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Y. Taniguchi

Publications and source records attributed to Y. Taniguchi.

At least 145 records · Page 8Linked to original sources
arXiv2007

Application of chiral perturbation theory to 2+1 flavor lattice QCD with O(a)-improved Wilson quarks

We apply chiral perturbation theory to the pseudoscalar meson mass and decay constant data obtained in the PACS-CS Project toward 2+1 flavor lattice QCD simulations with the O(a)-improved Wilson quarks. We examine the existence of chiral logarithms in the quark mass range from m_{ud}=47 MeV down to 6 MeV on a (2.8 fm)^3 box with the lattice spacing a=0.09 fm. Several low energy constants are determined. We also discuss the magnitude of finite size effects based on chiral perturbation theory.

hep-lat↗
arXiv2007

The H$α$ Luminosity Function and Star Formation Rate at $z \approx 0.24$ in the Cosmos 2 Square-Degree Field

To derive a new H$α$ luminosity function and to understand the clustering properties of star-forming galaxies at $z \approx 0.24$, we have made a narrow-band imaging survey for H$α$ emitting galaxies in the HST COSMOS 2 square degree field. We used the narrow-band filter NB816 ($λ_c = 8150$ Å, $Δλ= 120$ Å) and sampled H$α$ emitters with $EW_{\rm obs}(\rm Hα+ [N\textsc{ii}]) > 12$ Åin a redshift range between $z=0.233$ and $z=0.251$ corresponding to a depth of 70 Mpc. We obtained 980 H$α$ emitting galaxies in a sky area of 5540 arcmin$^2$, corresponding to a survey volume of $3.1 \times 10^4 {\rm Mpc^3}$. We derive a H$α$ luminosity function with a best-fit Schechter function parameter set of $α= -1.35^{+0.11}_{-0.13}$, $\logϕ_* = -2.65^{+0.27}_{-0.38}$, and $\log L_* ({\rm erg s^{-1}}) = 41.94^{+0.38}_{-0.23}$. The H$α$ luminosity density is $2.7^{+0.7}_{-0.6} \times 10^{39}$ ergs s$^{-1}$ Mpc$^{-3}$. After subtracting the AGN contribution (15 %) to the H$α$ luminosity density, the star formation rate density is evaluated as $1.8^{+0.7}_{-0.4} \times 10^{-2}$ $M_{\sun}$ yr$^{-1}$ Mpc$^{-3}$. The angular two-point correlation function of H$α$ emitting galaxies of $\log L({\rm Hα}) > 39.8$ is well fit by a power law form of $w(θ) = 0.013^{+0.002}_{-0.001} θ^{-0.88 \pm 0.03}$, corresponding to the correlation function of $ξ(r) = (r/1.9{\rm Mpc})^{-1.88}$. We also find that the H$α$ emitters with higher H$α$ luminosity are more strongly clustered than those with lower luminosity.

astro-ph↗
arXiv2007

Deep GEMINI GMOS-IFU spectroscopy of BAL QSOs: I. Decoupling the BAL, QSO, starburst, NLR, supergiant bubbles and galactic wind in Mrk 231

In this work we present the first results of a study of BAL QSOs (at low and high redshift), based on very deep Gemini GMOS integral field spectroscopy. In particular, the results obtained for the nearest BAL IR QSO Mrk 231 are presented. Very deep three-dimensional spectra and maps clearly show that the BAL systems I and II are extended (reaching 1.4-1.6" = 1.2-1.3 kpc, from the nucleus) and clearly elongated at the position angle close to the radio jet PA. Which suggest that the BAL systems I and II are both associated with the radio jet, and supporting the bipolar jet-wind model for some BALs. For the nuclear region of Mrk 231, the QSO and host-galaxy components were modelled, using a new technique of decoupling 3D spectra. From this study, the following main results were found: (i) in the pure host galaxy spectrum an extreme nuclear starburst component was clearly observed, mainly as a very strong increase in the flux, at the blue wavelengths; (ii) the BAL system I is observed in the spectrum of the host galaxy; (iii) in the clean/pure QSO emission spectrum, only broad lines were detected. 3D GMOS individual spectra (specially in the IR Ca II triplet) and maps confirm the presence of an extreme and young nuclear starburst (8 < age < 15 Myr), which was detected mainly in a ring or toroid with a radius r = 0.3" = 200 pc, around the very nucleus. The physical properties of the four expanding nuclear bubbles were analysed, using the GMOS 3D spectra and maps. These results suggest that an important part of the nuclear NLR is generated by the OF process and the associated low velocity ionizing shocks.

