鈴木 仁研

We investigate the relation between the surface densities of the gas and stars in various regions in the disks of M101 and M81 to investigate the Kennicutt-Schmidt law. The galaxies were observed with the Far-Infrared Surveyor (FIS) onboard AKARI at central wavelengths of 65, 90, 140 and 160 mu m. The spectral energy distribution of the whole galaxies shows the presence of a cold dust component in addition to a warm dust component. The cold and warm dust components can be related to the gas mass and newly-formed stellar mass, respectively, whose relation in various regions shows a power-law correlation. There are significant differences in the power-law index between outer arms with four giant H-II regions and inner arms in M101, while the power-law index for spiral arms of M81 is similar to that for inner arms in M101.

We describe the development of large format array of superconducting tunnel junction detectors that is readout by SONY GaAs-JFET cryogenic integrated circuits. High quality SIS photon detectors have high dynamic impedance that can be readout by low gate leakage GaAs-JFET circuits. Our imaging array design, with niobium SIS photon detectors and GaAs-JFET cryogenics electronics, uses integrating amplifiers, multiplexers and shift-registers to readout large number of pixels that is similar to CMOS digital cameras. We have designed and fabricated GaAs-JFET cryogenic integrated circuits, such as AC-coupled capacitive trans-impedance amplifier, multiplexers with sample-andholds and shift-registers, for 32-channel readout module. The Advanced Technology Center of National Astronomical Observatory of Japan have started extensive development program for large format array of SIS photon detectors. © 2009 American Institute of Physics.

In this paper, the optical design of astronomical detector array with SIS for 600 - 700 GHz is proposed. A unit has 127 pixel, and SIS junctions are coupled to double slot antennas and extended hemisphere lens made from Silicon or Alumina ceramics. A lens with multi-pixel system is compared to 1 lens with 1 antenna system (fly-eye)from the view point of antenna spacing, aberration, and beam efficiency. © 2009 IEEE.

We present a theoretical model for Type Ib supernova (SN) 2006jc. We calculate the evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The synthetic bolometric LC is compared with the observed bolometric LC constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as 40 M-circle dot on the zero-age main sequence. The star undergoes extensive mass loss to reduce its mass down to as small as 6.9 M-circle dot, thus becoming a WCO Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed. This could explain the NIR brightening and the dust feature seen in the MIR spectrum. We suggest that the progenitor of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss, and such massive stars are important sites of dust formation. We derive the parameters of the explosion model in order to reproduce the bolometric LC of SN 2006jc by the radioactive decays: the ejecta mass 4.9 M-circle dot, hypernova-like explosion energy 1052 ergs, and ejected Ni-56 mass 0.22 M-circle dot. We also calculate the circumstellar interaction and find that a CSM with a flat density structure is required to reproduce the X-ray LC of SN 2006jc. This suggests a drastic change of the mass-loss rate and/or the wind velocity that is consistent with the past luminous blue variable (LBV)-like event.

We performed mid-infrared spectroscopic observations of 18 local dusty elliptical galaxies by using the Infrared Spectrograph (IRS) on board Spitzer. We have significantly detected polycyclic aromatic hydrocarbon (PAH) features from 14 out of the 18 galaxies and, thus, found that the presence of PAHs is not rare but rather common in dusty elliptical galaxies. Most of these galaxies show an unusually weak 7.7 μm emission feature relative to 11.3 and 17 μm emission features. A large fraction of the galaxies also exhibit H2 rotational line and ionic fine-structure line emissions, which have no significant correlation with the PAH emissions. The PAH features are well correlated with the continuum at 35 μm, whereas they are not correlated with the continuum at 6 μm. We conclude that the PAH emission of the elliptical galaxies is mostly of interstellar origin rather than of stellar origin, and that the unusual PAH interband strength ratios are likely to be due to a large fraction of neutral to ionized PAHs. © 2008. The American Astronomical Society. All rights reserved.

AKARI, the Japanese infrared astronomical satellite, was launched on 2006 February 21 ( UT) and put into a sun-synchronous polar orbit at an altitude of 700 km. Cosmic radiations, particularly protons in the South Atlantic Anomaly (SAA), were expected to affect the performance of the stressed Ge:Ga array far-infrared detector on board AKARI. One of the influences is the radioactivation of the detector housing; gamma-rays from the radioactivated detector housing interact with Ge: Ga elements, producing spikes (so-called glitches) in the electric outputs of the detector. Prior to the launch, we performed a 100 MeV proton-beam irradiation test for an engineering model of the stressed Ge: Ga array, which simulated the SAA passage. In the test, we observed glitches in the detector output that were due to the radioactivation of the detector housing. By investigating the test data, we have computed the glitch rate of the flight array detector expected in the AKARI orbit, including its change with time from the launch to the end of the AKARI mission. After the launch of AKARI, we have compared the performance observed in the orbit to that predicted by the proton-beam test. The glitch rate really changed with time after the launch; we have found that the in-orbit behavior is consistent with the prediction.

We have observed 18 nearby dusty elliptical galaxies in the near- to far-infrared with Spitzer and AKARI. We have found that polycyclic aromatic hydrocarbons are present in 14 out of the 18 elliptical galaxies.

