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Nordholt, J.E. et al. (2003) The Genesis solar wind concentrator. Space Sci. Rev. 105, 561-599. Steinberg, J.T. et al. 2005 Suprathermal electrons in high-speed streams from coronal holes: Counterstreaming on open field lines at 1 AU. J. Geophys. Res. 110, A06103. Wiens, R.C. et al. 1991 Solar-wind krypton and solid/gas fractionation in the early solar nebula. Geophys. Res. Lett. 18, 207-210. Wiens, R.C. et al. 1992 A comparison of solar wind and estimated solar system xenon abundances: A test for solid/gas fractionation in the solar nebula. Proc.22nd Lunar Planet. Sci. Conf., pp. 153-159.

Akari – A Light to Illuminate the Dusty Universe [By Takao Nakagawa & Hiroshi Murakami (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency)]

kari, the first Japanese satellite dedicated to infrared astronomy, was launched on 21 February 2006, and

started observations in May of the same year (Murakami et al. 2007). Akari is fitted with a 68.5 cm cooled telescope and two focal-plane instruments which together survey the sky in six wavelength bands from mid- to far-infrared. These instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180 μm in the pointed observation mode, though occasionally inserted into a continuous survey operation. The wide field of view covered by the large-format arrays in the instruments makes Akari highly suitable for efficient surveys. The Akari All-Sky Survey covered more than 90% of the whole sky with a higher spatial resolution and wavelength coverage than was obtained by IRAS. Point-source catalogues of the All-Sky Survey are to be released to the astronomical community in due course.

Akari ran out of liquid helium, its on-board supply of cryogen, on 26 August 2007 after 18 months of successful observations. Akari is now making observations in the near-infrared with mechanical coolers.

There follows an overview of recent scientific results obtained by the Akari mission. Akari and its Scientific Instruments

Figure 1 gives an overall view of the Akari satellite and Table 1 summarizes its specifications. The satellite consists of two main sections: the satellite bus module and the science module. The latter is a cryostat with a cryostatically-cooled telescope and focal-plane instruments. The cryostat, with its sun shield, is mounted on the bus module through carbon-

A

About the Author

Roger Wiens is a Technical Staff Member at Los Alamos National Laboratory. He has been involved with Genesis since its inception, having been the driving force, alongside the PI Don Burnett of Caltech, for proving the feasibility and scientific value of the Genesis mission. He was also the lead Co-I for development of the three Los Alamos instruments built for Genesis. Currently, Dr Wiens is the Principal Investigator on ChemCam, a suite of remote sensing instruments for the Mars Science Laboratory Rover to be launched in 2011. Dr Wiens is pictured above giving an interview for the BBC at the Dugway Proving Grounds in Utah during the Genesis return ‘event’.

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fibre reinforced plastic (CFRP) trusses, and is thereby thermally isolated from the bus module. The satellite bus module includes subsystems that provide such functions as the

power supply, communications, command and data handling, attitude and orbit control, and temperature control and monitoring.

Figure 1. The infrared astronomical satellite Akari in space (left), and on the ground (right).

The Akari liquid-helium cryostat

(Nakagawa et al. 2007) has a very high efficiency rating, providing a long cryogenic lifetime with just a small amount of liquid helium. The actual cooling lifetime in orbit was 550 days with only 179 litres of helium. The helium tank was small enough able to provide room for a large-aperture telescope in the cryostat within the weight and volume limits imposed by the launch vehicle. The high

efficiency was realized by utilizing two-stage Stirling-cycle cryocoolers and efficient radiative cooling. The outer shell of the cryostat was shaded from sunlight by a sun shield, and was cooled down to about 200 K by radiative cooling.