astro-ph↗
arXiv2007

Evolution of the Frequency of Luminous (\geq L_V*) Close Galaxy Pairs at z < 1.2 in the COSMOS Field

We measure the fraction of luminous galaxies in pairs at projected separations of 5-20 kpc out to z=1.2 in the COSMOS field using ACS images and photometric redshifts derived from an extensive multiwavelength dataset. Analysis of a complete sample of 106,188 galaxies more luminous than M_V=-19.8 (~ L_V*) in the redshift range 0.1 < z < 1.2 yields 1,749 galaxy pairs. These data are supplemented by a local z=0-0.1 value for the galaxy pair fraction derived from the Sloan Digital Sky Survey (SDSS). After statistically correcting the COSMOS pair sample for chance line-of-sight superpositions, the evolution in the pair fraction is fit by a power law \propto (1+z)^{n=3.1 \pm 0.1}. If this strongly evolving pair fraction continues out to higher redshift, ~ 50% of all luminous galaxies at z ~ 2 are in close pairs. This clearly signifies that galaxy mergers are a very significant and possibly dominant mechanism for galaxy evolution during the epoch of galaxy formation at z=1 to 3.

astro-ph↗
arXiv2007

Multi-epoch VLBA observations of 3C 66A

We present the results of six-epoch Very Long Baseline Array (VLBA) observations of 3C~66A. The high-resolution Very Long Baseline Interferometer (VLBI) maps obtained at multi-frequency (2.3, 8.4, and 22.2 GHz) simultaneously enabled us to identify the brightest compact component with the core. We find that the spectrum of the core can be reasonably fitted by the synchrotron self-absorption model. Our VLBA maps show that the jet of 3C~66A has two bendings at about 1.2 and 4 mas from the core. We also give possible identifications of our jet components with the components in previous VLBA observations by analysing their proper motions. We find consistent differences of the position from the core in one component between different frequencies at six epochs.

astro-ph↗
arXiv2007

Hierarchical Object Formation in the Peculiar Velocity Field

Using the initial peculiar velocity field, we analytically study the hierarchical formation of gravitationally bound objects. The field is smoothed over a scale that corresponds to the mass of a given class of objects. Through the Zel'dovich approximation, the smoothed field determines how the objects cluster together to form a new class of more massive objects. The standard cosmological parameters lead to the evolution of primordial clouds with 10^6 M(sun) -> galaxies with 10^12 M(sun) -> clusters of galaxies with 10^15 M(sun) -> superclusters of galaxies with 10^16 M(sun). The epochs obtained for the formation of these classes of objects are consistent with observations.

astro-ph↗
arXiv2007

The angular correlations of galaxies in the COSMOS field

We present measurements of the two-point galaxy angular correlation function w(θ) in the COSMOS field. Independent determinations of w(θ) as a function of magnitude limit are presented for both the HST ACS catalog and also for the ground-based data from Subaru and the CFHT. Despite having significantly different masks, these three determinations agree well. At bright magnitudes (IAB<22), our data generally match very well with existing measurements and with mock catalogs based on semi-analytic galaxy formation calculations of Kitzbichler and White from the Millennium Simulation. The exception is that our result is at the upper end of the expected cosmic variance scatter for θ> 10 arcmin, which we attribute to a particularly rich structure known to exist at z~0.8. For fainter samples, however, the level of clustering is somewhat higher than reported by some previous studies: in all three catalogues we find w(θ=1')~0.014 at a median IAB magnitude of 24. At these very faintest magnitudes, our measurements agree well with the latest determinations from the Canada-France Legacy Survey. This level of clustering is approximately double what is predicted by the semi-analytic catalogs (at all angles). The semi-analytic results allow an estimate of cosmic variance, which is too small to account for the discrepancy. We therefore conclude that the mean amplitude of clustering at this level is higher than previously estimated.

