Spitzer/IRS Full Spectral Modeling to Characterize Mineralogical Properties of Silicate Dust in Heavily Obscured AGNs


Simulations of the spectral resolving power of a compact space-borne immersion-echelle spectrometer using mid-infrared wave tracing

Journal of Astronomical Telescopes, Instruments, and Systems


Infrared Absorption and Its Sources of CdZnTe at Cryogenic Temperature


Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915 NW with Velocity Decomposition of CO Rovibrational Absorption Lines


The role of SPICA-like missions and the Origins Space Telescope in the quest for heavily obscured AGN and synergies with Athena

Publications of the Astronomical Society of Australia


A systematic study of silicate absorption features in heavily obscured AGNs observed by Spitzer/IRS


[CII] emission properties of the massive star-forming region RCW 36 in a filamentary molecular cloud

 Aims: We investigate the properties of [C II] 158 μm emission of RCW 36 in a dense filamentary cloud.
 Methods: [C II] observations of RCW 36, covering an area of ~30' × 30', were carried out with a Fabry-Pérot spectrometer on board a 100-cm balloon-borne far-infrared (IR) telescope with an angular resolution of 90''. Using AKARI and Herschel images, we compared the spatial distribution of the [C II] intensity with the emission from the large grains and polycyclic aromatic hydrocarbon (PAH).
 Results: The [C II] emission is in good spatial agreement with shell-like structures of a bipolar lobe observed in IR images, which extend along the direction perpendicular to the direction of cold dense filament. We found that the [C II]-160 μm relation for RCW 36 shows a higher brightness ratio of [C II]/160 μm than that for RCW 38, while the [C II]-9 μm relation for RCW 36 is in good agreement with that for RCW 38.
 Conclusions: Via a spectral decomposition analysis on a pixel-by-pixel basis using IR images, the [C II] emission is spatially well correlated with PAH and cold dust emissions. This means that the observed [C II] emission predominantly comes from photo-dissociation regions. Moreover, the L[C II]/LFIR ratio shows large variation (10-2-10-3), as compared with the L[C II]/LPAH ratio. In view of the observed tight correlation between L[C II]/LFIR and the optical depth at λ = 160 μm, the large variation in L[C II]/LFIR can be simply explained by the geometrical effect, that is, LFIR has contributions from the entire dust-cloud column along the line of sight, while L[C II] has contributions from far-UV illuminated cloud surfaces. Based on the picture of the geometry effect, the enhanced brightness ratio of [C II]/160 μm is attributed to the difference in gas structures where massive stars are formed: filamentary (RCW 36) and clumpy (RCW 38) molecular clouds; thus suggesting that RCW 36 is dominated by far-UV illuminated cloud surfaces, as compared with RCW 38.


How Does the Polar Dust Affect the Correlation between Dust Covering Factor and Eddington Ratio in Type 1 Quasars Selected from the Sloan Digital Sky Survey Data Release 16?

We revisit the dependence of the covering factor (CF) of dust torus on physical properties of active galactic nuclei (AGNs) by taking into account an AGN polar dust emission. The CF is converted from a ratio of infrared (IR) luminosity contributed from AGN dust torus ( ${L}_{athrm{IR}}^{athrm{torus}}$ ) and AGN bolometric luminosity (Lbol), by assuming a nonlinear relation between luminosity ratio and intrinsic CF. We select 37,181 type 1 quasars at z < 0.7 from the Sloan Digital Sky Survey Data Release 16 quasar catalog. Their Lbol, black hole mass (MBH), and Eddington ratio (λEdd) are derived by spectral fitting with QSFit. We conduct spectral energy distribution decomposition by using X-CIGALE with a clumpy torus and polar dust model to estimate ${L}_{athrm{IR}}^{athrm{torus}}$ without being affected by the contribution of stellar and AGN polar dust to IR emission. For 5752 quasars whose physical quantities are securely determined, we perform a correlation analysis on CF and (i) Lbol, (ii) MBH, and (iii) λEdd. As a result, anticorrelations for CF-Lbol, CF-MBH, and CF-λEdd are confirmed. We find that incorporating the AGN polar dust emission makes those anticorrelations stronger compared to those without considering it. This indicates that polar dust wind probably driven by AGN radiative pressure is one of the key components to regulate obscuring material of AGNs.


Hydrogen recombination near-infrared line mapping of Centaurus A with IRSF/SIRIUS

Centaurus A (Cen A) is one of the most famous galaxies hosting an active galactic nucleus (AGN), where the interaction between AGN activities and surrounding interstellar and intergalactic media has been investigated. Recent studies reported detections of Hα emission from clouds in the galactic halo toward the northeast and southwest of the nucleus of Cen A, suggesting that AGN jets may have triggered star formation there. We performed near-infrared line mapping of Cen A with the IRSF 1.4 m telescope, using the narrow-band filter tuned for Paβ, from which we find that Paβ emission is not detected significantly from either of the northeast or southwest regions. The upper limit of the Paβ/Hα ratio in the northeast region is compatible with that expected for a typical H II region, in line with the scenario that AGNs have triggered star formation there. On the other hand, the upper limit of Paβ/Hα in the southwest region is significantly lower than that expected for a typical H II region. A possible explanation of the low Paβ/Hα ratio in the southwest region is the scattering of Hα and Paβ photons from the center of Cen A by dust grains in the halo clouds. From the upper limit of Paβ/Hα in the southwest region, we obtain constraints on the dust size distribution, which is found to be compatible with those seen in the interstellar medium of our Galaxy.

Publications of the Astronomical Society of Japan


Search for Optically Dark Infrared Galaxies without Counterparts of Subaru Hyper Suprime-Cam in the AKARI North Ecliptic Pole Wide Survey Field

We present the physical properties of AKARI sources without optical counterparts in optical images from the Hyper Suprime-Cam (HSC) on the Subaru telescope. Using the AKARI infrared (IR) source catalog and HSC optical catalog, we select 583 objects that do not have HSC counterparts in the AKARI North Ecliptic Pole wide survey field (∼5 deg2). Because the HSC limiting magnitude is deep (gAB ∼ 28.6), these are good candidates for extremely red star-forming galaxies (SFGs) and/or active galactic nuclei (AGNs), possibly at high redshifts. We compile multiwavelength data out to 500 μm and use them for fitting the spectral energy distribution with CIGALE to investigate the physical properties of AKARI galaxies without optical counterparts. We also compare their physical quantities with AKARI mid-IR selected galaxies with HSC counterparts. The estimated redshifts of AKARI objects without HSC counterparts range up to z ∼ 4, significantly higher than for AKARI objects with HSC counterparts. We find that (i) 3.6 - 4.5 μm color, (ii) AGN luminosity, (iii) stellar mass, (iv) star formation rate, and (v) V-band dust attenuation in the interstellar medium of AKARI objects without HSC counterparts are systematically larger than those of AKARI objects with counterparts. These results suggest that our sample includes luminous, heavily dust-obscured SFGs/AGNs at z ∼ 1-4 that are missed by previous optical surveys, providing very interesting targets for the coming era of the James Webb Space Telescope.


A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel. II. Spatial distributions of dust components around the bubbles

Galactic infrared (IR) bubbles, which can be seen as shell-like structures at mid-IR wavelengths, are known to possess massive stars within their shell boundaries. In our previous study (Hanaoka, 2019, PASJ, 71, 6), we expanded the research area to the whole Galactic plane (0° ? l ? 360°, |b| ? 5°) and studied systematic differences in the shell morphology and the IR luminosity of the IR bubbles between inner and outer Galactic regions. In this study, utilizing high spatial- resolution data of AKARI and WISE in the mid-IR and Herschel in the far- IR, we investigate the spatial distributions of dust components around each IR bubble to discuss the relation between the star-formation activity and the dust properties of the IR bubbles. For the 247 IR bubbles studied in Hanaoka (2019, PASJ, 71, 6), 165 IR bubbles are investigated in this study, which have the Herschel data (|b|? 1°) and known distances. We created their spectral energy distributions on a pixel-by-pixel basis around each IR bubble, and decomposed them with a dust model consisting of polycyclic aromatic hydrocarbons (PAHs), hot dust, warm dust and cold dust. As a result, we find that the offsets of dust heating sources from the shell centers in inner Galactic regions are systematically larger than those in outer Galactic regions. Many of the broken bubbles in inner Galactic regions show large angles between the offset and the direction of the broken shell from the center. Moreover, the spatial variations of the PAH intensity and cold dust emissivity around the IR bubbles in inner Galactic regions are larger than those in outer Galactic regions. We discuss these results in light of the interstellar environments and the formation mechanism of the massive stars associated with the IR bubbles.


Near- to mid-infrared spectroscopy of the heavily obscured AGN LEDA 1712304 with AKARI/IRC

Context. Although heavily obscured active galactic nuclei (AGNs) have been found by many observational studies, the properties of the surrounding dust are poorly understood. Using AKARI/IRC spectroscopy, we discovered a new heavily obscured AGN in LEDA 1712304 which shows a deep spectral absorption feature due to silicate dust. Aims: We study the infrared (IR) spectral properties of circumnuclear silicate dust in LEDA 1712304. Methods: We performed IR spectral fitting, considering silicate dust properties such as composition, porosity, size, and crystallinity. Spectral energy distribution fitting was also performed on the flux densities in the UV to submillimeter range to investigate the global spectral properties. Results: The best-fit model indicates 0.1 μm-sized porous amorphous olivine (Mg2xFe2-2xSiO4; x = 0.4) with 4% crystalline pyroxene. The optical depth is τsil ? 2.3, while the total IR luminosity and stellar mass are estimated to be LIR = (5 ± 1)×1010 L? and Mstar = (2.7 ± 0.8)×109 M?, respectively. In such low LIR and Mstar ranges, there are few galaxies that show such a large τsil. Conclusion. The silicate dust in the AGN torus of LEDA 1712304 has properties that are notably similar to those in other AGNs overall, but slightly different in the wing shape of the absorption profile. The porosity of the silicate dust suggests dust coagulation or processing in the circumnuclear environments, while the crystallinity suggests that the silicate dust is relatively fresh.


