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Y. Taniguchi

Publications and source records attributed to Y. Taniguchi.

At least 199 records · Page 11Linked to original sources
arXiv2004

A Strong Lyman-alpha Emitter at z=6.33 in the Subaru Deep Field Selected as an i' Dropout

We report on the discovery of a star-forming galaxy at z=6.33 in the Subaru Deep Field. This object is selected as a candidate of an i'-dropout, high-redshift galaxy around z=6 because of its red i'-z' color in our deep optical imaging survey in the Subaru Deep Field. Our follow up optical spectroscopy reveals that this object is a strong Ly-alpha emitter with only very faint ultraviolet continuum. The rest-frame equivalent width of the detected Ly-alpha emission is as much as 130 A. Thus the light detected in our z' image is largely attributed to the Ly-alpha emission, i.e., ~40% of the z'-band flux is the strong Ly-alpha emission, giving a very red i'-z' color. This is consistent with the photometric property of this object because the narrow-band data obtained with the NB921 filter shows a significant depression, z'-NB921 = -0.54 mag. By using the photometric data, we show that some other objects among the 48 i'-dropout high-redshift galaxy candidates found in the Subaru Deep Field also show a significant NB921 depression. We briefly discuss the nature of these NB921-depressed objects.

astro-ph↗
arXiv2004

A scaling study of the step scaling function in SU(3) gauge theory with improved gauge actions

We study the scaling behavior of the step scaling function for SU(3) gauge theory, employing the renormalization-group improved Iwasaki gauge action and the perturbatively improved Lüscher-Weisz gauge action. We confirm that the step scaling functions from the improved gauge actions agree with that previously obtained from the plaquette action within errors in the continuum limit at both weak and strong coupling regions. We also investigate how different choices of boundary counter terms for the improved gauge actions affect the scaling behavior. In the extrapolation to the continuum limit, we observe that the cut off dependence becomes moderate for the Iwasaki action, if a perturbative reduction of scaling violations is applied to the simulation results. We also measure the low energy scale ratio with the Iwasaki action, and confirm its universality.

hep-lat↗
arXiv2004

The nearest extreme starburst: bubbles, young star clusters, and outflow in NGC 3256

In this Work we report, for the extreme starburst in the IR merger NGC 3256: (i) The detection of 4 galactic bubbles, associated with SN explosions.(ii) The first analysis of the spatial distribution of young star clusters (YSC) candidates.(iii) The kinematic study of the ionized gas in the core of of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission line profile could be explained by the presence in the core of YSC with outflow.

astro-ph↗
arXiv2004

A Subaru Search for Ly-alpha Blobs in and around the Proto-cluster Region at Redshift z=3.1

We report the properties of the 35 robust candidates of Ly-alpha blobs (LABs), which are larger than 16 arcsec^2 in isophotal area and brighter than 0.7 x 10^-16 ergs s^-1 cm^-2, searched in and around the proto-cluster region at redshift z=3.1 discovered by Steidel et al. in the SSA22 field, based on wide-field (31'x23') and deep narrow-band (NB497; 4977/77) and broad-band (B,V, and R) images taken with the prime-focus camera on the Subaru telescope. The two previously known giant LABs are the most luminous and the largest ones in our survey volume of 1.3 x 10^5 Mpc^3. We revealed the internal structures of the two giant LABs and discovered some bubble-like features, which suggest that intensive starburst and galactic superwind phenomena occurred in these objects in the past. The rest 33 LABs have isophotal area of about 16-78 arcsec^2 and flux of 0.7-7 x 10^-16 ergs s^-1 cm^-2. These 35 LABs show a continuous distribution of isophotal area and emission line flux. The distributions of average surface brightness and morphology are widespread from relatively compact high surface brightness objects to very diffuse low surface brightness ones. The physical origins of these LABs may be (i) photo-ionization by massive stars, or active galactic nuclei, or (ii) cooling radiation from gravitationally heated gas, or (iii) shock heating by starburst driven galactic superwind. One third of them are apparently not associated with ultra-violet continuum sources that are bright enough to produce Ly-alpha emission, assuming a Salpeter initial mass function. The 90% of these LABs are located inside the high surface density region of the 283 relatively compact and strong Ly-alpha emitters selected in our previous study. This suggests that these LABs may be the phenomena related to dense environment at high redshift.

