The AKARI NEP-Deep survey: a mid-infrared source catalogue

We present a new catalogue of mid-IR sources using the AKARI NEP-Deep survey. The InfraRed Camera (IRC) onboard AKARI has a comprehensive mid- IR wavelength coverage with 9 photometric bands at 2-24 μm. We utilized all of these bands to cover a nearly circular area adjacent to the north ecliptic pole (NEP). We designed the catalogue to include most of sources detected in 7, 9, 11, 15 and 18 μm bands, and found 7284 sources in a 0.67 deg2 area. From our simulations, we estimate that the catalogue is ~80 per cent complete to 200 μJy at 15-18 μm, and ~10 per cent of sources are missed, owing to source blending. Star-galaxy separation is conducted using only AKARI photometry, as a result of which 10 per cent of catalogued sources are found to be stars. The number counts at 11, 15, 18, and 24 μm are presented for both stars and galaxies. A drastic increase in the source density is found in between 11 and 15 μm at the flux level of ~ 300 μJy. This is likely due to the redshifted PAH emission at 8 μm, given our rough estimate of redshifts from an AKARI colour-colour plot. Along with the mid-IR source catalogue, we present optical-NIR photometry for sources falling inside a Subaru/Sprime-cam image covering part of the AKARI NEP-Deep field, which is deep enough to detect most of AKARI mid-IR sources, and useful to study optical characteristics of a complete mid-IR source sample. Full Tables 4 and 5 are 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/537/A24


AKARI Observation of the Fluctuation of the Near-infrared Background

We report a search for fluctuations of the sky brightness toward the north ecliptic pole with the Japanese infrared astronomical satellite AKARI, at 2.4, 3.2, and 4.1 μm. We obtained circular maps with 10' diameter fields of view, which clearly show a spatial structure on the scale of a few hundred arcseconds. A power spectrum analysis shows that there is a significant excess fluctuation at angular scales larger than 100'' that cannot be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies, or clustering of low-redshift galaxies. These results are consistent with observations at 3.6 and 4.5 μm by NASA's Spitzer Space Telescope. The fluctuating component observed at large angular scales has a blue stellar spectrum which is similar to that of the spectrum of the excess isotropic emission observed with the Infrared Telescope in Space. A significant spatial correlation between wavelength bands was found, and the slopes of the linear correlations are consistent with the spectrum of the excess fluctuation. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e., Population III stars. The observed fluctuation provides an important constraint on the era of the first stars.


Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey

We present the results of an unbiased asteroid survey in the mid- infrared wavelength region with the Infrared Camera (IRC) on board the Japanese infrared satellite AKARI. About 20% of the point source events recorded in the AKARI All-Sky Survey observations are not used for the IRC Point Source Catalog (IRC-PSC) in its production process because of a lack of multiple detection by position. Asteroids, which are moving objects on the celestial sphere, remain in these ``residual events''. We identify asteroids out of the residual events by matching them with the positions of known asteroids. For the identified asteroids, we calculate the size and albedo based on the Standard Thermal Model. Finally we have a new brand of asteroid catalog, named the Asteroid Catalog Using AKARI (AcuA), which contains 5120 objects, about twice as many as the IRAS asteroid catalog. The catalog objects comprise 4953 main belt asteroids, 58 near-Earth asteroids, and 109 Jovian Trojan asteroids. The catalog is publicly available via the Internet.

Publications of the Astronomical Society of Japan


Far-infrared luminosity function of local star-forming galaxies in the AKARI Deep Field-South

We present a far-infrared galaxy luminosity function for the local universe. We have obtained 389 spectroscopic redshifts for galaxies observed at 90 μm in the AKARI Deep Field-South, using the AAOmega fibre spectrograph via optical identifications in the digitized sky survey and 4-m class optical imaging. For the luminosity function presented in this paper, we have used those galaxies which have redshifts 0 < z < 0.25, have optical magnitudes and are not part of a newly discovered cluster of galaxies (giving a total of 130 sources). Infrared and optical completeness functions were estimated using earlier Spitzer data and automated plate measurement (APM) B-band optical data, respectively, and the luminosity function has been prepared using the 1/Vmax method. We also separate the luminosity function between galaxies which show evidence of predominantly star-forming activity and predominantly active galactic nucleus (AGN) activity in their optical spectra. Our luminosity function is in good agreement with the previous 90-μm luminosity function from the European Large Area Infrared Space Observatory (ISO) Survey, and we also present a luminosity function with combined AKARI and ISO data. The result is in reasonable agreement with predictions based on the earlier Infrared Astronomical Satellite (IRAS) ?m PSCz catalogue, and with a recent backward evolution model.

Monthly Notices of the Royal Astronomical Society


Cosmic Optical Background: The View from Pioneer 10/11

We present the new constraints on the cosmic optical background (COB) obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP) data. After careful examination of data quality, the usable measurements free from the zodiacal light are integrated into sky maps at the blue (~0.44 μm) and red (~0.64 μm) band. Accurate starlight subtraction is achieved by referring to all-sky star catalogs and a Galactic stellar population synthesis model down to 32.0 mag. We find that the residual light is separated into two components: one component shows a clear correlation with thermal 100 μm brightness, while another betrays a constant level in the lowest 100 μm brightness region. The presence of the second component is significant after all the uncertainties and possible residual light in the Galaxy are taken into account, and thus it most likely has the extragalactic origin (i.e., the COB). The derived COB brightness is (1.8 ± 0.9) × 10-9 and (1.2 ± 0.9) × 10-9 erg s-1 cm-2 sr-1 ?-1 at the blue and red bands, respectively, or 7.9 ± 4.0 and 7.7 ± 5.8 nW m-2 sr-1. From comparison with the integrated brightness of galaxies, we conclude that bulk of the COB is comprised of normal galaxies which have already been resolved in the current deepest observations. There seems to be little room for contributions of other populations including "first stars" at these wavelengths. On the other hand, the first component of the IPP residual light represents the diffuse Galactic light (DGL)?scattered starlight by the interstellar dust. We derive mean DGL-to-100 μm brightness ratios of 2.1 × 10-3 and 4.6 × 10-3 at the two bands, which are roughly consistent with the previous observations toward the denser dust regions. Extended red emission in the diffuse interstellar medium is also confirmed.


Detection of the Cosmic Far-infrared Background in AKARI Deep Field South

We report new limits on the absolute brightness and spatial fluctuations of the cosmic infrared background (CIB) via the AKARI satellite. We carried out observations at 65, 90, 140, and 160 μm as a cosmological survey in AKARI Deep Field South, which is one of the lowest cirrus regions with a contiguous area of the sky. After removing bright galaxies and subtracting zodiacal and Galactic foregrounds from the measured sky brightness, we successfully measured the CIB brightness and its fluctuations across a wide range of angular scales, from arcminutes to degrees. The measured CIB brightness is consistent with previous results reported from COBE data, but significantly higher than the lower limits at 70 and 160 μm obtained via Spitzer from the stacking analysis of selected 24 μm sources. The discrepancy with the Spitzer result is possibly due to a new galaxy population at high redshift obscured by hot dust or unknown diffuse emission. From a power spectrum analysis at 90 μm, two components were identified: the CIB fluctuations with shot noise due to individual galaxies in a small angular scale from the beam size up to 10 arcminutes, and Galactic cirrus emission dominating at the largest angular scales of a few degrees. The overall shape of the power spectrum at 90 μm is very similar to that at longer wavelengths, as observed by Spitzer and the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST). Our power spectrum, with an intermediate angular scale of 10-30 arcminutes, gives a firm upper limit for galaxy clustering, which was found by Spitzer and BLAST. Moreover, the color of the CIB fluctuations, which is obtained by combining our data with the previous results, is as red as ultra-luminous infrared galaxies at high redshift. These galaxies are not likely to provide the majority of the CIB emission at 90 μm, but are responsible for the fluctuations. Our results provide new constraints on the evolution and clustering properties of distant infrared galaxies and any diffuse emission from the early universe.


Laboratory and In-Flight Measurements at 10-55 K of InSb Near-Infrared Detector Performance for the Warm Mission of the AKARI Satellite

The warm mission phase of AKARI, the Japanese infrared astronomical satellite, has started after its 180 liter liquid helium cryogen was exhausted. Since then, we have conducted near-infrared observations with the Infrared Camera (IRC), while the telescope is slowly warming up. To explore the possibility of continuing observations at higher temperatures, we evaluate the performance of the InSb detector array, a flight backup model for the IRC, in a laboratory at various operating temperatures between 10 K and 55 K. By combining the laboratory measurements with the in-flight measurements of the AKARI/IRC detector array, we consistently derive the changes of relative sensitivity, dark current, total noise, and the number of hot pixels with operating temperature. All of them show small changes in a range of temperature from 10 K to 40 K. However, at temperatures above 40 K, the dark current and the number of hot pixels start to increase rapidly, while the relative sensitivity decreases and the total noise increases gradually. We obtain the dependence of the performance on bias voltages to suggest an optimal operation for a future AKARI warmer phase.

Publications of the Astronomical Society of the Pacific


Characterization and Improvement of the Image Quality of the Data Taken with the Infrared Camera (IRC) Mid-Infrared Channels on Board AKARI

Mid-infrared images frequently suffer artifacts and extended point- spread functions (PSFs). We investigate the characteristics of the artifacts and the PSFs in images obtained with the infrared camera (IRC) on board AKARI at four mid-infrared bands of the S7 (7 μm), S11 (11 μm), L15 (15 μm), and L24 (24 μm). Removal of the artifacts significantly improves the reliability of the reference data for flat-fielding at the L15 and L24 bands. A set of models of the IRC PSFs is also constructed from on-orbit data. These PSFs have extended components that come from diffraction and scattering within the detector arrays. We estimate the aperture correction factors for point sources and the surface brightness correction factors for diffuse sources. We conclude that the surface brightness correction factors range from 0.95 to 0.8, taking account of the extended component of the PSFs. To correct for the extended PSF effects for the study of faint structures, we also develop an image reconstruction method, which consists of the deconvolution with the PSF and the convolution with an appropriate Gaussian. The appropriate removal of the artifacts, improved flat-fielding, and image reconstruction with the extended PSFs enable us to investigate detailed structures of extended sources in IRC mid-infrared images.