The interplay between active galactic nuclei and star formation activities of type 1 active galactic nuclei probed by polycyclic aromatic hydrocarbon 3.3 μm emission feature with AKARI

We investigate the connection between active galactic nucleus (AGN) and star formation activities of AGN host galaxies by studying the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature of 79 type 1 AGNs using the AKARI space telescope. Utilizing the slitless spectroscopic capability of the AKARI Infrared Camera, we obtained the spectra in the wavelength range of 2-5 μm from extended regions of the sample galaxies in order to measure star formation activity from the entire host galaxies. We detected the 3.3 μm PAH emission feature from 18 sample galaxies and measured the luminosities of the feature (LPAH3.3). We found that LPAH3.3 is significantly correlated with AGN luminosities (LAGN), such as 5100 ? monochromatic luminosity, and X-ray luminosity regardless of host galaxy morphology and radio-loudness. The correlation between LPAH3.3 and LAGN follows LPAH3.3 ∝ LAGN^{0.9}. Therefore we suggest that host galaxies with stronger AGN activities have stronger star formation activities. We also found that the ratios between LPAH3.3 and the bolometric infrared luminosity (LIR) of our sample galaxies are lower than for non-AGN galaxies due to increased LIR. We suggest that this can be attributed to the contribution of AGN to LIR.


Star formation and polycyclic aromatic hydrocarbons in ELAIS N1 galaxies as seen by AKARI

We have examined the relationship between star formation and polycyclic aromatic hydrocarbons (PAHs) in a variety of galaxies. PAHs are excited by the ultraviolet photons of young stars, but they are disassociated by strong UV radiation in starbursts. Therefore their emission (which is in the wavelength range covered by AKARI) can be used as a star formation tracer in main sequence galaxies. We selected our targets in the ELAIS N1 field with AKARI detections, matched them with the Herschel Point Source Catalog, and collected other publicly available photometric data. Their spectral energy distributions (SEDs) were fitted, and several parameters of the galaxies were estimated, e.g., star formation rate (SFR), stellar mass, and the fraction of PAHs compared to dust mass (qPAH), and we examined the relationships between these parameters. The final sample consisted of 48 galaxies, with redshifts from 0.04 to 2.36. The estimated qPAH values were lower on average than typical values in the literature. This could be due to various reasons, such as low metallicity, or ongoing active galactic nucleus or starburst activity. Of our sample, 83% of the objects fell in the star-forming main sequence of galaxies, while only 8% could be considered as starbursts. We found a decreasing qPAH trend with increasing AV and consequently LIR, suggesting the possible presence of compact star-forming regions. We compared the qPAH values with the known relations of the PAH luminosities, but they did not always follow the same trends (SFR, LIR), and showed only slight correlation with the PAH luminosities.


A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel

Galactic infrared (IR) bubbles, which have shell-like structures in the mid-IR wavelengths, are known to contain massive stars near their centers. Infrared bubbles in inner Galactic regions (|l| ? 65°, |b| ? 1°) have so far been studied well to understand the massive star formation mechanisms. In this study, we expand the research area to the whole Galactic plane (0° ? l < 360°, |b| ? 5°), using the AKARI all- sky survey data. We limit our study to large bubbles with angular radii of >1' to reliably identify and characterize them. For the 247 IR bubbles in total, we derived the radii and the covering fractions of the shells, based on the method developed by Y. Hattori et al. (2016, PASJ, 68, 37). We also created their spectral energy distributions, using the AKARI and Herschel photometric data, and decomposed them with a dust model to obtain the total IR luminosity and the luminosity of each dust component, i.e., polycyclic aromatic hydrocarbons (PAHs), warm dust, and cold dust. As a result, we find that there are systematic differences in the IR properties of the bubbles between the inner and outer Galactic regions. The total IR luminosities are lower in outer Galactic regions, while there is no systematic difference in the range of the shell radii between inner and outer Galactic regions. More IR bubbles tend to be observed as broken bubbles rather than closed ones and the fractional luminosities of the PAH emission are significantly higher in outer Galactic regions. We discuss the implications of these results for the massive stars and the interstellar environments associated with the Galactic IR bubbles.


Evaluation of the compensation ratio of heavily-Ga doped Ge for far-infrared detectors in astronomy

Ge-based blocked impurity band detectors fabricated with the surface- activated wafer bonding (SAB) method are expected to realize larger format arrays for far-infrared astronomical observations. To make sensitive p-type Ge detectors, the minor impurity (N D) concentration of a heavily-impurity doped Ge wafers is required to be <1014 cm-3 in addition to the major impurity (N A) concentration of ?1016 cm-3. Thus, a compensation ratio K (= N D/N A) below 10-2 should be achieved in advance to SAB. We measured the resistivity and carrier density of heavily-Ga doped Ge wafers at temperatures of 3-300 K. However, N D and N A of the wafers cannot be obtained from the conventional model for p-type semiconductors due to the significant contribution of the impurity band conduction (IBC). Then, an extended model including the IBC process was constructed, which was found to well reproduce the measured data over the whole temperature range. From the values obtained from the model fitting, it is revealed that our heavily-Ga doped Ge wafers show N A ? 1016 cm-3 with ultra-low K below 10-3.


AKARI mid-infrared slitless spectroscopic survey of star-forming galaxies at z ≲ 0.5

Context. Deep mid-infrared (MIR) surveys have revealed numerous strongly star-forming galaxies at redshift z ? 2. Their MIR fluxes are produced by a combination of continuum and polycyclic aromatic hydrocarbon (PAH) emission features. The PAH features can dominate the total MIR flux, but are difficult to measure without spectroscopy. Aims: We aim to study star-forming galaxies by using a blind spectroscopic survey at MIR wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z ? 0.5, by paying particular attention to their PAH properties. Methods: We conducted a low-resolution (R ? 50) slitless spectroscopic survey at 5-13 μm of 9 μm flux-selected sources (>0.3 mJy) around the north ecliptic pole with the infrared camera (IRC) onboard AKARI. After removing 11 AGN candidates by using the IRC photometry, we identify 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 μm features at z < 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and IRC imaging covering 0.37-18 μm were produced, and analysed in conjunction with the PAH spectroscopy. We defined the PAH enhancement by using the luminosity ratio of the 7.7 μm PAH feature over the 3.5 μm stellar component of the SEDs. Results: The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 μm bumps, except that the PAH enhancement significantly varies as a function of the PAH luminosities. We identify a PAH-enhanced population at z ? 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a very young and optically very thick starburst with a very old population can successfully reproduce most of their SED characteristics, although we cannot confirm this optically think component from our spectral analysis.


SPICA-A Large Cryogenic Infrared Space Telescope: Unveiling the Obscured Universe

Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity.

Publications of the Astronomical Society of Australia


A systematic study of Galactic infrared bubbles along the whole Galactic plane with the AKARI all-sky surveys

Galactic infrared (IR) bubbles are known to contain massive stars near their centers, and crucial to study massive star formation mechanisms. In our previous study (Hattori et al. 2016), IR bubbles located in inner Galactic regions (absolute value of l less than or equal to 65 deg, absolute value of b less than or equal to 1 deg) are classified into broken and closed bubbles, depending on their morphologies, to find that the broken bubbles are indicative of cloud-cloud collision. We expand the previous study to the whole Galactic plane using the AKARI all-sky survey data. We limit our study on large (R greater than 1') bubbles to reliably identify and classify them even in outer Galactic regions and relatively high-latitude regions where neither Spitzer nor Herschel data are available. As a result, we newly discover about 100 Galactic IR bubbles in outer Galactic regions (absolute value of l greater than 65 deg, absolute value of b less than or equal to 5 deg). We find that a significantly higher fraction of bubbles are classified into broken ones in outer Galactic regions than in inner Galactic regions. Following the same procedure as in Hattori et al. (2016), we also examine the properties of the bubbles, decomposing their spectral energy distributions consisting of AKARI and Herschel photometric data with a dust model. In the paper, we show the result of our comparative study on the properties of the Galactic IR bubbles between the inner and outer Galactic regions, and discuss the cause of their systematic difference.

The Cosmic Wheel and the Legacy of the AKARI Archive: From Galaxies and Stars to Planets and Life


A relationship of polycyclic aromatic hydrocarbon features with galaxy merger in star-forming galaxies at z < 0.2

Using the AKARI, Wide-field Infrared Survey Explorer (WISE), Infrared Astronomical Satellite (IRAS), Sloan Digital Sky Survey (SDSS) and Hubble Space Telescope (HST) data, we investigated the relation of polycyclic aromatic hydrocarbon (PAH) mass (MPAH), very small grain mass (MVSG), big grain mass (MBG) and stellar mass (Mstar) with galaxy merger for 55 star-forming galaxies at redshift z < 0.2. Using the SDSS image at z < 0.1 and the HST image at z > 0.1, we divided the galaxies into merger galaxies and non-merger galaxies with the morphological parameter asymmetry A, and quantified merging stages of galaxies based on the morphological indicators, the second-order momentum of the brightest 20 per cent region M20 and the Gini coefficient. We find that MPAH/MBG of merger galaxies tend to be lower than that of non-merger galaxies and there are no systematic differences of MVSG/MBG and MBG/Mstar between merger galaxies and non-merger galaxies. We find that galaxies with very low MPAH/MBG seem to be merger galaxies at late stages. These results suggest that PAHs are partly destroyed at late stages of merging processes. Furthermore, we investigated MPAH/MBG variations in radiation field intensity strength G0 and the emission line ratio of [O I] λ 6300/Hα that is a shock tracer for merger galaxies and find that MPAH/MBG decreases with increasing both G0 and [O I]/Hα. PAH destruction is likely to be caused by two processes: strong radiation fields and large-scale shocks during merging processes of galaxies.

