We use the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) project as a template to demonstrate how deep spectrophotometric surveys covering large cosmological volumes over extended fields (1– $15\, \rm{deg^2}$ ) with a mid-IR imaging spectrometer (17– $36\, \rm{\rm{\upmu m}}$ ) in conjunction with deep $70\, \rm{\rm{\upmu m}}$ photometry with a far-IR camera, at wavelengths which are not affected by dust extinction can answer the most crucial questions in current galaxy evolution studies. A SPICA-like mission will be able for the first time to provide an unobscured three-dimensional (3D, i.e. x, y, and redshift z) view of galaxy evolution back to an age of the universe of less than $\sim$ 2 Gyrs, in the mid-IR rest frame. This survey strategy will produce a full census of the Star Formation Rate (SFR) in the universe, using polycyclic aromatic hydrocarbons (PAH) bands and fine-structure ionic lines, reaching the characteristic knee of the galaxy luminosity function, where the bulk of the population is distributed, at any redshift up to $z \sim 3.5$ . Deep follow-up pointed spectroscopic observations with grating spectrometers onboard the satellite, across the full IR spectral range (17– $210\, \rm{\rm{\upmu m}}$ ), would simultaneously measure Black Hole Accretion Rate (BHAR), from high-ionisation fine-structure lines, and SFR, from PAH and low- to mid-ionisation lines in thousands of galaxies from solar to low metallicities, down to the knee of their luminosity functions. The analysis of the resulting atlas of IR spectra will reveal the physical processes at play in evolving galaxies across cosmic time, especially its heavily dust-embedded phase during the activity peak at the cosmic noon ( $z \sim 1$ –3), through IR emission lines and features that are insensitive to the dust obscuration.

We have examined the relationship between star formation and polycyclic aromatic hydrocarbons (PAHs) by fitting the spectral energy distributions (SED) of AKARI selected galaxies. PAHs are excited by the ultraviolet (UV) photons of young stars and can trace star formation in galaxies, but they are disassociated by the strong UV radiation in starbursts. AKARI covered the mid-infrared, where the PAHs emit their radiation, with a high density of photometric bands. These observations allow us to estimate the star formation rate and the PAH mass fraction of the dust in galaxies. In the future the James Webb Space Telescope (JWST) will also make measurements in this wavelength range. This research can therefore be considered as a pathfinder to similar studies that will come later from JWST observations.

We have detected [C I] 3P1–3P0 emissions in the gaseous debris disks of 49 Ceti and β Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C I] are found to resemble those of CO(J=3–2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks, and is likely formed by the photodissociation of CO. Assuming an optically thin [C I] emission with the excitation temperature ranging from 30 to 100 K, the column density of C is evaluated to be (2.2 ± 0.2) × 1017 and (2.5 ± 0.7) × 1016 cm−2 for 49 Ceti and β Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 ± 19 and 69 ± 42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H2 molecules in the gas disk; i.e., there is an appreciable contribution of secondary gas from dust grains.

With AKARI, we have performed a systematic study of interstellar dust grains in various environments of galaxies. In many cases, the IR emission of dust is an important tool to trace star-forming activities in galaxies. However it is much more than just star-formation tracers. AKARI has revealed the detailed properties of dust grains in regions not relevant to star formation as well, some of which are found not to follow our old empirical knowledge. Because of its unique capabilities, such as near- and far-IR spectroscopy, and all-sky coverage, AKARI has provided new knowledge on the processing of carbonaceous grains including polycyclic aromatic hydrocarbons. We present the latest results obtained from our AKARI observations of the ISM in our Galaxy and nearby galaxies.

Many elliptical galaxies possess an appreciable amount of X-ray-emitting hot plasma, providing a harsh interstellar environment for the survival of dust grains and polycyclic aromatic hydrocarbons (PAHs). Despite such a hostile environment, it has been found that a significant fraction of X-ray elliptical galaxies contain a considerable amount of dust, which cannot be explained solely from replenishment by old stars. Some of them even show the presence of PAHs. We present the results of AKARI and Spitzer observations of dust and PAHs in X-ray elliptical galaxies. We investigate their possible origins and discuss the implications of their presence for the evolution of elliptical galaxies.

Stephan's Quintet (SQ, HCG92) is a well studied compact group of galaxies with a disturbed intergalactic medium (IGM). An “intruder” galaxy NGC 7318b is currently colliding with the IGM at a relative velocity of 1000 km s−1, causing a large-scale shock front. We observed SQ with the Far-Infrared Surveyor (FIS) aboard AKARI in four far-infrared (far-IR) bands at 65, 90, 140, and 160μm. The 160μm image clearly shows an additional peak of emission overlying structure extending in the North-South direction along the shock ridge seen in the 140μm band, and in H2 and X-ray emission. Whereas most of the far-IR emission in the shocked region is from cold dust (20 K), the [CII]158μm emission - whose luminosity is comparable to that of the warm H2 gas - can significantly contribute to the single peak emission in the 160μm band. We conclude that the [CII] line emission comes from the warm H2 gas in the shock. Our result represents the first detection of shock-excited [CII] line emission.

Using the reconstructed imaging data obtained with the Infrared Camera (IRC) on board AKARI, mid-infrared (MIR; 5-30 μm) emission characteristics of the superwind galaxy M82 are studied. The MIR images at four wavelengths (7, 11, 15, and 24 μm) show extended (out to distances of 4 kpc) emission mainly from polycyclic aromatic hydrocarbons (PAHs). The MIR SED of M82 halo is surprisingly constant. Using far-infrared imaging data obtained by Herschel/SPIRE, we reveal that the PAH abundance relative to the big (sub-micron sized) grains radially increases by about a factor of three. These results imply that PAHs may be formed in small and dense molecular clumps in the halo and efficiently supplied to the intergalactic space by the galactic superwind.

