arXiv subjects

A. Tomita

Publications and source records attributed to A. Tomita.

18 recordsLinked to original sources

arXiv2026

Two-dimensional metallicity distribution of the ionized gas in NGC 628 and NGC 6946

We present here two H II region catalogues with azimuthal resolution for the two grand design galaxies NGC 628 and NGC 6946. With the help of these catalogues, we study several properties of the star-forming processes occurring in spiral galaxies. We obtained direct imaging in the narrow-band filters centred at Hα, H\b{eta}, [O II]λ3727, and [O III]λλ4959, 5007 and their respective continua. After the calibration and correction of the data, we obtained for each H II region the de-reddened fluxes in the aforementioned lines, the size, the Hα equivalent width, and, using two different empirical calibrations, the metallicity. Employing a method based on the Delaunay triangulation, a two-dimensional (2D) representation of the metallicity was obtained. Data for 209 H II regions of NGC 628 and 226 H II regions of NGC 6946 are obtained. The radial behaviours of the Hα equivalent width, the excitation, and the oxygen abundance are derived. Two-dimensional representations of the metallicity and the excitation are calculated for the galaxies in the study. The two empirical calibrations of the metallicity are compared. The oxygen abundance gradients obtained in this study agree with previously published values. However, more regions were examined than in previous studies. We find a difference of about 0.6 dex between the two empirical calibrations employed. Finally, the 2D representations of the metallicity reveal high metallicity knots in NGC 628, and for NGC 6946 a high metallicity azimuthal structure is discovered. These high metallicity regions seem to be linked to the arms of the galaxies and are probably produced by an increase in the temperature of the ionizing clusters in the H II regions, which may be linked to variations in the initial mass functions of the galaxies between the arm and interarm regions.

astro-ph.GA↗

arXiv2011

Field test of quantum key distribution in the Tokyo QKD Network

A novel secure communication network with quantum key distribution in a metropolitan area is reported. Different QKD schemes are integrated to demonstrate secure TV conferencing over a distance of 45km, stable long-term operation, and application to secure mobile phones.

quant-ph↗

arXiv2010

Performance of hybrid entanglement photon pair source for quantum key distribution

We report on the experimental demonstration of a source of hybrid entanglement pairs between two different degrees of freedom, a 1550 nm time-bin qubit and an 810 nm polarization qubit. The polarization qubit at 810 nm is transformed by an asymmetric Mach-Zehnder interferometer consisted of a Glan laser prism and a polarization-maintaining fiber. We obtained visibilities of 95.8% and 88% along Z-Z and X-X axes on the Poincare sphere, respectively with a coincidence count rate of more than 800 c/s after entanglement format transformation. These values are well above the threshold of 70.7% needed to violate a Bell inequality and allow distilling a secure key in the quantum key distribution.

quant-ph↗

arXiv2008

Cross-talk suppressed multi-anode MCP-PMT

We have developed a 4-channel multi-anode MCP-PMT, SL10, which exhibits a performance of sigma_TTS ~ 30 ps for single photons with G ~ 10^6 and QE=20% under a magnetic field of B <= 1.5 T. The cross-talk among anodes has been extensively studied. We have taken two measures to suppress it: one is to configure the SL10 to an effectively independent 4 small pieces of MCP-PMT's by segmenting an electrode of the second MCP-layer; the other is to use a constant fractional discriminator. Remarkable improvement has been achieved.

physics.ins-det↗

arXiv2008

Quantum information with Gaussian states

Quantum optical Gaussian states are a type of important robust quantum states which are manipulatable by the existing technologies. So far, most of the important quantum information experiments are done with such states, including bright Gaussian light and weak Gaussian light. Extending the existing results of quantum information with discrete quantum states to the case of continuous variable quantum states is an interesting theoretical job. The quantum Gaussian states play a central role in such a case. We review the properties and applications of Gaussian states in quantum information with emphasis on the fundamental concepts, the calculation techniques and the effects of imperfections of the real-life experimental setups. Topics here include the elementary properties of Gaussian states and relevant quantum information device, entanglement-based quantum tasks such as quantum teleportation, quantum cryptography with weak and strong Gaussian states and the quantum channel capacity, mathematical theory of quantum entanglement and state estimation for Gaussian states.

quant-ph↗

arXiv2003

The Virgo High-Resolution CO Survey I. CO Atlas

We present the results of the Virgo high-resolution CO survey (ViCS) obtained with the Nobeyama Millimeter-wave Array (NMA). This survey was made in the course of a long-term project at Nobeyama from 1999 December through 2002 April. The objects were selected from Virgo cluster members, considering CO richness from single dish flux, mild inclination, and lack of strong tidal perturbations. The central 1 arc min regions (4.7 kpc) of 15 spiral galaxies were observed with resolutions of 2 to 5 arcsec and 10 to 20 km/s, and sensitivities of 20 mJy/ beam for a 10 km/s channel. The objects lie at the same distance of the Virgo cluster (16.1 Mpc), which is advantageous for comparisons among individual galaxies. We describe the details of observations and data reduction, and present an atlas of integrated CO intensity maps, velocity fields and position-velocity diagrams along the major axes. The molecular gas morphology in the Virgo galaxies shows a wealth of variety, not specifically depending on the Hubble types.

