Tsutomu T. Takeuchi

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.

Electronic Spectra and Their Relation to the ( π,π) Collective Mode in High- Tc Superconductors

The photoemission line shape near (pi, 0) in Bi(2)Sr(2)CaCu(2)O(8+delta) below T(c) is characterized by a sharp peak, followed at higher energy by a dip and hump. We study the evolution of this line shape as a function of momentum, temperature, and doping. We find the hump scales with the peak and persists above T(c) in the pseudogap state. We present strong evidence that the peak-dip-hump structure arises from the interaction of electrons with a collective mode of wave vector (pi, pi). The inferred mode energy and its doping dependence agree well with a magnetic resonance observed by neutron scattering.

Superconducting Gap Anisotropy and Quasiparticle Interactions: A Doping Dependent Photoemission Study

Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple coskx 2 cosky form, which suggests an increasing importance of long range interactions as the insulator is approached.

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.

Dust formation history of galaxies: a critical role of metallicity for the dust mass growth by accreting materials in the interstellar medium

This paper investigates the main driver of dust mass growth in the interstellar medium (ISM) by using a chemical evolution model of a galaxy with metals (elements heavier than helium) in the dust phase, in addition to the total amount of metals. We consider asymptotic giant branch (AGB) stars, type II supernovae (SNe II), and dust mass growth in the ISM, as the sources of dust, and SN shocks as the destruction mechanism of dust. Furthermore, to describe the dust evolution precisely, our model takes into account the age and metallicity (the ratio of metal mass to ISM mass) dependence of the sources of dust. We have particularly focused on the dust mass growth, and found that in the ISM this is regulated by the metallicity. To quantify this aspect, we introduce a “critical metallicity”, which is the metallicity at which the contribution of stars (AGB stars and SNe II) equals that of the dust mass growth in the ISM. If the star-formation timescale is shorter, the value of the critical metallicity is higher, but the galactic age at which the metallicity reaches the critical metallicity is shorter. From observations, it was expected that the dust mass growth was the dominant source of dust in the Milky Way and dusty QSOs at high redshifts. By introducing a critical metallicity, it is clearly shown that the dust mass growth is the main source of dust in such galaxies with various star-formation timescales and ages. The dust mass growth in the ISM is regulated by metallicity, and we emphasize that the critical metallicity serves as an indicator to judge whether the grain growth in the ISM is the dominant source of dust in a galaxy, especially because of the strong, and nonlinear, dependence on the metallicity.

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 starformation 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 ΩIR evolves as ∝(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.

What determines the grain size distribution in galaxies

Dust in galaxies forms and evolves by various processes, and these dust processes change the grain size distribution and amount of dust in the interstellar medium (ISM). We construct a dust evolution model taking into account the grain size distribution, and investigate what kind of dust processes determine the grain size distribution at each stage of galaxy evolution. In addition to the dust production by Type II supernovae (SNe II) and asymptotic giant branch (AGB) stars, we consider three processes in the ISM: (i) dust destruction by SN shocks, (ii) metal accretion on to the surface of pre-existing grains in the cold neutral medium (CNM; called grain growth) and (iii) grain–grain collisions (shattering and coagulation) in the warm neutral medium and CNM. We found that the grain size distribution in galaxies is controlled by stellar sources in the early stage of galaxy evolution, and that afterwards the main processes that govern the size distribution changes to those in the ISM, and this change occurs at earlier stage of galaxy evolution for a shorter star formation time-scale (for star formation time-scales = 0.5, 5 and 50 Gyr, the change occurs about galactic aget ∼ 0.6, 2 and 5 Gyr, respectively). If we only take into account the processes which directly affect the total dust mass (dust production by SNe II and AGB stars, dust destruction by SN shocks and grain growth), the grain size distribution is biased to large grains (a ∼ 0.2–0.5 μm, where a is the grain radius). Therefore, shattering is crucial to produce small (a 0.01 μm) grains. Since shattering produces a large abundance of small grains (consequently, the surface-to-volume ratio of grains increases), it enhances the efficiency of grain growth, contributing to the significant increase of the total dust mass. Grain growth creates a large bump in the grain size distribution around a ∼ 0.01 μm. Coagulation occurs effectively after the number of small grains is enhanced by shattering, and the grain size distribution is deformed to have a bump at a ∼ 0.03–0.05 μ ma tt ∼ 10 Gyr. We conclude that the evolutions of the total dust mass and the grain size distribution in galaxies are closely related to each other, and the grain size distribution changes considerably through the galaxy evolution because the dominant dust processes which regulate the grain size distribution change.

REEXAMINATION OF THE INFRARED EXCESS-ULTRAVIOLET SLOPE RELATION OF LOCAL GALAXIES

The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (β) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star-forming galaxies, especially at high redshifts. Many authors, however, have pointed out that there is a significant dispersion and/or deviation from the originally proposed IRX-β relation depending on sample selection. We reexamined the IRX-β relation by measuring the far- and near-UV flux densities of the original sample galaxies with GALEX and AKARI imaging data and constructed a revised formula. We found that the newly obtained IRX values were lower than the original relation because of the significant underestimation of the UV flux densities of the galaxies, caused by the small aperture of IUE. Furthermore, since the original relation was based on IRAS data that covered a wavelength range of λ = 42-122 μm, we obtained an appropriate IRX-β relation with total dust emission (TIR): log (L TIR/L FUV) = log [100.4(3.06 + 1.58β) – 1] + 0.22 using the data from AKARI, which has wider wavelength coverage toward longer wavelengths. This new relation is consistent with most of the preceding results for samples selected at optical and UV, though there is significant scatter around it. We also found that even the quiescent class of IR galaxies follows this new relation, though luminous and ultraluminous IR galaxies distribute completely differently as previously thought.

Spectral energy distributions of an AKARI-SDSS-GALEX sample of galaxies

Context. The nearby universe remains the best laboratory to understand the physical properties of galaxies and is a reference for any comparison with high redshift observations. The all sky (or very large) surveys that have been performed from the ultraviolet (UV) to the far-infrared (far-IR) provide us with large datasets of very large wavelength coverage to perform a reference study. Aims. We investigate the dust attenuation characteristics, as well as the star formation rate (SFR) calibrations of a sample of nearby galaxies observed over 13 bands from 0.15 to 160 μm. Methods. A sample of 363 galaxies is built from the AKARI /FIS all sky survey cross-correlated with the SDSS and GALEX surveys. Broad-band spectral energy distributions are fitted with the CIGALE code optimized to analyse variations in the dust attenuation curves and SFR measurements and based on an energetic budget between the stellar and dust emission. Results. Our galaxy sample is primarily selected in far-IR and mostly constituted of massive, actively star-forming galaxies. There is some evidence for a dust attenuation law that is slightly steeper than that used for starburst galaxies but we are unable to constrain the presence or not of a bump at 220 nm. We confirm that a time-dependent dust attenuation is necessary to perform the best fits. Various calibrations of the dust attenuation in the UV as a function of UV-optical colours are discussed. A calibration of the current SFR combining UV and total IR emissions is proposed with an accurate estimate of dust heating by old stars. For the whole sample, 17% of the total dust luminosity is unrelated to the recent star formation.

ARPES on Na0.6CoO2: Fermi surface and unusual band dispersion

The electronic structure of single crystals Na