86 research outputs found
Growth of quantum three-dimensional structure of InGaAs emitting at ~1 µm applicable for a broadband near-infrared light source
We obtained a high-intensity and broadband emission centered at ~1 µm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduced misfit dislocations. However, under certain growth conditions for the In concentration and growth temperature, the growth mode of the InGaAs layer can be transformed from two-dimensional to 3D growth. We found the optimal conditions to obtain a broadband emission from 3D structures with a high intensity and controlled center wavelength at ~1 µm. This method offers an alternative approach for fabricating a broadband near-infrared light source for telecommunication and medical imaging systems such as for optical coherence tomography
Intrinsic Shape of Star-Forming BzK Galaxies at z~2 in GOODS-N
We study structure of star-forming galaxies at z~2 in GOODS-N field selected
as sBzK galaxies down to K_{AB} <24.0 mag. Among 1029 sBzK galaxies, 551
galaxies (54%) show a single component in ACS/F850LP image obtained with the
Hubble Space Telescope; the rest show multiple components. We fit the
single-component sBzK galaxies with the single S\'ersic profile using the
ACS/F850LP image and find that a majority of them (64%) show S\'ersic index of
n=0.5-2.5, indicating that they have a disk-like structure. The resulting
effective radii typically range from 1.0 to 3.0 kpc in the rest-frame UV
wavelength. After correcting the effective radii to those in the rest-frame
optical wavelength, we find that the single-component sBzK galaxies locate in
the region where the local and z~1 disk galaxies distribute in the stellar
mass-size diagram, suggesting comparable surface stellar mass density between
the sBzK and z~0-1 disk galaxies. All these properties suggest that the
single-component sBzK galaxies are progenitors of the present-day disk
galaxies. However, by studying their intrinsic shape through comparison between
the observed distribution of apparent axial ratios and the distribution for
triaxial models with axes (A>B>C), we find that the mean B/A ratio is
0.61^{+0.05}_{-0.08} and disk thickness C/A is 0.28^{+0.03}_{-0.04}. This
indicates that the single-component sBzK galaxies at z~2 have a bar-like or
oval shape rather than a round disk shape. The shape seems to resemble to a
bar/oval structure that form through bar instability; if it is the case, the
intrinsic shape may give us a clue to understand dynamical evolution of
baryonic matter in a dark matter halo.Comment: 14 pages, 13 figure, 2 tables, Accepted for publication in Ap
Development of a broadband superluminescent diode based on self-assembled InAs quantum dots and demonstration of high-axial-resolution optical coherence tomography imaging
We developed a near-infrared (NIR) superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) and demonstrated high-axial-resolution optical coherence tomography (OCT) imaging using this QD-based SLD (QD-SLD). The QD-SLD utilized InAs QDs with controlled emission wavelengths as a NIR broadband light emitter, and a tilted waveguide with segmented electrodes was prepared for edge-emitting broadband electroluminescence (EL) spanning approximately 1–1.3 μm. The bandwidth of the EL spectrum was increased up to 144 nm at a temperature of 25 °C controlled using a thermoelectric cooler. The inverse Fourier transform of the EL spectrum predicted a minimum resolution of 3.6 μm in air. The QD-SLD was subsequently introduced into a spectral-domain (SD)-OCT setup, and SD-OCT imaging was performed for industrial and biological test samples. The OCT images obtained using the QD-SLD showed an axial resolution of ~4 μm, which was almost the same as that predicted from the spectrum. This axial resolution is less than the typical size of a single biological cell (~5 μm), and the practical demonstration of high-axial-resolution OCT imaging shows the application of QD-SLDs as a compact OCT light source, which enables the development of a portable OCT system
Average Metallicity and Star Formation Rate of Lya Emitters Probed by a Triple Narrow-Band Survey
We present the average metallicity and star-formation rate of Lya emitters
(LAEs) measured from our large-area survey with three narrow-band (NB) filters
covering the Lya, [OII]3727, and Ha+[NII] lines of LAEs at z=2.2. We select 919
z=2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS
spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM
near-infrared NB filters whose central wavelengths are matched to redshifted
[OII] and Ha nebular lines, respectively. By stacking the near-infrared images
of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the
majority of which are too faint to be identified individually by narrow-band
imaging or deep spectroscopy. The stacked object has an Ha luminosity of
1.7x10^{42} erg s^{-1} corresponding to a star formation rate (SFR) of 14
M_{sun} yr^{-1}. We place, for the first time, a firm lower limit to the
average metallicity of LAEs of Z>~0.09 Z_{sun} (2sigma) based on the
[OII]/(Ha+[NII]) index together with photo-ionization models and empirical
relations. This lower limit of metallicity rules out the hypothesis that LAEs,
so far observed at z~2, are extremely metal poor (Z<2x10^{-2} Z_{sun}) young
galaxies at the 4sigma level. This limit is higher than a simple extrapolation
of the observed mass-metallicity relation of z~2 UV-selected galaxies toward
lower masses (5x10^{8} M_{sun}), but roughly consistent with a recently
proposed fundamental mass-metallicity relation when the LAEs' relatively low
SFR is taken into account. The Ha and Lya luminosities of our NB-selected LAEs
indicate that the escape fraction of Lya photons is ~12-30 %, much higher than
the values derived for other galaxy populations at z~2.Comment: 21 pages, 15 figures, 8 tables. Accepted for publication in Ap
EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with (Fe/O) and (O/H) : Possible Traces of Super Massive () Stars in Early Galaxies
We present element abundance ratios and ionizing radiation of local young
low-mass (~ M_sun) extremely metal poor galaxies (EMPGs) with a 2%
solar oxygen abundance (O/H)_sun and a high specific star-formation rate
(sSFR~300 Gyr), and other (extremely) metal poor galaxies, which are
compiled from Extremely Metal-Poor Representatives Explored by the Subaru
Survey (EMPRESS) and the literature. Weak emission lines such as [FeIII]4658
and HeII4686 are detected in very deep optical spectra of the EMPGs taken with
8m-class telescopes including Keck and Subaru (Kojima et al. 2019, Izotov et
al. 2018), enabling us to derive element abundance ratios with photoionization
models. We find that neon- and argon-to-oxygen ratios are comparable to those
of known local dwarf galaxies, and that the nitrogen-to-oxygen abundance ratios
(N/O) are lower than 20% (N/O)_sun consistent with the low oxygen abundance.
However, the iron-to-oxygen abundance ratios (Fe/O) of the EMPGs are generally
high; the EMPGs with the 2%-solar oxygen abundance show high Fe/O ratios of
~90-140% (Fe/O)_sun, which are unlikely explained by suggested scenarios of
Type Ia supernova iron productions, iron's dust depletion, and metal-poor gas
inflow onto previously metal-riched galaxies with solar abundances. Moreover,
these EMPGs have very high HeII4686/H ratios of ~1/40, which are not
reproduced by existing models of high-mass X-ray binaries whose progenitor
stellar masses are less than 120 M_sun. Comparing stellar-nucleosynthesis and
photoionization models with a comprehensive sample of EMPGs identified by this
and previous EMPG studies, we propose that both the high Fe/O ratios and the
high HeII4686/H ratios are explained by the past existence of super
massive (300 M_sun) stars, which may evolve into intermediate-mass black
holes (100 M_sun).Comment: ApJ in press. 23 pages, 7 Figures, 6 Table
Extremely Metal-Poor Representatives Explored by the Subaru Survey (EMPRESS). I. A Successful Machine Learning Selection of Metal-Poor Galaxies and the Discovery of a Galaxy with M*<10^6 M_sun and 0.016 Z_sun
We have initiated a new survey for local extremely metal-poor galaxies
(EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (~500 deg^2) optical
images reaching a 5 sigma limit of ~26 magnitude, about 100 times deeper than
the Sloan Digital Sky Survey (SDSS). To select Z/Z_sun<0.1 EMPGs from ~40
million sources detected in the Subaru images, we first develop a
machine-learning (ML) classifier based on a deep neural network algorithm with
a training data set consisting of optical photometry of galaxy, star, and QSO
models. We test our ML classifier with SDSS objects having spectroscopic
metallicity measurements, and confirm that our ML classifier accomplishes
86%-completeness and 46%-purity EMPG classifications with photometric data.