astro-ph↗
arXiv2004

Non-perturbative renormalization of meson decay constants in quenched QCD for a renormalization group improved gauge action

Renormalization constants ($Z$-factors) of vector and axial-vector currents are determined non-perturbatively in quenched QCD for a renormalization group improved gauge action and a tadpole improved clover quark action using the Schrödinger functional method. Non-perturbative values of $Z$-factors turn out to be smaller than one-loop perturbative values by $O(15%)$ at lattice spacing of $a^{-1}\approx$ 1 GeV. The pseudoscalar and vector meson decay constants calculated with the non-perturbative $Z$-factors show a much better scaling behavior compared to previous results obtained with tadpole improved one-loop $Z$-factors. In particular, the non-perturbative $Z$-factors normalized at infinite physical volume show that scaling violation of the decay constants are within about 10% up to the lattice spacing $a^{-1}\sim 1$ GeV. The continuum estimates obtained from data in the range $a^{-1}=$ 1 -- 2 GeV agree with those determined from finer lattices ($a^{-1}\sim 2-4$ GeV) with the standard action.

hep-lat↗
arXiv2004

Lattice QCD calculation of the proton decay matrix element in the continuum limit

We present a quenched lattice QCD calculation of the αand βparameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range a\approx 0.1-0.064 fm to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit, |α(NDR,2GeV)|=0.0090(09)(^{+5}_{-19})GeV^3 and |β(NDR,2GeV)|=0.0096(09)(^{+6}_{-20})GeV^3 with αand βin a relatively opposite sign, where the first error is statistical and the second is due to the uncertainty in the determination of the physical scale.

hep-lat↗
arXiv2004

Galaxy Interaction and Starburst-Seyfert Connection

Galaxy interactions are studied in terms of the starburst-Seyfert connection. The starburst requires a high rate of gas supply. Since the efficiency for supplying the gas is high in a galaxy interaction, although the companion is not necessarily discernible, Seyfert galaxies with circumnuclear starbursts are expected to be interacting. Since the large amounts of circumnuclear gas and dust obscure the broad-line region, they are expected to be observed as Seyfert 2. The active galactic nucleus itself does not require a high rate of gas supply. Seyfert galaxies without circumnuclear starbursts are not necessarily expected to be interacting even at the highest luminosities. They are not necessarily expected to evolve from Seyfert galaxies with circumnuclear starbursts. We derive these and other theoretical expectations and confirm them with statistics on observational data of magnitude-limited samples of Seyfert galaxies.

astro-ph↗
arXiv2003

Non-perturbative calculation of $Z_V$ and $Z_A$ in domain-wall QCD on a finite box

We report on a non-perturbative evaluation of the renormalization factors for the vector and axial-vector currents, $Z_V$ and $Z_A$, in the quenched domain-wall QCD (DWQCD) with plaquette and renormalization group improved gauge actions. We take the Dirichlet boundary condition for both gauge and domain-wall fermion fields on the finite box, and introduce the flavor-chiral Ward-Takahashi identities to calculate the renormalization factors. As a test of the method, we numerically confirm the expected relation that $Z_V \simeq Z_A$ in DWQCD. Employing two different box sizes for the numerical simulations at several values of the gauge coupling constant $g^2$ and the domain-wall height $M$, we extrapolate $Z_V$ to the infinite volume to remove $a/L$ errors. We finally give the interpolation formula of $Z_V$ in the infinite volume as a function of $g^2$ and $M$.