Table 1. Specifications of Akari Size diameter: 2.0 m max.; height (at launch): 3.7 m; height (in orbit), 3.3 m (in observational configuration): width: 5.5. m Mass 952 kg at launch Orbit Sun synchronous polar orbit; 700 km altitude Launch 21 February 2006 by M-V launch vehicle Telescope 68.5 cm effective aperture Cooling Hybrid system with liquid helium and two-stage Stirling-cycle coolers

The Akari telescope system (Kaneda et al. 2007a) is a Ritchey-Chretien type with an effective aperture size of 68.5 cm. Its focal plane is shared between two infrared instruments (see Table 2) and the focal-plane star sensors. The mirror material is of a sandwich construction with silicon carbide (SiC), consisting of a porous SiC core coated with CVD (Chemical Vapour Deposition) SiC. The high stiffness of SiC made it possible to make very light-weight mirrors. The primary mirror, which has a physical diameter of 71 cm, weighs only 11 kg.

One of the focal-plane instruments, the Far-Infrared Surveyor – FIS (Kawada et al. 2007), was designed mainly to perform an All-Sky Survey in four far-infrared wavelength

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bands using Ge-Ga and stressed Ge-Ga photoconductor arrays. The FIS instrument also has a spectroscopic capability with a Fourier-transform spectrometer (Kawada et al. 2008).

The other instrument, the Infrared Camera – IRC (Onaka et al. 2007, Ohyama et al. 2007, Tanabé et al. 2008), consists of three channels: NIR, MIR-S and MIR-L, which cover the 1.8 - 5.5 μm, 4.6 - 13.4 μm and 12.6 - 26.5 μm wavelength ranges, respectively. Each channel has three broad-band filters and additional dispersive elements for spectro-scopy. The IRC was originally designed to perform imaging and spectroscopic obser-vations with large-format array detectors in the pointed observation mode. The IRC was also used for the All-Sky Survey at 9 and 18 μm.

Observational Periods

Akari was launched on 21 February 2006 (UT). The telescope aperture lid was ejected on 13 April 2006, after which AKARI began its observations of the sky. In the performance-verification phase, which lasted for one month after discarding the aperture lid, every instrument was turned on and their basic performances checked. The focus of the telescope was adjusted during this phase (Kaneda et al. 2007a). Observations were then started on 8 May 2006 and were separated into three phases. Phase 1 observations were made in the first six months after the performance-verification phase. Akari performed the first All-Sky Survey during this phase, and also some pointed observations at high ecliptic latitudes. Phase 1 began on 8 May 2006 and ended six months later on 9 November 2006. The second phase began on 10 November 2006 and lasted until 26 August 2007 – the date when the supply of liquid helium ceased. The second All-Sky Survey to increase sky cover-age and make many pointed observations were made during this phase. Akari is now in Phase 3, in which the instrument is cooled by the mechanical cooler following the helium exhaustion and is focused on pointed observations using the IRC/NIR channel.

Table 2. Akari Focal-Plane Instruments FIS: Bands: N60 (65 μm), Wide-S (90 μm), Wide-L (140 μm) and L160 (160 μm)

Pixel scale: 29.5´´ for 65/90 μm; 49.1 for 140/160 μm

Spectroscopic resolution: 9 cm-1

IRC: Bands: NIR 2.4, 3.2, 4.1 μm MIR-S 7.0, 9.0, 11.0 μm MIR-L 15, 18, 24 μm

Pixel scale: 1.46´´ × 1.46´´ for NIR, 2.34´´ × 2.34´´ for MIR-S, 2.51´´ ×2.39´´ for MIR-L Spectroscopic resolution: 0.0097– 0.17 μm

Figure 2. Akari All-Sky map obtained at 9 μm from which the zodiacal emission component has been removed.

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Scientific Results All-Sky Survey results. Akari performed its All-Sky Survey in six wavelength bands in the infrared. More than 90% of the sky was covered with two or more scans. Figure 2 shows a 9 μm image of the All-Sky map obtained by the Akari mission. The bright, horizontal stripe running across the centre is the galactic plane, and the brightest region in the very centre of the image is the centre of our galaxy. The source of the radiation emitted in the several bright regions that can be seen along or close to the galactic plane correspond to active star-forming regions wher dust is heated by newly born stars. A point source catalogue is also being compiled from the All-Sky Survey: the first version of the catalogue of infrared sources is expected to be released in the later part of 2009.