Monthly Notices of the Royal Astronomical Society


SPICA and the Chemical Evolution of Galaxies: The Rise of Metals and Dust

The physical processes driving the chemical evolution of galaxies in the last 11Gyr cannot be understood without directly probing the dust- obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of the star formation and black hole accretion activity in galaxies at 1 < z < 3. Spectroscopic observations with a cryogenic infrared observatory like SPICA, will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-infrared range in galaxies at high-z. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to z 3, and the dust composition of galaxies at high-z. Possible synergies with facilities available in the late 2020s are also discussed.


Galaxy Evolution Studies with the SPace IR Telescope for Cosmology and Astrophysics (SPICA): The Power of IR Spectroscopy

IR spectroscopy in the range 12-230 μm with the SPace IR telescope for Cosmology and Astrophysics (SPICA) will reveal the physical processes governing the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the James Webb Space Telescope and the upcoming Extremely Large Telescopes at shorter wavelengths and the Atacama Large Millimeter Array at longer wavelengths. The SPICA, with its 2.5-m telescope actively cooled to below 8 K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields, and gas-phase metallicities will be measured in dust- obscured galaxies and active galactic nuclei, sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. Active galactic nuclei and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. The SPICA's large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z 6.


Unbiased Large Spectroscopic Surveys of Galaxies Selected by SPICA Using Dust Bands

The mid-infrared range contains many spectral features associated with large molecules and dust grains such as polycyclic aromatic hydrocarbons and silicates. These are usually very strong compared to fine-structure gas lines, and thus valuable in studying the spectral properties of faint distant galaxies. In this paper, we evaluate the capability of low-resolution mid-infrared spectroscopic surveys of galaxies that could be performed by SPICA. The surveys are designed to address the question how star formation and black hole accretion activities evolved over cosmic time through spectral diagnostics of the physical conditions of the interstellar/circumnuclear media in galaxies. On the basis of results obtained with Herschel far-infrared photometric surveys of distant galaxies and Spitzer and AKARI near- to mid-infrared spectroscopic observations of nearby galaxies, we estimate the numbers of the galaxies at redshift z > 0.5, which are expected to be detected in the polycyclic aromatic hydrocarbon features or dust continuum by a wide (10 deg2) or deep (1 deg2) blind survey, both for a given observation time of 600 h. As by-products of the wide blind survey, we also expect to detect debris disks, through the mid-infrared excess above the photospheric emission of nearby main- sequence stars, and we estimate their number. We demonstrate that the SPICA mid-infrared surveys will efficiently provide us with unprecedentedly large spectral samples, which can be studied further in the far-infrared with SPICA.


Ultraviolet to optical diffuse sky emission as seen by the Hubble Space Telescope Faint Object Spectrograph

We present an analysis of the blank-sky spectra observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of zodiacal light (ZL), diffuse Galactic light (DGL), and residual emission. The observations were performed towards 54 fields distributed widely over the sky, with spectral coverage from 0.2 to 0.7 μm. In order to avoid contaminating light from earthshine, we use the data collected only in orbital nighttime. The observed intensity is decomposed into the ZL, DGL, and residual emission, in eight photometric bands spanning our spectral coverage. We found that the derived ZL reflectance spectrum is flat in the optical, which indicates major contribution of C-type asteroids to the interplanetary dust (IPD). In addition, the ZL reflectance spectrum has an absorption feature at ?0.3 μm. The shape of the DGL spectrum is consistent with those found in earlier measurements and model predictions. While the residual emission contains a contribution from the extragalactic background light, we found that the spectral shape of the residual looks similar to the ZL spectrum. Moreover, its optical intensity is much higher than that measured from beyond the IPD cloud by Pioneer 10/11, and also than that of the integrated galaxy light. These findings may indicate the presence of an isotropic ZL component, which is missed in the conventional ZL models.

Publications of the Astronomical Society of Japan


A Quality Check of the Akari Mid-Infrared All-Sky Diffuse Map Toward the Massive Star-Forming Regions NGC 6334 and NGC 6357

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 NANTEN12CO($J$ = 1-- 0) data and the $AKARI$ 9 $u$m All-Sky diffuse map in order to evaluate the calibration accuracy of the $AKARI$ data. We confirm 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 10circimes10circ. 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.

Publications of The Korean Astronomical Society


The Current Status of the Akari Mid-Infrared All-Sky Diffuse Maps


A Source Extraction Method for the Akari Mid-Ir Faint Source Catalogue


Modeling of the Zodiacal Light for the Akari Mid-Ir All-Sky Diffuse Maps


Debris Disks and the Zodiacal Light Explored by the Akari Mid-Infrared All-Sky Survey


Search for Debris Disks by Akari and Irsf


Properties of Dust in Various Environments of Nearby Galaxies


Study of CO2/H2O Ice Abundance Ratios in Nearby Galaxies with the Akari Near-Infrared Spectroscopy


A Systematic Study of Dust in Early-Type Galaxies with Akari


Akari Observations of Dusty Tori of Active Galactic Nuclei


Near-Infrared Spectroscopy of CO Ro-Vibrational Absorption Toward Heavily Obscured AGNs


Infrared - X-Ray Connection in Nearby Active Galactic Nuclei; Akari and MAXI Results


Luminosity Dependence of the Covering Factor of the Dust Torus in Active Galactic Nuclei Revealed by Akari


AKARI Infrared Camera Observations of the 3.3 μm PAH Feature in Swift/BAT AGNs


Overview of North Ecliptic Pole Deep Multi-Wavelength Survey Nep-Deep

The recent updates of the North Ecliptic Pole deep (0.5~deg2, NEP- Deep) multi-wavelength survey covering from X-ray to radio-wave is presented. The NEP-Deep provides us with several thousands of 15~$u$m or 18~$u$m selected sample of galaxies, which is the largest sample ever made at this wavelengths. A continuous filter coverage in the mid- infrared wavelength (7, 9, 11, 15, 18, and 24~$u$m) is unique and vital to diagnose the contributions from starbursts and AGNs in the galaxies out to $z$=2.The new goal of the project is to resolve the nature of the cosmic star formation history at the violent epoch (e.g. $z$=1--2), and to find a clue to understand its decline from $z$=1 to present universe by utilizing the unique power of the multi-wavelength survey. The progress in this context is briefly mentioned.


Hyper Suprime-Camera Survey of the Akari NEP Wide Field

The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z ?1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field (5.4 deg^2), using ?10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r ?25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star- formation rate density (CSFRD). For example, if they all lie at 1 < z < 2, the CSFRD will be twice as high at the epoch. We are carrying out deep imaging of the NEP field in 5 broad bands (g,r,i,z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate mid-IR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust.

Publications of The Korean Astronomical Society


Evaluation of Far-Infrared Bib-Type GE Detectors Fabricated with the Surface-Activated Wafer Bonding Technology


Akari All-Sky Bright Source Catalogue: Far-Infrared Luminous Quasars and the Optical Far-Infrared Correlation


Laboratory Experiments of Off-Axis Mirror Optics of Aluminum for Space Infrared Missions


Spatial Variations of PAH Properties in M17SW Revealed by Spitzer/IRS Spectral Mapping

We present Spitzer/IRS mid-infrared spectral maps of the Galactic star- forming region M17 as well as IRSF/SIRIUS Brγ and Nobeyama 45 m/FOREST 13CO (J = 1-0) maps. The spectra show prominent features due to polycyclic aromatic hydrocarbons (PAHs) at wavelengths of 6.2, 7.7, 8.6, 11.3, 12.0, 12.7, 13.5, and 14.2 μm. We find that the PAH emission features are bright in the region between the H II region traced by Brγ and the molecular cloud traced by 13CO, supporting that the PAH emission originates mostly from photo-dissociation regions. Based on the spatially resolved Spitzer/IRS maps, we examine spatial variations of the PAH properties in detail. As a result, we find that the interband ratio of PAH 7.7 μm/PAH 11.3 μm varies locally near M17SW, but rather independently of the distance from the OB stars in M17, suggesting that the degree of PAH ionization is mainly controlled by local conditions rather than the global UV environments determined by the OB stars in M17. We also find that the interband ratios of the PAH 12.0 μm, 12.7 μm, 13.5 μm, and 14.2 μm features to the PAH 11.3 μm feature are high near the M17 center, which suggests structural changes of PAHs through processing due to intense UV radiation, producing abundant edgy irregular PAHs near the M17 center.


X-ray and infrared diagnostics of nearby active galactic nuclei with MAXI and AKARI

Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far infrared wavelengths with Monitor of All-sky X-ray Image (MAXI) and the Japanese infrared observatory AKARI, respectively. One hundred of the X-ray sources listed in the second release of the MAXI all-sky X-ray source catalog are currently identified as non-blazar-type active galactic nuclei. These include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1 and 27 type-2 objects. The AKARI all-sky survey point source catalog was searched for their mid- and far-infrared counterparts at 9, 18, and 90 μm. As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV) and infrared luminosities of these objects were investigated, together with their color information. Adopting the canonical photon index, Γ = 1.9, of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness ratio between the 3-4 and 4-10 keV ranges derived with MAXI was roughly converted into the absorption column density. After the X-ray luminosity was corrected for absorption from the estimated column density, the well-known X-ray-to-infrared luminosity correlation was confirmed, at least in the Compton-thin regime. In contrast, NGC 1365, the only Compton-thick object in the MAXI catalog, was found to deviate from the correlation toward a significantly lower X-ray luminosity by nearly an order of magnitude. It was verified that the relation between the X-ray hardness below 10 keV and X-ray-to-infrared color acts as an effective tool to pick up Compton-thick objects. The difference in the infrared colors between the type-1 and type-2 Seyfert galaxies and its physical implication on the classification and unification of active galactic nuclei are briefly discussed.

