arXiv subjects

Hidenori Takahashi

Publications and source records attributed to Hidenori Takahashi.

At least 37 records · Page 2Linked to original sources

arXiv2020

Environmental impact on star-forming galaxies in a $z \sim 0.9$ cluster during course of galaxy accretion

Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at $z=0.923$ using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrow-band filter, NB1261, matches to H$α$ emission from the cluster at $z=0.923$. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H$α$ emitters associated with the cluster. They have significant overlap with MIPS 24$μ$m sources and are located exclusively in the star forming regime on the rest-frame $UVJ$ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment; cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase.

astro-ph.GA↗

arXiv2020

Glassy dielectric anomaly and negative magneto-capacitance effect in electron-doped Ca$_{1-x}$Sr$_x$Mn$_{0.85}$Sb$_{0.15}$O$_3$

Manganites exhibit various types of electronic phenomena, and these electronic characteristics can be controlled by carrier doping. Herein, we report the dielectric and magnetic properties of electron-doped manganite Ca$_{1-x}$Sr$_x$Mn$_{0.85}$Sb$_{0.15}$O$_3$ ($x$ = 0, 0.1, 0.2, and 0.3). The temperature dependence of the real part of the dielectric constant exhibits a broad and large peak just below the kink temperature of magnetization and a sharp decrease at lower temperatures, accompanied by an anomaly of the imaginary part. Furthermore, isovalent Sr substitution enhances the temperature of the dielectric peak by more than 50 K. Interestingly, the dielectric peak exhibits a negative magnetic-field effect. For all measured samples, the low-temperature variation of the dielectric constant can be qualitatively explained based on the Maxwell-Wagner (MW) model that describes a system composed of grain boundaries and semiconducting grains. However, the observed peak and its negative magneto-capacitance effect at high temperatures cannot be reproduced by a combination of the MW model and magnetoresistance effect. The dielectric peak strongly indicates polaronic relaxation in the present system. These results suggest that polarons form clusters with a dipole ordering and magneto-electric coupling, which might be consistently understood by the charge-ordering scenario.

cond-mat.mtrl-sci↗

arXiv2019

An optical search for transients lasting a few seconds

Using a prototype of the Tomo-e Gozen wide-field CMOS mosaic camera, we acquire wide-field optical images at a cadence of 2 Hz and search them for transient sources of duration 1.5 to 11.5 seconds. Over the course of eight nights, our survey encompasses the equivalent of roughly two days on one square degree, to a fluence equivalent to a limiting magnitude about $V = 15.6$ in a 1-second exposure. After examining by eye the candidates identified by a software pipeline, we find no sources which meet all our criteria. We compute upper limits to the rate of optical transients consistent with our survey, and compare those to the rates expected and observed for representative sources of ephemeral optical light.

astro-ph.IM↗

arXiv2019

New constraint on the atmosphere of (50000) Quaoar from a stellar occultation

We report observations of a stellar occultation by the classical Kuiper belt object (50000) Quaoar occurred on 28 June 2019. A single-chord high-cadence (2 Hz) photometry dataset was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow to set new $1σ$ and $3σ$ upper limits of 6 and 16 nbar, respectively, for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar's expected mean surface temperature ($T \sim 44$ K) and imply the absence of a $\sim$10 nbar-level global atmosphere formed by methane ice on Quaoar's surface.

astro-ph.EP↗

arXiv2019

Ground-based Pa$α$ Narrow-band Imaging of Local Luminous Infrared Galaxies II: Bulge Structure And Star Formation Activity

We present properties of two types of bulges (classical- and pseudo- bulges) in 20 luminous infrared galaxies (LIRGs) observed in the near infrared of the $H$, $K_s$ and 1.91$μ$m narrow-band targeting at the hydrogen Pa$α$ emission line by the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope. To classify the two types of bulges, we first perform a two-dimensional bulge-disk decomposition analysis in the $K_\mathrm{s}$-band images. The result shows a tentative bimodal distribution of Sérsic indices with a separation at $\log(n_b)\sim0.5$, which is consistent with that of classical and normal galaxies. We next measure extents of the distribution of star forming regions in Pa$α$ emission line images, normalized with the size of the bulges, and find that they decrease with increasing Sérsic indices. These results suggest that star-forming galaxies with classical bulges have compact star forming regions concentrated within the bulges, while those with pseudobulges have extended star forming regions beyond the bulges, suggesting that there are different formation scenarios at work in classical and pseudobulges.