Jeong et al. (2007) undertook a comparison of spatially-resolved observations of IRAS sources from the Akari All-Sky Survey during the performance verification phase of the mission. They extracted reliable point sources and matched these with the IRAS point source catalogue. By comparing IRAS and Akari fluxes, they found that the flux measurements of some IRAS sources could have been over- or under-estimated, and had been affected by the local background rather than the global background. They also found possible candidates for new AKARI sources and confirmed that AKARI observations resolved some IRAS sources into multiple sources. Asteroids. Infrared observations provide us with very important information on various objects in the solar system. For example, the radiometric derivation of estimates for the albedos and diameters of asteroids using thermal-radiation observations is a well-established and powerful technique. Hasegawa et al. (2008) applied this method to the Apollo-type asteroid 162173 1999 JU3. Akari

observed the asteroid during its close Earth approach. A thermophysical model analysis of the data obtained gave an estimate for the radiometric diameter of the asteroid of 0.92±0.12 km. The model solutions are connected to high thermal inertia values, indicated that the surface of the asteroid is predominantly covered by boulders and bare rocks, while areas with a regolith of thick dust are less common. Evolved Stars and the Mass-Loss Process. The mass-loss process, which dominates the evolution of stars is still a poorly understood phenomenon. It is believed that the process is the source of dust formation. Globular clusters are well suited for a study of this process because they contain enough examples of evolved stars at almost the same stage of evolution. Ita et al. (2007) observed two globular clusters, NGC 104 and NGC 362, with Akari’s infrared camera. They used the flux density ratio from the IRC at 11.0 µm compared with that of the 2MASS survey of Ks at 2 µm (F11/F2) and the IRC 24.0 µm to 7.0 µm flux-density ratio (F24/F7) as diagnostics of circumstellar dust emission. 2MASS is the Two Micron All Sky Survey which was performed in the period 1997-2001. Dust emissions were detected mainly from variable stars, obviously on the asymptotic giant branch, but some variable stars that reside below the tip of the first-ascending giant branch also showed dust emissions. They found eight red sources with the F24/F7 ratio being greater than unity in NGC 362. Six out of the eight had no 2MASS counterparts. However, they found no such source in NGC 104.

In searching for emissions from the cold dust within globular clusters, Matsunaga et al. (2008) observed 12 globular clusters with the FIS. They detected diffuse emissions towards NGC 6402 and 2808. However, for most of the other clusters, they confirmed the lack of intracluster dust. They evaluated the upper limits of the intracluster dust mass to be

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between 10−5 and 10−3 M depending on the dust temperature. The lifetime of the intracluster dust inferred from the upper limits is shorter than 5 Myr (Td = 70 K) or 50 Myr (35 K). Such a short lifetime indicates that some mechanism(s) is (are) at work that remove the intracluster dust.

As the stellar wind is expected to interact with the local interstellar medium (ISM), Ueta et al. (2008) examined maps from scans around an M supergiant αOri at 65, 90, 140 and 160 μm obtained from Akari. The higher spatial resolution data with clearly showed the shape of the stellar wind bow shock around αOri. The shape of the bow shock allowed the relative motion of αOri in the local interstellar medium to be derived. AKARI images also reveal a vortex ring due to instabilities on the surface of the bow shock as suggested by numerical models. This research exemplifies the potential of AKARI all-sky data for this line of research in revealing the nature of interactions between the stellar wind and the interstellar medium.

Supernovae and dust formation. Supernova (SN) explosions play an important role in the evolution of the interstellar medium (ISM) by generating strong shocks which heat and accelerate the medium and destroy dust grains. A significant number of dust grains may also be formed in the SN ejecta. Infrared (IR) observations can significantly improve our understanding of the physical processes associated with dust grains, because they essentially only radiate in the IR. Koo et al. (2007) reported the serendipitous detection of the infrared-bright supernova remnant (SNR) B0104-72.3 in the Small Magellanic Cloud by the IRC on Akari. This represented the first detection of an SNR shell in this near/mid-infrared waveband in the Small Magellanic

Cloud. The IRC colour indicated that the infrared emission might be from shocked H2 molecules with some possible contributions from ionic lines.