astro-ph↗

arXiv2002

The UV (GALEX) and FIR (ASTRO-F) All Sky Surveys: the measure of the dust extinction in the local universe

Before the end of 2002 will be launched the GALEX satellite (a NASA/SMEX project) which will observe all the sky in Ultraviolet (UV) through filters at 1500 and 2300 A down to m(AB) 21. In 2004 will be launched the ASTRO-F satellite which will perform an all sky survey at Far-Infrared (FIR) wavelengths. The cross-correlation of both surveys will lead to very large samples of galaxies for which FIR and UV fluxes will be available. Using the FIR to UV flux ratio as a quantitative tracer of the dust extinction we will be able to measure the extinction in the nearby universe (z<0.2) and to perform a statistically significant analysis of the extinction as a function of galactic properties. Of particular interest is the construction of pure FIR and UV selected samples for which the extinction will be measured as templates for the observation of high redshift galaxies.

astro-ph↗

arXiv2002

A simple way to detect the state transition caused by the nondiagonal abelian Berry phase

In a nondegenerate syste, the abelian Berry's phase will never cause transitions among the Hamiltonian's eigenstate. However, in a degenerate syatem, it is well known that the state transition can be caused by the non-abelian Berry phase. Actually, in a such a system, the phase factor is not always nonabelian. Even in the case that the phase is a nondiagonal matrix, it still can be an abelian phase and can cause the state transitions. We then propose a simple scheme to detect such an effect of the Berry phase to the degenerate states by using the optical entangled pair state. In this scheme, we need not control any external parameters during the quantum state evolution.

quant-ph↗

arXiv2000

Complete Bell state measurement with controlled photon absorption and quantum interference

A solid state device to discriminate all the four Bell states is proposed. The device is composed of controlled absorption crystals, rotators, and retarders. The controlled absorption, where the state of one photon affects the absorption of the other photon, is realized by two photon absorption in a cubic crystal. The controlled absorption crystal detects a particular Bell state and is transparent for the other Bell states. The rotators and retarders transform a Bell state to another. This device may solve the problems in the early quantum teleportation experiments in photon polarization states.

quant-ph↗

arXiv2000

Quantum Key Distribution using Two Coherent States of Light and their Superposition

Quantum mechanical complementarity ensures the security of the key-distribution scheme reported by Brassard and Bennet in 1984 (BB84), but does not prohibit use of multi-photons as a signal carrier. We describe a novel BB84 scheme in which two nearly orthogonal coherent states carry the key, and the superposition of these states (cat states) protects the communication channel from eavesdropping. Information leakage to eavesdroppers can be determined from the visibility of the interferential fringes in the distribution of the outcome when a certain quadrature component is measured through homodyne detection. The effect of channel loss and detector inefficiency is discussed.

quant-ph↗

arXiv1999

Central Kinematics and Rotation Curve of the Sb Galaxy NGC 4527 in CO, Halpha, and [NII] Lines

We have obtained interferometer observations of the central region of the Sb galaxy NGC 4527 in the 12CO (J=1-0) line emission using the Nobeyama Millimeter Array. We also obtained optical (Halpha, [NII]) spectroscopy using the Okayama 188-cm reflector along the major axis. The kinematical structure and the distribution of HII regions show symmetry around the nucleus, while the distribution of molecular gas is asymmetric. The molecular-gas mass shares only 10% of the dynamical mass in the central 1 kpc radius region. Using position-velocity diagrams, we have derived a center-to-disk rotation curve. It rises steeply in the central region, attaining a maximum of about 250 km/s at 400 pc radius, and then decreases to a minimum at 2 kpc radius, followed by a disk and outer flat part. The rotation curve may provide us with the most similar case to that of the Milky Way Galaxy.

astro-ph↗

arXiv1999

Central Rotation Curves of Spiral Galaxies

We present high-resolution central-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies. We discuss their general characteristics, particularly their central behavior, as well as dependencies on morphological types, activity, and peculiarity. The rotation curves generally show a steep nuclear rise, and high-velocity central rotation, followed by a broad maximum in the disk and then by a flat rotation due to the massive halo. Since the central high velocity and steep rise are common to all massive galaxies, it cannot be due to non-circular motions. Disk rotation curves of barred galaxies show larger dispersion than those of normal galaxies which is probably due to non-circular motions. Interacting galaxies show often perturbed outer rotation curves, while their central rotation shows no particular peculiarity. Also, central activities, such as starbursts and AGN, appear to show no particular correlation with the property of rotation curves. This would suggest that the central activities are triggered by a more local effect than the global dynamical property.

