
years ago. Subaru has stared at this field for over 200 hours revealing details
that are a hundred million times fainter than what you can see with theunassisted naked eye. These observations are necessary to study how galaxies
have changed over time. Some of the results indicate that bright and massive
galaxies form and evolve differently than fainter less massive galaxies. Moresignificant results are sure to follow.