Infrared luminosity functions of AKARI Sloan Digital Sky Survey galaxies

By cross-correlating the AKARI all-sky survey in six infrared (IR) bands (9, 18, 65, 90, 140 and 160 μm) with the Sloan Digital Sky Survey (SDSS) galaxies, we identified 2357 IR galaxies with a spectroscopic redshift. This is not just one of the largest samples of local IR galaxies, but AKARI provides crucial far-IR (FIR) bands for accurately measuring the galaxy spectral energy distribution (SED) across the peak of the dust emission at > 100 μ m. By fitting modern IR SED models to the AKARI photometry, we measured the total infrared luminosity (LIR) of individual galaxies. Using this LIR, we constructed the luminosity functions (LF) of IR galaxies at a median redshift of z= 0.031. The LF agrees well with that at z= 0.0082 (the Revised Bright Galaxy Sample), showing smooth and continuous evolution towards higher redshift LFs measured in the AKARI North Ecliptic Pole (NEP) deep field. By integrating the IR LF weighted by LIR, we measured the local cosmic IR luminosity density of ΩIR= (3.8+5.8-1.2) × 108 L? Mpc-3. We separate galaxies into active galactic nuclei (AGN), star-forming galaxies (SFG) and composite by using the [N II]/Hα versus [O III]/Hβ line ratios. The fraction of AGN shows a continuous increase with increasing LIR from 25 to 90 per cent at 9 < log LIR < 12.5. The SFRHα and ? show good correlations with LIR for SFG and AGN, respectively. The self-absorption-corrected Hα/Hβ ratio shows a weak increase with LIR with a substantial scatter. When we separate IR LFs into contributions from AGN and SFG, the AGN contribution becomes dominant at LIR > 1011 L?, coinciding with the break of both the SFG and AGN IR LFs. At LIR? 1011 L?, SFG dominates IR LFs. Only 1.1 ± 0.1 per cent of ΩIR is produced by luminous infrared galaxies (LIR > 1011 L?), and only 0.03 ± 0.01 per cent by ultraluminous infrared galaxies (LIR > 1012 L?) in the local Universe. Compared with high-redshift results from the AKARI NEP deep survey, we observed a strong evolution of ΩSFGIR∝ (1 +z)4.1±0.4 and ΩAGNIR∝ (1 +z)4.1±0.5. Our results show that all of our measured quantities (IR LFs, L*, ΩAGNIR, ΩSFGIR) show smooth and steady increase from lower redshift (the Revised Bright Galaxy Sample) to higher redshift (the AKARI NEP deep survey).


AKARI-CAS Online Service for AKARI All-Sky Catalogues

The AKARI All-Sky Catalogues are an important infrared astronomical database for next-generation astronomy that take over the IRAS catalog. We have developed an online service, AKARI Catalogue Archive Server (AKARI-CAS), for astronomers. The service includes useful and attractive search tools and visual tools. One of the new features of AKARI-CAS is cached SIMBAD/NED entries, which can match AKARI catalogs with other catalogs stored in SIMBAD or NED. To allow advanced queries to the databases, direct input of SQL is also supported. In those queries, fast dynamic cross-identification between registered catalogs is a remarkable feature. In addition, multiwavelength quick-look images are displayed in the visualization tools, which will increase the value of the service. In the construction of our service, we considered a wide variety of astronomers' requirements. As a result of our discussion, we concluded that supporting users' SQL submissions is the best solution for the requirements. Therefore, we implemented an RDBMS layer so that it covered important facilities, including the whole processing of tables. We found that PostgreSQL is the best open-source RDBMS products for such purpose, and we wrote codes for both simple and advanced searches into the SQL stored functions. To implement such stored functions for fast radial search and cross-identification with minimum cost, we applied a simple technique that is not based on HTM or HEALPix. In contrast, the online application layer became compact and was written in simple procedural PHP codes. In total, our system realizes cost-effective maintenance and enhancements.


Electrical and Photoconductive Properties at 1.8 K of Germanium p+-i Junction Device Fabricated by Surface-Activated Wafer Bonding

We have evaluated the electrical and photoconductive properties of a Ge p+-i junction device, fabricated by surface-activated wafer bonding (SAB) technology, at temperatures of 1.8-5 K. The p+-i junction consists of two bonded layers, Ge heavily doped with Ga at a concentration of 1×1016 cm-3 and non- doped intrinsic Ge. The bonded Ge wafer was diced to a 1-mm cubic test element having two layers of thickness 0.5 mm and two facing electrodes. We measured the current-voltage characteristics of the device at 1.8-5 K, and its photoresponses against stepped illumination with far-infrared light at 1.8 K. The device shows the expected cryogenic performance in terms of electrical and photoconductive properties, demonstrating the promising applicability of SAB-processed Ge p+-i junction devices in blocked-impurity-band-type Ge detectors.


Properties of Dust and PAHs in the Hot Plasma of the Elliptical Galaxy NGC 4125 Revealed with AKARI and Spitzer Space Telescope

We present the spatial distributions of dust and polycyclic aromatic hydrocarbons (PAHs) in the elliptical galaxy NGC 4125, revealed by AKARI and Spitzer. NGC 4125 is relatively bright in dust and PAH emision for elliptical galaxies, although it certainly possesses diffuse interstellar hot plasma, indicated by the high spatial resolution X-ray data of Chandra. We investigate how the dust and PAHs interact with the X-ray plasma or avoid the interaction by comparing their spatial distributions. We find that the distributions of the PAHs and dust are different from each other, both showing a significant deviation from a smooth stellar distribution. The PAH emission predominantly comes from a dust lane, a compact dense molecular gas region in the galactic center, where the PAHs are likely to have been protected from the interaction with the X-ray plasma. The dust emission has more extended structures, similar to the distribution of the X-ray plasma, suggesting their interaction to some extent. We also discuss a possible origin of the dust and PAHs in the galaxy.

Publications of the Astronomical Society of Japan


AKARI detections of hot dust in luminous infrared galaxies. Search for dusty active galactic nuclei

Aims: We present a new sample of active galactic nuclei (AGNs) identified using the catalog of the AKARI Mid-infrared (MIR) All-Sky Survey. Our MIR search has the advantage of detecting AGNs that are obscured at optical wavelengths by extinction. Methods: We first selected AKARI 9 μm excess sources with F(9 μm)/F(KS) > 2 where KS magnitudes were taken from the Two Micron All Sky Survey. We then obtained follow-up near-infrared spectroscopy with the AKARI/IRC to confirm that the excess is caused by hot dust. We also obtained optical spectroscopy with the Kast Double Spectrograph on the Shane 3-m telescope at Lick Observatory. Results: On the basis of these observations, we detected hot dust with a characteristic temperature of ? 500 K in two luminous infrared galaxies. The hot dust is suspected to be associated with AGNs that exhibit their nonstellar activity not in the optical, but in the near- and mid-infrared bands, i.e., they harbor buried AGNs. The host galaxy stellar masses of ~4-6 × 109 M? are small compared with the hosts in optically-selected AGN populations. These objects were missed by previous surveys, demonstrating the power of the AKARI MIR All-Sky Survey to widen AGN searches to include more heavily obscured objects. The existence of multiple dusty star clusters with massive stars cannot be completely ruled out with our current data.


Effects of High-Energy Ionizing Particles on the Si:As Mid-Infrared Detector Array on Board the AKARI Satellite

We evaluate the effects of high-energy ionizing particles on the Si:As impurity band conduction (IBC) mid-infrared detector on board AKARI, the Japanese infrared astronomical satellite. IBC-type detectors are known to be little influenced by ionizing radiation. However, we find that the detector is significantly affected by in-orbit ionizing radiation even after spikes induced by ionizing particles are removed. The effects are described as changes mostly in the offset of detector output, but not in the gain. We conclude that the changes in the offset are caused mainly by increase in dark current. We establish a method to correct these ionizing radiation effects. The method is essential to improve the quality and to increase the sky coverage of the AKARI mid-infrared all- sky-survey map.


AKARI Near-infrared Spectroscopic Observations of Interstellar Ices in the Edge-on Starburst Galaxy NGC 253

We present the spatially resolved near-infrared (2.5-5.0 μm) spectra of the edge-on starburst galaxy NGC 253 obtained with the Infrared Camera on board AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H2O: 3.05 μm, CO2: 4.27 μm, and XCN: 4.62 μm) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 μm and the hydrogen recombination line Brα at 4.05 μm. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO2)/N(H2O) = 0.17 ± 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 ± 0.03), although a much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC 253.


Supernova dust for the extinction law in a young infrared galaxy at z? 1

We apply the supernova (SN) extinction curves to reproduce the observed properties of SST J1604+4304 which is a young infrared (IR) galaxy at z? 1. The SN extinction curves used in this work were obtained from models of unmixed ejecta of Type II supernovae for the Salpeter initial mass function with a mass range from 8 to 30 M? or 8 to 40 M?. The effect of dust distributions on the attenuation of starlight is investigated by performing the χ2 fitting method against various dust distributions. These are the commonly used uniform dust screen, the clumpy dust screen and the internal dust geometry. We add to these geometries three scattering properties, namely, no scattering, isotropic scattering and forward-only scattering. Judging from the χ2 values, we find that the uniform screen models with any scattering property provide good approximations to the real dust geometry. Internal dust is inefficient to attenuate starlight and thus cannot be the dominant source of the extinction. We show that the SN extinction curves reproduce the data of SST J1604+4304 comparable to or better than the Calzetti extinction curve. The Milky Way extinction curve is not in satisfactory agreement with the data unless several dusty clumps are in the line of sight. This trend may be explained by the abundance of SN-origin dust in these galaxies; SN dust is the most abundant in the young IR galaxy at z? 1, abundant in local starbursts and less abundant in the Galaxy. If dust in SST J1604+4304 is dominated by SN dust, the dust production rate is ?0.1 M? per SN.

Monthly Notices of the Royal Astronomical Society


Erratum: Stellar population and dust extinction in an ultraluminous infrared galaxy at z= 1.135


Outflow in Overlooked Luminous Quasar: Subaru Observations of AKARI J1757+5907

We present Subaru observations of the newly discovered luminous quasar AKARI J1757+5907, which shows an absorption outflow in its spectrum. The absorption consists of 9 distinct troughs, and our analysis focuses on the troughs at ?-1000 km s-1 for which we could measure accurate column densities of He I*, Fe II, and Mg II. We used photoionization models to constrain the ionization parameter, total hydrogen column density, and number density of the outflowing gas. These constraints yielded lower limits for the distance, mass-flow rate, and kinetic luminosity for outflows of 3.7 kpc, 70 Modot yr-1, and 2.0 ×1043 erg s-1, respectively. Such a mass-flow rate value can contribute significantly to metal enrichment of the intra-cluster medium. We found that this moderate velocity outflow is similar to those recently discovered in massive post-starburst galaxies. Finally, we describe the scientific potential of future observations targeting this object.