Publications of the Astronomical Society of Japan


Development for Germanium Blocked Impurity Band Far-Infrared Image Sensors with Fully-Depleted Silicon-On-Insulator CMOS Readout Integrated Circuit

We are developing far-infrared (FIR) imaging sensors for low-background and high-sensitivity applications such as infrared astronomy. Previous FIR monolithic imaging sensors, such as an extrinsic germanium photo- conductor (Ge PC) with a PMOS readout integrated circuit (ROIC) hybridized by indium pixel-to-pixel interconnection, had three difficulties: (1) short cut-off wavelength (120 pmu m), (2) large power consumption (10 pmu W/pixel), and (3) large mismatch in thermal expansion between the Ge PC and the Si ROIC. In order to overcome these difficulties, we developed (1) a blocked impurity band detector fabricated by a surface- activated bond technology, whose cut-off wavelength is longer than 160 pmu m, (2) a fully-depleted silicon-on- insulator CMOS ROIC which works below 4 K with 1 pmu W/pixel operating power, and (3) a new concept, Si-supported Ge detector, which shows tolerance to thermal cycling down to 3 K. With these new techniques, we are now developing a 32 × 32 FIR imaging sensor.


Development of Blocked-Impurity-Band-Type Ge Detectors Fabricated with the Surface-Activated Wafer Bonding Method for Far-Infrared Astronomy

We report the current status of the development of our new detectors for far-infrared (FIR) astronomy. We develop Blocked-Impurity-Band (BIB)-type Ge detectors to realize large-format compact arrays covering a wide FIR wavelength range up to 200 pmu m. We fabricated Ge junction devices of different physical parameters with a BIB-type structure, using the room temperature, surface-activated wafer bonding (SAB) method. We measured the absolute responsivity and the spectral response curve of each device at low temperatures, using an internal blackbody source in a cryostat and a Fourier transform spectrometer, respectively. The results show that the SAB Ge junction devices have significantly higher absolute responsivities and longer cut-off wavelengths of the spectral response than the conventional bulk Ge:Ga device. Based upon the results, we discuss the optimum parameters of SAB Ge junction devices for FIR detectors. We conclude that SAB Ge junction devices possess a promising applicability to next-generation FIR detectors covering wavelengths up to ? 200 pmu m with high responsivity. As a next step, we plan to fabricate a BIB-type Ge array device in combination with a low-power cryogenic readout integrated circuit.


A Demonstration of TIA Using FD-SOI CMOS OPAMP for Far-Infrared Astronomy

We are developing a fully depleted silicon-on-insulator (FD-SOI) CMOS readout integrated circuit (ROIC) operated at temperatures below ? 4 K. Its application is planned for the readout circuit of high-impedance far-infrared detectors for astronomical observations. We designed a trans-impedance amplifier (TIA) using a CMOS operational amplifier (OPAMP) with FD-SOI technique. The TIA is optimized to readout signals from a germanium blocked impurity band (Ge BIB) detector which is highly sensitive to wavelengths of up to ? 200 pmu m. For the first time, we demonstrated the FD-SOI CMOS OPAMP combined with the Ge BIB detector at 4.5 K. The result promises to solve issues faced by conventional cryogenic ROICs.


SPICA Mid-infrared Instrument (SMI): technical concepts and scientific capabilities

SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane scientific instruments planned for new SPICA, and the Japanese instrument proposed and managed by a university consortium in Japan. SMI covers the wavelength range of 12 to 36 μm, using the following three spectroscopic channels with unprecedentedly high sensitivities: low- resolution spectroscopy (LRS; R = 50 - 120, 17 - 36 μm), mid-resolution spectroscopy (MRS; R = 1300 - 2300, 18 - 36 μm), and high-resolution spectroscopy (HRS; R = 28000, 12 - 18 μm). The key functions of these channels are high-speed dustband mapping with LRS, high-sensitivity multi-purpose spectral mapping with MRS, and high-resolution molecular- gas spectroscopy with HRS. This paper describes the technical concept and scientific capabilities of SMI.

Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave


A New Sample of Obscured AGNs Selected from the XMM-Newton and AKARI Surveys

We report a new sample of obscured active galactic nuclei (AGNs) selected from the XMM-Newton serendipitous source and AKARI point-source catalogs. We match X-ray sources with infrared (18 and 90 μm) sources located at | b| t 10circ to create a sample consisting of 173 objects. Their optical classifications and absorption column densities measured by X-ray spectra are compiled and study efficient selection criteria to find obscured AGNs. We apply the criteria (1) X-ray hardness ratio defined by using the 2-4.5 keV and 4.5-12 keV bands > -0.1 and (2) EPIC-PN count rate (CR) in the 0.2-12 keV to infrared flux ratio CR/{F}90t 0.1 or CR/{F}18t 1, where F18 and F90 are infrared fluxes at 18 and 90 μm in Jy, respectively, to search for obscured AGNs. X-ray spectra of 48 candidates, for which no X-ray results have been published, are analyzed and X-ray evidence for the presence of obscured AGNs such as a convex shape X-ray spectrum indicative of absorption of {N}{{H}} ? 1022-24 cm-2, a very flat continuum, or a strong Fe-K emission line with an equivalent width of t 700 {{eV}} is found in 26 objects. Six of them are classified as Compton-thick AGNs, and four are represented by either Compton-thin or Compton-thick spectral models. The success rate of finding obscured AGNs combining our analysis and the literature is 92% if the 18 μm condition is used. Of the 26 objects, 4 are optically classified as an H ii nucleus and are new ``elusive AGNs'' in which star formation activity likely overwhelms AGN emission in the optical and infrared bands.


Clustering of the AKARI NEP deep field 24 μm selected galaxies

Aims: We present a method of selection of 24 μm galaxies from the AKARI north ecliptic pole (NEP) deep field down to 150 μJy and measurements of their two-point correlation function. We aim to associate various 24 μm selected galaxy populations with present day galaxies and to investigate the impact of their environment on the direction of their subsequent evolution. Methods: We discuss using of Support Vector Machines (SVM) algorithm applied to infrared photometric data to perform star-galaxy separation, in which we achieve an accuracy higher than 80%. The photometric redshift information, obtained through the CIGALE code, is used to explore the redshift dependence of the correlation function parameter (r0) as well as the linear bias evolution. This parameter relates galaxy distribution to the one of the underlying dark matter. We connect the investigated sources to their potential local descendants through a simplified model of the clustering evolution without interactions. Results: We observe two different populations of star-forming galaxies, at zmed ~ 0.25, zmed ~ 0.9. Measurements of total infrared luminosities (LTIR) show that the sample at zmed ~ 0.25 is composed mostly of local star-forming galaxies, while the sample at zmed ~ 0.9 is composed of luminous infrared galaxies (LIRGs) with LTIR ~ 1011.62 L?. We find that dark halo mass is not necessarily correlated with the LTIR: for subsamples with LTIR = 1011.15 L? at zmed ~ 0.7 we observe a higher clustering length (r0 = 6.21 ± 0.78[ h-1Mpc ]) than for a subsample with mean LTIR = 1011.84 L? at zmed ~ 1.1 (r0 = 5.86 ± 0.69h-1Mpc). We find that galaxies at zmed ~ 0.9 can be ancestors of present day L? early type galaxies, which exhibit a very high r0 ~ 8h-1 Mpc.


Hyper-luminous dust-obscured galaxies discovered by the Hyper Suprime-Cam on Subaru and WISE

We present the photometric properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer, we discovered 48 DOGs with i - Ks > 1.2 and i - [22] > 7.0, where i, Ks, and [22] represent AB magnitude in the i-band, Ks-band, and 22 μm, respectively, in the GAMA 14 hr field (? 9 deg2). Among these objects, 31 (? 65%) show power-law spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show an NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma z = 1.99 ± 0.45, we calculated their total IR luminosity using an empirical relation between 22 μm luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5 ± 1.1) × 1013 L?, which classifies them as hyper-luminous infrared galaxies. We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22 μm flux greater than 3.0 mJy and with i-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log φ = -6.59 ± 0.11 [Mpc-3]. The IR LF for DOGs including data obtained from the literature is fitted well by a double-power law. The derived lower limit for the IR LD for our sample is ϱIR ? 3.8 × 107 [L? Mpc-3] and its contributions to the total IR LD, IR LD of all ultra-luminous infrared galaxies, and that of all DOGs are > 3%, > 9%, and > 15%, respectively.


Coronagraphic Demonstration Experiment Using Aluminum Mirrors for Space Infrared Astronomical Observations

For future space infrared astronomical coronagraphy, we perform experimental studies on the application of aluminum mirrors to a coronagraph. Cooled reflective optics is required for broad-band mid- infrared observations in space, while high-precision optics is required for coronagraphy. For the coronagraph instrument originally proposed for the next-generation infrared astronomical satellite project SPICA (SCI: SPICA Coronagraph Instrument), we fabricated and evaluated the optics consisting of high-precision aluminum off-axis mirrors with diamond- turned surfaces, and conducted a coronagraphic demonstration experiment using the optics with a coronagraph mask. We first measured the wave front errors (WFEs) of the aluminum mirrors with a He-Ne Fizeau interferometer to confirm that the power spectral densities of the WFEs satisfy the SCI requirements. Then we integrated the mirrors into an optical system and evaluated the overall performance of the system. As a result, we estimate the total WFE of the optics to be 33 nm (rms), each mirror contributing 10-20 nm (rms) for the central 14 mm area of the optics, and obtain a contrast of 10-5.4 as a coronagraph in the visible light. At a wavelength of 5 um, the coronagraphic system is expected to achieve a contrast of ~10-7 based on our model calculation with the measured optical performance. Thus our experiment demonstrates that aluminum mirror optics is applicable to a highly WFE- sensitive instrument such as a coronagraph in space.

