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We present the characterization and calibration of the Slow-Scan observation mode of the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The FIS, one of the two focal-plane instruments on AKARI, has four photometric bands between 50–180$\mu$m with two types of Ge:Ga array detectors. In addition to the All-Sky Survey, FIS has also taken detailed far-infrared images of selected targets by using the Slow-Scan mode. The sensitivity of the Slow-Scan mode is one to two orders of magnitude better than that of the All-Sky Survey, because the exposure time on a targeted source is much longer. The point spread functions (PSFs) were obtained by observing several bright point-like objects, such as asteroids, stars, and galaxies. The derived full widths at the half maximum (FWHMs) are $\sim$30$^{\prime\prime}$for the two shorter wavelength bands and $\sim$40$^{\prime\prime}$for the two longer wavelength bands, being consistent with those expected by optical simulation, although a certain amount of excess is seen in the tails of the PSFs. A flux calibration was performed by observations of well-established photometric calibration standards (asteroids and stars) over a wide range of fluxes. After establishing the method of aperture photometry, the photometric accuracy for point-sources is better than $\pm$15% in all of the bands, expect for the longest wavelength.

We have developed an imaging Fourier transform spectrometer (FTS) for space-based far-infrared astronomical observations. The FTS employs newly developed photoconductive detector arrays with a capacitive trans-impedance amplifier, which makes the FTS a completely unique instrument. The FTS was installed as a function of the far-infrared instrument (FIS: Far-Infrared Surveyor) aboard the Japanese astronomical satellite, AKARI, which was launched on 2006 February 21 (UT) from Uchinoura Space Center. The FIS-FTS had been operated for more than one year before liquid helium ran out on 2007 August 26. The FIS-FTS was operated nearly six hundreds times, which corresponds to more than one hundred hours of astronomical observations and almost the same amount of time for calibrations. As expected from laboratory measurements, the FIS-FTS performed well and has produced a large set of astronomical data for valuable objects. Meanwhile, it has become clear that the detector transient effect is a considerable factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the FIS-FTS and interesting phenomena related to FTS using photoconductive detectors are described, and future applications of this kind of FTS system are discussed.

AKARI, the Japanese infrared astronomical satellite, was launched on 2006 February 21 (UT) and put into a sun-synchronous polar orbit at an altitude of 700 km. Cosmic radiations, particularly protons in the South Atlantic Anomaly (SAA), were expected to affect the performance of the stressed Ge:Ga array far-infrared detector on board AKARI. One of the influences is the radioactivation of the detector housing; ? -rays from the radioactivated detector housing interact with Ge:Ga elements, producing spikes (so-called glitches) in the electric outputs of the detector. Prior to the launch, we performed a 100 MeV proton-beam irradiation test for an engineering model of the stressed Ge:Ga array, which simulated the SAA passage. In the test, we observed glitches in the detector output that were due to the radioactivation of the detector housing. By investigating the test data, we have computed the glitch rate of the flight array detector expected in the AKARIorbit, including its change with time from the launch to the end of the AKARImission. After the launch of AKARI, we have compared the performance observed in the orbit to that predicted by the proton-beam test. The glitch rate really changed with time after the launch; we have found that the in-orbit behavior is consistent with the prediction.

We report initial results of far-infrared observations of the Lockman Hole with Far-Infrared Surveyor onboard the AKARI infrared satellite. On the basis of slow-scan observations of a $0\rlap{.}^{\circ}6 \times 1\rlap{.}^{\circ}2$contiguous area, we obtained source number counts at 65, 90, and 140 $\mu $m down to 77, 26, and 194 mJy (3$\sigma$), respectively. The counts at 65 and 140 $\mu $m show good agreement with the Spitzer results. However, our 90 $\mu $m counts are clearly lower than the predicted counts by recent evolutionary models that fit the Spitzer counts in all the MIPS bands. Our 90 $\mu $m counts above 26 mJy account for about 7% of the cosmic background. These results provide strong constraints on the evolutionary scenario, and suggest that the current models may require modifications.

