We report our research on aluminum mirror optics for future infrared astronomical satellites. For space infrared missions, cooling the whole instrument is crucial to suppress the infrared background and detector noise. In this aspect, aluminum is appropriate for cryogenic optics, because the same material can be used for the whole structure of the instrument including optical components thanks to its excellent machinability, which helps to mitigate optical misalignment at low temperatures. We have fabricated alu- minum mirrors with ultra-precision machining and measured the wave front errors (WFEs) of the mirrors with a Fizeau interferometer. Based on the power spectral densities of the WFEs, we conrmed that the surface accuracy of all the mirrors satised the requirements for the SPICA Coronagraph Instrument. We then integrated the mirrors into an optical system, and examined the image quality of the system with an optical laser. As a result, the total WFE is estimated to be 33 nm (rms) from the Strehl ratio. This is consistent with the WFEs estimated from the measurement of the individual mirrors.

For future space IR missions, such as SPICA, it is crucial to establish an experimental method for eval- uating the performance of mid-IR detectors. In particular, the wavelength dependence of the sensitivity is important but difficult to be measured properly. We are now preparing a testing system for mid-IR Si:As/Si:Sb detectors on SPICA. We have designed a cryogenic optical system in which IR signal light from a pinhole is collimated, passed through an optical filter, and focused onto a detector. With this system, we can measure the photoresponse of the detector for various IR light using optical lters with different wavelength properties. We have fabricated aluminum mirrors which are adopted to minimize thermal distortion effects and evaluated the surface figure errors. The total wavefront error of the optical system is 1.3 μm RMS, which is small enough for the target wavelengths (20-37 μm) of SPICA. The point spread function measured at a room temperature is consistent with that predicted by the simulation. We report the optical performance of the system at cryogenic temperatures.

We propose a cosmological survey to probe star formation and nuclear activity in galaxies at redshifts of z=2-4 by polycyclic aromatic hydrocarbon (PAH) features using the SPICA mid-infrared instrument (SMI) with a spectral resolution of R=20. We will cover a wavelength range of 20-36 μm that corresponds to z=2-4 for the PAH features (11.3, 7.7, and 6.2 μm). The sensitivity will be 1 X 10-19 W/m2 (5 σ) in case of a reference survey that covers 4 arcmin2 field in a one-hour observation. It corresponds to LIR=2 X 1011 L⊙ at z=3 and will give us more than 10000 galaxies in a 450 hour survey.

We demonstrate the luminosity dependence of the covering factor (CF) of active galactic nuclei (AGNs), based on AKARI mid-infrared all-sky survey catalog. Combining the AKARI with Sloan Digital Sky Survey (SDSS) spectroscopic data, we selected 243 galaxies at 9 m and 255 galaxies at 18 m. We then identied 64 AGNs at 9 μm and 105 AGNs at 18 μm by their optical emission lines. Following that, we estimated the CF as the fraction of type 2 AGN in all AGNs. We found that the CF decreased with increasing 18 μm luminosity, regardless of the choice of type 2 AGN classification criteria.

The dusty torus of Active Galactic Nuclei (AGNs) is one of the important components for the unification theory of AGNs. The geometry and properties of the dusty torus are key factors in understanding the nature of AGNs as well as the formation and evolution of AGNs. However, they are still under discussion. Infrared observation is useful for understanding the dusty torus as thermal emission from hot dust with the dust sublimation temperature (~ 1500 K) has been observed in the infrared. We have analyzed infrared spectroscopic data of low-redshift and high-redshift quasars, which are luminous AGNs. For the low-redshift quasars, we constructed the spectral energy distributions (SEDs) with AKARI near-infrared and Spitzer mid-infrared spectra and decomposed the SEDs into a power-law component from the nuclei, silicate features, and blackbody components with different temperatures from the dusty torus. From the decomposition, the temperature of the innermost dusty torus shows the range between 900-2000 K. For the high-redshift quasars, AKARI traced rest-frame optical and near-infrared spectra of AGNs. Combining with WISE data, we have found that the temperature of the innermost dusty torus in high redshift quasars is lower than that in typical quasars. The hydrogen Hα emission line from the braod emission line region in the quasars also shows narrow full width at half maximum of 3000-4000 km s-1. These results indicate that the dusty torus and the broad emission line region are more extended than those of typical quasars.

