Sin'itirou Makiuti

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.

Large-format and compact stressed Ge:Ga array for the ASTRO-F (IRIS) mission

Abstract We describe the development of a stressed Ge:Ga array detector with a large pixel format but a compact mechanical structure. The detector will be deployed in IRIS, a Japanese satellite to be launched in 2004, which will conduct an all-sky, far-infrared survey as well as spectroscopic observations of specific objects. The array has a 5 × 15 pixel format. Three of the five rows are for the 100 – 200 μm band, and the other two are for the 150 – 200 μm band. In the focal plane of the IRIS telescope, each pixel corresponds to a field of view of 50″ × 50″. A uniaxial mechanical stress is applied to the detector chips in each row using a single stressing mechanism. This results in a compact focal-plane array. Light pipes with entrance apertures of 0.9 × 0.9 mm size are distributed with a pitch of 1 mm. A charge-integrating amplifier (CIA) circuit is used as the readout. Bare-chip amplifiers and multiplexers are placed behind the Ge:Ga chips and are cooled to 1.8 K. The entire system, including chips and readouts, weighs 300 grams. We have thus succeeded in building a compact array detector suitable for a satellite payload.

Predicting dust extinction properties of star-forming galaxies from Hα/UV ratio

Using star-forming galaxies sample in the nearby Universe (0.02<z<0.10) selected from the SDSS (DR7) and GALEX all-sky survey (GR5), we present a new empirical calibration for predicting dust extinction of galaxies from H-alpha-to-FUV flux ratio. We find that the H-alpha dust extinction (A(Ha)) derived with H-alpha/H-beta ratio (Balmer decrement) increases with increasing H-alpha/UV ratio as expected, but there remains a considerable scatter around the relation, which is largely dependent on stellar mass and/or H-alpha equivalent width (EW(Ha)). At fixed H-alpha/UV ratio, galaxies with higher stellar mass (or galaxies with lower EW(Ha)) tend to be more highly obscured by dust. We quantify this trend and establish an empirical calibration for predicting A(Ha) with a combination of H-alpha/UV ratio, stellar mass and EW(Ha), with which we can successfully reduce the systematic uncertainties accompanying the simple H-alpha/UV approach by ~15-30%. The new recipes proposed in this study will provide a convenient tool for predicting dust extinction level of galaxies particularly when Balmer decrement is not available. By comparing A(Ha) (derived with Balmer decrement) and A(UV) (derived with IR/UV luminosity ratio) for a subsample of galaxies for which AKARI FIR photometry is available, we demonstrate that more massive galaxies tend to have higher extra extinction towards the nebular regions compared to the stellar continuum light. Considering recent studies reporting smaller extra extinction towards nebular regions for high-redshift galaxies, we argue that the dust geometry within high-redshift galaxies resemble more like low-mass galaxies in the nearby Universe.

A deep ATCA 20 cm radio survey of the AKARI Deep Field South near the South Ecliptic Pole

The results of a deep radio survey at 20 cm wavelength are reported for a region containing the AKARI Deep Field South (ADF-S) near the South Ecliptic Pole (SEP), using the Australia Telescope Compact Array (ATCA). The survey (hereafter referred to as the ATCA-ADFS survey) has 1σ detection limits ranging from 18.7 to 50 μJy beam−1 over an area of ∼1.1 deg2, and ∼2.5 deg2 to lower sensitivity. The observations, data reduction and source count analysis are presented along with a description of the overall scientific objectives, and a catalogue containing 530 radio sources detected with a resolution of 6.2 × 4.9 arcsec. The derived differential source counts show a pronounced excess of sources fainter than ∼1 mJy, consistent with an emerging population of star-forming galaxies. Cross-correlating the radio with AKARI sources and archival data we find 95 cross-matches, with most galaxies having optical R-magnitudes in the range 18–24 mag, similar to that found in other optical deep field identifications, and 52 components lying within 1 arcsec of a radio position in at least one further catalogue (either IR or optical). We have reported redshifts for a sub-sample of our catalogue finding that they vary between galaxies in the local Universe and those having redshifts of up to 0.825. Associating the radio sources with the Spitzer catalogue at 24 μm, we find 173 matches within one Spitzer pixel, of which a small sample of the identifications are clearly radio loud compared to the bulk of the galaxies. The radio luminosity plot and a colour–colour analysis suggest that the majority of the radio sources are in fact luminous star-forming galaxies rather than radio-loud active galactic nuclei (AGN). There are additionally five cross-matches between the Atacama Submillimetre Telescope Experiment (ASTE) or the Balloon-borne Large Aperture Submillimetre Telescope (BLAST) galaxies and radio sources from this survey, two of which are also detected at 90 μm, and 41 cross-matches with submillimetre sources detected in the Herschel Multi-tiered Extragalactic Survey (HerMES) Public Data release.