astro-ph↗
arXiv2007

The First Release COSMOS Optical and Near-IR Data and Catalog

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3um and 2.4um. These include data taken on the Subaru 8.3m telescope, the KPNO and CTIO 4m telescopes, and the CFHT 3.6m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.

astro-ph↗
arXiv2007

2+1 flavor light hadron spectrum and quark masses with the O(a) improved Wilson-clover quark formalism

We present a summary of results of the joint CP-PACS and JLQCD project toward a 2+1 flavor full QCD simulation with the O(a)-improved Wilson quark formalism and the Iwasaki gauge action. Configurations were generated during 2002-2005 at three lattice spacings, a~0.076, 0.100 and 0.122 fm, keeping the physical volume constant at (2.0fm)^3. Up and down quark masses are taken in the range m_{PS}/m_V~0.6-0.78. We have completed the analysis for the light meson spectrum and quark masses in the continuum limit using the full configuration set. The predicted meson masses reproduce experimental values in the continuum limit at a 1% level. The average up and down, and strange quark masses turn out to be m_{ud}^{\bar{MS}}(μ=2 GeV)=3.50(14)({}^{+26}_{-15}) MeV and m_s^{\bar{MS}}(μ=2 GeV)=91.8(3.9)({}^{+6.8}_{-4.1}) MeV. We discuss our future strategy toward definitive results on hadron spectroscopy with the Wilson-clover formalism.

hep-lat↗
arXiv2007

The [OII]3727 Luminosity function and Star Formation Rate at z~1.2 in the COSMOS 2 Square-degree Field and the Subaru Deep Field

We have carried out a wide-field imaging survey for [OII]3727 emitting galaxies at z~1.2 in the HST COSMOS 2 square degree field using the Suprime-Cam on the Subaru Telescope. The survey covers a sky area of 6700 arcmin^2 in the COSMOS field, and a redshift range between 1.17 and 1.20 (Delta_z = 0.03), corresponding to a survey volume of 5.56*10^5 Mpc^3. We obtain a sample of 3176 [OII] emitting galaxies with observed emission-line equivalent widths greater than 26 AA. Since our survey tends to sample brighter [OII]3727 emitting galaxies, we also analyze a sample of fainter [OII]3727 emitting galaxies found in the Subaru Deep Field (SDF). We find an extinction-corrected [OII] luminosity density of 10^{40.35^+0.08_-0.06} ergs s^-1 Mpc-3, corresponding to star formation rate density of 0.32^+0.06_-0.04 M_sun yr-1 Mpc^-3 in the COSMOS field at z~1.2. This is the largest survey for [OII]3727 emitters beyond z=1 currently available.

astro-ph↗
arXiv2007

Large Structures and Galaxy Evolution in COSMOS at z < 1.1

We present the first identification of large-scale structures (LSS) at z $< 1.1$ in the Cosmic Evolution Survey (COSMOS). The structures are identified from adaptive smoothing of galaxy counts in the pseudo-3d space ($α,δ$,z) using the COSMOS photometric redshift catalog. The technique is tested on a simulation including galaxies distributed in model clusters and a field galaxy population -- recovering structures on all scales from 1 to 20\arcmin without {\it a priori} assumptions for the structure size or density profile. Our procedure makes {\bf no} {\it a priori} selection on galaxy spectral energy distribution (SED, for example the Red Sequence), enabling an unbiased investigation of environmental effects on galaxy evolution. The COSMOS photometric redshift catalog yields a sample of $1.5\times10^5$ galaxies with redshift accuracy, $Δz_{FWHM}/(1+z) \leq 0.1$ at z $< 1.1$ down to I$_{AB} \leq 25$ mag. Using this sample of galaxies, we identify 42 large-scale structures and clusters. abstract truncated for astroph 25 line limit -- see preprint