Luminosity functions of local infrared galaxies with AKARI: implications for the cosmic star formation history and AGN evolution

Infrared (IR) luminosity is fundamental to understanding the cosmic star formation history and active galactic nuclei (AGN) evolution, since their most intense stages are often obscured by dust. However, local IR luminosity function estimates today are still based on the IRAS survey in the 1980s, with wavelength coverage only up to 100 μm. The AKARI IR space telescope performed an all-sky survey in six IR bands (9, 18, 65, 90, 140 and 160 μm) with 3-10 times better sensitivity, covering the crucial far-IR wavelengths across the peak of the dust emission. Combined with a better spatial resolution, AKARI can much more precisely measure the total infrared luminosity (LTIR) of individual galaxies, and thus, the total infrared luminosity density in the local Universe. By fitting modern IR spectral energy distribution (SED) models, we have remeasured LTIR of the IRAS Revised Bright Galaxy Sample, which is a complete sample of local galaxies with S60 μm > 5.24 Jy. We present mid-IR monochromatic luminosity (νLν) to LTIR correlations for Spitzer8 μm, AKARI9 μm, IRAS12 μm, WISE12 μm, ISO15 μm, AKARI18 μm, WISE22 μm and Spitzer24 μm filters. These measures of LMIR are well correlated with LTIR, with scatter in the range 13-44 per cent. The best-fitting LMIR-to-LTIR conversions provide us with estimates of LTIR using only a single MIR band, in which several deep all-sky surveys are becoming available such as AKARI MIR and WISE. Although we have found some overestimates of LTIR by IRAS due to contaminating cirrus/sources, the resulting AKARI IR luminosity function (LF) agrees well with that from IRAS. We integrate the LF weighted by LTIR to obtain a cosmic IR luminosity density of ΩTIR= (8.5+1.5-2.3) × 107 L? Mpc-3, of which 7 ± 1 per cent is produced by luminous infrared galaxies (LIRGs) (LTIR > 1011 L?), and only 0.4 ± 0.1 per cent is from ultraluminous infrared galaxies (ULIRGs) (LTIR > 1012 L?) in the local Universe, in stark contrast to high-redshift results. We separate the contributions from AGN and star-forming galaxies (SFGs). The SFG IR LF shows a steep decline at the bright end. Combined with high-redshift results from the AKARI NEP deep survey, these data show a strong evolution of ΩSFTIR∝ (1 +z)4.0±0.5 and ΩAGNTIR∝ (1 +z)4.4±0.4. For ΩAGNTIR, the ULIRG contribution exceeds that from LIRGs already by z? 1. A rapid evolution in both ΩAGNTIR and ΩSFGTIR suggests the correlation between star formation and black hole accretion rate continues up to higher redshifts. We compare the evolution of ΩAGNTIR to that of X-ray luminosity density. The ΩAGNTIR/ΩX-ray AGN ratio shows a possible increase at z > 1, suggesting an increase of obscured AGN at z > 1.


Implications from the optical to ultraviolet flux ratio of Fe II emission in quasars

We investigate Fe II emission in the broad-line region (BLR) of active galactic nuclei by analysing the Fe II(UV), Fe II(λ4570) and Mg II emission lines in 884 quasars in the Sloan Digital Sky Survey Quasar catalogue in a redshift range of 0.727 < z < 0.804. Fe II(λ4570)/Fe II(UV) is used to infer the column density of Fe II- emitting clouds and explore the excitation mechanism of Fe II emission lines. As suggested before in various works, the classical photoionization models fail to account for Fe II(λ4570)/Fe II(UV) by a factor of 10, which may suggest anisotropy of UV Fe II emission, or an alternative mechanism like shocks. The column density distribution derived from Fe II(λ4570)/Fe II(UV) indicates that radiation pressure plays an important role in BLR gas dynamics. We find a positive correlation between Fe II(λ4570)/Fe II(UV) and the Eddington ratio. We also find that the ionizing photon fraction must be much smaller than that previously suggested unless Fe II-emitting clouds are super- Eddington. Finally, we propose a physical interpretation of a striking set of correlations between various emission-line properties, known as `Eigenvector 1'.


A survey of T Tauri stars with AKARI towards the Taurus-Auriga region

Context. The first Japanese infrared astronomical satellite, AKARI, has completed an All-Sky Survey at mid- to far-infrared wavelengths with higher spatial resolutions and sensitivities than the previous survey with Infrared Astronomical Satellite (IRAS). Aims: We search for new T Tauri star (TTS) candidates with the mid-infrared (MIR) part of the AKARI All-Sky Survey at 9 and 18 μm wavelengths. Methods: We used the point source catalogue (PSC) obtained by the Infrared Camera (IRC) on board AKARI. We combined the 2MASS PSC and the 3rd version of the USNO CCD Astrograph Catalogue (UCAC) with the AKARI IRC-PSC, and surveyed 517 known TTSs over a 1800-square-degree part of the Taurus- Auriga region to develop criteria to extract TTSs. We considered asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae (PNe), and galaxies, which have similar MIR colours, to separate TTSs from these sources. We finally searched for new TTS candidates from AKARI IRC-PSC in the same Taurus-Auriga region. Results: Of the 517 known TTSs, we detected 133 sources with AKARI: 46 sources were not detected by IRAS. Based on the colour-colour and colour-magnitude diagrams made from the AKARI, 2MASS, and UCAC surveys, we propose the criteria to extract TTS candidates from the AKARI All-Sky data, and 68/133 AKARI detected TTSs have passed these criteria. On the basis of our criteria, we selected 176/14725 AKARI sources as TTS candidates that are located around the Taurus-Auriga region. Comparing these sources with SIMBAD, we found that 148 are previously identified sources including 115 young stellar objects (YSOs), and 28 unidentified sources. Conclusions: Based on SIMBAD identifications, we infer the TTS- identification probability using our criteria to be ~75%. We find 28 TTS candidates, of which we expect ~21 to be confirmed once follow-up observations can be obtained. Although the probability of ~75% is not so high, it is affected by the completeness of the SIMBAD database, and we can search for TTSs over the whole sky, and all star-forming regions. Tables 1 and 2 are only available in electronic form 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/519/A83


A deep survey of the AKARI north ecliptic pole field . I. WSRT 20 cm radio survey description, observations and data reduction

Aims: The Westerbork Radio Synthesis Telescope, WSRT, has been used to make a deep radio survey of an ~1.7 degree2 field coinciding with the AKARI north ecliptic pole deep field. The observations, data reduction and source count analysis are presented, along with a description of the overall scientific objectives. Methods: The survey consisted of 10 pointings, mosaiced with enough overlap to maintain a similar sensitivity across the central region that reached as low as 21 μJy beam-1 at 1.4 GHz. Results: A catalogue containing 462 sources detected with a resolution of 17.0'' × 15.5'' is presented. The differential source counts calculated from the WSRT data have been compared with those from the shallow VLA-NEP survey of Kollgaard et al. 1994, and show a pronounced excess for sources fainter than ~1 mJy, consistent with the presence of a population of star forming galaxies at sub-mJy flux levels. Conclusions: The AKARI north ecliptic pole deep field is the focus of a major observing campaign conducted across the entire spectral region. The combination of these data sets, along with the deep nature of the radio observations will allow unique studies of a large range of topics including the redshift evolution of the luminosity function of radio sources, the clustering environment of radio galaxies, the nature of obscured radio-loud active galactic nuclei, and the radio /far-infrared correlation for distant galaxies. This catalogue provides the basic data set for a future series of paper dealing with source identifications, morphologies, and the associated properties of the identified radio sources.


Detection of Parent H2O and CO2 Molecules in the 2.5-5 μm Spectrum of Comet C/2007 N3 (Lulin) Observed with AKARI

Comet C/2007 N3 (Lulin) was observed with the Japanese infrared satellite AKARI in the near-infrared at a post-perihelion heliocentric distance of 1.7 AU. Observations were performed with the spectroscopic (2.5-5.0 μm) and imaging (2.4, 3.2, and 4.1 μm) modes on 2009 March 30 and 31 UT, respectively. AKARI images of the comet exhibit a sunward crescent-like shape coma and a dust tail extended toward the anti-solar direction. The 4.1 μm image (CO/CO2 and dust grains) shows a distribution different from the 2.4 and 3.2 μm images (H2O and dust grains). The observed spectrum shows distinct bands at 2.66 and 4.26 μm, attributed to H2O and CO2, respectively. This is the fifth comet in which CO2 has been directly detected in the near-infrared spectrum. In addition, CO at 4.67 μm and a broad 3.2-3.6 μm emission band from C-H bearing molecules were detected in the AKARI spectrum. The relative abundance ratios CO2/H2O and CO/H2O derived from the molecular production rates are ~4%-5% and <2%, respectively. Comet Lulin belongs to the group that has relatively low abundances of CO and CO2 among all observed comets.


Bright source catalogues based on the new mid- and far-infrared all-sky survey by the infrared astronomical satellite AKARI were released into the public domain in March 2010. The mid-infrared catalogue contains more than 870 thousand sources observed at 9 and 18 μm, and the far- infrared catalogue provides information of about 427 thousand sources at 65, 90, 140, and 160 μm. The AKARI catalogues will take over the IRAS catalogues and will become one of the most important catalogues in astronomy. We present the characteristics of the AKARI infrared source catalogues as well as current activity for the future versions.

Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave


The AKARI/IRC mid-infrared all-sky survey

Context. AKARI is the first Japanese astronomical satellite dedicated to infrared astronomy. One of the main purposes of AKARI is the all-sky survey performed with six infrared bands between 9 μm and 200 μm during the period from 2006 May 6 to 2007 August 28. In this paper, we present the mid-infrared part (9 μm and 18 μm bands) of the survey carried out with one of the on-board instruments, the infrared camera (IRC). Aims: We present unprecedented observational results of the 9 μm and 18 μm AKARI all-sky survey and detail the operation and data processing leading to the point source detection and measurements. Methods: The raw data are processed to produce small images for every scan, and the point sources candidates are derived above the 5ς noise level per single scan. The celestial coordinates and fluxes of the events are determined statistically and the reliability of their detections is secured through multiple detections of the same source within milli- seconds, hours, and months from each other. Results: The sky coverage is more than 90% for both bands. A total of 877 091 sources (851 189 for 9 μm, 195 893 for 18 μm) are confirmed and included in the current release of the point source catalog. The detection limit for point sources is 50 mJy and 90 mJy for the 9 μm and 18 μm bands, respectively. The position accuracy is estimated to be better than 2''. Uncertainties in the in-flight absolute flux calibration are estimated to be 3% for the 9 μm band and 4% for the 18 μm band. The coordinates and fluxes of detected sources in this survey are also compared with those of the IRAS survey and are found to be statistically consistent. Catalog is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi- bin/qcat?J/A+A/514/A1


AKARI's infrared view on nearby stars. Using AKARI infrared camera all-sky survey, 2MASS, and Hipparcos catalogs

Context. The AKARI, a Japanese infrared space mission, has performed an All-Sky Survey in six infrared-bands from 9 to 180 μm with higher spatial resolutions and better sensitivities than IRAS. Aims: We investigate the mid-infrared (9 and 18 μm) point source catalog (PSC) obtained with the infrared camera (IRC) onboard AKARI, in order to understand the infrared nature of the known objects and to identify previously unknown objects. Methods: Color-color diagrams and a color-magnitude diagram were plotted with the AKARI-IRC PSC and other available all-sky survey catalogs. We combined the Hipparcos astrometric catalog and the 2MASS all-sky survey catalog with the AKARI-IRC PSC. We furthermore searched literature and SIMBAD astronomical database for object types, spectral types, and luminosity classes. We identified the locations of representative stars and objects on the color-magnitude and color-color diagram schemes. The properties of unclassified sources can be inferred from their locations on these diagrams. Results: We found that the (B-V) vs. (V-S9W) color-color diagram is useful for identifying the stars with infrared excess emerged from circumstellar envelopes or disks. Be stars with infrared excess are separated well from other types of stars in this diagram. Whereas (J-L18W) vs. (S9W- L18W) diagram is a powerful tool for classifying several object types. Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars form distinct sequences in this color-color diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, and planetary nebulae (PNe) have the largest mid-infrared color excess and can be identified in the infrared catalog. Finally, we plot the L18W vs. (S9W- L18W) color-magnitude diagram, using the AKARI data together with Hipparcos parallaxes. This diagram can be used to identify low-mass YSOs and AGB stars. We found that this diagram is comparable to the [24] vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources using the Spitzer Space Telescope data. Our understanding of Galactic objects will be used to interpret color-magnitude diagram of stellar populations in the nearby galaxies that Spitzer Space Telescope observed. Conclusions: Our study of the AKARI color-color and color-magnitude diagrams will be used to explore properties of unknown objects in the future. In addition, our analysis highlights a future key project to understand stellar evolution with a circumstellar envelope, once the forthcoming astronometrical data with GAIA are available. Catalog (full Tables 3 and 4) are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi- bin/qcat?J/A+A/514/A2


Polycyclic aromatic hydrocarbon (PAH) luminous galaxies at z ~ 1

Aims: The NEP-deep survey, an extragalactic AKARI survey towards the north ecliptic pole (NEP), provides a comprehensive wavelength coverage from 2 to 24 μm using all 9 photometric bands of the infrared camera (IRC). It allows us to photometrically identify galaxies whose mid-IR emission is clearly dominated by PAHs. Methods: We propose a single-colour selection method to identify such galaxies, using two mid-IR flux ratios at 11-to-7 μm and 15-to-9 μm (PAH-to-continuum flux ratio in the rest frame), which are useful for identifying starburst galaxies at z ~ 0.5 and 1, respectively. We perform a fitting of the spectral energy distributions (SEDs) from optical to mid-IR wavelengths, using an evolutionary starburst model with a proper treatment of radiative transfer (SBURT), in order to investigate their nature. Results: The SBURT model reproduces observed optical-to-mid-IR SEDs of more than a half of the PAH-selected galaxies. Based on the 8 μm luminosity, we find ultra luminous infrared galaxies (ULIRGs) among PAH- selected galaxies. Their PAH luminosity is higher than local ULIRGs with a similar luminosity, and the PAH-to-total IR luminosity ratio is consistent with that of less luminous starburst galaxies. They are a unique galaxy population at high redshifts, and we call these PAH- selected ULIRGs ``PAH-luminous'' galaxies. Although they are not as massive as submillimetre galaxies at z ~ 2, they have the stellar mass of > 3 × 1010 M_? and therefore are moderately massive.


Evolution of infrared luminosity functions of galaxies in the AKARI NEP-deep field. Revealing the cosmic star formation history hidden by dust

Aims: Dust-obscured star-formation increases with increasing intensity and increasing redshift. We aim to reveal the cosmic star- formation history obscured by dust using deep infrared observation with AKARI. Methods: We constructed restframe 8 μm, 12 μm, and total infrared (TIR) luminosity functions (LFs) at 0.15 < z < 2.2 using 4128 infrared sources in the AKARI NEP-deep field. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24 μm) by the AKARI satellite allowed us to estimate restframe 8 μm and 12 μm luminosities without using a large extrapolation based on an SED fit, which was the largest uncertainty in previous work. Results: We find that all 8 μm (0.38 < z < 2.2), 12 μm (0.15 < z < 1.16), and TIR LFs (0.2 < z <1.6) show continuous and strong evolution toward higher redshift. Our direct estimate of 8 μm LFs is useful since previous work often had to use a large extrapolation from the Spitzer 24 μm to 8 μm, where SED modeling is more difficult because of the PAH emissions. In terms of cosmic infrared luminosity density (Ω_IR), which was obtained by integrating analytic fits to the LFs, we find good agreement with previous work at z<1.2. We find the Ω_IR evolves as propto(1 + z)4.4± 1.0. When we separate contributions to Ω_IR by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We find that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z = 0.35 to z = 1.4. This research is based on the observations with AKARI, a JAXA project with the participation of ESA.Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.


Environmental dependence of 8 μm luminosity functions of galaxies at z ~ 0.8. Comparison between RXJ1716.4+6708 and the AKARI NEP-deep field

Aims: We aim to reveal environmental dependence of infrared luminosity functions (IR LFs) of galaxies at z ~ 0.8 using the AKARI satellite. AKARI's wide field of view and unique mid-IR filters help us to construct restframe 8 μm LFs directly without relying on SED models. Methods: We construct restframe 8 μm IR LFs in the cluster region RXJ1716.4+6708 at z = 0.81, and compare them with a blank field using the AKARI north ecliptic pole deep field data at the same redshift. AKARI's wide field of view (10' × 10') is suitable to investigate wide range of galaxy environments. AKARI's 15 μm filter is advantageous here since it directly probes restframe 8 μm at z ~ 0.8, without relying on a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. Results: We have found that cluster IR LFs at restframe 8 μm have a factor of 2.4 smaller L^* and a steeper faint-end slope than that of the field. Confirming this trend, we also found that faint-end slopes of the cluster LFs becomes flatter and flatter with decreasing local galaxy density. These changes in LFs cannot be explained by a simple infall of field galaxy population into a cluster. Physics that can preferentially suppress IR luminous galaxies in high density regions is required to explain the observed results. This research is based on the observations with AKARI, a JAXA project with the participation of ESA.Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.


Source counts at 15 microns from the AKARI NEP survey

We present galaxy counts at 15 microns using the Japanese AKARI satelitte's NEP-deep and NEP-wide legacy surveys at the north ecliptic pole. The total number of sources detected are approximately 6700 and 10 700 down to limiting fluxes of 117 and 250 microJy (5 sigma) for the NEP-deep and NEP-wide survey respectively. We construct the Euclidean normalized differential source counts for both data sets (assuming 80 percent completeness levels of 200 and 270 microJy respectively) to produce the widest and deepest contiguous survey at 15 microns to date covering the entire flux range from the deepest to shallowest surveys made with the infrared space observatory (ISO) over areas sufficiently significant to overcome cosmic variance, detecting six times as many sources as the largest survey carried out with ISO. We compare the results from AKARI with the previous surveys with ISO at the same wavelength and the Spitzer observations at 16 microns using the peek-up camera on its IRS instrument. The AKARI source counts are consistent with other results to date reproducing the steep evolutionary rise at fluxes less than a milliJansky and super-Euclidean slopes. We find the the AKARI source counts show a slight excess at fluxes fainter than 200 microJanskys which is not predicted by previous source count models at 15 microns. However, we caution that at this level we may be suffering from the effects of source confusion in our data. At brighter fluxes greater than a milliJansky, the NEP-wide survey source counts agree with the Northern ISO-ELAIS field results, resolving the discrepancy of the bright end calibration in the ISO 15 micron source counts.


The AKARI FU-HYU galaxy evolution program: first results from the GOODS-N field

The AKARI FU-HYU mission program carried out mid-infrared imaging of several well studied Spitzer fields preferentially selecting fields already rich in multi-wavelength data from radio to X-ray wavelengths filling in the wavelength desert between the Spitzer IRAC and MIPS bands. We present the initial results for the FU-HYU survey in the GOODS-N field. We utilize the supreme multiwavelength coverage in the GOODS-N field to produce a multiwavelength catalogue from infrared to ultraviolet wavelengths, containing more than 4393 sources, including photometric redshifts. Using the FU-HYU catalogue we present colour- colour diagrams that map the passage of PAH features through our observation bands. We find that the longer mid-infrared bands from AKARI (IRC-L18W 18 micron band) and Spitzer (MIPS24 24 micron band) provide an accurate measure of the total MIR emission of the sources and therefore their probable total mid-infrared luminosity. We also find that colours incorporating the AKARI IRC-S11 11 micron band produce a bimodal distribution where an excess at 11 microns preferentially selects moderate redshift star-forming galaxies. These powerful colour-colour diagnostics are further used as tools to extract anomalous colour populations, in particular a population of Silicate Break galaxies from the GOODS-N field showing that dusty starbursts can be selected of specific redshift ranges (z = 1.2-1.6) by mid-infrared drop-out techniques. The FU-HYU catalogue will be made publically available to the astronomical community.


The AGN fraction of submm-selected galaxies and contributions to the submm/mm-wave extragalactic background light

We present a comparison of the SCUBA half degree extragalactic survey (SHADES) at 450 μm, 850 μm and 1100 μm with deep guaranteed time 15 μm AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24 μm 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. Our stacking analyses find AKARI 15 μm galaxies with ?200 μJy contribute >10% of the 450 μm background, but only <4% of the 1100 μm background, suggesting that different populations contribute at mm- wavelengths. We confirm our earlier result that the ultra-deep 450 μm SCUBA-2 cosmology survey will be dominated by populations already detected by AKARI and Spitzer mid-infrared surveys. The superb mid- infrared wavelength coverage afforded by combining Spitzer and AKARI photometry is an excellent diagnostic of AGN contributions, and we find that (23-52)% of submm-selected galaxies have AGN bolometric fractions fAGN > 0.3.