We study CO2/H2O ice abundance ratios in nearby galaxies using AKARI near-infrared slit spec- troscopy. Past studies of the ices intensively examined CO2/H2O ratios mainly in our Galaxy, and found that there were considerable variations in the CO2/H2O ratios from object to object. The cause of the variations is, however, still under debate. As a result of the analysis of our sample that includes 1031 regions in 158 galaxies, the CO2/H2O ratios are in a range of 0.05-0.30. In the dataset, we nd that the CO2/H2O ratios positively correlate with the Brα/PAH 3.3 μm ratios which re ect the massive star formation activity. Furthermore, we find that the CO2/H2O ratios positively correlate with the specific star formation rates of the galaxies where the ices are detected, that re ect the evolutionary stage of a galaxy. These results suggest that the CO2/H2O ratios are enhanced in active star-forming regions and young galaxies.

We have performed systematic studies of the properties of dust in various environments of nearby galaxies with AKARI. The unique capabilities of AKARI, such as near-infrared (near-IR) spectroscopy combined with all-sky coverage in the mid- and far-IR, enable us to study processing of dust, particularly carbonaceous grains includings polycyclic aromatic hydrocarbons (PAHs), for unbiased samples of nearby galaxies. In this paper, we first review our recent results on individual galaxies, highlighting the uniqueness of AKARI data for studies of nearby galaxies. Then we present results of our systematic studies on nearby starburst and early-type galaxies. From the former study based on the near-IR spectroscopy and mid-IR all-sky survey data, we find that the properties of PAHs change systematically from IR galaxies to ultra- luminous IR galaxies, depending on the IR luminosity of a galaxy or galaxy population. From the latter study based on the mid- and far-IR all-sky survey data, we find that there is a global correlation between the amounts of dust and old stars in early-type galaxies, giving an observational constraint on the origin of the dust.

We present our AKARI study of massive star forming regions where a large-scale cloud-cloud collision possibly contributes to massive star formation. Our targets are Spitzer bubbles, which consist of two types of bubbles, closed and broken ones; the latter is a candidate of the objects created by cloud-cloud collisions. We performed mid- and far-infrared surface photometry toward Spitzer bubbles to obtain the relationship between the total infrared luminosity, LIR, and the bubble radius, R. As a result, we nd that LIR is roughly proportional to R where  = 2:10:4. Broken bubbles tend to have larger radii than closed bubbles for the same LIR.

We detected bright mid- to far-infrared emission from the helium nova V445 Puppis in the AKARI all-sky survey data taken in 2006. Assuming an optically thin condition, we decomposed the spectral energy distribution (SED) of V445 Puppis in October 2006 by model tting and found that the SED can be explained by a combination of cold amorphous carbon (125 K and the mass of 4:5+6:6 2:7 X 10-4 M⊙) and warm amorphous carbon (250 K and the mass of 1:8+1:0 -0:5 X 10-5 M⊙). Assuming that the former is pre-existing dust formed in the past nova outbursts and the latter is newly formed dust in December 2000's nova wind, this result suggests that the amount of dust formed around V445 Puppis in a single outburst is larger than 10-5 M⊙, which is larger than those in any other classical novae ever reported.

