Haruyuki Okuda

The Infrared Astronomical Mission AKARI

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid- to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180 mu m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.

The Far-Infrared Surveyor (FIS) for AKARI

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.

Magnetic field configuration at the galactic center investigated by wide field near-infrared polarimetry

We present a polarimetric map of a 20 ? 20 area toward the Galactic center. The polarization of point sources has been measured in the J, H, and KS bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m telescope IRSF. One percent or better accuracy of polarization degree is achieved for sources with J < 14.5, H < 13.5, and KS < 12.0. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we have obtained a polarization originating from magnetically aligned dust grains at the central region of our Galaxy of at most 1-2 kpc. The distribution of the position angles shows a peak at ~20?, nearly parallel to the Galactic plane, suggesting a toroidal magnetic configuration. The derived direction of the magnetic field is in good agreement with that obtained from far-infrared/submillimeter observations, which detect polarized thermal emission from dust in the molecular clouds at the Galactic center. Our results show that, by subtracting foreground components, near-infrared polarimetry allows investigation of the magnetic field structure at the Galactic center.

A deep 6.7 μm survey in the SSA13 field with ISO

We present results of a deep mid-infrared survey in the SSA13 field with the Infrared Space Observatory (ISO). In order to probe the near-infrared light at high redshifts, we surveyed the field with the broad band LW2 (5-8.5 µm) filter of the mid-infrared camera ISOCAM. Adopting a highly redundant imaging strategy for the 23 h observation and carefully treating gradual changes in the detector responsivity caused by a very high rate of cosmic ray impacts, we succeeded in reaching an 80% completeness limit of 16 µJy in the central 7 arcmin 2 region. Utilizing the signal-to-noise ratio map, we detected 65 sources down to 6 µJy in the 16 arcmin 2 field. Integral galaxy number counts at 6.7 µm are then derived, reaching 1.3 × 10 4 deg −2 at the faint limit with a slope of −1.6 between 13 µJy and 130 µJy. Integrating individual sources in this flux range, the resolved fraction of the extragalactic background light at 6.7 µm is estimated to be 0.56 nW m −2 sr −1 . These results, which reach a flux limit three times fainter than those in the Hubble Deep Fields, are in fairly good agreement with a model prediction by Franceschini et al. (1997). Finally, we discuss the relation of distant massive E/S0 galaxies to the faint 6.7 µm galaxy population.

ISO deep far-infrared survey in the lockman hole: III. Catalogs and source counts at 90 & 170 μm

We present the catalogs and source counts for the C 90 (reference wavelength of 90m) and C 160 (170m) bands, which were extracted from our analysis of an ISO deep far-infrared survey conducted as part of the Japan/UH ISO cosmology project. The total survey area is0: 9d eg 2 in two fields within the Lockman Hole. The analysis consists of source extraction using the IRAF DAOPHOT package and simulations carried out by adding artificial sources to the maps to estimate the detection rate, the flux bias, the positional accuracy, and the noise. The flux calibration was performed using the Sb galaxy UGC 06009 - the photometric error was estimated to be50% at C 90 and65% at C 160. The total noise estimated from the simulation is dominated by the confusion noise due to the high source density. The confusion noise is 20 mJy at C 90 and35 mJy at C 160, which is much larger than the instrumental noise which is at the level of a few mJy or less. The catalogs were constructed by selecting 223 C 90 sources and 72 C 160 sources with a Signal to Noise Ratio ( SN R )o f three or greater. The distribution of the observed associations between C 90 and C 160 sources indicates that the 1 positional errors are20 00 and35 00 at C 90 and C 160, respectively. The corrections for the detection rate and the flux bias are significant for sources fainter than 200 mJy at C 90 and 250 mJy at C 160. Most of the sources detected both at C 90 and C 160 have a F(C 160)/F(C 90) color redder than the Sb galaxy UGC 06009. Such a red color could result from reddening due to the flux bias or a K-correction brightening due to the eect of redshift. Red sources brighter than 200 mJy at C 160 may be very luminous galaxies like Arp 220 at moderate redshift. The source counts are derived by applying the corrections for the detection rate and flux bias. The resultant counts are quite consistent with the constraints derived from the fluctuation analysis performed in Paper II. The C 160 counts are also consistent with the results from the FIRBACK project. Our C 90 survey, which is 2- 3 times deeper than those previously published, reveals an upturn in the count slope at around 200 mJy. While recent models give a reasonable fit to the C 160 counts, none of them are successful in accounting for the upturn in the C 90 counts. If the upturn is caused by ultraluminous IR galaxies, their redshifts would need to be at z 0:5, implying a major event in galaxy evolution at moderate redshift.