Stellar population and dust extinction in an ultraluminous infrared galaxy at z = 1.135

We present the detailed optical to far-infrared (far-IR) observations of SST J1604+4304, an ultraluminous IR galaxy at z = 1.135. Analysing the stellar absorption lines, namely, the CaII H & K and Balmer H lines in the optical spectrum, we derive the upper limits of an age for the stellar population. Given this constraint, the minimum χ2 method is used to fit the stellar population models to the observed spectral energy distribution from 0.44 to 5.8 μm. We find the following properties. The stellar population has an age 40-200 Myr with a metallicity 2.5 Zsolar. The starlight is reddened by E(B - V) = 0.8. The reddening is caused by the foreground dust screen, indicating that dust is depleted in the starburst site and the starburst site is surrounded by a dust shell. The IR (8-1000 μm) luminosity is Lir = 1.78 +/- 0.63 × 1012Lsolar. This is two times greater than that expected from the observed starlight, suggesting either that 1/2 of the starburst site is completely obscured at UV-optical wavelengths, or that 1/2 of Lir comes from active galactic nucleus (AGN) emission. The inferred dust mass is 2.0 +/- 1.0 × 108Msolar. This is sufficient to form a shell surrounding the galaxy with an optical depth E(B - V) = 0.8. From our best stellar population model - an instantaneous starburst with an age 40 Myr - we infer the rate of 19 supernovae per year. Simply analytical models imply that 2.5 Zsolar in stars was reached when the gas mass reduced to 30 per cent of the galaxy mass. The gas metallcity is 4.8Zsolar at this point. The gas-to-dust mass ratio is then 120 +/- 73. The inferred dust production rate is 0.24 +/- 0.12Msolar per SN. If 1/2 of Lir comes from AGN emission, the rate is 0.48 +/- 0.24Msolar per SN. We discuss the evolutionary link of SST J1604+4304 to other galaxy populations in terms of the stellar masses and the galactic winds, including optically selected low-luminosity Lyman α-emitters and submillimeter selected high-luminosity galaxies.

Monthly Notices of the Royal Astronomical Society


AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous polar orbit at the altitude of 700 km. One of the major observation programs of the AKARI is an all-sky survey in the mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was carried out with the Infrared Camera (IRC) at the 9 and 18 μm bands with the sensitivity of about 50 and 120 mJy (5ς per scan), respectively. The spatial resolution is about 9.4'' at both bands. AKARI mid-infrared (MIR) all-sky survey substantially improves the MIR dataset of the IRAS survey of two decades ago and provides a significant database for studies of various fields of astronomy ranging from star-formation and debris disk systems to cosmology. This paper describes the current status of the data reduction and the characteristics of the AKARI MIR all-sky survey data.

AKARI, a Light to Illuminate the Misty Universe


Near to Mid-Infrared Observations of Recent Supernovae with Infrared Camera (IRC) onboard AKARI

We present our latest results on near- to mid-infrared observations of supernovae within one year after the explosion with Infrared Camera (IRC) on board AKARI. In this project, we aim to explore the dust formation scenario in the ejecta of core-collapse supernovae. So far, observations of several recent supernovae including SN2006jc and SN2008ax have been carried out as part of the Directors Time of AKARI. At the same time, we have set about the near-infrared slit-less spectroscopic observations of nearby galaxies with high supernovae frequency in preparation for a future supernova in the AKARI Phase-3 Open Time Program ``Near-infrared Slit-less Spectroscopy of Nearby Galaxies; Waiting for Supernovae Momentarily (NEWSY)'' (P.I. Sakon, I.). The obtained near- to mid-infrared spectral energy distribution (SED) of early-time supernovae is quite valuable and unique to investigate the properties of dust formed around the massive star and will further deepen our knowledge on the origin of dust especially in the early universe.


AKARI Deep Extragalactic Survey towards the North Ecliptic Pole: The NEP-Deep Survey

We have conducted the largest extragalactic survey with IRC pointed observations, towards the north ecliptic pole (NEP). Using this survey, which covers 0.38 deg2, we demonstrate that IRC all-band photometry at 2-24 μm is capable of tracing the steep rise of flux at the blue side of PAH 6.2 μm feature. Single mid-infrared colors, such as S11-S7 and L15-S9W, can be used to select PAH-dominated starburst galaxies at z ? 0.5. These PAH-selected galaxies include new type of ultra luminous infrared galaxies whose SED resembles that of less luminous starburst galaxies by two orders of magnitude. We present highlights from the initial results of the NEP-Deep survey.


Far-Infrared Cosmological Survey in AKARI Deep Field South: Galaxy Number Counts

The AKARI far-infrared deep cosmological survey has been carried out toward the region with the lowest cirrus density in the whole sky, near the South Ecliptic Pole (AKARI Deep Survey South: ADF-S). We present the details of this survey, and show the obtained galaxy number counts. More than 2200 galaxies were detected down to a flux level of 10 mJy at 90 μm, and suggest the necessity for a new model to explain galaxy evolution.


Tuning in the Radio: Deep Radio Surveys Supporting the AKARI North and South Ecliptic Pole Ultra Deep Fields

We present a progress report on two deep radio surveys to support the AKARI North and South Ecliptic Pole Deep fields, and a first correlation between the extragalactic radio source population and their 20 cm fluxes.


First Results from the AKARI FU-HYU Mission Program

The AKARI FU-HYU mission program has carried out mid-infrared imaging of several well studied Spitzer fields. This imaging fills in the wavelength coverage lacking from the Spitzer surveys and gives an extremely high scientific return for minimal input for AKARI. We select fields already rich in multi-wavelength data from radio to X-ray wavelengths and present the results from our initial analysis in the GOODS-N field. We utilize the comprehansive multiwavelength coverage in the GOODS-N field to produce a multiwavelength catalogue from infrared to ultraviolet wavelengths including photometric redshifts. Using the FU-HYU catalogue we present colour-colour diagrams that map the passage of PAH features through our observation bands. These colour-colours diagrams are used as tools to extract anomalous colour populations, in particular a population of Silicate Break galaxies from the GOODS-N field.


We have carried out a reduction of the ``NEP-Wide'' data for four 9 bands between 2 and 24 μm with the AKARI InfraRed Camera. The data consists of 446 pointed observations and covers a circular area of ? 5.8 sq. deg. centered on North Ecliptic Pole. We made mosaic images in all of the bands except at 24 μm. The source detection and photometry were done on the mosaic images using SExtractor, and we have generated a band merged catalogue for all of the IRC bands (except for 24 μm) containing ?110,000 sources. The photometry was checked against the NEP-Deep results and found to be consistent with them.


A Milestone to SPICA Extragalactic Surveys: The AKARI NEP Survey

Large area surveys in the infrared wavelengths have revealed a significant evolution of the star formation activity of the universe in the past. The extragalactic sur- vey we have conduced with AKARI towards the north ecliptic pole (NEP) is unique, in terms of a comprehensive wavelength coverage from 2 to 24 micron using all 9 photometric bands of the Infrared Camera (IRC). We demonstrate that this IRC all-band photometry is capable of tracing a steep rise in the flux at the blue side of the polycyclic aromatic hydrocarbon (PAH) 6.2 micron emission feature of infrared luminous galaxies at z < 1. This allows us to estimate redshifts of mid-IR sources and identify `ultra-luminous starburst galaxies', based on mid-IR spectral energy distributions (SEDs). SPICA could inherit this unique capability of AKARI and extend the study to typical galaxy populations at z ~ 2, i.e. a critical period of galaxy formation.

The Next-Generation Infrared Space Mission: SPICA


AKARI Near- and Mid-Infrared Spectroscopy of APM 08279+5255 at z = 3.91

We present rest-frame optical/near-infrared spectra of the gravitationally lensed quasar APM 08279+5255 at z = 3.91 that has been taken using the Infrared Camera (IRC) onboard the AKARI infrared satellite. The observed continuum consists of two components; a power- law component dominating optical wavelengths which is the direct light from the central source and thermal emission dominating near-infrared wavelengths which is attributed to the emission from hot dust in the circumnuclear region. The thermal emission well represents optically thick emission by hot dust at T ~ 1300 K with τ2 μm > 2 and apparent mass, M hot > 10 M sun. Thus, our observations directly detected the optically thick region of hot dust in APM 08279+5255. H I recombination lines of Hα (0.656 μm), Paα (1.875 μm), and Paβ (1.282 μm) are clearly detected at 3.2, 6.3, and 9.3 μm. Simulations with the photoionization models suggest that APM 08279+5255 has broad-line region (BLR) clouds characterized by log n H ~ 12-14 for the gas density, log U ~ -2 to -6 for the ionization parameter, and E(B - V) ~ 0.3-0.6 for the BLR. Thus, optically thick emission of hot dust supports an idea on nonspherical distribution of dust near the central source, consistent with the active galactic nuclei model with the dust torus. The temperature of hot dust and flux ratios of these H I lines are similar to those observed in low-redshift quasars. There are significant time variations in the H I lines, which are probably caused by variations in the brightness of the central source. Based on observations with AKARI, a JAXA project with the participation of ESA.


Ultraviolet FeII emission in z ~ 2 quasars

We present spectra of six luminous quasars at z ~ 2, covering rest wavelengths 1600-3200 ?. The fluxes of the UV FeII emission lines and MgII λ2798 doublet, the line widths of MgII and the 3000 ? luminosity were obtained from the spectra. These quantities were compared with those of low-redshift quasars at z = 0.06-0.55 studied by Tsuzuki et al. In a plot of the FeII(UV)/MgII flux ratio as a function of the central black hole mass, FeII(UV)/MgII in our z ~ 2 quasars is systematically greater than in the low-redshift quasars. We confirmed that luminosity is not responsible for this excess. It is unclear whether this excess is caused by rich Fe abundance at z ~ 2 over low-redshift or by non- abundance effects such as high gas density, strong radiation field and high microturbulent velocity.

Monthly Notices of the Royal Astronomical Society


Photometric redshift accuracy in AKARI deep surveys

We investigate the photometric redshift accuracy achievable with the AKARI infrared data in deep multiband surveys, such as in the North Ecliptic Pole field. We demonstrate that the passage of redshifted polycyclic aromatic hydrocarbons (PAH) and silicate features into the mid-infrared wavelength window covered by AKARI is a valuable means to recover the redshifts of starburst galaxies. To this end, we have collected a sample of ~60 galaxies drawn from the Great Observatories Origins Deep Survey-North Field with spectroscopic redshift 0.5 <~ zspec <~ 1.5 and photometry from 3.6 to 24μm, provided by the Spitzer, Infrared Space Observatory and AKARI satellites. The infrared spectra are fitted using synthetic galaxy spectral energy distributions which account for starburst and active nuclei emission. For ~90 per cent of the sources in our sample, the redshift is recovered with an accuracy |zphot - zspec|/(1 + zspec) <~ 10 per cent. A similar analysis performed on a set of simulated spectra shows that the AKARI infrared data alone can provide photometric redshifts accurate to |zphot - zspec|/(1 + zspec) ~ 10 per cent (1ς) at z <~ 2. At higher redshifts, the PAH features are shifted outside the wavelength range covered by AKARI and the photo-z estimates rely on the less prominent 1.6μm stellar bump; the accuracy achievable in this case on (1 + z) is ~10-15 per cent, provided that the active galactic nuclei contribution to the infrared emission is subdominant. Our technique is no more prone to redshift aliasing than optical-ultraviolet photo-z, and it may be possible to reduce this aliasing further with the addition of submillimetre and/or radio data.