Figure 3. The three colour composite image of Betelgeuse and its surroundings derived from images at 65 μm (blue), 90 μm (green) and 140 (red) μm taken by the FIS on Akari. The arc-like structure to the upper left of the star is the bow shock is due to collision with the stellar wind and the interstellar matter in the direction of star’s motion (Ueta et al. 2008).

Seok et al. (2008) made a systematic study of supernova remnants (SNRs) using the IRC survey of the Large Magellanic Cloud (LMC) in five bands centred on 3, 7, 11, 15 and 24 μm. They identified eight SNRs with distinguishable IR emissions, and concluded that the mid-infrared emissions in the five SNRs that showed morphologies similar to the X-rays were dominated by thermal emission from hot dust that had been heated by X-ray emitting plasma.

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Figure 4. Three-colour composite images of eight supernova remnants in the Large Magellanic Cloud from images at 7 μm (blue), 11 μm (green) and 15 μm (red) taken with the IRC (Seok et al. 2008). Contours indicate the intensity of the X-ray emissions observed by the NASA’s Chandra X-ray observatory.

Using the IRC on Akari, Sakon et al. (2009) made observations of the supernova (SN) 2006jc just 200 days after its discovery in the near- to mid-infrared (MIR). The near-infrared (2-5 μm) spectrum of SN 2006jc was found to be well interpreted in terms of the thermal emission from warm amorphous carbon at 800 ± 10 K formed in the SN ejecta. MIR photometric data have shown excess emissions, which are likely to be accounted for by the emission from warm amorphous carbon dust at 320 ± 10 K. This latter dust is expected to have been formed in the mass-loss wind associated with the Wolf-Rayet stellar activity before the SN explosion. The result suggests that a significant amount of dust is condensed in the mass-loss wind prior to the SN explosion.

Star Formation Activity. The study of star formation activity has been one of the most important tasks of infrared astronomy. Akari, with its wide spectral coverage and large-scale mapping capability, has been making significant contributions in this area (e.g., Sato et al. 2008). Takita et al. (2009) reported the fortuitous detection of a mysterious source TYC 3159-6-1 towards the Cygnus-X region using the MIR All-Sky Survey data. Ishihara et al. (2007) observed the reflection nebulae IC 4954 and IC4955 region with the IRC and FIS in seven bands from 7 to 160 μm. The spatial variation in the mid-infrared colour suggests that the star formation in IC4954/4955 is progressing from south-west to north-east. Five candidates for young stellar objects have been detected as point sources for

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Figure 5. Left: Three-colour composite image from 9, 11 and 18 μm data taken by the IRC. Red circles indicate the positions of newly born stars. Right: Two-colour composite image of the surrounding region of the IRC4954/4955 Nebula with 9 and 18 μm data. The brightest region is IC 4954/4955. Notice the dark hollow region in the centre of the image (Ishihara et al. 2007). the first time in the 11 μm image and it is suggested that the current star formation sequence has been triggered by previous star formation activities. A wide-area map created from the Akari mid-infrared All-Sky Survey, together with HI 21 cm data suggest a large hollow structure of degree scale, on the edge of which the IC4954/4955 region has been created, indicating star formation over three generations at largely different spatial scales. Akari also found another type of triggered star-formation activity. Koo et al. (2008) reported the discovery of a star-forming loop around the young, Crab-like supernova remnant (SNR) G54.1+0.3. They concluded that the triggering must have occurred near the end of the progenitor's life, possibly after it had evolved off the main sequence.

Another unique characteristic of Akari is its continuous infrared spectroscopic coverage capability. Shimonishi et al. (2008) conducted a spectroscopic survey of the Large Magellanic Cloud (LMC) with the mission’s IRC. They detected absorption features of H2O ice at 3.05 μm and CO2 ice at 4.27 μm towards

seven massive young stellar objects (YSOs). For the first time, these astronomical objects have been confirmed spectroscopically to be YSOs. Shimonshi and his colleagues 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 massive galactic YSOs (0.17 ± 0.03). They suggested that the strong ultraviolet radiation field and/or the high dust temperature in the LMC might be responsible for the observed high CO2 ice abundance.