Development of lightweight SiC mirrors for the space infrared telescope for cosmology and astrophysics (SPICA) mission

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japanese astronomical infrared satellite project with a 3.5-m telescope. The target year for launch is 2017. The telescope is cooled down to 4.5 K in space by a combination of newly-developed mechanical coolers with an efficient radiative cooling system at the L2 point. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 4.5 K. Material for the SPICA telescope mirrors is silicon carbide (SiC). Among various types of SiC, primary candidates comprise normally-sintered SiC, reaction-sintered SiC, and carbon-fiber-reinforced SiC; the latter two have been being developed in Japan. This paper reports the current design and status of the SPICA telescope along with our recent activities on the cryogenic optical testing of SiC and C/SiC composite mirrors, including the development of an innovative support mechanism for cryogenic mirrors, which are based on lessons learned from a SiC 70 cm telescope onboard the previous Japanese infrared astronomical mission AKARI.

Cryogenic optical measurements of 12-segment-bonded carbon-fiber-reinforced silicon carbide composite mirror with support mechanism

A 720 mm diameter 12-segment-bonded carbon-fiber-reinforced silicon carbide (C/SiC) composite mirror has been fabricated and tested at cryogenic temperatures. Interferometric measurements show significant cryogenic deformation of the C/SiC composite mirror, which is well reproduced by a model analysis with measured properties of the bonded segments. It is concluded that the deformation is due mostly to variation in coefficients of thermal expansion among segments. In parallel, a 4-degree-of-freedom ball-bearing support mechanism has been developed for cryogenic applications. The C/SiC composite mirror was mounted on an aluminum base plate with the support mechanism and tested again. Cryogenic deformation of the mirror attributed to thermal contraction of the aluminum base plate via the support mechanism is highly reduced by the support, confirming that the newly developed support mechanism is promising for its future application to large-aperture cooled space telescopes.

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

AKARI infrared bright source catalogues

Bright source catalogues based on the new mid- and far-infrared all-sky survey by the infrared astronomical satellite AKARI were released into the public domain in March 2010. The mid-infrared catalogue contains more than 870 thousand sources observed at 9 and 18 μm, and the far-infrared catalogue provides information of about 427 thousand sources at 65, 90, 140, and 160 μm. The AKARI catalogues will take over the IRAS catalogues and will become one of the most important catalogues in astronomy. We present the characteristics of the AKARI infrared source catalogues as well as current activity for the future versions.

The First release of the AKARI-FIS Bright Source Catalogue.

The infrared astronomy satellite AKARI has made all‐sky surveys at six wavelength bands (9, 18 μm with the Infrared Camera (IRC), 65, 90, 140, and 160 μm with the Far‐Infrared Surveyor (FIS)). The first version of the FIS Bright Source Catalogue (β−1) has been provided to the AKARI science team for initial astronomical analyses. The catalogue will be made public in Autumn 2009 after further revisions. The IRC point source catalogue is in parallel preparation.

AKARI all-sky bright source catalogue: far-infrared luminous quasars and the optical far-infrared correlation

We have identified 22 quasars in the AKARI far-infrared all-sky Bright Source Catalogue, using a matching radius of 1 are magnified with respect to the predicted far-infrared luminosity, and consider this may be due to gravitational lensing. If confirmed, this would provide a new way to identify lenses; if not, we may have identified an interesting new population of extreme starbursting quasars.