Publications of the Astronomical Society of the Pacific


Systematic Variations in CO2/H2O Ice Abundance Ratios in Nearby Galaxies Found with AKARI Near-infrared Spectroscopy

We report CO2/H2O ice abundance ratios in seven nearby star-forming galaxies based on the AKARI near-infrared (2.5-5.0 μm) spectra. The CO2/H2O ice abundance ratios show clear variations between 0.05 and 0.2 with the averaged value of 0.14 ± 0.01. The previous study on M82 revealed that the CO2/H2O ice abundance ratios strongly correlate with the intensity ratios of the hydrogen recombination Brα line to the polycyclic aromatic hydrocarbon (PAH) 3.3 μm feature. In the present study, however, we find no correlation for the seven galaxies as a whole due to systematic differences in the relation between CO2/H2O ice abundance and Brα/PAH 3.3 μm intensity ratios from galaxy to galaxy. This result suggests that there is another parameter that determines the CO2/H2O ice abundance ratios in a galaxy in addition to the Brα/PAH 3.3 μm ratios. We find that the CO2/H2O ice abundance ratios positively correlate with the specific star formation rates of the galaxies. From these results, we conclude that CO2/H2O ice abundance ratios tend to be high in young star-forming galaxies.


The AKARI 2.5-5.0 μm Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature

We present 2.5-5.0 μm spectra of 83 nearby (0.002 < z < 0.48) and bright (K < 14 mag) type-1 active galactic nuclei (AGNs) taken with the Infrared Camera on board AKARI. The 2.5-5.0 μm spectral region contains emission lines such as Brβ (2.63 μm), Brα (4.05 μm), and polycyclic aromatic hydrocarbons (3.3 μm), which can be used for studying the black hole (BH) masses and star formation activity in the host galaxies of AGNs. The spectral region also suffers less dust extinction than in the ultra violet (UV) or optical wavelengths, which may provide an unobscured view of dusty AGNs. Our sample is selected from bright quasar surveys of Palomar-Green and SNUQSO, and AGNs with reverberation-mapped BH masses from Peterson et al. Using 11 AGNs with reliable detection of Brackett lines, we derive the Brackett-line-based BH mass estimators. We also find that the observed Brackett line ratios can be explained with the commonly adopted physical conditions of the broad line region. Moreover, we fit the hot and warm dust components of the dust torus by adding photometric data of SDSS, 2MASS, WISE, and ISO to the AKARI spectra, finding hot and warm dust temperatures of ~1100 K and ~220 K, respectively, rather than the commonly cited hot dust temperature of 1500 K.

The Astrophysical Journal. Supplement Series


AKARI infrared camera observations of the 3.3 μm PAH feature in Swift/BAT AGNs

We explore the relationships between the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the nine-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E ? 10 keV. These X-ray spectra provide measurements of the neutral hydrogen column density (NH) towards the AGNs. We use the 3.3 μm PAH luminosity (L3.3μm) as a proxy for star-formation activity and hard X-ray luminosity (L14-195 keV) as an indicator of the AGN activity. We search for possible differences in star-formation activity between type 1 (unabsorbed) and type 2 (absorbed) AGNs. We have made several statistical analyses taking the upper limits of the PAH lines into account utilizing survival analysis methods. The results of our log (L14-195 keV) versus log (L3.3 μm) regression show a positive correlation and the slope for the type 1/unobscured AGNs is steeper than that of type 2/obscured AGNs at a 3 ς level. Our analysis also shows that the circumnuclear star formation is more enhanced in type 2/absorbed AGNs than type 1/unabsorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs, while there is no significant dependence of star-formation activities on the AGN type in the high X-ray luminosities/Eddington ratios.

Publications of the Astronomical Society of Japan


Successive Logic-in-Memory Operation in Spin Wave-Based Devices With Domain Wall Data Coding Scheme


AKARI IRC 2.5-5 μm Spectroscopy of Infrared Galaxies over a Wide Luminosity Range

We present the result of a systematic infrared 2.5-5 μm spectroscopic study of 22 nearby infrared galaxies over a wide infrared luminosity range (1010 L ? < L IR < 1013 L ?) obtained from the AKARI Infrared Camera (IRC). The unique band of the AKARI IRC spectroscopy enables us to access both the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature from star-forming activity and the continuum of torus-dust emission heated by an active galactic nucleus (AGN). Applying our AGN diagnostics to the AKARI spectra, we discover 14 buried AGNs. The large fraction of buried AGNs suggests that AGN activity behind the dust is almost ubiquitous in ultra-/luminous infrared galaxies (U/LIRGs). We also find that both the fraction and energy contribution of buried AGNs increase with infrared luminosity from 1010 L ? to 1013 L ?, including normal infrared galaxies with L IR < 1011 L ?. The energy contribution from AGNs in the total infrared luminosity is only ~7% in LIRGs and ~20% in ULIRGs, suggesting that the majority of the infrared luminosity originates from starburst activity. Using the PAH emission, we investigate the luminosity relation between star formation and AGNs. We find that these infrared galaxies exhibit higher star formation rates than optically selected Seyfert galaxies with the same AGN luminosities, implying that infrared galaxies could be an early evolutionary phase of AGN.


The first source counts at 18 μm from the AKARI NEP Survey

We present the first galaxy counts at 18 μm using the Japanese AKARI satellite's survey at the North Ecliptic Pole (NEP), produced from the images from the NEP-Deep and NEP-Wide surveys covering 0.6 and 5.8 deg2, respectively. We describe a procedure using a point source filtering algorithm to remove background structure and a minimum variance method for our source extraction and photometry that delivers the optimum signal to noise for our extracted sources, confirming this by comparison with standard photometry methods. The final source counts are complete and reliable over three orders of magnitude in flux density, resulting in sensitivities (80 per cent completeness) of 0.15 and 0.3 mJy for the NEP-Deep and NEP-Wide surveys, respectively, a factor of 1.3 deeper than previous catalogues constructed from this field. The differential source counts exhibit a characteristic upturn from Euclidean expectations at around a milliJansky and a corresponding evolutionary bump between 0.2-0.4 mJy consistent with previous mid- infrared surveys with ISO and Spitzer at 15 and 24 μm. We compare our results with galaxy evolution models confirming the striking divergence from the non-evolving scenario. The models and observations are in broad agreement implying that the source counts are consistent with a strongly evolving population of luminous infrared galaxies at redshifts higher than unity. Integrating our source counts down to the limit of the NEP survey at the 150 μJy level we calculate that AKARI has resolved approximately 55 per cent of the 18 μm cosmic infrared background relative to the predictions of contemporary source count models.

Monthly Notices of the Royal Astronomical Society


AKARI observations of interstellar dust grains in our Galaxy and nearby galaxies

The infrared (IR) emission from interstellar dust grains is a powerful tool to trace star-formation activities in galaxies. Beyond such star- formation tracers, spectral information on polycyclic aromatic hydrocarbons (PAHs) and large grains, or even their photometric intensity ratios, has deep physical implications for understanding the properties of the interstellar medium. With the AKARI satellite launched in 2006, we have performed a systematic study of interstellar dust grains in various environments of galaxies including our Galaxy. Because of its unique capabilities, such as mid-/far-IR all-sky surveys and near -/far-IR spectroscopy, AKARI has provided new knowledge on the processing of dust, particularly carbonaceous grains including PAHs, in the interstellar space. For example, the near-IR spectroscopy has revealed structural changes of hydrocarbon grains in harsh environments of galaxies. In this paper, we focus on the properties of the PAH emission obtained by the AKARI mid-IR all-sky survey and near-IR spectroscopy.


Luminosity and Redshift Dependence of the Covering Factor of Active Galactic Nuclei viewed with WISE and Sloan Digital Sky Survey

In this work, we investigate the dependence of the covering factor (CF) of active galactic nuclei (AGNs) on the mid-infrared (MIR) luminosity and the redshift. We constructed 12 and 22 μm luminosity functions (LFs) at 0.006 <=z <= 0.3 using Wide-field Infrared Survey Explorer (WISE) data. Combining the WISE catalog with Sloan Digital Sky Survey (SDSS) spectroscopic data, we selected 223,982 galaxies at 12 μm and 25,721 galaxies at 22 μm for spectroscopic classification. We then identified 16,355 AGNs at 12 μm and 4683 AGNs at 22 μm by their optical emission lines and cataloged classifications in the SDSS. Following that, we estimated the CF as the fraction of Type 2 AGN in all AGNs whose MIR emissions are dominated by the active nucleus (not their host galaxies) based on their MIR colors. We found that the CF decreased with increasing MIR luminosity, regardless of the choice of Type 2 AGN classification criteria, and the CF did not change significantly with redshift for z <= 0.2. Furthermore, we carried out various tests to determine the influence of selection bias and confirmed that similar dependences exist, even when taking these uncertainties into account. The luminosity dependence of the CF can be explained by the receding torus model, but the "modified" receding torus model gives a slightly better fit, as suggested by Simpson.


Spin wave based parallel logic operations for binary data coded with domain walls

We numerically investigate the feasibility of spin wave (SW) based parallel logic operations, where the phase of SW packet (SWP) is exploited as a state variable and the phase shift caused by the interaction with domain wall (DW) is utilized as a logic inversion functionality. A designed functional element consists of parallel ferromagnetic nanowires (6 nm-thick, 36 nm-width, 5120 nm-length, and 200 nm separation) with the perpendicular magnetization and sub-μm scale overlaid conductors. The logic outputs for binary data, coded with the existence ("1") or absence ("0") of the DW, are inductively read out from interferometric aspect of the superposed SWPs, one of them propagating through the stored data area. A practical exclusive-or operation, based on 2ϖ periodicity in the phase logic, is demonstrated for the individual nanowire with an order of different output voltage Vout, depending on the logic output for the stored data. The inductive output from the two nanowires exhibits well defined three different signal levels, corresponding to the information distance (Hamming distance) between 2-bit data stored in the multiple nanowires.