The central region of our galaxy is a unique area, and the area contains various important regions for the study of star formation activity. Yasuda et al. (2009) observed the Quintuplet- and Arches-cluster regions in the galactic centre with the Fourier Transform Spectrometer (FTS) of the FIS. The FIS-FTS mapping data revealed differences in the spatial distribution among the far-infrared [OIII], [NII] and [CII] line emissions near the Arches cluster; the emission of an ionic line with a higher ionization potential was closely associated with the Arches cluster. This clearly indicates that UV photons from the Arches

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cluster are ionizing the surface of nearby molecular clouds, and also penetrating deeper to dissociate the cloud. Nearby galaxies. Akari made detailed observations of near-by galaxies and has revealed their nature through its wide spectral coverage. Especially in the shorter wavelength range, Akari has provided essential information on the classification of stars in near-by galaxies. Ita et al. (2008) surveyed the Large Magellanic Cloud employing five imaging filters (3, 7, 11, 15 and 24 μm) with the IRC and detected over 5.9 × 105 near-infrared and 6.4 × 104 mid-infrared point sources. They found a new sequence in the colour-magnitude diagram, which was attributed to red giants with a luminosity fainter than that of the tip of the first red giant branch. They suggested that this sequence was likely to be related to the broad emission feature of aluminium oxide at 11.5 μm.

Akari’s spectroscopic capability over a wide spectral range provides a powerful tool for the study of the nature of the ISM in nearby galaxies. Sakon et al. (2007) made mid-infrared imaging and spectroscopic observations with the IRC of the nearby late-type spiral NGC6946. They observed unidentified infrared (UIR) bands at 6.2, 7.7, 8.6 and 11.2 μm, showing the variation of the relative strength of features in the star forming and inter-arm regions. They suggested that the ratio of the relative strength of these features could be a a powerful tool to measure star formation activity in remote galaxies if the ratios and their variations were properly examined for a large enough set of samples. Kaneda et al. (2007b) presented the near- to mid-infrared (–2.5-13 μm) spectrum of the giant elliptical galaxy NGC 1316 (Fornax A) obtained with the IRC. These researchers showed that NGC 1316 had a peculiar polycyclic aromatic hydrocarbon (PAH) emission spectrum with an unusually high ratio of the emissions at 11.3 μm to those at 7.7 μm and no significant PAH emission feature at 3.3

μm. They detected a strong absorption feature at 4.3 μm, which may be attributed to solid-state CO2 in grain mantles.

Various types of nearby galaxies have been observed with the FIS on Akari, where the FIS’s four-band imaging capability is playing an important role in the study of star formation in these galaxies. In their respective papers, Kaneda et al. (2007c) and Suzuki et al. (2007) have described their FIS observations of nearby spiral galaxies. On the basis of FIS observations of M101, Suzuki et al. (2007) showed that cold dust was mostly concentrated near the centre, and appeared to be smoothly distributed over the entire extent of the galaxy, whereas the distribution of warm dust indicated some correlation with the spiral arms, and had a spotty structure – such as four distinctive bright HII regions in the outer disk. Star formation activity in the four bright HII regions could be promoted by external effects, such as the infall of intergalactic gas.

Kaneda et al. (2008) have reported Akari observations of the elliptical galaxy NGC4589. The spatial distributions of the dust and PAHs resemble each other, both showing significant deviations from the smooth stellar distribution. They extended their observations to the main stellar rotation and the direction of the twisted inner dust lane, thus following the relics of the merger. Kaneda and his colleagues concluded that a large fraction of the dust and PAHs in NGC4589 were likely to have originated from a past merger event.