astro-ph.GA↗

arXiv2019

Trion-based High-speed Electroluminescence from Semiconducting Carbon Nanotube Films

High-speed light emitters integrated on silicon chips can enable novel architectures for silicon-based optoelectronics, such as on-chip optical interconnects and silicon photonics. However, conventional light sources based on compound semiconductors face major challenges for their integration with the silicon-based platforms because of the difficulty of their direct growth on a silicon substrate. Here, we report high-brightness, high-speed, ultra-small-size on-chip electroluminescence (EL) emitters based on semiconducting single-walled carbon nanotubes (SWNTs) thin films. The peaks of the EL emission spectra are 0.2-eV red-shifted from the peaks of the absorption and photoluminescence emission spectra, which suggests emission from trions. High-speed responses of ~ 100 ps were experimentally observed from the trion-based EL emitters, which indicates the possibility of several-GHz modulation. The pulsed light generation was also obtained by applying pulse voltage. These high-speed and ultra-small-size EL emitters can enable novel on-chip optoelectronic devices for highly integrated optoelectronics and silicon photonics.

physics.app-ph↗

arXiv2018

Luminosity Function of Faint Sporadic Meteors measured with a Wide-Field CMOS mosaic camera Tomo-e PM

Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of ${\sim}1.98\,\mathrm{deg^2}$ at 2\,Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from $+4$ to $+10\,\mathrm{mag}$ in the $V$-band, corresponding to about $8.3{\times}10^{-2}$ to $3.3{\times}10^{-4}\,\mathrm{g}$ in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter $r = 3.1{\pm}0.4$ and a meteor rate $\log_{10}N_0 = -5.5{\pm}0.5$. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozen is about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozen will provide a more robust measurement of the luminosity function.

astro-ph.EP↗

arXiv2016

The rotation period distributions of 4--10 Myr T Tauri stars in Orion OB1: New constraints on pre-main-sequence angular momentum evolution

Most existing studies of the angular momentum evolution of young stellar populations have focused on the youngest (1-3 Myr) T Tauri stars. In contrast, the angular momentum distributions of older T Tauri stars (4-10 Myr) have been less studied, even though they hold key insight to understanding stellar angular momentum evolution at a time when protoplanetary disks have largely dissipated and when models therefore predict changes in the rotational evolution that can in principle be tested. We present a study of photometric variability among 1,974 confirmed T Tauri members of various sub-regions of the Orion OB1 association, and with ages spanning 4-10 Myr, using optical time-series from three different surveys. For 564 of the stars (~32% of the weak-lined T Tauri stars and ~13% of the classical T Tauri stars in our sample) we detect statistically significant periodic variations which we attribute to the stellar rotation periods, making this one of the largest samples of T Tauri star rotation periods yet published. We observe a clear change in the overall rotation period distributions over the age range 4-10 Myr, with the progressively older sub-populations exhibiting systematically faster rotation. This result is consistent with angular momentum evolution model predictions of an important qualitative change in the stellar rotation periods starting at ~5 Myr, an age range for which very few observational constraints were previously available.

astro-ph.SR↗

arXiv2015

Concurrent Formation of Carbon and Silicate Dust in Nova V1280 Sco

We present infrared multi-epoch observations of the dust forming nova V1280 Sco over $\sim$2000 days from the outburst. The temporal evolution of the infrared spectral energy distributions at 1272, 1616 and 1947 days can be explained by the emissions produced by amorphous carbon dust of mass (6.6--8.7)$\times$10$^{-8}$M$_{\odot}$ with a representative grain size of 0.01$~μ$m and astronomical silicate dust of mass (3.4--4.3)$\times$10$^{-7}$M$_{\odot}$ with a representative grain size of 0.3--0.5$~μ$m. Both of these dust species travel farther away from the white dwarf without an apparent mass evolution throughout those later epochs. The dust formation scenario around V1280 Sco suggested from our analyses is that the amorphous carbon dust is formed in the nova ejecta followed by the formation of silicate dust in the expanding nova ejecta or as a result of the interaction between the nova wind and the circumstellar medium.