Properties of Newly Formed Dust by SN 2006JC Based on Near- to Mid-Infrared Observation With AKARI

We present our latest results on near- to mid-infrared (MIR) observation of supernova (SN) 2006jc at 200 days after the discovery using the Infrared Camera (IRC) on board AKARI. The near-infrared (2-5 μm) spectrum of SN 2006jc is obtained for the first time and is found to be well interpreted in terms of the thermal emission from amorphous carbon of 800 ± 10 K with the mass of 6.9 ± 0.5 × 10-5 M sun that was formed in the SN ejecta. This dust mass newly formed in the ejecta of SN 2006jc is in a range similar to those obtained for other several dust-forming core-collapse supernovae based on recent observations (i.e., 10-3-10-5 M sun). MIR photometric data with AKARI/IRC MIR-S/S7, S9W, and S11 bands have shown excess emission over the thermal emission by hot amorphous carbon of 800 K. This MIR excess emission is likely to be accounted for by the emission from warm amorphous carbon dust of 320 ± 10 K with the mass of 2.7+0.7 -0.5 × 10-3 M sun rather than by the band emission of astronomical silicate and/or silica grains. This warm amorphous carbon dust is expected to have been formed in the mass-loss wind associated with the Wolf-Rayet stellar activity before the SN explosion. Our result suggests that a significant amount of dust is condensed in the mass-loss wind prior to the SN explosion.


Diffuse 18 μm Emission around TYC 3159-6-1 Discovered by the AKARI MIR All-Sky Survey

We report on observations of the mysterious object TYC 3159-6-1 located toward the Cygnus X region. It shows interesting characteristics in the AKARI mid-infrared All-Sky Survey. The central star is clearly detected as a point source at 9μ, while no point-like source, but a large shell- like structure is seen around the source at 18μ. The optical spectrum indicates the presence of the weak Hα emission on the red smooth continuum, whereas the mid-infrared N-band spectrum shows neither excess emission nor significant silicate absorption. Interferometric continuum observations at 104GHz do not show any appreciable peak at the position of the star. On the basis of these observations, we investigate three possibilities of concerning the nature of TYC 3159-6-1: a nearby young stellar object, a heavily extincted high-mass star, and an asymptotic giant branch (AGB) star with a detached shell. We conclude that none of these cases can account for the observations consistently, and the nature of TYC 3159-6-1 remains a mystery.

Publications of the Astronomical Society of Japan


North Ecliptic Pole Wide Field Survey of AKARI: Survey Strategy and Data Characteristics

We present the survey strategy and the data characteristics of the North Ecliptic Pole (NEP) Wide Survey of AKARI. The survey was carried out for about one year starting from 2006 May with 9 passbands from 2.5 to 24μm and the areal coverage of about 5.8degree? centered on NEP. The survey depth reaches to 21.8 AB magnitude near infrared (NIR) bands, and ?18.6 AB magnitude at the mid infrared (MIR) bands such as 15 and 18μm. The total number of sources detected in this survey is about 104000, with more sources in NIR than in the MIR. We have cross matched infrared sources with optically identified sources in CFHT imaging survey which covered about 2degree? within NEP-Wide survey region in order to characterize the nature of infrared sources. The majority of the MIR sources at 15 and 18μm bands are found to be star forming disk galaxies, with smaller fraction of early type galaxies and AGNs. We found that a large fraction (60%--80%) of bright sources in 9 and 11μm is stars while stellar fraction decreases toward fainter sources. We present the histograms of the sources at MIR bands at 9, 11, 15, and 18μm. The number of sources per magnitude thus varies as m0.6 for longer wavelength sources while shorter wavelength sources show steeper variation with m, where m is the AB magnitude.


A Young Planetary Nebula in the Large Magellanic Cloud near the South Ecliptic Pole


AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous polar orbit at the altitude of 700 km. One of the major observation programs of the AKARI is an all-sky survey in the mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was carried out with the Infrared Camera (IRC) at the 9 and 18 μm bands with the sensitivity of about 50 and 120 mJy (5ς per scan), respectively. The spatial resolution is about 9.''4 at both bands. The 9 μm band probes the UIR bands effectively, whereas the 18 μm band traces the thermal emission from warm dust grains. We present an overview of the mid- infrared all-sky survey and report some initial results to demonstrate its great potential in the study of star-forming regions in our Galaxy.

The Evolving ISM in the Milky Way and Nearby Galaxies


Mapping dusty star formation in and around a cluster at z = 0.81 by wide-field imaging with AKARI

We present environmental dependence of dusty star-forming activity in and around the cluster RXJ1716.4+6708 at z = 0.81 based on wide-field and multiwavelength observations with the Prime Focus Camera on the Subaru Telescope (Suprime-Cam) and the Infrared Camera onboard the AKARI satellite. Our optical data show that the optical colour distribution of galaxies starts to dramatically change from blue to red at the medium- density environment such as cluster outskirts, groups and filaments. By combining with the AKARI infrared data, we find that 15-μm-detected galaxies tend to have optical colours between the red sequence and the blue cloud with a tail into the red sequence, consistent with being dusty star-forming galaxies. The spatial distribution of the 15-μm- detected galaxies over ~200 arcmin2 around the cluster reveals that few 15-μm galaxies are detected in the cluster central region. This is probably due to the low star-forming activity in the cluster core. However, interestingly, the fraction of 15-μm-detected galaxies in the medium-density environments is as high as in the low- density field, despite the fact that the optical colours start to change in the medium-density environments. Furthermore, we find that 15-μm- detected galaxies which have optically red colours (candidates for dusty red galaxies) and galaxies with high specific star formation rates are also concentrated in the medium-density environment. These results imply that the star-forming activity in galaxies in groups and filaments is enhanced due to some environmental effects specific to the medium- density environment (e.g. galaxy-galaxy interaction), and such a phenomenon is probably directly connected to the truncation of star- forming activity in galaxies seen as the dramatic change in optical colours in such environment.


Absolute Photometric Calibration of the Infrared Camera (IRC) aboard AKARI

The absolute photometric calibration of imaging observations with the Infrared Camera (IRC) aboard the AKARI satellite was performed by monitoring the same stars regularly and by observing aset of standard stars. By our monitoring observations, we confirmed that all channels of the IRC were stable to within 4% and that their sensitivities were constant until the liquid helium was exhausted. Using the data of these repeated observations, we evaluated the intrinsic errors as afunction of the brightnesses of objects and found that the errors increase rapidly toward fainter objects. We also checked the consistency between short and long exposure times, and confirmed that the data sampling had been executed as designed. Finally, by comparing the estimated in-band flux densities and the observed data values of standard stars, we obtained conversion factors to the absolute flux densities of all the band/exposure configurations. Their absolute uncertainties are estimated to be less than 6%.


AKARI/IRC Deep Survey in the North Ecliptic Pole Region

We have made adeep and wide imaging survey with all nine AKARI/IRC bands from 2 to 24 μm within ahalf degree of the North Ecliptic Pole. The survey covered acircular area of 0.38deg2 centered at RA = 17h56m, Dec = 66°37' where adeep optical multi- band survey has been conducted by Subaru/Suprime-Cam. The 5ς sensitivity of the survey for point sources is 11.0, 48, 117, and 275 μJy at wavelengths 3, 7, 15, and 24 μm, respectively. The survey is limited by sky noise at wavelengths from 7 to 24 μm, and limited by source confusion from 2 to 4 μm. We have also made apoint source catalog at each band, consisting of more than 5000 sources with a 50% completeness limit of 93 μ Jy at 15 μm. Our results are consistent with the pilot survey at faint fluxes and has better statistical significance at the bright fluxes. This is the first near- and mid-infrared sub-mJy extragalactic survey with contiguous wavelength coverage from 2 to 24 μm and a large band-merged catalogue. It will provide powerful and unique diagnostics of obscured star-formation and AGN activities in the galaxies up to z = 2.


Galaxy Clusters at 0.9 < z < 1.7 in the AKARI NEP Deep Field

There is ahuge gap between the properties of red-sequence selected massive galaxy clusters at z < 1 and Lyman-break selected proto- clusters at z > 3. It is important to understand when and how the z > 3 proto-clusters evolve into passive clusters at z < 1. We aim to fill this cluster desert by using space-based N4 (4 μm) imaging with AKARI. The z' - N4 color is apowerful separator of cluster galaxies at z > 1, taking advantage of the 4000? break and the 1.6 μm bump. We carefully selected 16 promising cluster candidates at 0.9 < z < 1.7, which all show an obvious over-density of galaxies and aprominent red-sequence. At this redshift range, the mid-infrared S15μm / S9μm flux ratio is an extinction-free indicator of galaxy star-formation activity due to the redshifted PAH emission lines (6.2, 7.7, and 8.6 μm). We show statistically that the cluster galaxies have alower S15μm / S9μm flux ratio than do field galaxies, i.e., cluster galaxies already have lower star-formation activity at 0.9 < z < 1.7, pushing the formation epoch of these galaxy clusters to a higher redshift.


Optical to Near-Infrared Spectrum of a Massive Evolved Galaxy at z = 1.26

We present the optical to near-infrared (IR) spectrum of the galaxy TSPS J1329-0957, a red and bright member of the class of extremely red objects (EROs) at z = 1.26. This galaxy was found in the course of the Tokyo-Stromlo Photometry Survey (TSPS) which we are conducting in the southern sky. The spectroscopic observations were carried out with the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near Infra-Red Spectrograph (GNIRS) mounted on the Gemini-South telescope. The wide wavelength coverage of 0.6-2.3 μm provides useful clues as to the nature of EROs while most published spectra are limited to a narrower spectral range which is dictated by the need for efficient redshift determination in a large survey. We compare our spectrum with several optical composite spectra obtained in recent large surveys, and with stellar population synthesis models. The effectiveness of using near-IR broadband data, instead of the spectral data, in deriving the galaxy properties are also investigated. We find that TSPS J1329-0957 formed when the universe was 2-3 Gyr old, and subsequently evolved passively to become one of the most massive galaxies found in the z = 1-2 universe. Its early type and estimated stellar mass of M* = 1011.5 M? clearly point to this galaxy being a direct ancestor of the brightest elliptical and spheroidal galaxies in the local universe.