astro-ph↗
arXiv2007

COSMOS : Hubble Space Telescope Observations

The Cosmic Evolution Survey (COSMOS) was initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope (HST) for high resolution imaging. Here we review the characteristics of the HST imaging with the Advanced Camera for Surveys (ACS) and parallel observations with NICMOS and WFPC2. A square field (1.8$\sq$°) has been imaged with single-orbit ACS I-F814W exposures with 50% completeness for sources 0.5\arcsec in diameter at I$_{AB} $ = 26.0 mag. The ACS imaging is a key part of the COSMOS survey, providing very high sensitivity and high resolution (0.09\arcsec FWHM, 0.05\arcsec pixels) imaging and detecting 1.2 million objects to a limiting magnitude of 26.5 (AB). These images yield resolved morphologies for several hundred thousand galaxies. The small HST PSF also provides greatly enhanced sensitivity for weak lensing investigations of the dark matter distribution.

astro-ph↗
arXiv2007

Lyman Alpha Emitters at Redshift 5.7 in the COSMOS Field

We present results from a narrow-band optical survey of a contiguous area of 1.95 deg^2, covered by the Cosmic Evolution Survey (COSMOS). Both optical narrow-band (lambda_c = 8150 AA and Delta_lambda = 120 AA) and broad-band (B, V, g', r', i', and z') imaging observations were performed with the Subaru prime-focus camera, Suprime-Cam on the Subaru Telescope. We provide the largest contiguous narrow-band survey, targetting Ly alpha emitters (LAEs) at z~5.7. We find a total of 119 LAE candidates at z~5.7. Over the wide-area covered by this survey, we find no strong evidence for large scale clustering of LAEs. We estimate a star formation rate (SFR) density of ~7*10^-4 M_sun yr^-1 Mpc^-3 for LAEs at z~5.7, and compare it with previous measurements.

astro-ph↗
arXiv2007

The redshift evolution of early-type galaxies in COSMOS: Do massive early-type galaxies form by dry mergers?

ABRIDGED: We study the evolution since z~1 of the rest-frame B luminosity function of the early-type galaxies (ETGs) in ~0.7 deg^2 in the COSMOS field. In order to identify ALL progenitors of local ETGs we construct the sample of high-z galaxies using two complementary criteria: (i) A morphological selection based on the Zurich Estimator of Structural Types, and (ii) A photometric selection based on the galaxy properties in the (U-V)-M_V color-magnitude diagram. We furthermore constrain both samples so as to ensure that the selected progenitors of ETGs are compatible with evolving into systems which obey the mu_B-r_{hl} Kormendy relation. Assuming the luminosity evolution derived from studies of the fundamental plane for high-z ETGs, our analysis shows no evidence for a decrease in the number density of the most massive ETGs out to z~ 0.7: Both the morphologically- and the photometrically-selected sub-samples show no evolution in the number density of bright (~L>2.5L*) ETGs. Allowing for different star formation histories, and cosmic variance, we estimate a maximum decrease in the number density of massive galaxies at that redshift of ~30%. We observe, however, in both the photometrical and morphological samples, a deficit of up to ~2-3 of fainter ETGs over the same cosmic period. Our results argue against a significant contribution of recent dissipationless ``dry'' mergers to the formation of the most massive ETGs. We suggest that the mass growth in low luminosity ETGs can be explained with a conversion from z~0.7 to z=0 of blue, irregular and disk galaxies into low- and intermediate-mass ``red'' ETGs, possibly also through gas rich mergers.

astro-ph↗
arXiv2007

The Cosmic Evolution Survey (COSMOS): a large-scale structure at z=0.73 and the relation of galaxy morphologies to local environment

