Special Issue of Publication of the Astronomical Society of Japan (PASJ) Highlights Recent Results from the Subaru Telescope
April 29, 2011
Recent results obtained with the Subaru Telescope appear in nineteen papers in a special, March 2011 issue of PASJ (Publication of Astronomical Society of Japan) entitled "Exploring the Universe with the Subaru Telescope: From Galaxies to the Solar System". This notable issue spans wide areas of astronomy, ranging from the Solar System to distant galaxies. The papers not only reflect the versatility of the Subaru Telescope but also its contribution to recent trends in astronomy. A brief summary of the papers' main themes follows.
The evolution of galaxies ８-12 billion years ago, the era when star formation was most active in the history of the universe
Although new star formation continues in the Milky Way, it was much more active in the past. On the whole, it appears that many more galaxies show active star formation ８-12 billion years ago (with a redshift between １-４), suggesting that this era holds a key to understanding the evolution of galaxies. In addition to obtaining cutting-edge results in studies of the most distant galaxies, researchers using the Subaru Telescope have recently made extensive observations of galaxies in the redshift range of １-４.
MOIRCS (Multi-Object Infrared Camera and Spectrograph), a near infrared instrument with a camera that boasts a wide field of view, has played a primary role in this research. Tanaka et al. reported the discovery of a group of galaxies that exhibit active star formation 11 billion years ago. Kajisawa et al. (a) reported on a deep survey with MOIRCS. Based on the survey data, Konishi et al. and Kajisawa et al. (b) discussed the morphology and star formation rate of the galaxies. Using another dataset obtained with MOIRCS, Tadaki et al. investigated the dependence of star formation activity on the environment (the number density of galaxies around it). These studies demonstrate that star formation in massive galaxies, which are found in regions with a high number density of galaxies, had already started to decline ８ billion years ago. Some smaller galaxies, which were growing in that early era of active star formation, show spiral structures and would eventually evolve into large galaxies like the Milky Way that exists today.
Supermassive black holes and star-forming galaxies
Supermassive black holes (SMBH) occur at the center of many galaxies. Recent observations indicate a strong connection between the evolution of a galaxy and its central black hole. Imanishi et al. focused on the significance of Active Galactic Nuclei (AGN), bright objects that receive their energy from mass accretion to their central blck hole. The team was especially interested in investigating the correlation between luminosity and star formation of particularly bright AGNs. In a virtual observatory (VO), Shirasaki et al. analyzed a large amount of arhived data originally obtained with the Subaru Telescope and found that distant AGN appear in regions with a high number density of galaxies, where collisions and mergers of galaxies are expected.
Black holes and star formation might be also be connected by the gas outflow from a galaxy. Aoki et al. obtained high-resolution spectra of the very bright quasar (QSO) newly discovered with the AKARI satellite (an infrared satellite), showing that the outflow originates from many spots around the center of the galaxy.
M82 is a nearby galaxy, about 12 million light years away from Earth, that shows active star formation. Although it is still unclear whether a supermassive black hole exists in the center of this galaxy, it is a good target for investigating the relationship between a galaxy's star formation and gas outflow, its so-called galactic wind. M82 contains dense dust, which prohibited detailed studies of its star formation. Ghandi et al. overcome this difficulty by making observations in the mid-infrared, using the images to explore many young star clusters near the center this galaxy's center, which could be the source of its galactic winds. Yoshida et al. measured the velocity of the dust in the galatic wind and discussed whether the matter ejected as galactic wind ultimately leaves or returns to the galaxy.
Stars in the Milky Way and the Local Group of galaxies
Scientists can study individual stars within the Milky Way separately from those in the dwarf galaxies around it. Recent spectroscopic studies using large telescopes are revealing the detailed chemical composition of stars in dwarf galaxies. Honda et al. measured the composition of a unique star in a dwarf galaxy that had a very low abundance of metals but an overabundance of heavy elements. The team succeeded in determining the origin of its heavy elements. Takeda et al. (a) contributed to an understanding of the chemical enrichment of our galaxy by measuring sulfur abundances for Milky Way objects.
Many mysteries remain about the structure and activity of normal stars. Takeda et al. (b) discovered the existence of a chromosphere (i.e., a layer above the photosphere) with a temperature as high as 10,000K for old stars. The research suggests that an unknown mechanism activates such a warm layer, even in slowly rotating stars.
Researchers using the Subaru Telescope are contributing to studies of extra-solar planets. Hirano et al. report the discovery of a planetary system with a Neptune-sized planet that shows spin-orbit misalignment.
Asteroids in the Solar System
Astronomers have studied asteroids as objects that yield information about the formation of the Solar system. The wide field of view of Subaru's prime focus camera (Suprime-Cam) has detected many asteroids. Dermawan et al. and Nakamura et al. have provided new insights into the structure of asteroids as well as their process of formation. They discovered many small asteroids with spherical shapes and diameters of 0.1-１ kilometers that show slow rotation. These constitute a new class of asteroids.
Instrumentation and software development
The continuous development of new instruments and software enables scientists to conduct more advanced research. The two papers by Ebizuka et al. discuss the development and performance evaluation of VPH (Volume Phase Holographic) grating and prisms, optical elements for modern spectrometers used in FOCAS (Faint Object Camera and Spectrograph) and MOIRCS. Furusawa et al. reported the development of software that will enable researchers to use an on-site data analysis system for Suprime-Cam. Overall, these developments improve the efficiency of observations.
Every year more than 100 scientific papers based on observations with the Subaru Telescope appear in many refereed journals. The PASJ is a journal published by the Astronomical Society of Japan. Accroding to a recent survey, PASJ's citation index is quickly increasing. This journal's special issue highlighting Subaru’s recent results will contribute to the advancement of astronomy worldwide.