With Akari’s FIS, Hirashita et al. (2008) observed eight blue compact dwarf galaxies (BCDs) at 160 μm. They found that the typical dust temperature of the BCD sampled was systematically higher than that of normal spiral galaxies. The interstellar rad-iation field estimated from the dust temperature ranged up to 100 times of the galactic value. This confirms the concentrated star forming activity in BCDs. Using the high spatial resolution of FIS observations, Kaneda et al. (2009) demonstrated that the edge-on starburst galaxy NGC 253 clearly had far infrared (FIR)

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Figure 6. Distribution of cold (blue) and warm (red) dust overlaid on the visible (green – showing the distribution of stars) and far-ultra violet (cyan – indicating the location of young stars) within M101 (Suzuki et al. 2007). dust emission extending into the halo of the galaxy. They identified two filamentary emission structures extending from the galactic disk up to 9 kpc in the northern direction and 6 kpc in the NW direction. From its spatial coincidence with the X-ray plasma outflow, the extended FIR emission is very likely to repres- ent outflowing dust entrained by superwinds. Active Galactic Nuclei and Ultra-luminous Infrared Galaxies. The spectroscopic cap-ability of the IRC with its continuous spectral coverage is particularly suitable for the study of obscured energy sources in ultra-luminous infrared galaxies. Imanishi et al. (2008) made systematic infrared 2.5-5 μm spectroscopic surveys of 45 nearby ultra-luminous infrared galaxies (ULIRGs) at z < 0.3. In roughly half of the observed ULIRGs classified optically as non-Seyferts, they found the signatures of luminous energy sources that produced no PAH emission and/or were more centrally concentrated than the surrounding dust. They interpreted these energy sources as buried AGNs.

The slitless spectroscopic capability of the IRC facilitates very efficient searches for emission-line galaxies. With the IRC, Oyabu et al. (2007) detected an Hα emission line in the

quasar RX J1759.4+6638, at a redshift of 4.3. This was the first spectroscopic detection of an Hα emission line in a quasar beyond z = 4. Galactic Clusters. Environmental factors must have played an important role in the history of galactic evolution. Most of the previous studies of the history of galaxy evolution in cluster of galaxies used optical colour to estimate star forming activity, but this approach could be affected significantly by dust extinction. Hence, wide-field MIR studies of galactic clusters covering the entire structure around a cluster are required to investigate the ‘true’ environmental dependence of the star formation activities of galaxies. Koyama et al. (2008) studied environmental dependence of dusty star forming activity in and around the cluster RXJ1716.4+6708 at z = 0.81 using Akari’s IRC and data from the 8-m Subaru telescope on the Lunar Crater Observation and Sensing Satellite Orbiter (LCROSS). The fraction of 15-μm-detected galaxies in medium-density environments was as high as in the low-density field, despite the fact that the optical colours started to change in medium-density environments. They also found that 15-μm-detected galaxies which had optically red colours (candidates as dusty red

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Figure 7. FIR images of NGC 253 obtained with the Akari FIS in the WIDES band (Kaneda et al. 2009). The contours are drawn at surface brightness levels of 10, 20, 40, 80, 160, 320, 640, 1280 & 2560 MJy str−1. galaxies) and galaxies with high specific star formation rates were also concentrated in the medium-density environment. These results imply that the star forming activity in galaxies in groups and filaments is enhanced due to some environmental effects specific to the medium-density environment (e.g., galaxy-galaxy interaction).

Although high-z clusters are exceed-ingly important objects for astronomical studies, there has been a missing link at 1 < z < 2 in the current cluster surveys. This gap was filled by Goto et al. (2008) with IRC N4 (4 μm) imaging. They carefully selected 16 promising cluster candidates at 0.9 < z < 1.7, which all showed an obvious over-density of galaxies and a prominent redshift sequence. They showed that, statistically speaking, cluster galaxies had lower star formation activity at 0.9 < z < 1.7, thus pushing the epoch for the formation of these galaxy clusters to a higher redshift. Deep Surveys. Akari conducted systematic deep surveys to understand the nature of high-z galaxies. One of these was a deep and wide field survey at near- and mid-infrared covering