astro-ph.GA↗

arXiv2015

ANIR : Atacama Near-Infrared Camera for the 1.0-m miniTAO Telescope

We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in northern Chile. The camera provides a field of view of 5'.1 $\times$ 5'.1 with a spatial resolution of 0".298 /pixel in the wavelength range of 0.95 to 2.4 $μ$m. Taking advantage of the dry site, the camera is capable of hydrogen Paschen-$α$ (Pa$α$, $λ=$1.8751 $μ$m in air) narrow-band imaging observations, at which wavelength ground-based observations have been quite difficult due to deep atmospheric absorption mainly from water vapor. We have been successfully obtaining Pa$α$ images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters ($N1875$, $N191$) including the atmospheric absorption show larger dispersion (~10%) than those at broad-band filters (a few %), indicating that they are affected by temporal fluctuations in Precipitable Water Vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and derive that the median and the dispersion of the distribution of the PWV are 0.40+/-0.30 mm for $N1875$ and 0.37+/-0.21 mm for $N191$, which are remarkably smaller (49+/-38% for $N1875$ and 59+/-26% for $N191$) than radiometry measurements at the base of Cerro Chajnantor (5100 m alt.). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3-1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a "ground-based" Pa$α$ observation.

astro-ph.IM↗

arXiv2015

Multi-wavelength observations of the black widow pulsar 2FGL J2339.6-0532 with OISTER and Suzaku

Multi-wavelength observations of the black-widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating up the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52$^{\circ}$ < i < 59$^{\circ}$, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10$^{11}$ cm from the pulsar, the pulsar wind is already in particle dominant-stage, with a magnetization parameter of $σ$ < 0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of orbital modulation. The observed phenomenon may be related to an unstable pulsar-wind activity or a weak mass accretion, both of which can result in the temporal extinction of radio-pulse.

astro-ph.HE↗

arXiv2014

Ground-based Pa$α$ Narrow-band Imaging of Local Luminous Infrared Galaxies I: Star Formation Rates and Surface Densities

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust, produced by their active star formation, and it is difficult to measure their activity in the optical wavelength. We have carried out Pa$α$ narrow-band imaging observations of 38 nearby star-forming galaxies including 33 LIRGs listed in $IRAS$ RBGS catalog with the Atacama Near InfraRed camera (ANIR) on the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO). Star formation rates (SFRs) estimated from the Pa$α$ fluxes, corrected for dust extinction using the Balmer Decrement Method (typically $A_V$ $\sim$ 4.3 mag), show a good correlation with those from the bolometric infrared luminosity of $IRAS$ data within a scatter of 0.27 dex. This suggests that the correction of dust extinction for Pa$α$ flux is sufficient in our sample. We measure the physical sizes and the surface density of infrared luminosities ($Σ_{L(\mathrm{IR})}$) and $SFR$ ($Σ_{SFR}$) of star-forming region for individual galaxies, and find that most of the galaxies follow a sequence of local ultra luminous or luminous infrared galaxies (U/LIRGs) on the $L(\mathrm{IR})$-$Σ_{L(\mathrm{IR})}$ and $SFR$-$Σ_{SFR}$ plane. We confirm that a transition of the sequence from normal galaxies to U/LIRGs is seen at $L(\mathrm{IR})=8\times10^{10}$ $L_{\odot}$. Also, we find that there is a large scatter in physical size, different from those of normal galaxies or ULIRGs. Considering the fact that most of U/LIRGs are merging or interacting galaxies, this scatter may be caused by strong external factors or differences of their merging stage.