The nearby face-on spiral galaxy M101 has been observed with the Far-Infrared Surveyor onboard AKARI. The far-infrared four-band images reveal fine spatial structures of M101, which include global spiral patterns, giant H II regions embedded in outer spiral arms, and a bar-like feature crossing the center. The spectral energy distribution of the whole galaxy shows the presence of a cold dust component (18$^{+4}_{-10}$K) in addition to a warm dust component (55$^{+9}_{-25}$K). The distribution of the cold dust is mostly concentrated near the center, and appears to be smoothly distributed over the entire extent of the galaxy, whereas the distribution of warm dust indicates some correlation with the spiral arms, and has spotty structures, such as four distinctive bright spots in the outer disk in addition to a bar-like feature near the center, tracing the CO intensity map. The star-formation activity of the giant H II regions that spatially correspond to the former bright spots is found to be significantly higher than that of the rest of the galaxy. The latter warm dust distribution implies that there are significant star-formation activities in the entire bar filled with molecular clouds. Unlike our Galaxy, M101 is a peculiar normal galaxy with extraordinary active star-forming regions.

Far-infrared (IR) images of the nearby Sb galaxy NGC 2841 and the Sc galaxy NGC 2976 at wavelengths of 65, 90, 140, and 160 $\mu$m have been obtained with the Far-Infrared Surveyor (FIS) onboard AKARI. Both galaxies reveal similar morphologies of dust rings. They are, however, significantly different in the dust temperature: a cold ($\sim$21 K) ring for NGC 2841 and a warm ($\sim$30 K) ring for NGC 2976, which presumably reflects the difference in the origin of the ring structure for the different Hubble types of the galaxy. In addition to the dust-ring structure, a warm dust component was detected from the central region of NGC 2841, which may be attributed to heating by its Low-Ionization Nuclear Emission-line Region nucleus. As for NGC 2976, an extended dust component was observed along the minor axis, which shows a distribution somewhat asymmetrical to the galactic disk; this might be associated with the H I bridge in the M 81/M 82 group that NGC 2976 belongs to. By taking advantage of a wealth of the far-IR bands of the FIS, it has been demonstrated that the spectral energy distribution of NGC 2841 is spatially more variable than that of NGC 2976.

We present the observations of the reflection nebulae IC4954 and IC4955 region with the Infrared Camera and the Far-Infrared Surveyor (FIS) on board the infrared astronomical satellite AKARI during its performance verification phase. We obtained 7 band images from 7 to 160$\mu $m with higher spatial resolution and higher sensitivities than previous observations. The spatial variation in the mid-infrared color suggests that the star-formation in IC4954/4955 is progressing from south-west to north-east. The FIS 4-band data from 65$\mu $m to 160$\mu $m allow us to correctly estimate the total infrared luminosity from the region, which is about one sixth of the energy emitted from the existing stellar sources. Five candidates for young stellar objects have been detected as point sources for the first time in the 11$\mu $m image and it is suggested that that current star-formation has been triggered by previous star-formation activities. A wide area map of the size of about $1^\circ$around the IC4954/4955 region was created from the AKARI mid-infrared All-Sky Survey data. Together with the H I 21 cm data, it suggests a large hollow structure of a degree scale, on whose edge the IC4954/4955 region has been created, indicating star formation over three generations in largely different spatial scales.

We present spatially resolved observations of IRAS sources from the Japanese infrared astronomy satellite AKARI All-Sky Survey during the performance verification phase of the mission. We extracted reliable point sources matched with the IRAS point source catalogue. By comparing IRAS and AKARI fluxes, we found that the flux measurements of some IRAS sources could have been over or underestimated, and affected by the local background, rather than the global background. We also found possible candidates for new AKARI sources and confirmed that AKARI observations resolved IRAS sources into multiple sources. All-Sky Survey observations are expected to verify the accuracies of IRAS flux measurements and to find new extragalactic point sources.