We have identified a large-scale structure at z~0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak-lensing convergence map and the distribution of extended X-ray sources in a mosaic of XMM observations. The main peak seen in these maps corresponds to a rich cluster with Tx= 3.51+0.60/-0.46 keV and Lx=(1.56+/-0.04) x 10^{44} erg/s ([0.1-2.4] keV band). We estimate an X-ray mass within $r500$ corresponding to M500~1.6 x 10^{14} Msun and a total lensing mass (extrapolated by fitting a NFW profile) M(NFW)=(6+/-3) x 10^15 Msun. We use an automated morphological classification of all galaxies brighter than I_AB=24 over the structure area to measure the fraction of early-type objects as a function of local projected density Sigma_10, based on photometric redshifts derived from ground-based deep multi-band photometry. We recover a robust morphology-density relation at this redshift, indicating, for comparable local densities, a smaller fraction of early-type galaxies than today. Interestingly, this difference is less strong at the highest densities and becomes more severe in intermediate environments. We also find, however, local "inversions'' of the observed global relation, possibly driven by the large-scale environment. In particular, we find direct correspondence of a large concentration of disk galaxies to (the colder side of) a possible shock region detected in the X-ray temperature map and surface brightness distribution of the dominant cluster. We interpret this as potential evidence of shock-induced star formation in existing galaxy disks, during the ongoing merger between two sub-clusters.

astro-ph↗
arXiv2007

The Cosmic Evolution Survey (COSMOS): The morphological content and enviromental dependence of the galaxy color-magnitude relation at z~0.7

We study the enviromental dependence and the morphological composition of the galaxy color-magnitude diagram at z~0.7, using a pilot sub-sample of ~2000 galaxies from the COSMOS surve, with I_AB<24, photometric redshift within 0.61<z<0.85 and galaxy morphologies based on the HST-ACS data. The C-M diagram shows a clear red-sequence dominated by early-type galaxies and also a remarkably well-defined "blue sequence'" described by late-type objects. While the percentage of objects populating the two sequences is a function of environment, with a clear morphology/color-density relation, their normalization and slope are independent of local density. We identify and study a number of objects with "anomalous'' colors, given their morphology. Red late-type galaxies are found to be mostly highly-inclined spiral galaxies, with colors dominated by internal reddening (33% contamination with respect to truly passive spheroidals). Conversely, the population of blue early-type galaxies is composed by objects of moderate luminosity and mass, concurring to only ~5% of the mass in spheroidal galaxies. The majority of them (~70%) occupy a position in the surface-brightness/effective-radius plane not consistent with them being precursors of current epoch elliptical galaxies. In a color-mass diagram, color sequences are even better defined, with red galaxies covering in general a wider range of masses at nearly constant color, and blue galaxies showing a more pronounced dependence of color on mass. While the red sequence is adequately reproduced by models of passive evolution, the blue sequence is better interpreted as a specific star-formation sequence. Its substantial invariance with respect to local density suggests that the overall, "secular'' star formation is driven more by galaxy mass than by environment. [...]

astro-ph↗
arXiv2007

Deep GALEX Imaging of the HST/COSMOS Field: A First Look at the Morphology of z~0.7 Star-forming Galaxies

We present a study of the morphological nature of redshift z~0.7 star-forming galaxies using a combination of HST/ACS, GALEX and ground-based images of the COSMOS field. Our sample consists of 8,146 galaxies, 5,777 of which are detected in the GALEX near-ultraviolet band down to a limiting magnitude of 25.5 (AB). We make use of the UV to estimate star formation rates, correcting for the effect of dust using the UV-slope, and compute, from the ACS F814W images, the C,A,S,G,M20 morphological parameters for all objects in our sample. We observe a morphological bimodality in the galaxy population and show that it has a strong correspondence with the FUV - g color bimodality. We conclude that UV-optical color predominantly evolves concurrently with morphology. We observe many of the most star-forming galaxies to have morphologies approaching that of early-type galaxies, and interpret this as evidence that strong starburst events are linked to bulge growth and constitute a process through which galaxies can be brought from the blue to the red sequence while simultaneously modifying their morphology accordingly. We conclude that the red sequence has continued growing at z~<0.7. We also observe z~0.7 galaxies to have physical properties similar to that of local galaxies, except for higher star formation rates. Whence we infer that the dimming of star-forming galaxies is responsible for most of the evolution in the star formation rate density of the Universe since that redshift, although our data are also consistent with a mild number evolution. [abridged]

astro-ph↗