astro-ph.GA↗

arXiv2012

AKARI Infrared Camera Survey of the Large Magellanic Cloud. I. Point Source Catalog

We present a near- to mid-infrared point source catalog of 5 photometric bands at 3.2, 7, 11, 15 and 24 um for a 10 deg2 area of the Large Magellanic Cloud (LMC) obtained with the Infrared Camera (IRC) onboard the AKARI satellite. To cover the survey area the observations were carried out at 3 separate seasons from 2006 May to June, 2006 October to December, and 2007 March to July. The 10-sigma limiting magnitudes of the present survey are 17.9, 13.8, 12.4, 9.9, and 8.6 mag at 3.2, 7, 11, 15 and 24 um, respectively. The photometric accuracy is estimated to be about 0.1 mag at 3.2 um and 0.06--0.07 mag in the other bands. The position accuracy is 0.3" at 3.2, 7 and 11um and 1.0" at 15 and 24 um. The sensitivities at 3.2, 7, and 24 um are roughly comparable to those of the Spitzer SAGE LMC point source catalog, while the AKARI catalog provides the data at 11 and 15 um, covering the mid-infrared spectral range contiguously. Two types of catalog are provided: a Catalog and an Archive. The Archive contains all the detected sources, while the Catalog only includes the sources that have a counterpart in the Spitzer SAGE point source catalog. The Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at 3.2, 7, 11, 15, and 24 um, respectively. Based on the catalog, we discuss the luminosity functions at each band, the color-color diagram, and the color-magnitude diagram using the 3.2, 7, and 11 um band data. Stars without circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects, and background galaxies are located at distinct regions in the diagrams, suggesting that the present catalog is useful for the classification of objects towards the LMC.

astro-ph.CO↗

arXiv2011

Widely Extended [OIII] 88 um Line Emission around the 30 Doradus Region Revealed with AKARI FIS-FTS

We present the distribution map of the far-infrared [OIII] 88um line emission around the 30 Doradus (30 Dor) region in the Large Magellanic Cloud obtained with the Fourier Transform Spectrometer of the Far-Infrared Surveyor onboard AKARI. The map reveals that the [OIII] emission is widely distributed by more than 10' around the super star cluster R136, implying that the 30 Dor region is affluent with interstellar radiation field hard enough to ionize O^{2+}. The observed [OIII] line intensities are as high as (1-2) x 10^{-6} W m^{-2} sr^{-1} on the peripheral regions 4'-5' away from the center of 30 Dor, which requires gas densities of 60-100 cm^{-3}. However the observed size of the distribution of the [OIII] emission is too large to be explained by massive stars in the 30 Dor region enshrouded by clouds with the constant gas density of 10^2 cm^{-3}. Therefore the surrounding structure is likely to be highly clumpy. We also find a global correlation between the [OIII] and the far-infrared continuum emission, suggesting that the gas and dust are well mixed in the highly-ionized region where the dust survives in clumpy dense clouds shielded from the energetic photons.

astro-ph.GA↗

arXiv2010

Calibration of the AKARI Far-Infrared Imaging Fourier Transform Spectrometer

The Far-Infrared Surveyor (FIS) onboard the AKARI satellite has a spectroscopic capability provided by a Fourier transform spectrometer (FIS-FTS). FIS-FTS is the first space-borne imaging FTS dedicated to far-infrared astronomical observations. We describe the calibration process of the FIS-FTS and discuss its accuracy and reliability. The calibration is based on the observational data of bright astronomical sources as well as two instrumental sources. We have compared the FIS-FTS spectra with the spectra obtained from the Long Wavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO) having a similar spectral coverage. The present calibration method accurately reproduces the spectra of several solar system objects having a reliable spectral model. Under this condition the relative uncertainty of the calibration of the continuum is estimated to be $\pm$ 15% for SW, $\pm$ 10% for 70-85 cm^(-1) of LW, and $\pm$ 20% for 60-70 cm^(-1) of LW; and the absolute uncertainty is estimated to be +35/-55% for SW, +35/-55% for 70-85 cm^(-1) of LW, and +40/-60% for 60-70 cm^(-1) of LW. These values are confirmed by comparison with theoretical models and previous observations by the ISO/LWS.