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 $\mu \rm m$, 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.

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.

We present the results of a wide-area mapping of the far-infrared continuum emission toward the Orion complex by using a Japanese balloon-borne telescope. The 155-$\, {\mu \mathrm {m}}$continuum emission was detected over a region of $1.5 \,\mathrm{deg}^2$around the KL nebula with ${3{}^{\mathrm {\prime }}}$resolution similar to that of the IRAS 100-$\, {\mu \mathrm {m}}$map. Assuming a single-temperature model of the thermal equilibrium dust, maps of the temperature and the optical thickness were derived from the 155-$\, {\mu \mathrm {m}}$intensity and the IRAS 100-$\, {\mu \mathrm {m}}$intensity. The derived dust temperature is 5–15 K lower and the derived dust optical depth is 5–300 times larger than those derived from the IRAS 60 and 100-$\, {\mu \mathrm {m}}$intensities due to the significant contribution of the statistically heated very small grains to the IRAS 60-$\, {\mu \mathrm {m}}$intensity. The optical-thickness distribution shows a filamentary dust ridge that has a ${1\rlap {.}{}^{\mathrm {\circ }}5}$extent in the north-south direction and well resembles the Integral-Shaped Filament (ISF) molecular gas distribution. The gas-to-dust ratio derived from the CO molecular gas distribution along the ISF is in the range 30–200, which may be interpreted as being an effect of CO depletion due to the photodissociation and/or the freezing on dust grains.

Abstract

The anomalous microwave emission (AME) still lacks a conclusive explanation. This excess of emission, roughly between 10 and 50 GHz, tends to defy attempts to explain it as synchrotron or free–free emission. The overlap with frequencies important for cosmic microwave background explorations, combined with a strong correlation with interstellar dust, drive cross-disciplinary collaboration between interstellar medium and observational cosmology. The apparent relationship with dust has prompted a “spinning dust” hypothesis. The typical peak frequency range of the AME profile implicates spinning grains on the order of 1 nm. This points to polycyclic aromatic hydrocarbons (PAHs). We use data from the AKARI/Infrared Camera (IRC), due to its thorough PAH-band coverage, to compare AME from the Planck Collaboration astrophysical component separation product with infrared dust emission in the λ Orionis AME-prominent region. We look also at infrared dust emission from other mid-infrared and far-infrared bands. The results and discussion contained here apply to an angular scale of approximately 1°. We find that dust mass certainly correlates with AME, and that PAH-related emission in the AKARI/IRC 9 μm band correlates slightly more strongly. Using hierarchical Bayesian inference and full-dust spectral energy distribution (SED) modeling we argue that AME in λ Orionis correlates more strongly with PAH mass than with total dust mass, lending support for a spinning PAH hypothesis within this region. We emphasize that future efforts to understand AME should focus on individual regions, and a detailed comparison of the PAH features with the variation of the AME SED.

A premature male infant weighing 1,508 g had appendicitis with perforation. Surgical intervention was decided on 9 days after birth because of abdominal signs, an erythematous rash, and the appearance of the abdominal radiograph. Disseminated intravascular coagulation was relieved by an exchange transfusion. Total parenteral nutrition was started 4 days after surgery and continued for 15 days. After 5 days of tube feeding he could take formula orally. He was discharged in good condition 62 days after operation.