AKARI North Ecliptic Pole Deep Survey. Revision of the catalogue via a new image analysis

Context. We present the revised near- to mid-infrared catalogue of the AKARI North Ecliptic Pole deep survey. The survey has the unique advantage of continuous filter coverage from 2 to 24 μm over nine photometric bands, but the initial version of the survey catalogue leaves room for improvement in the image analysis stage; the original images are strongly contaminated by the behaviour of the detector and the optical system. Aims: The purpose of this study is to devise new image analysis methods and to improve the detection limit and reliability of the source extraction. Methods: We removed the scattered light and stray light from the Earth limb, and corrected for artificial patterns in the images by creating appropriate templates. We also removed any artificial sources due to bright sources by using their properties or masked them out visually. In addition, for the mid- infrared source extraction, we created detection images by stacking all six bands. This reduced the sky noise and enabled us to detect fainter sources more reliably. For the near-infrared source catalogue, we considered only objects with counterparts from ground-based catalogues to avoid fake sources. For our ground-based catalogues, we used catalogues based on the CFHT/MegaCam z' band, CFHT/WIRCam Ks band and Subaru/Scam z' band. Objects with multiple counterparts were all listed in the catalogue with a merged flag for the AKARI flux. Results: The detection limits of all mid-infrared bands were improved by ~20%, and the total number of detected objects was increased by ~2000 compared with the previous version of the catalogue; it now has 9560 objects. The 5ς detection limits in our catalogue are 11, 9, 10, 30, 34, 57, 87, 93, and 256 μJy in the N2, N3, N4, S7, S9W, S11, L15, L18W, and L24 bands, respectively. The astrometric accuracies of these band detections are 0.48, 0.52, 0.55, 0.99, 0.95, 1.1, 1.2, 1.3, and 1.6 arcsec, respectively. The false-detection rate of all nine bands was decreased to less than 0.3%. In total, 27 770 objects are listed in the catalogue, 11 349 of which have mid-infrared fluxes. The catalogue is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/559/A132 or at the ISAS/JAXA observers page, http://www.ir.isas.jax a.jp/ASTRO-F/Observation/


AKARI Observations of Interstellar Polycyclic Aromatic Hydrocarbons

We review the results from AKARI observations of PAHs. We also discuss our future prospect for this study using the next Japan-led infrared space mission, SPICA.

International Astrobiology Workshop 2013


Detection of Hα emission from z > 3.5 submillimetre luminous galaxies with AKARI-FUHYU spectroscopy

We present tentative Hα emission line detections of four submillimetre- detected galaxies at z > 3.5: the radio galaxies 8C1909+722 and 4C60.07 at signal-to-noise ratios (SNRs) of 3.1 and 2.5, and two submillimetre-selected galaxies (SMGs) near the first of these at SNRs of 10.0 and 2.4, made with the AKARI space telescope as part of the Follow-Up Hayai-Yasui-Umai mission programme. These are the highest redshift Hα detections in such galaxies, made possible by AKARI's unique near-infrared spectroscopic capability. The two radio galaxies had known redshifts and surrounding structure, and we have detected broad Hα components indicating the presence of dust-shrouded quasars. We conclude that powerful active galactic nuclei (AGNs) at z > 3.5 occur in peaks of the star formation density fields, supporting a close connection between stellar mass build-up and black hole mass assembly at this redshift. We also show that 4C60.07 is a binary AGN. The Hα detections of the two SMGs are the first redshift determinations for these sources, confirming their physical association around their companion radio galaxy. The Hα-derived star formation rates (SFRs) for the SMGs are lower than their far-infrared derived SFRs by a factor of ?10, suggesting a level of dust obscuration similar to that found in studies at ?1 < z < 2.7.


VizieR Online Data Catalog: AGNs in submm-selected Lockman Hole galaxies (Serjeant+, 2010)

We present a comparison of the SCUBA half degree extragalactic survey (SHADES) at 450μm, 850μm and 1100μm with deep guaranteed time 15μm AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24μm in the Lockman hole east. The AKARI data was analysed using bespoke software based in part on the drizzling and minimum-variance matched filtering developed for SHADES, and was cross-calibrated against ISO fluxes. (2 data files).


Clustering of far-infrared galaxies in the AKARI All-Sky Survey North

We present the measurements of the angular two-point correlation function for AKARI 90-μm point sources, detected outside the Milky Way plane and other regions characterized by high Galactic extinction in the northern Galactic hemisphere, and categorized as extragalactic sources according to our far-infrared-color based criterion. Together with our previous work (Pollo et al., 2013) this is the first measurement of the large-scale angular clustering of galaxies selected in the far-infrared after IRAS. We present the first attempt to estimate the spatial clustering properties of AKARI All-Sky galaxies and we conclude that they are mostly a very nearby ( z ? 0.1) population of moderately clustered galaxies. We measure their correlation length r 0 ~ 4.5 h -1 Mpc, which is consistent with the assumption that the FIS AKARI All-Sky surveys observes mostly a nearby star-forming population of galaxies.


A Relation of the PAH 3.3 μm Feature with Star-forming Activity for Galaxies with a Wide Range of Infrared Luminosity

For star-forming galaxies, we investigated a global relation between the polycyclic aromatic hydrocarbon (PAH) emission luminosity at 3.3 μm, LPAH3.3, and the infrared (8-1000 μm) luminosity, LIR, to understand how the PAH 3.3 μm feature relates to star-formation activity. With AKARI, we performed near-infrared (2.5-5 μm) spectroscopy of 184 galaxies having LIR ? 108-1013 L?. We classified the samples into infrared galaxies (IRGs: LIR < 1011 L?), luminous infrared galaxies (LIRGs: LIR ? 1011 -1012 L?) and ultra-luminous infrared galaxies (ULIRGs: LIR > 1012 L?). We excluded sources likely to be contaminated by AGN activity, based on the rest-frame equivalent width of the PAH emission feature (< 40 nm) and the power-law index, representing the slope of continuum emission (Γ > 1 Fν ∝ λΓ). Of these samples, 13 IRGs, 67 LIRGs, and 20 ULIRGs show the PAH emission feature at λ rest = 3.3 μm in their spectra. We find that the LPAH3.3/LIR ratio considerably decreases toward the luminous end. Utilizing the mass and temperature of dust grains as well as the Brα emission for the galaxies, we discuss the cause of the relative decrease in the PAH emission with LIR.

Publications of the Astronomical Society of Japan


The 9 and 18 Micrometer Luminosity Functions of Various Types of Galaxies with AKARI: Implication for the Dust Torus Structure of AGN

We present the 9 and 18 μm luminosity functions (LFs) of galaxies at 0.006 ? z ? 0.8 (with an average redshift of ? 0.04) using the AKARI mid-infrared all-sky survey catalog. We selected 243 galaxies at 9 μm and 255 galaxies at 18 μm from the Sloan Digital Sky Survey (SDSS) spectroscopy region. These galaxies were then classified by their optical emission lines, such as the line width of Hα or by their emission line ratios of [O III]/Hβ and [N II]/Hα into five types: Type 1 active galactic nuclei (AGN) (Type 1); Type 2 AGN (Type 2); low- ionization narrow emission line galaxies (LINER); galaxies with both star formation and narrow-line AGN activity (composite galaxies); and star-forming galaxies (SF). We found that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73 ± 0.36, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18 μ m luminosity.


Difference in the Spatial Distribution between H2O and CO2 Ices in M 82 Found with AKARI

With AKARI, we obtain the spatially resolved near-infrared (NIR) (2.5-5.0 μm) spectra for the nearby starburst galaxy M 82. These spectra clearly show absorption features due to interstellar ices. Based on the spectra, we created the column density maps of H2O and CO2 ices. As a result, we find that the spatial distribution of H2O ice is significantly different from that of CO2 ice; H2O ice is widely distributed, while CO2 ice is concentrated near the galactic center. Our result reveals for the first time variations in CO2/H2O ice abundance ratio on a galactic scale, suggesting that an ice-forming interstellar environment changes within a galaxy. We discuss the cause of the spatial variations in the ice abundance ratio, utilizing spectral information on the hydrogen recombination Brα and Brβ lines and the polycyclic aromatic hydrocarbon 3.3 μm emission appearing in the AKARI NIR spectra.


Diffuse Galactic Light in the Field of the Translucent High Galactic Latitude Cloud MBM32

We have conducted B-, g-, V-, and R-band imaging in a 45' × 40' field containing part of the high Galactic latitude translucent cloud MBM32, and correlated the intensity of diffuse optical light S ν(λ) with that of 100 μm emission S ν(100 μm). A χ2 minimum analysis is applied to fit a linear function to the measured correlation and derive the slope parameter b(λ) = ?S ν(λ)/?S ν(100 μm) of the best-fit linear function. Compiling a sample by combining our b(λ) and published ones, we show that the b(λ) strength varies from cloud to cloud by a factor of four. Finding that b(λ) decreases as S ν(100 μm) increases in the sample, we suggest that a nonlinear correlation including a quadratic term of S ν(100 μm)2 should be fitted to the measured correlation. The variation of optical depth, which is AV = 0.16-2.0 in the sample, can change b(λ) by a factor of 2-3. There would be some contribution to the large b(λ) variation from the forward- scattering characteristic of dust grains which is coupled to the non- isotropic interstellar radiation field (ISRF). Models of the scattering of diffuse Galactic light (DGL) underestimate the b(λ) values by a factor of two. This could be reconciled by deficiency in UV photons in the ISRF or by a moderate increase in dust albedo. Our b(λ) spectrum favors a contribution from extended red emission (ERE) to the diffuse optical light; b(λ) rises from B to V faster than the models, seems to peak around 6000 ? and decreases toward long wavelengths. Such a characteristic is expected from the models in which the DGL is combined with ERE.


Clustering of far-infrared galaxies in the AKARI All-Sky Survey

We present the first measurement of the angular two-point correlation function for AKARI 90-μm point sources, detected outside of the Milky Way plane and other regions characterized by high Galactic extinction, and categorized as extragalactic sources according to our far-infrared- color based criterion (<CitationRef CitationID="CR36">Pollo et al., 2010). This is the first measurement of the large-scale angular clustering of galaxies selected in the far-infrared after IRAS measurements. Although a full description of the clustering properties of these galaxies will be obtained by more detailed studies, using either a spatial correlation function, or better information about properties and, at least, photometric redshifts of these galaxies, the angular correlation function remains the first diagnostic tool to establish the clustering properties of the catalog and the observed galaxy population. We find a non-zero clustering signal in both hemispheres extending up to ~40 degrees, without any significant fluctuations at larger scales. The observed correlation function is well fitted by a power-law function. The notable differences between the northern and southern hemispheres are found, which can probably be attributed to the photometry problems, and might point to the necessity of performing a better calibration in the data from the southern hemisphere.