astro-ph.IM↗

arXiv2009

Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARI

We investigate the structure of the interstellar medium (ISM) and identify the location of possible embedded excitation sources from far-infrared (FIR) line and mid-infrared continuum emission maps. We carried out imaging spectroscopic observations of four giant Galactic star-forming regions with the Fourier Transform Spectrometer (FTS) onboard AKARI. We obtained [OIII] 88 micron and [CII] 158 micron line intensity maps of all the regions: G3.270-0.101, G333.6-0.2, NGC3603, and M17. For G3.270-0.101, we obtained high-spatial-resolution [OIII] 88 micron line-emission maps and a FIR continuum map for the first time, which imply that [OIII] 88 micron emission identifies the excitation sources more clearly than the radio continuum emission. In G333.6-0.2, we found a local [OIII] 88 micron emission peak, which is indicative of an excitation source. This is supported by the 18 micron continuum emission, which is considered to trace the hot dust distribution. For all regions, the [CII] 158 micron emission is distributed widely as suggested by previous observations of star-forming regions. We conclude that [OIII] 88 micron emission traces the excitation sources more accurately than the radio continuum emission, especially where there is a high density and/or column density gradient. The FIR spectroscopy provides a promising means of understanding the nature of star-forming regions.

astro-ph.GA↗

arXiv2008

Performance of the Imaging Fourier Transform Spectrometer with Photoconductive Detector Arrays: An Application for the AKARI Far-Infrared Instrument

We have developed an imaging Fourier transform spectrometer (FTS) for space-based far-infrared astronomical observations. The FTS employs a newly developed photoconductive detector arrays with a capacitive trans-impedance amplifier, which makes the FTS a completely unique instrument. The FTS was installed as a function of the far-infrared instrument (FIS: Far-Infrared Surveyor) on the Japanese astronomical satellite, AKARI, which was launched on February 21, 2006 (UT) from the Uchinoura Space Center. The FIS-FTS had been operated for more than one year before liquid helium ran out on August 26, 2007. The FIS-FTS was operated nearly six hundreds times, which corresponds to more than one hundred hours of astronomical observations and almost the same amount of time for calibrations. As expected from laboratory measurements, the FIS-FTS performed well and has produced a large set of astronomical data for valuable objects. Meanwhile, it becomes clear that the detector transient effect is a considerable factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the FIS-FTS and interesting phenomena related to FTS using photoconductive detectors are described, and future applications of this kind of FTS system are discussed.

astro-ph↗

arXiv2008

AKARI IRC survey of the Large Magellanic Cloud: Outline of the survey and initial results

We observed an area of 10 deg^2 of the Large Magellanic Cloud using the Infrared Camera on board AKARI. The observations were carried out using five imaging filters (3, 7, 11, 15, and 24 micron) and a dispersion prism (2 -- 5 micron, $λ/ Δλ$ $\sim$ 20) equipped in the IRC. This paper describes the outline of our survey project and presents some initial results using the imaging data that detected over 5.9x10^5 near-infrared and 6.4x10^4 mid-infrared point sources. The 10 $σ$ detection limits of our survey are about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3, 7, 11, 15, and 24 micron, respectively. The 11 and 15 micron data, which are unique to AKARI IRC, allow us to construct color-magnitude diagrams that are useful to identify stars with circumstellar dust. We found a new sequence in the color-magnitude diagram, which is attributed to red giants with luminosity fainter than that of the tip of the first red giant branch. We suggest that this sequence is likely to be related to the broad emission feature of aluminium oxide at 11.5 micron. The 11 and 15 micron data also indicate that the ([11] - [15]) micron color of both oxygen-rich and carbon-rich red giants once becomes blue and then turns red again in the course of their evolution, probably due to the change in the flux ratio of the silicate or silicon carbide emission feature at 10 or 11.3 micron to the 15 micron flux.

astro-ph↗