We demonstrate the use of the AKARI FIS All-Sky Survey maps in the study of extragalactic objects. A quick but reliable estimate of the Galactic foreground is essential for extragalactic research in general. We explored the galactic foreground and calculated hydrogen column densities using AKARI FIS and other recent all-sky survey data, and compared our results to former estimates. Our AKARI-FIS-based foreground values were then used toward gamma-ray burst (GRB) sources as input for X-ray afterglow spectrum fitting. From those fits the intrinsic column densities at the GRB sources were derived. The high-angular-resolution AKARI-FIS-based Galactic foreground hydrogen column densities are statistically very similar, but for most of the tested directions somewhat lower than previous estimates based on low-resolution data. This is due to the low filling factor of high-density enhancements in all galactic latitudes. Accordingly, our AKARI-FIS-based new intrinsic hydrogen column densities are usually higher or similar compared to the values calculated based, e.g., on the low-resolution Leiden/Argentine/Bonn survey data and listed in the Leicester database. The variation, however, is typically smaller than the error of the estimate from the fits of the X-ray afterglow spectra. There are a number of directions where the improvement of the foreground estimates resulted in an overestimate of magnitude or higher increment of the derived intrinsic hydrogen column densities. We concluded that most of the GRBs with formerly extremely low intrinsic hydrogen column densities are in fact normal, but we confirmed that GRB050233 is indeed a non-enveloped long GRB.

We calculate the accretion mass of interstellar objects (ISOs) like ‘Oumuamua on to low-mass Population III stars (Pop. III survivors), and estimate the surface pollution of Pop. III survivors. The ISO number density estimated from the discovery of ‘Oumuamua is so high (∼0.2 au−3) that Pop. III survivors have chances of colliding with ISOs ≳ 105times per 1 Gyr. ‘Oumuamua itself would be sublimated near Pop. III survivors, since its size is small; ∼100 m. However, ISOs with size ≳3 km would reach the Pop. III survivor surfaces. Supposing an ISO cumulative number density with size larger than Dis n∝D−α, Pop. III survivors can accrete ISO mass ≳10−16M⊙, or ISO iron mass ≳10−17M⊙, if α < 4. This iron mass is larger than the accretion mass of interstellar medium (ISM) by several orders of magnitude. Taking into account material mixing in the convection zone of Pop. III survivors, we find that their surface pollution is typically [Fe/H] ≲ −8 in most cases; however, the surface pollution of Pop. III survivors with 0.8 M⊙can be [Fe/H] ≳ −6 because of the very shallow convective layer. If we consider Pop. III survivors located at the Galactocentric distance of 8 kpc, the dependence of the metal pollution is as follows. If α > 4, Pop. III survivors have no chance at colliding with ISOs with D≳ 3 km, and remain metal-free. If 3 < α < 4, Pop. III survivors would be most polluted by ISOs up to [Fe/H] ∼ −7. If α < 3 up to D∼ 10 km, Pop. III survivors could hide in metal-poor stars so far discovered. Pop. III survivors would be more polluted with decreasing Galactocentric distance. Although the metal pollution depends on α and the Galactocentric distance, we first show the importance of ISOs for the metal pollution of Pop. III survivors.

Zodiacal emission is thermal emission from interplanetary dust. Its contribution to the sky brightness is non-negligible in the region near the ecliptic plane, even in the far-infrared (far-IR) wavelength regime. We analyze zodiacal emission observed by the AKARI far-IR all-sky survey, which covers 97% of the entire sky at arcminute-scale resolution in four photometric bands, with central wavelengths of 65, 90, 140, and 160 μm. AKARI detected small-scale structures in the zodiacal dust cloud, including the asteroidal dust bands and the circumsolar ring, at far-IR wavelengths. Although the smooth component of the zodiacal emission structure in the far-IR sky can be reproduced well by models based on existing far-IR observations, previous zodiacal emission models have discrepancies in the small-scale structures compared with observations. We investigate the geometry of the small-scale dust-band structures in the AKARI far-IR all-sky maps and construct template maps of the asteroidal dust bands and the circumsolar ring components based on the AKARI far-IR maps. In the maps, ± 1$_{.}^{\circ}$4, ± 2$_{.}^{\circ}$1, and ± 10° asteroidal dust-band structures are detected in the 65 μm and 90 μm bands. A possible ± 17° band may also have been detected. No evident dust-band structures are identified in either the 140 μm or the 160 μm bands. By subtracting the dust-band templates constructed in this paper, we can achieve a similar level of flux calibration of the AKARI far-IR all-sky maps in the |β| < 40° region to that in the region for |β| > 40°.