a contiguous wavelength coverage (from 2 to 26 μm) in nine bands in the North Ecliptic Pole (NEP) region with the IRC. Wada et al. (2007, 2008) have provided an overview of the NEP-deep survey. On the basis of the data from the NEP-deep survey acquired earlier rather than later, Lee et al. (2007) described the properties of selected sources at 11 μm, Matsuhara et al. (2007) presented the results of optical identifications for 257 mid-infrared sources detected at 15 μm, and Takagi et al. (2007) discussed an initial analysis of data from Akari’s IRC on 18 μm-selected galaxies using all nine photometric bands at 2-24 μm. The differential source counts at 15 μm by Wada et al. (2007) clearly showed that the results were not consistent with non-evolution models; evolution models with some new population (e.g., Pearson 2005) are required to explain the results (see Figure 8).

Akari made a series of deep survey observations also with FIS. Matsuura et al. (2007) reported initial results of far-infrared observations of the Lockman Hole. Their counts at 65 and 140 μm showed good agreement with previous results. However, Akari 90 μm counts were clearly lower than

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the predicted counts by recent evolutionary models that fit the Spitzer counts. Matsuura et al. claimed that results provided strong constraints on the evolutionary scenario, and suggested that current models might require modifications. Summary and Concluding Remarks

The infrared astronomical mission Akari was successfully launched in February 2006, and completed its designated major observation programmes, including the All-Sky Survey, by 26 August 2007 when it ran out of liquid helium. During this period, Akari observed various types of sources from the objects in our solar system to high-z galaxies

as described above. Akari is now conducting a post-helium mission with near-infrared observations including its unique capability for near-infrared spectroscopy with continuous spectral coverage.

Akari is a JAXA project in which ESA has participated in the satellite tracking and telescope pointing operations. Data analysis is being performed in collaboration with the Imperial College London, the Open University, the University of Sussex, the University of Groningen/SRON, and Seoul National University.

The first version of the Akari All Sky catalogue is expected to be published before the end of 2009.

Figure 8. A comparison of Akari IRC 15 μm differential source counts (both raw and corrected for incompleteness) with the surveys carried out by IRAS (shifted from 12 μm), ISO ISOCAM, and Spitzer IRS results. The source counts are normalized to a Euclidian flat universe. A no-evolution model and the contemporary evolutionary model of Pearson (2005) are also plotted for reference (Wada et al. 2007).

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Kawada, M. et al. 2007 The Far-Infrared Surveyor (FIS) for AKARI. Publ. Astron. Soc. Japan, 60, S389-S400. Kawada, M. et al. 2008 Performance of an imaging Fourier Transform Spectrometer with photoconductive detector arrays: An application for the AKARI far-infrared instrument. Publ. Astron. Soc. Japan, 60, S389-S397. Koo, B.C. et al. 2007 AKRI detection of the infrared-bright supernova remnant B0104-72.3 in the Small Magellanic Cloud. Publ. Astron. Soc. Japan, 59, S455-S461. Koo, B.C. et al. 2008 A massive-star forming infrared loop around the Crab-like supernova remnant G54.1+0.3: Post-Main-Sequence Triggered Star Formation?, Astrophys. J., 673, L147-L150. Koyama, Y. et al. 2008 Mapping dusty star formation in and around a cluster at z = 0.81 by wide-field imaging with AKARI. MNRAS, 391, 1758-1770. Lee, H.M. et al. 2007 Nature of infrared sources in 11μm selected sample from early data of the AKARI North Ecliptic Pole Deep Survey. Publ. Astron. Soc. Japan, 59, S529-S542. Matsuhara, H. et al. 2007 Optical identification of 15 μm sources in the AKARI performance verification field toward the North Ecliptic Pole. Publ. Astron. Soc. Japan, 60, S543-S555. Matsunaga, N. et al. 2008 An AKARI search for intracluster dust of globular clusters. Publ. Astron. Soc. Japan, 60, S415-S428. Matsuura, S. et al. 2007 AKARI Far-infrared source counts in the Lockman Hole. Publ. Astron. Soc. Japan, 59, S503-S513. Murakami, H. et al. 2007 The Infrared Astronomical Mission AKARI. Publ. Astron. Soc. Japan, 59, S369-S376. Nakagawa, T. et al. 2007 Flight performance of the AKARI cryogenic system. Publ. Astron. Soc. Japan, 59, S377-S387. Onaka, T. et al. 2007 The Infrared Camera (IRC) for AKARI – Design and imaging performance. Publ. Astron. Soc. Japan, 59, S401-S410. Ohyama, Y. et al. 2007 Near-infrared and mid-infrared spectroscopy with the Infrared Camera (IRC) for AKARI. Publ. Astron. Soc. Japan, 59, S411-S422. Oyabu, S. et al. 2007 Detection of an Hα emission line on a quasar, RX J1759.4+6638, at z = 4.3 with AKARI. Publ. Astron. Soc. Japan, 59, S497-S501.