The AKARI far-infrared deep survey has been carried out toward the region with the lowest cirrus density in the whole sky, near the South Ecliptic Pole. We present the details of this survey, and show the obtained galaxy counts. More than 2,200 galaxies were detected down to a flux level of 20 mJy, and suggest the necessity for a new model to explain galaxy evolution.

Panoramic Views of Galaxy Formation and Evolution


Evolution of Galaxy Clusters from an AKARI Mission Program, CLEVL

We present the status of the AKARI Mission Program on the evolution of cluster of galaxies, CLEVL. In order to understand the evolution of galaxies in cluster environment, we have conducted an AKARI imaging survey of galaxy clusters over a wide redshift range. For 8 low redshift clusters (z < 0.3), we performed 2-24 micron imaging in 6 passbands. For intermediate redshift clusters (0.3 < z < 1.3), we have examined the galaxy properties, and the environmental effect by conducting deep NIR-MIR imaging. For high redshift clusters (z > 1.3), we have imaged fields around radio or submm galaxies looking for signs of over-densities. Our program covers a large scale (?5 Mpc) over each target, enabling us to investigate the interaction of cluster members and its surrounding environment. The multi-wavelength capability enables us to use the same MIR star formation indicator over 0 < z < 3 for a consistent estimate of the star formation rate, and to study dust emission from circumstellar disks.


The State and Evolution of the Partly-Ionized Gas in AGNs Probed with Broad O I and Ca II Emission Lines

We are carrying out a program to explore prominent Fe II emission-line regions in AGNs with near-infrared (NIR) O I and Ca II lines as tracers. To date we have observed and compiled the relevant O I (λ1304, λ8446, and λ11287) and Ca II (λ8579 triplet) lines in 11 quasars at 0.06 le z le 1.08. The comparison with photoionization model calculations suggests that gas with a density n_{H} = 1011.5 - 1012.0 cm^{-3} is present in an outer portion of the broad emission-line region (BELR) illuminated by the ionizing radiation whose flux corresponds to the ionization parameter U = 10-3.0 - 10-2.5 on average. While the revealed gas density is similar, the ionizing radiation flux appears to be diverse among the quasars.


Number Density Evolution of Ks-Band-Selected High-Redshift Galaxy Populations in the AKARI North Ecliptic Pole Field

We present the number counts of Ks-band-selected high- redshift galaxy populations such as extremely red objects (EROs), B-, z-, and K-band-selected galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. These high-redshift galaxy samples are extracted from a multicolor catalog combining optical data from Suprime-Cam on the 8.2 m Subaru Telescope with near-infrared data from the Florida Multiobject Imaging Near-IR Grism Observational Spectrometer on the Kitt Peak National Observatory 2.1 m telescope over 540 arcmin2 in the NEP region field. The final catalog contains 308 EROs (Ks < 19.0; 54% are dusty star-forming EROs, and the rest are passive old EROs), 137 star-forming BzKs, and 38 passive old BzKs (Ks < 19.0) and 64 DRGs (Ks < 18.6). We also produce individual component source counts for both the dusty star-forming and passive populations. We compare the observed number counts of the high redshift passively evolving galaxy population with a backward pure luminosity evolution (PLE) model allowing different degrees of number density evolution. We find that the PLE model without density evolution fails to explain the observed counts at faint magnitudes, while the model incorporating negative density evolution is consistent with the observed counts of the passively evolving population. We also compare our observed counts of dusty star-forming EROs with a phenomenological evolutionary model postulating that the near-infrared EROs can be explained by the source densities of the far-infrared-submillimeter populations. Our model predicts that the dusty ERO source counts can be explained assuming a 25% contribution of submillimeter star-forming galaxies with the majority of brighter Ks-band-detected dusty EROs having luminous (rather than HR 10 type ultraluminous) submillimeter counterparts. We propose that the fainter Ks > 19.5 population is dominated by the submillijansky submillimeter population. We also predict a turnover in dusty ERO counts around 19 < Ks < 20.


Low-Ionization Emission Regions in Quasars: Gas Properties Probed with Broad O I and Ca II Lines

We have compiled the emission-line fluxes of O I λ8446, O I λ11287, and the near-infrared (IR) Ca II triplet (λ8579) observed in 11 quasars. These lines are considered to emerge from the same gas as do the Fe II lines in the low-ionized portion of the broad emission line region (BELR). The compiled quasars are distributed over wide ranges of redshift (0.06 <= z<= 1.08) and of luminosity (-29.8 <= MB <= - 22.1), thus providing a useful sample to investigate the line-emitting gas properties in various quasar environments. The measured line strengths and velocities, as functions of the quasar properties, are analyzed using photoionization model calculations. We found that the flux ratio between the Ca II triplet and O I λ8446 is hardly dependent on the redshift or luminosity, indicating similar gas densities in the emission region from quasar to quasar. On the other hand, a scatter of the O I λ11287/λ8446 ratios appears to imply the diversity of the ionization parameter. These facts invoke a picture of the line-emitting gases in quasars that have similar densities and are located at regions exposed to various ionizing radiation fluxes. The observed O I line widths are found to be remarkably similar over more than 3 orders of magnitude in luminosity, which indicates a kinematically determined location of the emission region and is in clear contrast to the case of H I lines. We also argue about the dust presence in the emission region since the region is suggested to be located near the dust sublimation point at the outer edge of the BELR.


An Optical Source Catalog of the North Ecliptic Pole Region

We present a five-band (u*, g', r', i', z') optical photometry catalog of the sources in the north ecliptic pole (NEP) region based on deep observations made with MegaCam at CFHT. The source catalog covers about 2 square degree area centered at the NEP and reaches depths of about 26 mag for u*, g', r' bands, about 25 mag for i' band, and about 24 mag for z' band (4 ς detection over a 1" aperture). The total number of cataloged sources brighter than r'=23 mag is about 56,000 including both point sources and extended sources. From the investigation of photometric properties using the color-magnitude diagrams and color-color diagrams, we have found that the colors of extended sources are mostly (u*-r')<3.0 and (g'-z')>0.5. This can be used to separate the extended sources from the point sources reliably, even for the faint source domain where typical morphological classification schemes hardly work efficiently. We have derived an empirical color-redshift relation of the red sequence galaxies using the Sloan Digital Sky Survey data. By applying this relation to our photometry catalog and searching for any spatial overdensities, we have found two galaxy clusters and one nearby galaxy group. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.

The Astrophysical Journal. Supplement Series


The Infrared Camera (IRC) for AKARI -- Design and Imaging Performance

The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low- resolution spectroscopy in the near- to mid-infrared (1.8-26.5'

Publications of the Astronomical Society of Japan


AKARI Infrared Imaging of Reflection Nebulae IC4954 and IC4955

We present the observations of the reflection nebulae IC4954 and IC4955 region with the Infrared Camera and the Far-Infrared Surveyor (FIS) on board the infrared astronomical satellite AKARI during its performance verification phase. We obtained 7 band images from 7 to 1601° around the IC4954/4955 region was created from the AKARI mid-infrared All-Sky Survey data. Together with the HI 21cm data, it suggests a large hollow structure of a degree scale, on whose edge the IC4954/4955 region has been created, indicating star formation over three generations in largely different spatial scales.


Properties of UIR Bands in NGC6946 Based on Mid-Infrared Imaging and Spectroscopy with Infrared Camera on Board AKARI

We present results on mid-infrared imaging and spectroscopic observations of the nearby late-type spiral NGC6946 with the Infrared Camera on board AKARI. Based on mid-infrared imaging with the S7 (7μm may be tools to measure the star-formation activity in remote galaxies if these ratios and their variations are well examined and established for a large sample.


The Infrared Astronomical Mission AKARI*

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.


Detection of an Hα Emission Line on a Quasar, RX J1759.4+6638, at z = 4.3 with AKARI

We report on the detection of an Hα) is consistent with those of previous reports for lower-redshift quasars.


AKARI Far-Infrared Source Counts in the Lockman Hole

We report initial results of far-infrared observations of the Lockman Hole with Far-Infrared Surveyor onboard the AKARI infrared satellite. On the basis of slow-scan observations of a 0°.6 × 1°.2 contiguous area, we obtained source number counts at 65, 90, and 140 μm counts above 26 mJy account for about 7% of the cosmic background. These results provide strong constraints on the evolutionary scenario, and suggest that the current models may require modifications.


Infrared Camera (IRC) Deep Survey in the Performance-Verification Phase

We report on the first results of a near- and mid-infrared deep survey with the Infrared Camera (IRC) onboard AKARI in the performance- verification phase. Simultaneous observations by the Near-InfraRed (NIR), Mid-InfraRed Short (MIR-S), and Mid-InfraRed Long (MIR-L) channels of the IRC with effective integration times of 4529, 4908, and 4417 seconds at 3, 7, and 15μm raw source counts agrees with those from deep surveys in the GOODS fields, carried out with the Spitzer IRS peak up imager and predictions of current galaxy evolution models. These results indicate that deep surveys with comprehensive wavelength coverage at mid-infrared wavelength are very important to investigate the evolution of infrared galaxies at high redshifts.


Nature of Infrared Sources in 11 μm Selected Sample from Early Data of the AKARI North Ecliptic Pole Deep Survey

We present the properties of 11 1012 L? based on detailed modelling of the SEDs. We also find four AGNs lying at various redshifts in the main sample. In addition, we discuss a few sources that have non- typical SEDs of the main sample, including a brown-dwarf candidate, a steep power-law source, a flat-spectrum object, and an early-type galaxy at moderate redshift.


Optical Identification of 15 μm Sources in the AKARI Performance Verification Field toward the North Ecliptic Pole

We present the results of optical identifications for 257 mid-infrared sources detected with a deep 15K_{s}

Publications of the Astronomical Society of Japan


Multi-Wavelength Analysis of 18 μm-Selected Galaxies in the AKARI/Infrared-Camera monitor fieldtowards the North Ecliptic Pole

We present an initial analysis of AKARI 18z Ultra-Luminous InfraRed Galaxies, and a large variation of the PAH inter-band strength ratio in galaxies at high redshifts.