hep-lat↗
arXiv2003

Non-perturbative renormalization of vector and axial vector currents in quenched QCD for a renormalization group improved gauge action

Renormalization constants of vector ($Z_V$) and axial-vector ($Z_A$) currents are determined non-perturbatively in quenched QCD for an RG-improved gauge action and a tadpole-improved clover quark action using the Schrödinger functional method. Meson decay constants $f_ρ$ and $f_π$ show much better scaling when $Z_V$ and $Z_A$ estimated for infinite physical volume are used instead of $Z$-factors from tadpole-improved one-loop perturbation theory.

hep-lat↗
arXiv2003

Two flavors of dynamical quarks on anisotropic lattices

We report on our study of two-flavor full QCD on anisotropic lattices using $O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge and quark anisotropies corresponding to the renormalized anisotropy $ξ=a_s/a_t = 2$ are determined as functions of $β$ and $κ$, which covers the region of spatial lattice spacings $a_s\approx 0.28$--0.16 fm and $m_{PS}/m_V\approx 0.6$--0.9. The calibrations of the bare anisotropies are performed with the Wilson loop and the meson dispersion relation at 4 lattice cutoffs and 5--6 quark masses. Using the calibration results we calculate the meson mass spectrum and the Sommer scale $r_0$. We confirm that the values of $r_0$ calculated for the calibration using pseudo scalar and vector meson energy momentum dispersion relation coincide in the continuum limit within errors. This work serves to lay ground toward studies of heavy quark systems and thermodynamics of QCD including the extraction of the equation of state in the continuum limit using Wilson-type quark actions.

hep-lat↗
arXiv2003

Non-Perturbative Determination of $c_{\rm SW}$ in Three-flavor Dynamical QCD

We present a fully non-perturbative determination of the $O(a)$ improvement coefficient $c_{\rm SW}$ in three-flavor dynamical QCD for the RG improved as well as the plaquette gauge actions, using the Schrödinger functional scheme. Results are compared with one-loop estimates at weak gauge coupling.

hep-lat↗
arXiv2003

A deep 6.7um survey in the SSA13 field with ISO

We present results of a deep mid-infrared survey in the SSA13 field with the Infrared Space Observatory (ISO). In order to probe the near-infrared light at high redshifts, we surveyed the field with the broad band LW2 (5-8.5um) filter of the mid-infrared camera ISOCAM. Adopting a highly redundant imaging strategy for the 23 hour observation and carefully treating gradual changes in the detector responsivity caused by a very high rate of cosmic ray impacts, we succeeded in reaching an 80% completeness limit of 16uJy in the central 7 arcmin2 region. Utilizing the signal-to-noise ratio map, we detected 65 sources down to 6uJy in the 16 arcmin2 field. Integral galaxy number counts at 6.7um are then derived, reaching 1.3e4/deg2 at the faint limit with a slope of -1.6 between 13uJy and 130uJy. Integrating individual sources in this flux range, the resolved fraction of the extragalactic background light at 6.7um is estimated to be 0.56nW/m2/sr. These results, which reach a flux limit three times fainter than those in the Hubble Deep Fields, are in fairly good agreement with a model prediction by Franceschini et al. (1997). Finally, we discuss the relation of distant massive E/S0 galaxies to the faint 6.7um galaxy population.

astro-ph↗
arXiv2003

Orbital Motion in the Radio Galaxy 3C 66B: Evidence for a Supermassive Black Hole Binary

Supermassive black hole binaries may exist in the centers of active galactic nuclei like quasars and radio galaxies and mergers between galaxies may result in the formation of supermassive binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 +/- 0.03 years, which provides a direct detection of a supermassive black hole binary.

astro-ph↗
arXiv2003

On the Origin of Lyman-$α$ Blobs at High Redshift: Kinematic Evidence for a Hyperwind Galaxy at z = 3.1