Liquid-helium-cooled Fabry-Perot spectrometer and the frequency switching method for far-infrared spectroscopic observations

The Fabry-Perot spectrometer designed for NIR spectroscopic observations on the Balloon-borne Infrared Telescope (BIRT) is described in detail. Particular attention is given to the newly developed frequency switching method used in the BIRT, which is especially suitable for observations of spatially extended emission because the frequency switching mode does not require spacial chopping. Observations are described from two successful experiments conducted in 1988 using the Fabry-Perot spectrometer on the BIRT, in both the spatial chopping mode and the frequency switching mode.

Balloon-Borne Infrared Telescope for far-infrared spectroscopy

The Japanese-made Balloon-borne Infrared Telescope (BIRT) designed for FIR astronomy is described. The BIRT system includes a 50-cm-diam telescope; an attitude-control system consisting of an attitude stabilization and a pointing and tracking subsystems; the ground support system consisting of four personal-computer systems; and electronics consisting of three small computer systems, servo circuits, power amplifiers, and other small circuits. Between 1985 and 1988, the BIRT has flown eight times, demonstrating that it is able to provide a suitable telescope observations on a stable platform with a long integration time. Structural diagrams of the BIRT overall system, the optical system, and the wobbling mechanism are presented along with a block diagram of the on-board electronics.

Mid-Infrared Identification of Faint Submillimeter Sources*

Faint submillimeter sources detected with the Submillimeter Common-User Bolometer Array on the James Clerk Maxwell Telescope have faced an identification problem due to the telescopes broad beam profile. Here we propose a new method to identify such submillimeter sources with a mid-infrared image having a finer point-spread function. The Infrared Space Observatory has provided a very deep 6.7 ?m image of the Hawaii Deep Field SSA13. All three faint 850 ?m sources in this field have their 6.7 ?m counterparts. They have been identified with interacting galaxy pairs in optical images. These pairs are also detected in the radio. Two of them are optically faint and very red (I > 24, I-K > 4), one of which has a hard X-ray detection with the Chandra satellite. As these observing properties are similar to those of local ultraluminous infrared galaxies, their photometric redshifts are derived based on submillimeter-to-mid-infrared flux ratios assuming a spectral energy distribution (SED) of Arp 220. Other photometric redshifts are obtained via ?2-minimization between the available photometry data and template SEDs. Both estimates are in the range z = 1-2, in good agreement with a spectroscopic redshift and a millimetric one. The reconstructed Arp 220 SEDs with these redshift estimates are consistent with all the photometry data except Chandras hard X-ray detection. The sources would be a few times more luminous than Arp 220. With an assumption that contributions from active galactic nuclei are negligible, it appears that extremely high star formation rates are occurring in galaxies at high redshifts with massive stellar contents already in place.

Characteristics of diffuse galactic mid- and far-infrared emission from interstellar dust derived by IRTS observation

Abstract The spectral characteristics of the diffuse galactic mid- and far infrared emission at λ = 10 – 60 μm are investigated using the IRTS and IRAS data. We estimate the grain temperature, total far-infrared intensity ( FIR ) and radiation density from the emission of the large grains at λ > 100 μm, assuming that the spectrum has a single temperature Planck function with a λ −2 emissivity law. We found that the spectral energy distribution of the diffuse galactic emission at wavelengths from 10 μm to 1 mm changed as a function of the dust temperature. In addition, we found clear correlation for the intensity of emissions at 12, 25, and 60 μm. The 12 μm intensity is proportional to FIR , and the ratios of the 25 and 60 μm intensities to FIR are proportional to the strength of the interstellar radiation field. These correlations are consistent with those found in the data of seven H II regions with various physical conditions. This suggests that the emitters of the emission at 12–60 μm are well mixed with large grains radiating at wavelength greater than 100 μm and implies that the ratio of the mass of these emitters to the mass of the large grains is constant in interstellar space. We conclude that the 12 μm emission is largely due to unidentified infrared features and that the 25 and 60 μm emission arises from very small grains transiently heated by multiple-photon

FIRBE: Far-Infrared Balloon-Borne Experiment

Abstract The recent activity in balloon-borne infrared observations in Japan is reviewed. Following this, the new balloon-borne telescope project is described. Near- and far-infrared diffuse emissions from the galaxy were firstly surveyed by the balloon telescopes of Japanese groups. In addition to this, the wide area survey of [CII] 158 micron line emission was extensively executed. Those results revealed the large-scale structures of stars and the interstellar medium of the Galaxy. The new project, FIRBE (Far-Infrared Balloon-Borne Experiment), is a successor of them. The FIRBE project is focused on mapping of the far-infrared emission from the Galaxy and external galaxies with the same spatial resolution as that of the IRAS . This is an on-going project, and we are making balloon flights in Japan and in India.