Large-scale extraplanar PAH emission in the Galactic center region found by AKARI mid-infrared all-sky survey

AKARI carried out all-sky surveys at wavelengths of 9, 18, 65, 90, 140 and 160 ? m. Among them, the 9 ? m map can efficiently trace the emission features of polycyclic aromatic hydrocarbons (PAHs). Utilizing this unique all-sky PAH map, we investigate the distribution of the PAH emission for the whole Galactic plane. In particular, the Galactic center regions suffer foreground contamination by the zodiacal light, and therefore we have carefully removed the zodiacal light component by modifying the Kelsall model. As a result, we find that the PAH emission is extended very widely (? 30? ) toward the north direction from the Galactic center region. Since it is known that there are very nearby (?150 pc) Ophiuchus clouds toward similar directions, we subtracted the foreground component associated with these clouds using the HI data. As a result, we confirm that there still remains a significant fraction of the widely-extended PAH emission toward this direction, suggesting that the excess PAH emission originates in the Galactic center region. The spatial distribution resembles that of the Fermi bubbles, well-known gamma-ray structures, which are thought to be created by a past outflow in the Galactic center. Moreover, the PAH/dust ratio is significantly enhanced in the region showing the excess PAH emission. The high PAH/dust ratio is possibly created by shattering of carbonaceous grains in the past outflow from the Galactic center.

Proceedings of The Life Cycle of Dust in the Universe: Observations


AKARI mid-infrared all-sky survey: development of the new inter-planetary dust (IPD) map and the world-first all-sky PAH map

We are constructing accurately calibrated 9 ?m and 18 ?m all-sky diffuse maps from the AKARI mid-infrared all-sky survey data. These maps are heavily affected by the foreground emission of the zodiacal light, which has an intensity peak at around these wavelengths. We carefully separate the zodiacal emission component from the maps using Kelsall's model. Through improvement of the parameters in the zodiacal light emission model, we obtained new insight on the structure and composition of the interplanetary dust in our solar system. The zodiacal light removed AKARI 9 ?m map is the world's first all-sky PAH map, that traces the emission features of Galactic polycyclic aromatic hydrocarbons (PAHs) at wavelengths of 6.2, 7.7, 8.6, and 11.3 ?m. On a global scale, PAHs show good spatial correlation with tracers of general ISM such as CO, HI, and far-IR dust emissions. On a local scale, we recognize the variation of physical state and compositions of hydrocarbons reflecting the variation of the local physical environment. This PAH map will be effectively used in diagnoses of various interstellar phenomena.


Slow-Scan Observations with the Infrared Camera (IRC) aboard AKARI

We present the characterization and calibration of the slow-scan observation mode of the Infrared Camera (IRC) aboard AKARI. The IRC Slow-scan observations were operated at the S9W (9μm) and L18W (18μm) bands. We developed a toolkit for data reduction of the IRC Slow-scan observations. We introduced a "self-pointing reconstruction" method to improve the positional accuracy to as good as 1". The sizes of the point spread functions were derived to be ?6" at the S9W band and ?7" at the L18W bands in full width at half maximum. Flux calibrations were achieved with observations of 3 and 4 infrared standard stars at the S9W and L18W bands, respectively. The flux uncertainties are estimated to be better than 20% from comparisons with the AKARI IRC PSC and the WISE preliminary catalog.


The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog

We present a photometric catalog of infrared (IR) sources based on the North Ecliptic Pole Wide field (NEP-Wide) survey of AKARI, which is an infrared space telescope launched by Japan. The NEP-Wide survey covered 5.4 deg2 area, a nearly circular shape centered on the NEP, using nine photometric filter-bands from 2-25 μm of the Infrared Camera (IRC). Extensive efforts were made to reduce possible false objects due to cosmic ray hits, multiplexer bleeding phenomena around bright sources, and other artifacts. The number of detected sources varied depending on the filter band: with about 109 000 sources being cataloged in the near-infrared (NIR) bands at 2-5 μm, about 20 000 sources in the shorter parts of the mid-infrard (MIR) bands between 7-11 μm, and about 16 000 sources in the longer parts of the MIR band, with ~4000 sources at 24 μm. The estimated 5ς detection limits are approximately 21 mag (mag) in the 2-5 μm bands, 19.5-19 mag in the 7-11 μm, and 18.8-18.5 mag in the 15-24 μm bands in the AB magnitude scale. The completenesses for those bands were evaluated as a function of magnitude: the 50% completeness limits are about 19.8 mag at 3 μm, 18.6 mag at 9 μm, and 18 mag at 18 μm band, respectively. To construct a reliable source catalog, all of the detected sources were examined by matching them with those in other wavelength data, including optical and ground-based NIR bands. The final band-merged catalog contains about 114 800 sources detected in the IRC filter bands. The properties of the sources are presented in terms of the distributions in various color-color diagrams. The full version of Table 4 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/548/A29


Updated Analysis of a "Dark" Galaxy and Its Blue Companion in the Virgo Cloud H I 1225 + 01

H I 1225+01 is an intergalactic gas cloud located on the outskirts of Virgo cluster. Its main components are two large clumps of comparable H I masses (M_{Hathsc{i}} im 109 M_dot) separated by about 100 kpc. One of the clumps hosts a blue low-surface-brightness galaxy J1227+0136, while the other has no identified stellar emission and is sometimes referred to as a promising candidate of a "dark galaxy," an optically invisible massive intergalactic system. We present a deep optical image covering the whole H I 1225+01 structure for the first time, as well as a collection of archival data from ultraviolet to far- infrared (IR) spectral region of the brightest knot "R1" in J1227+0136. We find that R1 has a young stellar population 10-100 Myr in age and mass ~106 M ?, near-IR excess brightness which may point to the presence of hot dust with color temperature ~600 K, and relatively faint mid- to far-IR fluxes corresponding to the dust mass of up to ~100 M ?. Overall, it seems to share the general properties with low-metallicity blue compact dwarf galaxies. On the other hand, no optical counterpart to the other clump is found in our deepest-ever image. Now the limiting surface brightness reaches down to R AB > 28 mag arcsec-2 for any emission extended over 10'' (comparable to R1), which is more than one hundred times fainter than the brightest part of the companion galaxy J1227+0136.


The 3.3 μm Polycyclic Aromatic Hydrocarbon Emission as a Star Formation Rate Indicator

Polycyclic aromatic hydrocarbon (PAH) emission features dominate the mid-infrared spectra of star-forming galaxies and can be useful to calibrate star formation rates (SFRs) and diagnose ionized states of grains. However, the PAH 3.3 μm feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability. In order to detect and calibrate the 3.3 μm PAH emission and investigate its potential as an SFR indicator, we carried out an AKARI mission program, AKARI mJy Unbiased Survey of Extragalactic Sources (AMUSES), and compared its sample with various literature samples. We obtained 2-5 μm low-resolution spectra of 20 flux-limited galaxies with mixed spectral energy distribution classes, which yielded the detection of the 3.3 μm PAH emission from 3 out of 20 galaxies. For the combined sample of AMUSES and literature samples, the 3.3 μm PAH luminosities correlate with the infrared luminosities of star-forming galaxies, albeit with a large scatter (1.5 dex). The correlation appears to break down at the domain of ultraluminous infrared galaxies (ULIRGs), and the power of the 3.3 μm PAH luminosity as a proxy for the infrared luminosity is hampered at log[L PAH3.3 erg-1 s-1] > ~42.0. Possible origins for this deviation in the correlation are discussed, including contributions from active galactic nuclei and strongly obscured young stellar objects, and the destruction of PAH molecules in ULIRGs.


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.

Monthly Notices of the Royal Astronomical Society


Improvement of Akari Nep-Deep 2-24 Micron Images/catalogues with New Calibrations

Publications of The Korean Astronomical Society


Lifecycle of the Interstellar Dust Grains in Our Galaxy Viewed with Akari/mir All-Sky Survey


Overview of the North Ecliptic Pole Deep Multi-Wavelength Survey NEP-DEEP


A Study of the Galactic Center Regions Using the Improved Data of the Mid-Infrared All-Sky Survey


Systematic Study of Interstellar Ices in Nearby Galaxies


The Central Region of the Barred Spiral Galaxy NGC 1097 Probed by Akari Near-Infrared Spectroscopy


Properties of Dust in Early-Type Galaxies Based on the All-Sky Data and Near-Infrared Spectra


Survey of Dusty Active Galactic Nuclei Based on the Mid-Infrared All-Sky Survey Catalog


Mid- and Far-Infrared Properties of Local Active Galactic Nuclei


Infrared and Hard X-Ray Diagnostics of AGN Identification from the Akari and Swift/bat All-Sky Surveys


Near-Infrared High-Resolution Spectroscopy of the Obscured AGN IRAS 01250+2832


The 3.3 Micron PAH Emission of the Mid-Infrared Excess Galaxies Discovered by the Akari Mid-Infrared All-Sky Survey


A Multi-Wavelength Study of Pah-Selected Starburst Galaxies


The 18 μm Luminosity Function of Galaxies with Akari


Angular Clustering of Fir-Selected Galaxies in the Akari All-Sky Survey

We present the first measurement of the angular two-point correlation function for AKARI 90-$u$m point sources, detected outside of the Milky Way plane and other regions characterized by high Galactic extinction, and categorized as extragalactic sources according to our far-infrared-color based criterion (Pollo et al. 2010). This is the first measurement of the large-scale angular clustering of galaxies selected in the far-infrared after IRAS measurements. Although a full description of clustering properties of these galaxies will be obtained by more detailed studies, using either spatial correlation function, or better information about properties and at least photometric redshifts of these galaxies, the angular correlation function remains the first diagnostics to establish the clustering properties of the catalog and observed galaxy population. We find a non-zero clustering signal in both hemispheres extending up to $im 40$ degrees, without any significant fluctuations at larger scales. The observed correlation function is well fitted by a power law function. The notable differences between a northern and southern hemisphere are found, which can be probably attributed to the photometry problems and point out to a necessity of performing a better calibration in the data from southern hemisphere.