State and evolution of the partly ionized gas in AGNs

Physical parameters of galaxies (as luminosity, stellar mass, age) are often derived by means of the model templates which best fit their spectro-photometric data. We have performed a quantitative test aimed at exploring the ability of this procedure in recovering the physical parameters of early-type galaxies at 1<z<2. A wide range of simulated SEDs, reproducing those of early-type galaxies at 1<z<2 with assigned age and mass, are used to build mock photometric catalogs with wavelength coverage and photometric uncertainties similar to those of two topical surveys (i.e. VVDS and GOODS). The best fitting analysis of the simulated photometric data allows to study the differences among the recovered parameters and the input ones. Results indicate that the stellar masses measured by means of optical bands are affected by larger uncertainties with respect to those obtained from near-IR bands, and they frequently underestimate the real values. The M/L ratio in the V band results strongly underestimated, even when derived from the recently proposed recipe based on rest-frame optical colours (e.g. (B-V)).

Il Nuovo Cimento B / Il Nuovo Cimento B Series 10


Observations of O I and Ca II Emission Lines in Quasars: Implications for the Site of Fe II Line Emission

We present results of the near-infrared (IR) spectroscopy of six quasars whose redshifts range from 0.158 to 1.084. Combined with the satellite ultraviolet data, the relative line strengths of O I λ1304, O I λ8446, O I λ11287, and the near-IR Ca II triplet are given. In addition, the corresponding O I line strengths measured in normal Seyfert 1s and narrow-line Seyfert 1s are collected from the literature. These lines are thought to emerge from the same gas as do the Fe II lines, so they are good tracers of the Fe II emission region within a broad emission line region (BELR) in active galactic nuclei (AGNs). In order to reveal the physical condition within the relevant emission region, we performed photoionized model calculations and compared them to the observations. It suggests that a rather dense gas with density nH~1011.5 cm-3 is present at an outer portion of the BELR, illuminated by the ionizing radiation corresponding to an ionization parameter U~10-2.5 and is primarily responsible for the observed O I, Ca II, and Fe II lines, based on the resemblance of their profiles. The three O I lines are proven to be formed through Lyβ fluorescence and collisional excitation. We also show that the λ1304 bump typically observed in AGN spectra consists of the comparable contributions of O I and Si II multiplets, and we discuss the origin of such a strong Si II emission. The results are interpreted in the context of the locally optimally emitting cloud (LOC) scenario to find the plausible gas distribution within the BELR as a function of distance from the central source and density.


J- and Ks-Band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field

We present the J- and Ks-band galaxy counts and galaxy colors covering 750 arcmin2 in the deep AKARI north ecliptic pole (NEP) field, using the Florida Multi-object Imaging Near-IR Grism Observational Spectrometer on the Kitt Peak National Observatory 2.1 m telescope. The limiting magnitudes with a signal-to-noise ratio of 3 in the deepest regions are 21.85 and 20.15 in the J and Ks bands, respectively, in the Vega magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are broadly in good agreement with those of other results in the literature; however, we find some indication of a change in the galaxy number count slope at J~19.5 and over the magnitude range 18.0<Ks<19.5. We interpret this feature as a change in the dominant population at these magnitudes because we also find an associated change in the B-Ks color distribution at these magnitudes, where the number of blue samples in the magnitude range 18.5<Ks<19.5 is significantly larger than that of Ks<17.5.


Observing the Birth and evolution of Galaxies - the ATCA-AKARI-ASTE/AzTEC deep South Ecliptic Pole Field

We propose deep 20 cm observations supporting the AKARI (3-160 micron)/ASTE/AzTEC (1.1 mm) SEP ultra deep ('Oyabu Field') survey of an extremely low cirrus region at the South Ecliptic Pole. Our combined IR/mm/Radio survey addresses the questions: How do protogalaxies and protospheroids form and evolve? How do AGN link with ULIRGs in their birth and evolution? What is the nature of the mm/submm extragalactic source population? We will address these by sampling the star formation history in the early universe to at least z~2. Compared to other Deep Surveys, a) AKARI multi-band IR measurements allow precision photo-z estimates of optically obscured objects, b) our multi-waveband contiguous area will mitigate effects of cosmic variance, c) the low cirrus noise at the SEP (< 0.08 MJy/sr) rivals that of the Lockman Hole "Astronomy's other ultra-deep 'cosmological window'", and d) our coverage of four FIR bands will characterise the far-IR dust emission hump of our starburst galaxies better than SPITZER's two MIPS bands allow. The ATCA data are crucial to galaxy identification, and determining the star formation rates and intrinsic luminosities through this unique Southern cosmological window.


Fe II Emission in 14 Low-Redshift Quasars. I. Observations

We present the spectra of 14 quasars with a wide coverage of rest wavelengths from 1000 to 7300 ?. The redshift ranges from z=0.061 to 0.555 and the luminosity from MB=-22.69 to -26.32. These spectra of high quality result from combining Hubble Space Telescope spectra with those taken from ground-based telescopes. We describe the procedure of generating the template spectrum of Fe II line emission from the spectrum of a narrow-line Seyfert 1 galaxy, I Zw 1, that covers two wavelength regions of 2200-3500 and 4200-5600 ?. Our template Fe II spectrum is semiempirical in the sense that the synthetic spectrum calculated with the CLOUDY photoionization code is used to separate the Fe II emission from the Mg II λ2798 line. The procedure of measuring the strengths of Fe II emission lines is twofold: (1) subtracting the continuum components by fitting models of the power-law and Balmer continua in the continuum windows, which are relatively free from line emissions, and (2) fitting models of the Fe II emission based on the Fe II template to the continuum-subtracted spectra. From 14 quasars including I Zw 1, we obtained the Fe II fluxes in five wavelength bands (U1 [2200-2660 ?], U2 [2660-3000 ?], U3 [3000-3500 ?], O1 [4400-4700 ?], and O2 [5100-5600 ?]), the total flux of Balmer continuum, and the fluxes of Mg II λ2798, Hα, and other emission lines, together with the full widths at half-maximum (FWHMs) of these lines. Regression analysis was performed by assuming a linear relation between any two of these quantities. Eight correlations were found with a confidence level higher than 99%: (1) larger Mg II FWHM for larger Hα FWHM, (2) larger Γ for fainter MB, (3) smaller Mg II FWHM for larger Γ, (4) larger Mg II FWHM for smaller Fe II(O1)/Mg II, (5) larger MBH for smaller Γ, (6) larger MBH for smaller Fe II(O1)/Mg II, (7) larger [O III]/Hβ for larger Mg II FWHM, and (8) larger Fe II(O1)/Mg II for larger Fe II(O1)/Fe II(U1). The fact that six of these eight are related to FWHM or MBH (~FWHM2) may imply that MBH is a fundamental quantity that controls Γ or the spectral energy distribution (SED) of the incident continuum, which in turn controls the Fe II emission. Furthermore, it is worthy of noting that Fe II(O1)/Fe II(U1) is found to tightly correlate with Fe II(O1)/Mg II, but not with Fe II(U1)/Mg II.


Deep Extragalactic Surveys around the Ecliptic Poles with AKARI (ASTRO-F)

AKARI (formerly ASTRO-F) is an infrared space telescope designed for an all-sky survey at 10-180 μm, and deep pointed surveys of selected areas at 2-180 μm. The deep pointed surveys with AKARI will significantly advance our understanding of galaxy evolution, the structure formation of the universe, the nature of buried AGNs, and the cosmic infrared background. We describe here the important characteristics of the AKARI mission, the orbit, and attitude control system, and investigate the optimum survey area based on the updated pre-flight sensitivities of AKARI, taking into account the cirrus confusion noise as well as the surface density of bright stars. The North Ecliptic Pole is concluded to be the best area for 2-26μm deep surveys, while the low-cirrus noise regions around the South Ecliptic Pole are worth considering for 50-180μm pointed surveys to high sensitivities limited by the galaxy confusion noise. Current observational plans concerning these pointed surveys are described in detail. Comparing these surveys with deep surveys using the Spitzer Space Telescope, the AKARI deep surveys are particularly unique in respect of their continuous wavelength coverage over the 2-26μm range in broad-band deep imaging, and their slitless spectroscopy mode over the same wavelength range.


Optical Identification of Infrared Space Observatory Far-Infrared Sources in the Lockman Hole Using a Deep Very Large Array 1.4 GHz Continuum Survey

By exploiting the far-infrared (FIR) and radio correlation, we have performed a likelihood-ratio analysis to identify optical counterparts to the FIR sources that have been found in an area of ~0.9 deg2 during the Infrared Space Observatory (ISO) deep FIR survey in the Lockman Hole. New ground-based observations have been conducted to build up the catalogs of radio and optical objects, which include a deep Very Large Array (VLA) observation at 1.4 GHz, optical R- and I-band imaging with the Subaru 8 m and University of Hawaii 2.2 m telescopes, and optical spectroscopy with the Keck II 10 m and WIYN 3.5 m telescopes. This work is based on FIR samples consisting of 116 and 20 sources selected with the criteria of FC(90 μm)>=43 mJy and FC(170 μm)>=102 mJy, respectively, where FC is the bias-corrected flux. Using the likelihood ratio analysis and the associated reliability, 44 FIR sources have been identified with radio sources. Optical confirmation of the 44 FIR/radio associations was then conducted using accurate radio positions. Redshifts have been obtained for 29 out of the 44 identified sources. One hyperluminous infrared galaxy (HyLIRG) with LFIR>1013 Lsolar and four ultraluminous infrared galaxies (ULIRGs) with LFIR=1012-1013 Lsolar are identified in our sample, while the remaining 24 FIR galaxies have LFIR<1012 Lsolar. The space density of the FIR sources at z=0.3-0.6 is 4.6×10-5 Mpc-3, which is 460 times larger than the local value, implying a rapid evolution of the ULIRG population. Most ISO FIR sources have L(1.4 GHz)/L(90 μm) similar to the star-forming galaxies Arp 220 and M82, indicating that star formation is the dominant mechanism for their FIR and radio luminosity. At least seven of our FIR sources show evidence for the presence of an active galactic nucleus (AGN) in optical emission lines, radio continuum excess, or X-ray activity. Three out of five (60%) of the ULIRGs/HyLIRGs are AGN galaxies, suggesting that the AGN fraction among the ULIRG/HyLIRG population may not change significantly between z~0.5 and the present epoch. Five of the seven AGN galaxies are within the ROSAT X-ray survey field, and two are within the XMM-Newton survey fields. X-ray emission has been detected in only one source, 1EX030, which is optically classified as a quasar. The nondetection in the XMM-Newton 2-10 keV band suggests a very thick absorption column density of 3×1024 cm-2 or AV~1200 mag obscuring the central source of the two AGN galaxies. Several sources have an extreme FIR luminosity relative to the optical R band, L(90 μm)/L(R)>500, which is rare even among the local ULIRG population. While source confusion or blending might offer an explanation in some cases, these observations may represent a new population of galaxies with an extreme amount of star formation in an undeveloped stellar system, i.e., formation of bulges or young elliptical galaxies.