Our understanding of dust emission, interaction, and evolution, is evolving. In recent years, electric dipole emission by spinning dust has been suggested to explain the anomalous microwave excess (AME), appearing between 10 and 90 Ghz. The observed frequencies suggest that spinning grains should be on the order of 10nm in size, hinting at polycyclic aromatic hydrocarbon molecules (PAHs). We present data from the AKARI/Infrared Camera (IRC) due to its high sensitivity to the PAH bands. By inspecting the IRC data for a few AME regions, we nd a preliminary indication that regions well-tted by a spinning- dust model have a higher 9 m than 18 m intensity vs. non-spinning-dust regions. Ongoing eorts to improve the analysis by using DustEM and including data from the AKARI Far Infrared Surveyor (FIS), IRAS, and Planck High Frequency Instrument (HFI) are described.

A wide spectral coverage from near-infrared (NIR) to far-infrared (FIR) of AKARI both for imaging and spectroscopy enables us to eciently study the emission from gas and dust in the interstellar medium (ISM). In particular, the Infrared Camera (IRC) onboard AKARI oers a unique opportunity to carry out sensitive spectroscopy in the NIR (2{5 m) for the rst time from a spaceborn telescope. This spectral range contains a number of important dust bands and gas lines, such as the aromatic and aliphatic emission bands at 3.3 and 3.4{3.5 m, H2O and CO2 ices at 3.0 and 4.3 m, CO, H2, and HI gas emission lines. In this paper we concentrate on the aromatic and aliphatic emission and ice absorption features. The balance between dust supply and destruction suggests signicant dust processing taking place as well as dust formation in the ISM. Detailed analysis of the aromatic and aliphatic bands of AKARI observations for a number of Hii regions and Hii region-like objects suggests processing of carbonaceous dust in the ISM. The ice formation process can also be studied with IRC NIR spectroscopy eciently. In this review, dust processing in the ISM divulged by recent analysis of AKARI data is discussed.

Debris disks are important observational clues to understanding on-going planetary system formation. They are usually identied by signicant mid-infrared excess on top of the photospheric emission of a central star on the basis of prediction from J-, H-, and Ks-band uxes and the stellar model spectra. For bright stars, 2MASS near-infrared uxes suffer large uncertainties due to the near-infrared camera satu- ration. Therefore we have performed follow-up observations with the IRSF 1.4 m near-infrared telescope located in South Africa to obtain accurate J-, H-, and Ks-band uxes of the central stars. Among 754 main-sequence stars which are detected in the AKARI 18 m band, we have performed photometry for 325 stars with IRSF. As a result, we have successfully improved the ux accuracy of the central stars from 9.2 % to 0.5 % on average. Using this dataset, we have detected 18 m excess emission from 57 stars in our samples with a 3 level. We nd that some of them have high ratios of the excess to the photospheric emission even around very old stars, which cannot be explained by the current planet-formation theories.

Debris disks are circumstellar dust disks around main-sequence stars. They are important observational clues to understanding the planetary system formation. The zodiacal light is the thermal emission from the dust disk in our Solar system. For a comprehensive understanding of the nature and the evolution of dust disks around main-sequence stars, we try a comparative study of debris disks and the zodiacal light. We search for debris disks using the AKARI mid-infrared all-sky point source catalog. By applying accurate ux estimate of the photospheric emission based on the follow-up near-infrared observations with IRSF, we have improved the detection rate of debris disks. For a detailed study of the structure and grain properties in the zodiacal dust cloud, as an example of dust disks around main-sequence stars, we analyze the AKARI mid-infrared all-sky diffuse maps. As a result of the debris disks search, we found old (>1 Gyr) debris disks which have large excess emission compared to their age, which cannot be explained simply by the conventional steady-state evolution model. From the zodiacal light analysis, we nd the possibility that the dust grains trapped in the Earth's resonance orbits have increased by a factor of 3 in the past 20 years. Combining these results, we discuss the non-steady processes in debris disks and the zodiacal light.