Detection of Hα Emission from z>3.5 Galaxies with Akari-Fuhyu NIR Spectroscopy

Publications of The Korean Astronomical Society


Akari Observation of the Fluctuation of the Near-Infrared Background


Star Formation and AGN Activity in Galaxies Classified Using the 1.6 μm Bump and PAH Features at z = 0.4-2

We have studied the star-formation and AGN activity of massive galaxies in the redshift range $z=0.4-2$, which are detected in a deep survey field using the AKARI InfraRed (IR) astronomical satellite and {m Subaru} telescope toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR) multiband photometry is used to trace their star- forming activities with the Polycyclic-Aromatic Hydrocarbon (PAH) emissions, which is also used to distinguish star-forming populations from AGN dominated ones and to estimate the Star Formation Rate (SFR) derived from their total emitting IR (TIR) luminosities. In combination with analyses of their stellar components, we have studied the MIR SED features of star-forming and AGN-harboring galaxies.

Publications of the Astronomical Society of Japan


Infrared and Hard X-Ray Diagnostics of Active Galactic Nucleus Identification from the Swift/BAT and AKARI All-sky Surveys

We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10 keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X -ray-detected AGNs. Cross-correlating the 22 month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 μm) and hard X-ray (14-195 keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR.


Mid- and Far-infrared Properties of a Complete Sample of Local Active Galactic Nuclei

We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky hard X-ray (14-195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with Infrared Astronomical Satellite and Wide-field Infrared Survey Explorer. Out of 135 non-blazer AGNs in the Swift/BAT nine-month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 μm band. We find good correlation between their hard X-ray and MIR luminosities over three orders of magnitude (42 < log λL λ(9, 18 μm) < 45), which is tighter than that with the FIR luminosities at 90 μm. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 μm in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the polycyclic aromatic hydrocarbon emission feature, suggesting that their host galaxies have strong starburst activities.


AKARI Mid-Infrared All-Sky Survey Diffuse Map

AKARI, the Japanese infrared astronomical satellite launched in February 2006, exhausted its liquid helium cryogen in August 2007. For about one and a half years of the cold mission phase, AKARI performed all-sky surveys in the two mid-infrared photometric bands centered at 9 and 18 microns with higher spatial resolutions and sensitivities than IRAS. Both bands cover slightly shorter wavelength ranges than the IRAS 12 and 25 micron bands and thus provide different information on the infrared sky. In particular, the AKARI 9 micron band map has unique advantage in tracing the distribution of polycyclic aromatic hydrocarbons (PAHs) for the whole sky. To enable discussion on faint diffuse interstellar emission, we have improved the AKARI mid-infrared all-sky diffuse maps by correcting artifacts such as those caused by space ionizing radiation and scattered light from the moon and very bright sources. The quality of these diffuse maps are now being checked within the AKARI team. We plan to release them to the public in near future.


SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for mid- and far-infrared astronomy, envisioned for launch in early 2020s. The core wavelength coverage of this mission is 5 to 210 micron. We present two SPICA Instruments in the mid-infrared region, Mid-infrared Camera and Spectrometer (MCS) and SPICA Coronagraphic Instrument (SCI). MCS will provide imaging and spectroscopic observing capabilities in the mid-infrared region with 4 modules. WFC (Wide Field Camera) has two 5 arcminutes square filed of view and covers the wavelength range 5 to 38 micron, HRS (High Resolution Spectrometer) covers the wavelength range 12 to 18 micron with resolving power about 30000, MRS (Mid Resolution Spectrometer) has integral field units by image slicer and covers the wavelength range 12 to 38 micron simultaneously using dichroic filter and two sets of spectrometers with (spectral) resolving power of 1100--3000, LRS (Low Resolution Spectrometer) adopts prism disperser and covers the wavelength range 5 to 48 micron with resolving power 50 to 100. SCI has been designed for a concentrated study of extra-solar planets (exoplanets). The primary objectives for the SCI are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in infrared, while the monitoring of transiting planets is another important target. In the SCI, coronagraphic and non-coronagraphic modes are applicable for both an imaging and a spectroscopy. The core wavelength range of the SCI is 3.5-27 micron. The SCI has capability of simultaneous observations of one target using two channels, a short channel with an InSb detector and a long wavelength channel with a Si:As detector.


Star-galaxy separation in the AKARI NEP deep field

Context. It is crucial to develop a method for classifying objects detected in deep surveys at infrared wavelengths. We specifically need a method to separate galaxies from stars using only the infrared information to study the properties of galaxies, e.g., to estimate the angular correlation function, without introducing any additional bias. Aims: We aim to separate stars and galaxies in the data from the AKARI north ecliptic pole (NEP) deep survey collected in nine AKARI/IRC bands from 2 to 24 μm that cover the near- and mid-infrared wavelengths (hereafter NIR and MIR). We plan to estimate the correlation function for NIR and MIR galaxies from a sample selected according to our criteria in future research. Methods: We used support vector machines (SVM) to study the distribution of stars and galaxies in the AKARIs multicolor space. We defined the training samples of these objects by calculating their infrared stellarity parameter (sgc). We created the most efficient classifier and then tested it on the whole sample. We confirmed the developed separation with auxiliary optical data obtained by the Subaru telescope and by creating Euclidean normalized number count plots. Results: We obtain a 90% accuracy in pinpointing galaxies and 98% accuracy for stars in infrared multicolor space with the infrared SVM classifier. The source counts and comparison with the optical data (with a consistency of 65% for selecting stars and 96% for galaxies) confirm that our star/galaxy separation methods are reliable. Conclusions: The infrared classifier derived with the SVM method based on infrared sgc - selected training samples proves to be very efficient and accurate in selecting stars and galaxies in deep surveys at infrared wavelengths carried out without any previous target object selection.


The Central Region of the Barred Spiral Galaxy NGC 1097 Probed by AKARI Near-infrared Spectroscopy

With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 μm) spectroscopy of the central kiloparsec region of the barred spiral galaxy, NGC 1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the area of ~50'' × 10'' with the resolution of ~5'', covering about a half of the ring and the galactic center. As a result, we spatially resolve the starburst ring in the polycyclic aromatic hydrocarbon 3.3 μm, the aliphatic hydrocarbon 3.4-3.6 μm features, and the hydrogen Brα 4.05 μm emission. They exhibit spatial distributions significantly different from each other, indicating that the environments vary considerably around the ring. In particular, the aliphatic features are enhanced near the bar connecting the ring with the nucleus, where the structure of hydrocarbon grains seems to be relatively disordered. Near the center, the continuum emission and the CO/SiO absorption features are strong, which indicates that the environments inside the ring are dominated by old stellar populations. The near-infrared spectra do not show any evidence for the presence of nuclear activity.


Processing of Polycyclic Aromatic Hydrocarbons in Molecular-Loop Regions near the Galactic Center Revealed by AKARI

We present an AKARI mid-infrared diffuse map of an area of about 4° × 3° near the Galactic center in the 9 μm band. The band intensity is mostly attributed to aromatic hydrocarbon infrared emissions of carbonaceous grains at wavelengths of 6.2, 7,7, 8.6, and 11.3 μm. We detected 9 μm emission structures extending from the Galactic plane up to a latitude of ? 2°.5, which have spatial correspondence to molecular loops revealed by NANTEN 12CO (J = 1-0) observations. We have found that the surface brightness at 9 μm is suppressed near the foot points of the CO loops. The ratios of the 9 μm to the IRAS 100 μm brightness show significant depression near such bright regions in CO emission. With AKARI near-infrared 2.5-5 μm spectroscopy, we find that the 3.3 μm aromatic hydrocarbon emission is absent in the region associated with the loop, suggesting the processing and destruction of carbonaceous grains in the CO molecular loops.


AKARI Observation of the North Ecliptic Pole (NEP) Supercluster at z = 0.087: Mid-infrared View of Transition Galaxies

We present the mid-infrared (MIR) properties of galaxies within a supercluster in the north ecliptic pole region at z ~ 0.087 observed with the AKARI satellite. We use data from the AKARI NEP-Wide (5.4 deg2) IR survey and the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show that near-IR (3 μm)-mid-IR (11 μm) color can be used as an indicator of the specific star formation rate and the presence of intermediate-age stellar populations. From the MIR observations, we find that red-sequence galaxies consist not only of passively evolving red early-type galaxies, but also of (1) "weak-SFGs" (disk-dominated star-forming galaxies that have star formation rates lower by ~4 × than blue-cloud galaxies) and (2) "intermediate-MXGs" (bulge-dominated galaxies showing stronger MIR dust emission than normal red early-type galaxies). These two populations can be a set of transition galaxies from blue, star-forming, late-type galaxies evolving into red, quiescent, early-type ones. We find that the weak-SFGs are predominant at intermediate masses (1010 M ? < M * < 1010.5 M ?) and are typically found in local densities similar to the outskirts of galaxy clusters. As much as 40% of the supercluster member galaxies in this mass range can be classified as weak-SFGs, but their proportion decreases to <10% at larger masses (M * > 1010.5 M ?) at any galaxy density. The fraction of the intermediate-MXG among red- sequence galaxies at 1010 M ? < M * < 1011 M ? also decreases as the density and mass increase. In particular, ~42% of the red-sequence galaxies with early-type morphologies are classified as intermediate-MXGs at intermediate densities. These results suggest that the star formation activity is strongly dependent on the stellar mass, but that the morphological transformation is mainly controlled by the environment.