We investigate the infrared emission bands from Polycyclic Aromatic Hydrocarbons (PAHs) in Galactic planetary nebulae (PNe). PAHs in PNe are assumed to be in transition from circumstellar to interstellar PAHs. We select 15 evolved PNe taking account of effective stellar temperatures and obtain infrared spectra of PNe from AKARI (2.5–5 μm) and Spitzer (5–14 μm) observations. Their evolutionary phase is estimated using [SIV]10.51/[NeII]12.81. We find that the near-infrared PAH bands are significantly enhanced along with stellar evolution sequence. We also find that the ratio of 3.4 to 3.3 μm bands is enhanced. The enhancement might indicate some chemical processing, such as hydrogenation, on small PAHs.

We present the first results of the AKARI Infrared Camera near-infrared spectroscopic survey of the Large Magellanic Cloud (LMC). The circumstellar material of young stellar objects (YSOs) are affected by galactic environments such as a metallicity or radiation field. Ices control the chemical balance of circumstellar environments of embedded YSOs. We detected absorption features of the H2O ice 3.05 μm and the CO2 ice 4.27 μm stretching mode toward seven massive YSOs in the LMC. This is the first detection of the 4.27 μm CO2 ice feature toward extragalactic YSOs. The present samples are for the first time spectroscopically confirmed to be YSOs. We used a curve-of-growth method to evaluate the column densities of the ices and derived the CO2/H2O ratio to be 0.45±0.17. This is clearly higher than that seen in Galactic massive YSOs (0.17±0.03). We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC may be responsible for the observed high CO2 ice abundance.

We have carried out the mid-infrared slit spectroscopic observations of sources in the LMC and in NGC 6946 with AKARI/IRC. We investigate the properties of the UIR bands in terms of the star forming activities. We find systematically larger ratios of UIR bands in 6–9 μm to 11.2 μm band in active star forming regions than in the quiet regions. This behavior is consistent with the photo-ionization model of PAHs. Our results suggest that the ratios of UIR bands in 6–9 μm to 11.2 μm band can be used as more efficient and vigorous tools to measure the extent of on-going star formation in remote galaxies rather than just the presence or absence of the features themselves.

The unidentified infrared (UIR) emission bands in the near- to mid-infrared are thought to originate from organic compounds in the interstellar medium. Recent space observations with Spitzer and AKARI have clearly revealed that the UIR bands are commonly seen in external galaxies, including elliptical galaxies, except for very metal-poor dwarf galaxies. They are also detected in extended structures of galaxies, such as extra-planar components and filaments produced by outflows, suggesting that the band carriers are ubiquitous organic compounds in galaxies. Since the UIR bands are prominent features in the infrared spectrum of galaxies and are linked to the star-formation activity, it is highly important to understand the nature, formation, processing, and destruction of the UIR band carriers in galaxies. While there is no systematic variation detected in the UIR spectrum in normal galaxies, significantly low values are derived for the ratio of the 7.7 μm to 11.2 μm bands in elliptical galaxies as well as in galaxies with low-luminosity AGNs compared to normal star-forming galaxies. Relatively low band ratios are also seen in the UIR band spectrum of extended structures in galaxies. If the same mechanism leads to the low band ratio, it would provide important information on the band carrier properties. It should also be noted that the band carriers are believed to be destroyed in a short time scale in environments where low band ratios are detected. The survival and supply processes in these environments are a key to understand the nature of the band carriers.

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.

SPICA is a cooled, single large-mirror space-telescope, which is under discussion as an succsesor of the ASTRO-F mission. One of the most ambitious challenges of the SPICA mission is the direct observations of exoplanets with a coronagraph instrument. We report cryogenic infrared optics to realize high quality wavefronts for the SPICA coronagraph.

The SPICA satellite will be launched by an H-IIA rocket to Sun-Earth L2 Halo orbit early in the 2010s. The SPICA telescope is a Ritchey-Chretien optics with 3.5m diameter primary mirror, and cooled down to 4.5 K in orbit by radiation cooling and mechanical cryo-coolers. Main working wavelengths are 5–200 micron. Advantages of the SPICA coronagraph are the infrared wavelenths where the contrast between planets and central stars are smaller than the optical wavelengths, and that the cooled space telescope consists of monolithic mirrors.

Development of light-weight cooled telescope is one of the most important tasks to realize SPICA. At the present, sintered SiC and carbon fiber reinforced SiC (C/SiC) composite are candidate materials for the mirrors, truss, and optical bench. For these materials, estimations and improvements of basic property and surface roughness in cryogenic temperatures have been carried out. Deformation of trial product mirrors by cooling is also examined.

We are developing cryogenic deformable mirrors (DMs) because wave front accuracy of the SPICA telescope is 0.35 micron RMS, which is not enough for our coronagraphic instrument. For MEMS (Micro Electro Mechanical System) DM and some others, measurements of thermal deformation by cooling, electrical response, and heat generation are undergoing. Developments of a tip-tilt system for cryogenic usage started to cancel vibration caused by the cryo-coolers and other components and to realize a diffraction limit resolution. The first result of our binary mask coronagraph experiment is also shown.