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Takagi, T. et al. 2007 Multi-wavelength analysis of 18 μm-selected galaxies in the AKARI/Infrared-Camera monitor field towards the North Ecliptic, Pole. Publ. Astron. Soc. Japan, 59, S557-S569.

Pearson, C. 2005 Spitzer and ISO galaxy counts in the mid-infrared. MNRAS, 358, 1417 - 1422. Sakon, I. et al. 2007 Properties of UIR bands in NGC6946 based on mid-infrared imaging and spectroscopy with Infrared Camera on board AKARI. Publ. Astron. Soc. Japan, 59, S483-S459.

Takita, S. et al. 2009 Diffuse 18 μm emission around TYC 3159-6-1 discovered by the AKARI MIR All-Sky Survey. Publ. Astron. Soc. Japan, 61, 291-299.

Sakon, I. et al. 2009 Properties of newly formed dust by SN 2006J based on near- to mid- infrared observation with AKARI. Astrophys. J., 692,546-555.

Tanabé, T. et al. 2008 Absolute photometric calibration of the Infrared Camera (IRC) aboard AKARI. Publ. Astron. Soc. Japan, 60, S375-S388. Sato, Y. et al. 2008 Identification of the exciting

source of CO outflow in the star formation region GGD 12-15. Publ. Astron. Soc. Japan, 60, S429-S433.

Ueta, T. et al. 2008 AKARI/FIS Mapping of the ISM-wind bow shock around α Orionis. Publ. Astron. Soc. Japan, 60,S407-S413. Wada, T. et al. 2007 Infrared Camera (IRC) deep survey in the performance-verification phase. Publ. Astron. Soc. Japan, 60, S515-S528.

Seok, J. Y. et al. 2008 Supernova remnants in the AKARI IRC survey of the Large Magellanic Cloud. Publ. Astron. Soc. Japan, 60, S453-S466.

Wada, T. et al. 2008 AKARI/IRC Deep survey in the north ecliptic pole region. Publ. Astron. Soc. Japan, 60, S517-S529.

Shimonishi, T. et al. 2008 AKARI Near-infrared spectroscopy: detection of H2O and CO2 ices toward young stellar objects in the Large Magellanic Cloud. Astrophys. J., 686, L99-L102. Yasuda, A. et al. 2009 AKARI Far-Infrared

spectroscopic observations of the galactic center region Publ. Astron. Soc. Japan, 61, 511-520.

Suzuki, T. et al. 2007 Spatial distributions of cold and warm interstellar dust in M101 resolved with AKARI/Far-Infrared Surveyor (FIS). Publ. Astron. Soc. Japan, 59, S473-S481.

About the Authors

Hiroshi Murakami is professor at the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). He is the director of Department of Infrared Astrophysics, and the project manager of akari. He earned his PhD degree in Physics in 1980 at Nagoya University.

Takao Nakagawa is professor at the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). He is PI of several Akari observation programmes and is also in charge of the Akari cryogenics. He earned his PhD degree in Astronomy in 1988 at the University of Tokyo.