We perform image stacking analysis of Sloan Digital Sky Survey (SDSS) photometric galaxies over the AKARI Far-Infrared Surveyor maps at 65 μm, 90 μm, and 140 μm. The resulting image profiles are decomposed into the central galaxy component (single term) and the nearby galaxy component (clustering term), as a function of the r-band magnitude, mr, of the central galaxy. We find that the mean far-infrared (FIR) flux of a galaxy with magnitude mris well fitted with $f^s_{90\mu {\rm m}}=13\times 10^{0.306(18-m_{\,r})}$[mJy]. The FIR amplitude of the clustering term is consistent with that expected from the angular-correlation function of the SDSS galaxies, but galaxy morphology dependence needs to be taken into account for a more quantitative conclusion. We also fit the spectral energy distribution of stacked galaxies at 65 μm, 90 μm, and 140 μm, and derive a mean dust temperature of ∼30 K. This is consistent with the typical dust temperature of galaxies that are FIR luminous and individually detected.

We present an initial analysis of the properties of an all-sky image obtained by the Far-Infrared Surveyor (FIS) onboard the AKARI satellite, at 65 μm (N60), 90 μm (WIDE-S), 140 μm (WIDE-L), and 160 μm (N160). An absolute flux calibration was determined by comparing the data with COBE/DIRBE data sets; the intensity range was as wide as from a few MJy sr−1to > 1 GJy sr−1. The uncertainties are considered to be the standard deviations with respect to the DIRBE data, and are less than 10% for intensities above 10, 3, 25, and 26 MJy sr−1at the N60, WIDE-S, WIDE-L, and N160bands, respectively. The characteristics of point sources in the image were also determined by stacking maps centred on photometric standard stars. The full width at half maxima of the point spread functions (PSFs) were 63″, 78″, and 88″ at the N60, WIDE-S, and WIDE-Lbands, respectively. The PSF at the N160band was not obtained due to the sensitivity, but it is thought to be the same as that of the WIDE-Lone.

We present a far-infrared all-sky atlas from a sensitive all-sky survey using the Japanese AKARI satellite. The survey covers > 99% of the sky in four photometric bands centred at 65 μm, 90 μm, 140 μm, and 160 μm, with spatial resolutions ranging from 1′ to 1${^{\prime\prime}_{.}}$5. These data provide crucial information on the investigation and characterisation of the properties of dusty material in the interstellar medium (ISM), since a significant portion of its energy is emitted between ∼ 50 and 200 μm. The large-scale distribution of interstellar clouds, their thermal dust temperatures, and their column densities can be investigated with the improved spatial resolution compared to earlier all-sky survey observations. In addition to the point source distribution, the large-scale distribution of ISM cirrus emission, and its filamentary structure, are well traced. We have made the first public release of the full-sky data to provide a legacy data set for use in the astronomical community.

Investigations of the point spread functions (PSFs) and flux calibrations for stacking analysis have been performed with the far-infrared (wavelength range of 60 to 140 μm) all-sky maps taken by the Far-Infrared Surveyor (FIS) on board the AKARI satellite. The PSFs are investigated by stacking the maps at the positions of standard stars with their fluxes of 0.02–10 Jy. The derived full widths at the half maximum (FWHMs) of the PSFs are ∼ 60′′at 65 and 90 μm and ∼ 90′′at 140 μm, which are much smaller than those of the previous all-sky maps obtained with the Infrared Astronomical Satellite IRAS (∼ 6′). Any flux dependence in the PSFs is not seen on the investigated flux range. By performing the flux calibrations, we found that absolute photometry for faint sources can be carried out with constant calibration factors, which range from 0.6 to 0.8. After applying the calibration factors, the photometric accuracies for the stacked sources in the 65, 90, and 140 μm bands are 9%, 3%, and 21%, respectively, even below the detection limits of the survey. No systematic dependence between the observed flux and model flux is found. These results indicate that the FIS map is a useful dataset for the stacking analyses of faint sources at far-infrared wavelengths.