We report the in-orbit performance of the AKARI/Far-Infrared Surveyor Ge:Ga photoconductors, focusing on the transient response and the radiation effects, to perform the characterization of these effects for data analyses. The behavior for these effects is found to be significantly different between the Short-Wavelength and Long-Wavelength array detectors of the FIS, most probably due to the difference in the array configuration. We discuss cosmic-ray radiation effects, referring to the results of pre-flight proton-beam irradiation measurements. We also describe our efforts to correct the slow transient response of the detectors by adopting a physical approach.

The nearby face-on spiral galaxy M 101 has been observed with the Far-Infrared Surveyor onboard AKARI. The far-infrared four-band images reveal fine spatial structures of M 101, which include global spiral patterns, giant H II regions embedded in outer spiral arms, and a bar-like feature crossing the center. The spectral energy distribution of the whole galaxy shows the presence of a cold dust component (18(-10)(+4) K) in addition to a warm dust component (55(-25)(+9) K). The distribution of the cold dust is mostly concentrated near the center, and appears to be smoothly distributed over the entire extent of the galaxy, whereas the distribution of warm dust indicates some correlation with the spiral arms, and has spotty structures, such as four distinctive bright spots in the outer disk in addition to a bar-like feature near the center, tracing the CO intensity map. The star-formation activity of the giant H II regions that spatially correspond to the former bright spots is found to be significantly higher than that of the rest of the galaxy. The latter warm dust distribution implies that there are significant star-formation activities in the entire bar filled with molecular clouds. Unlike our Galaxy, M 101 is a peculiar normal galaxy with extraordinary active star-forming regions.

The Far-Infrared Surveyor (FIS) is one of two focal-plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 mu m, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcminutes, and the pixel pitch matches the diffraction limit of the telescope. Derived point-spread functions (PSFs) from observations of asteroids are similar to those given by the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and the performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.

We present the observations of the reflection nebulae IC4954 and IC4955 region with the Infrared Camera and the Far-Infrared Surveyor (FIS) on board the infrared astronomical satellite AKARI during its performance verification phase. We obtained 7 band images from 7 to 160 mu m with higher spatial resolution and higher sensitivities than previous observations. The spatial variation in the mid-infrared color suggests that the star-formation in IC 4954/4955 is progressing from south-west to north-east. The FIS 4-band data from 65 mu m to 160 Am allow us to correctly estimate the total infrared luminosity from the region, which is about one sixth of the energy emitted from the existing stellar sources. Five candidates for young stellar objects have been detected as point sources for the first time in the 11 mu m image and it is suggested that that current star-formation has been triggered by previous star-formation activities. A wide area map of the size of about 1 degrees around the IC 4954/4955 region was created from the AKARI mid-infrared All-Sky Survey data. Together with the H 121 cm data, it suggests a large hollow structure of a degree scale, on whose edge the IC 4954/4955 region has been created, indicating star formation over three generations in largely different spatial scales.

Far-infrared (IR) images of the nearby Sb galaxy NGC 2841 and the Sc galaxy NGC 2976 at wavelengths of 65, 90, 140, and 160 mu m have been obtained with the Far-Infrared Surveyor (FIS) onboard AKARI. Both galaxies reveal similar morphologies of dust rings. They are, however, significantly different in the dust temperature: a cold (similar to 21 K) ring for NGC 2841 and a warm (similar to 30 K) ring for NGC 2976, which presumably reflects the difference in the origin of the ring structure for the different Hubble types of the galaxy. In addition to the dust-ring structure, a warm dust component was detected from the central region of NGC 2841, which may be attributed to heating by its Low-Ionization Nuclear Emission-line Region nucleus. As for NGC 2976, an extended dust component was observed along the minor axis, which shows a distribution somewhat asymmetrical to the galactic disk; this might be associated with the H I bridge in the M 81/M 82 group that NGC 2976 belongs to. By taking advantage of a wealth of the far-IR bands of the FIS, it has been demonstrated that the spectral energy distribution of NGC 2841 is spatially more variable than that of NGC 2976.

AKARI (formerly ASTRO-F) is an infrared space telescope designed for an all-sky survey at 10-180 mu m, and deep pointed surveys of selected areas at 2-180 mu m. The deep pointed surveys with AKARI will significantly advance our understanding of galaxy evolution, the structure formation of the universe, the nature of buried AGNs, and the cosmic infrared background. We describe here the important characteristics of the AKARI mission, the orbit, and attitude control system, and investigate the optimum survey area based on the updated pre-flight sensitivities of AKARI, taking into account the cirrus confusion noise as well as the surface density of bright stars. The North Ecliptic Pole is concluded to be the best area for 2-26 mu m deep surveys, while the low-cirrus noise regions around the South Ecliptic Pole are worth considering for 50-180 mu m pointed surveys to high sensitivities limited by the galaxy confusion noise. Current observational plans concerning these pointed surveys are described in detail. Comparing these surveys with deep surveys using the Spitzer Space Telescope, the AKARI deep surveys are particularly unique in respect of their continuous wavelength coverage over the 2-26 Am range in broad-band deep imaging, and their slitless spectroscopy mode over the same wavelength range.