astro-ph↗

arXiv1999

Optical and CO Radio Observations of Poor Cluster Zwicky 1615.8+3505

The cluster Zwicky 1615.8+3505 is considered to be a dynamically young poor cluster. To investigate the morphology and star-formation activity of galaxies under the environment of a dynamically young poor cluster, we have performed V, R, and I surface photometry, optical low-resolution spectroscopy, and 12CO (J=1-0) line observations for member galaxies. Our data show that more than 90% of the observed galaxies show regular morphologies and no star-formation activities, indicating that the environment does not affect these galaxy properties. Among sixteen galaxies observed, only NGC 6104 shows a significant star-formation activity, and shows a distorted morphology, indicating a tidal interaction. This galaxy contains double knots, and only one knot possesses Seyfert activity, though the sizes and luminosities are similar to each other; we also discuss this feature.

astro-ph↗

arXiv1998

Photometric Observations of Star Formation Activity in Early Type Spirals

We observationally study the current star formation activities of early type spiral galaxies. We construct a complete sample of 15 early type spirals having far-infrared (FIR) to optical B band luminosity ratios, L(FIR)/L(B), larger than the average of the type, and make their CCD imaging of the R and H-alpha bands. The equivalent widths of H-alpha emission increase with increasing L(FIR)/L(B), indicating that L(FIR)/L(B) can be an indicator of star formation for such early type spirals with star formation activities higher than the average. For all of the observed early type spirals, the extended HII regions exist at the central regions with some asymmetric features. H-alpha emission is more concentrated to the galactic center than the R band light, and the degree of the concentration increases with the star formation activity. We also analyze the relation between the star formation activities and the existence of companion galaxies in the sample galaxies and other bright early type spirals. No correlation is found and this suggests that the interaction is not responsible for all of the star formation activities of early type spirals.

astro-ph↗

arXiv1998

H-Alpha Velocity Fields of H II Regions in Nearby Dwarf Irregular Galaxies

We present H-alpha velocity fields of thirteen giant H II regions in four nearby dwarf irregular galaxies, NGC 2366, Holmberg II, IC 2574, and WLM. We classify the velocity features as well as the morphologies of the H II regions. The H-alpha velocity features are divided into three categories; three H II regions show chaotic feature with a typical scale of variation of a few 100 pc in size and a few 10 km s^{-1} in velocity, one shows expanding-bubble feature, and the remaining nine have calm velocity fields. There is a correlation between the H-alpha velocity feature and the morphology of H II regions. We measured bulk motion of the H II regions relative to the ambient H I velocity for the H II regions with calm velocity fields and found a typical velocity difference of about 5 km s^{-1}. We discuss a model for origin of star-forming regions based on the presence of the velocity difference between H-alpha and H I gas as well as the H I characteristics.

astro-ph↗

arXiv1997

New Physics and CP Angles Measurement at B Factory

We have analyzed how much the $CP$ angles to be measured at B factories can deviate from the geometrical ones defined in unitarity triangle under the existence of new physics. The measurements are given in rephasing invariant form. If KM matrix is not a $3\times 3$ and unitary matrix, $\tildeϕ_1$ and $\tildeϕ_3$ is affected, and the value of $\tildeϕ_3$ depends on the decay mode. The deviation is constrained to be less than the experimental precision attained in the next decade by the available data of the magnitude of KM matrix elements. Deviation of the sum of three angles from $π$ cannot be detected unless new physics contributes significantly to $b$ decay or $D$ meson system.

hep-ph↗

arXiv1995

$W_R$ effects on $CP$ angles determination at a $B$ factory

The right-handed charged current gauge boson $W_R$ can affect significantly on the determination of the $CP$ violation angles to be measured at $B$ factories if the right-handed current quark mixing matrix $V^R$ is taken to a specific form to satisfy the bounds by neutral $K$ meson systems. The $W_R$ contribution can be sizable in $B^0$-$\overline{B^0}$ mixing and tree level $b$ quark decay. The deviation of $CP$ angles in unitarity triangle from the standard model values can be as large as $-37^\circ$ or $ +22^\circ$ for $ϕ_3$ ($γ$), and $66^\circ \sim 115^\circ$ for $ϕ_1$ ($β$) and $ϕ_2$ ($α$).

hep-ph↗

arXiv1995

Distribution of Blue Galaxies in a Merging Cluster of Galaxies Abell 168

The fraction of star-forming galaxies in rich clusters of galaxies increases rapidly with the redshift. This is interpreted as the result of a rapid evolution of cluster galaxies, though its mechanism is not yet clear. One hypothesis is that if galaxies run into the dense intracluster medium (ICM) regions, starbursts can be induced due to compression of molecular clouds in the galaxies by a raised "external" ICM pressure. In a merging cluster, there would be dense ICM regions and some galaxies may experience a rapid increase of external pressure. Thus, if the mechanism works, starbursts would occur in such galaxies. Such a situation is considered to be realized in Coma cluster, and galaxies showing a recent starburst have a characteristic spatial distribution; they populate an elongated region between two sub-clusters. We examined the above hypothesis by measuring the spatial distribution of blue galaxies, regarded as star-forming galaxies in Abell~168 to check whether a case like Coma is realized in this recently merging cluster. However, we could not find an enhanced blue-galaxy distribution between two sub-clusters. We discuss the causes of our result, including possibilities of surviving the hypothesis.

astro-ph↗