The zodiacal light emission is the thermal emission from the interplanetary dust and the dominant diuse radiation in the mid- to far-infrared wavelength region. Even in the far-infrared, the contribution of the zodiacal emission is not negligible at the region near the ecliptic plane. The AKARI far-infrared all-sky survey covered 97% of the whole sky in four photometric bands with band central wavelengths of 65, 90, 140, and 160 m. AKARI detected the small-scale structure of the zodiacal dust cloud, such as the asteroidal dust bands and the circumsolar ring, in far-infrared wavelength region. Although the most part of the zodiacal light structure in the AKARI far-infrared all-sky image can be well reproduced with the DIRBE zodiacal light model, there are discrepancies in the small-scale structures. In particular, the intensity and the ecliptic latitude of the peak position of the asteroidal dust bands cannot be repro- duced precisely with the DIRBE models. The AKARI observational data during more than one year has advantages over the 10-month DIRBE data in modeling the full-sky zodiacal dust cloud. The resulting small-scale zodiacal light structure template has been used to subtract the zodiacal light from the AKARI all-sky maps.

The AKARI 9 and 18 m diuse maps reveal the all-sky distribution of the interstellar medium with relatively high spatial resolution of 600. The zodiacal light is a dominant foreground component in the mid-infrared. Thus, removal of the zodiacal light is a critical issue to study low surface brightness Galactic diuse emission. We carried out modeling of the zodiacal light based on the Kelsall model which is constructed from the COBE data. In the previous study, only a time-varying component of the zodiacal light brightness was used for determination of the model parameters. However, there remains a residual component of the zodiacal light around the ecliptic plane even after removal with the model. Therefore, instead of using a time-varying component, we use the absolute brightness of the zodiacal light and we nd that the new model can better remove the residual component. As a result, the best-fit model parameters are changed from those in the previous study. We discuss the properties of the zodiacal light based on our new result.

We plan to produce a faint source catalogue from the AKARI mid-infrared (IR) all-sky diffuse maps. In the publicly-available AKARI mid-IR point source catalogue (PSC), sources were extracted from single- scan images, and conrmed by using the other scan images. By stacking multiple scan images, we can detect fainter sources which are not listed in the PSC. We optimized the source extraction process using a 6◦  6◦ area around the star-forming region, Cepheus B. Then, we divided the all-sky data into three seasonal images, and checked the positions and the uxes of the detected sources on the images. As a result, our new source extraction method works well; 90% of the sources are also identied in the WISE catalogue. In this method, we obtain the detection limit twice deeper than that of the PSC. The number of sources increases by a factor of 2, as compared with the PSC.

We are creating all-sky diffuse maps from the AKARI mid-infrared survey data with the two photometric bands centered at wavelengths of 9 and 18 m. The AKARI mid-infrared diffuse maps achieve higher spatial resolution and higher sensitivity than the IRAS maps. In particular, the 9 m data are unique resources as an all-sky tracer of the emission of polycyclic aromatic hydrocarbons (PAHs). However, the original data suffer many artifacts. Thus, we have been developing correction methods. Among them, we have recently improved correction methods for the non-linearity and the reset anomaly of the detector response. These corrections successfully reduce the artifact level down to 0.1 MJy sr􀀀1 on average, which is essential for discussion on faint extended emission (e.g., the Galactic PAH emission). We have also made progress in the subtraction of the scattered light caused in the camera optics. We plan to release the improved diffuse maps to the public within a year.

We present a comparative study of CO and polycyclic aromatic hydrocarbon (PAH) emission toward a region including the massive star-forming regions of NGC 6334 and NGC 6357. We use the NANTEN 12CO(J=1{0) data and the AKARI 9 m All-Sky diffuse map in order to evaluate the calibration accuracy of the AKARI data. We conrm that the overall CO distribution shows a good spatial correspondence with the PAH emission, and their intensities exhibit a good power-law correlation with a spatial resolution down to 4′ over the region of 10◦10◦. We also reveal poorer correlation for small scale structures between the two quantities toward NGC 6357, due to strong UV radiation from local sources. Larger scatter in the correlation toward NGC 6357 indicates higher ionization degree and/or PAH excitation than that of NGC 6334.