We present deep optical spectroscopy of an extended Ly$α$ emission-line blob located in an over-dense region at redshift $z \approx 3.1$; `blob 1' of Steidel et al. (2000). The origin of such Ly$α$ blobs has been debated for some time; two of the most plausible models are (1) that it comes from a dust-enshrouded, extreme starburst galaxy with a large-scale galactic outflow (superwind/hyperwind) or (2) that it is the cooling radiation of proto-galaxies in dark matter halos. Examination of the kinematic properties of the Ly$α$ emission-line gas should allow us to determine its nature. With this motivation, we performed optical spectroscopy of `blob 1' using the Subaru Telescope, and found that its kinematic properties can be well explained in terms of superwind activity.

astro-ph↗
arXiv2003

Calculation of Non-Leptonic Kaon Decay Amplitudes from $K\toπ$ Matrix Elements in Quenched Domain-Wall QCD

We explore application of the domain wall fermion formalism of lattice QCD to calculate the $K\toππ$ decay amplitudes in terms of the $K\toπ$ and $K\to 0$ hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using domain-wall fermion action for quarks and an RG-improved gauge action for gluons on a $16^3\times 32\times 16$ and $24^3\times 32\times 16$ lattice at $β=2.6$ corresponding to the lattice spacing $1/a\approx 2$GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the $ΔI=1/2$ matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We confirm the chiral properties required of the $K\toπ$ matrix elements. Matching the lattice matrix elements to those in the continuum at $μ=1/a$ using the perturbative renormalization factor to one loop order, and running to the scale $μ=m_c=1.3$ GeV with the renormalization group for $N_f=3$ flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the $ΔI=3/2$ decay amplitude shows a good agreement with experiment in the chiral limit. The $ΔI=1/2$ amplitude, on the other hand, is about 50--60% of the experimental one even after chiral extrapolation. In view ofthe insufficient enhancement of the $ΔI=1/2$ contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of $ε'/ε$. We find that the $ΔI=3/2$ contribution is larger than the $ΔI=1/2$ contribution so that $ε'/ε$ is negative and has a magnitude of order $10^{-4}$. Possible reasons for these unsatisfactory results are discussed.

hep-lat↗
arXiv2003

Flavor Singlet Meson Mass in the Continuum Limit in Two-Flavor Lattice QCD

We present results for the mass of the eta-prime meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group improved gauge action, and Sheikholeslami and Wohlert's fermion action with tadpole-improved csw. Correlation functions are measured at three values of the coupling constant beta corresponding to the lattice spacing a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate eta-prime propagators using local sources, and find that excited state contributions are much reduced by smearing. A full analysis for the smeared propagators gives metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.

hep-lat↗
arXiv2003

The Discovery of Two Lyman$α$ Emitters Beyond Redshift 6 in the Subaru Deep Field

We have performed a deep optical imaging survey using a narrowband filter ($NB921$) centered at $λ=$ 9196 Å~ together with $i^\prime$ and $z^\prime$ broadband filters covering an 814 arcmin$^2$ area of the Subaru Deep Field. We obtained a sample of 73 strong $NB921$-excess objects based on the following two color criteria; $z^\prime - NB921 > 1$ and $i^\prime - z^\prime > 1.3$. We then obtained optical spectroscopy of nine objects in our $NB921$-excess sample, and identified at least two Ly$α$ emitters at$z=6.541 \pm 0.002$ and $z=6.578 \pm 0.002$, each of which shows the characteristic sharp cutoff together with the continuum depression at wavelengths shortward of the line peak. The latter object is more distant than HCM-6A at $z=6.56$ and thus this is the most distant known object found so far. These new data allow us to estimate the first meaningful lower limit of the star formation rate density beyond redshift 6; $ρ_{\rm SFR} \sim 5.2 \times 10^{-4} M_\odot$ yr$^{-1}$ Mpc$^{-3}$. Since it is expected that the actual density is higher by a factor of several than this value, our new observation reveals that a moderately high level of star formation activity already occurred at $z \sim$ 6.6.

astro-ph↗