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We investigate the photometric redshift accuracy achievable with the AKARI infrared data in deep multi-band surveys, such as in the North Ecliptic Pole field. We demonstrate that the passage of redshifted policyclic aromatic hydrocarbons 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 GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The infrared spectra are fitted using synthetic galaxy Spectral Energy Distributions which account for starburst and active nuclei emission. For ~90% of the sources in our sample the redshift is recovered with an accuracy |z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets of simulated spectra shows that the AKARI infrared data alone can provide photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) 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 1.6 micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%, provided that the AGN contribution to the infrared emission is subdominant. Our technique is no more prone to redshift aliasing than optical-uv photo-z, and it may be possible to reduce this aliasing further with the addition of submillimetre and/or radio data., Comment: 27 pages, 12 figures, 4 tables. Accepted for publication on MNRAS

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 um 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 broad-band 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* = 10^{11.5} Msun clearly point to this galaxy being a direct ancestor of the brightest elliptical and spheroidal galaxies in the local universe., Comment: 18 pages, 4 figures. Accepted for publication in ApJ

We have compiled the emission-line fluxes of O I 8446, O I 11287, and the near-IR Ca II triplet (8579) 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 < M_B < -22.1), thus representing 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 Ca II and O I 8446 is hardly dependent on the redshift or luminosity, indicating similar gas density in the emission region from quasar to quasar. On the other hand, a scatter of the O I 11287/8446 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 well-studied 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., Comment: Accepted for publication in ApJ; minor rewordings made

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., Comment: 13 pages, 4 figures, and 3 tables. Accepted for publication in the AKARI special issue of the Publications of the Astronomical Society of Japan

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--26.5um) in the pointed observation mode of AKARI. IRC is also operated in the survey mode to make an all-sky survey at 9 and 18um. It comprises three channels. The NIR channel (1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S (4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity band conduction arrays. Each of the three channels has a field-of-view of about 10' x 10' and are operated simultaneously. The NIR and MIR-S share the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about $25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the formation and evolution of galaxies, the evolution of planetary disks, the process of star-formation, the properties of interstellar matter under various physical conditions, and the nature and evolution of solar system objects. The in-flight performance of IRC has been confirmed to be in agreement with the pre-flight expectation. This paper summarizes the design and the in-flight operation and imaging performance of IRC., Comment: Publications of the Astronomical Society of Japan, in press

We present an initial analysis of AKARI 18um-selected galaxies using all 9 photometric bands at 2-24um available in the InfraRed Camera (IRC), in order to demonstrate new capabilities of AKARI cosmological surveys. We detected 72 sources at 18um in an area of 50.2 arcmin^2 in the AKARI/IRC monitor field towards the North Ecliptic Pole (NEP). From this sample, 25 galaxies with probable redshifts z>~ 0.5 are selected with a single colour cut (N2-N3>0.1) for a detailed SED analysis with ground-based BVRi'z'JK data. Using an SED radiative transfer model of starbursts covering the wavelength range UV -- submm, we derive photometric redshifts from the optical-MIR SEDs of 18um-selected galaxies. From the best-fit SED models, we show that the IRC all-band photometry is capable of tracing the steep rise in flux at the blue side of the PAH 6.2um emission feature. This indicates that the IRC all-band photometry is useful to constrain the redshift of infrared galaxies, specifically for dusty galaxies with a less prominent 4000A break. Also, we find that the flux dip between the PAH 7.7 and 11.2um emission feature is recognizable in the observed SEDs of galaxies at z~1. By using such a colour anomaly due to the PAH and silicate absorption features, unique samples of ULIRGs at z~1, `silicate-break' galaxies, can be constructed from large cosmological surveys of AKARI towards the NEP, i.e. the NEP-Deep and NEP-Wide survey. This pilot study suggests the possibility of detecting many interesting galaxy properties in the NEP-Deep and Wide surveys, such as a systematic difference in SEDs between high- and low-z ULIRGs, and a large variation of the PAH inter-band strength ratio in galaxies at high redshifts. [abridged], Comment: Accepted for publication in PASJ, AKARI special issue

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 OI 1304, OI 8446, OI 11287, and the near-IR CaII triplet are given. In addition, the corresponding OI 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 FeII lines, so they are good tracers of the FeII 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 ~ 10^(11.5) 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 OI, CaII, and FeII lines, based on the resemblance of their profiles. The three OI lines are proven to be formed through Ly beta fluorescence and collisional excitation. We also show that the lambda1304 bump typically observed in AGN spectra consists of the comparable contributions of OI and SiII multiplets, and we discuss the origin of such a strong SiII 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., Comment: Accepted for publication in ApJ; some rewordings made

By exploiting the far-infrared(FIR) and radio correlation, we have performed the Likelihood-Ratio analysis to identify optical counterparts to the far-infrared sources in the Lockman Hole. Using the likelihood ratio analysis and the associated reliability, 44 FIR sources have been identified with radio sources. Redshifts have been obtained for 29 out of 44 identified sources. One hyper-luminous infrared galaxy (HyLIRG) with and four ultraluminous infrared galaxies (ULIRGs) are identified in our sample. The space density of the FIR sources at z = 0.3-0.6 is 4.6\times 10^{-5}Mpc^{-3}, implying a rapid evolution of the ULIRG population. Most of \ISO FIR sources have their FIR-radio ratios similar to star-forming galaxies ARP 220 and M82. 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 ULIRG/HyLIRGs are AGN galaxies. 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 non-detection in the XMM-Newton 2-10 keV band suggests a very thick absorption obscuring the central source of the two AGN galaxies. Several sources have an extreme FIR luminosity relative to the optical R-band, L(90\mu\mathrm{m})/L(R) > 500, which is rare even among the local ULIRG population. While source confusion or blending might offer an explanation in some cases, they may represent a new population of galaxies with an extreme activity of star formation in an undeveloped stellar system -- i.e., formation of bulges or young ellipticals., Comment: 55 pages, 16 figures. To appear in AJ

During the course of our deep optical imaging survey for Ly alpha emitters at z approximately 5.7 in the field around the z=5.74 quasar SDSSp J104433.04-012502.2, we have found a candidate strong emission-line source. Follow-up optical spectroscopy shows that the emission line profile of this object is asymmetric, showing excess red-wing emission. These properties are consistent with an identification of Ly alpha emission at a redshift of z=5.687 +/- 0.002. The observed broad line width, Delta V_{FWHM} ~= 340 km s^{-1} and excess red-wing emission also suggest that this object hosts a galactic superwind., Comment: 5 pages, 4 figures (Figure 2 and Figure 4 are JPEG files). ApJ (Letters), in press

Eight luminous quasars with $ -30 < M_B < -27$ at z = 1.4 - 3.7 have been observed in the mid- and far-infrared using ISO. All the quasars have been detected in the mid-infrared bands of ISOCAM, while no far-infrared detections have been made with ISOPHOT. Supplementing ISO observations with photometry in the optical and near-infrared made from the ground mostly within 17 months after the ISO observations, SEDs (Spectral Energy Distributions) from the UV to far-infrared have been obtained. SEDs (Spectral Energy Distributions) from the UV to far-infrared have been obtained while supplementing ISO observations with photometry in the optical and near-infrared made from the ground within 17 months. The SEDs are compared with the MED (Mean spectral Energy Distributions) of low-redshift quasars with $-27 < M_B < -22$. It is shown that our far-infrared observations were limited by confusion noise due to crowded sources., Comment: 9 pages, 3 figures: accepted for publication in Astronomy and Astrophysics