Applying our ML classifier to the photometric data of the Subaru sources as
well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG
candidates from the Subaru and SDSS photometric data, respectively. We conduct
optical follow-up spectroscopy for 10 out of our EMPG candidates with
Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS, and find that the 10 EMPG
candidates are star-forming galaxies at z=0.007-0.03 with large H_beta
equivalent widths of 104-265 A, stellar masses of log(M*/M_sun)=5.0-7.1, and
high specific star-formation rates of ~300 Gyr^{-1}, which are similar to those
of early galaxies at z>6 reported recently. We spectroscopically confirm that 3
out of 10 candidates are truly EMPGs with Z/Z_sun<0.1, one of which is HSC
J1631+4426, the most metal-poor galaxy with Z/Z_sun=0.016 reported ever.Comment: 30 pages, 26 figures, and 8 tables; (Revision: metallicities changed
due to the use of a more pricise dust correction method, but conclusion does
not change, Minor: a table, some figures, and sentences are added for a clear
explanation.
First Data Release of the Hyper Suprime-Cam Subaru Strategic Program
The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered
imaging survey aimed at addressing some of the most outstanding questions in
astronomy today, including the nature of dark matter and dark energy. The
survey has been awarded 300 nights of observing time at the Subaru Telescope
and it started in March 2014. This paper presents the first public data release
of HSC-SSP. This release includes data taken in the first 1.7 years of
observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers
covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and
~27.0 mag, respectively (5sigma for point sources). All the layers are observed
in five broad bands (grizy), and the Deep and UltraDeep layers are observed in
narrow bands as well. We achieve an impressive image quality of 0.6 arcsec in
the i-band in the Wide layer. We show that we achieve 1-2 per cent PSF
photometry (rms) both internally and externally (against Pan-STARRS1), and ~10
mas and 40 mas internal and external astrometric accuracy, respectively. Both
the calibrated images and catalogs are made available to the community through
dedicated user interfaces and database servers. In addition to the pipeline
products, we also provide value-added products such as photometric redshifts
and a collection of public spectroscopic redshifts. Detailed descriptions of
all the data can be found online. The data release website is
https://hsc-release.mtk.nao.ac.jp/.Comment: 34 pages, 20 figures, 7 tables, moderate revision, accepted for
publication in PAS
Far-East Asian Toxoplasma isolates share ancestry with North and South/Central American recombinant lineages
Ihara F., Kyan H., Takashima Y., et al. Far-East Asian Toxoplasma isolates share ancestry with North and South/Central American recombinant lineages. Nature Communications 15, 4278 (2024); https://doi.org/10.1038/s41467-024-47625-6.Toxoplasma gondii is a global protozoan pathogen. Clonal lineages predominate in Europe, North America, Africa, and China, whereas highly recombinant parasites are endemic in South/Central America. Far East Asian T. gondii isolates are not included in current global population genetic structure analyses at WGS resolution. Here we report a genome-wide population study that compared eight Japanese and two Chinese isolates against representative worldwide T. gondii genomes using POPSICLE, a novel population structure analyzing software. Also included were 7 genomes resurrected from non-viable isolates by target enrichment sequencing. Visualization of the genome structure by POPSICLE shows a mixture of Chinese haplogroup (HG) 13 haploblocks introgressed within the genomes of Japanese HG2 and North American HG12. Furthermore, two ancestral lineages were identified in the Japanese strains; one lineage shares a common ancestor with HG11 found in both Japanese strains and North American HG12. The other ancestral lineage, found in T. gondii isolates from a small island in Japan, is admixed with genetically diversified South/Central American strains. Taken together, this study suggests multiple ancestral links between Far East Asian and American T. gondii strains and provides insight into the transmission history of this cosmopolitan organism
The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of
the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of
scientists from Japan, Taiwan and Princeton University is using HSC to carry
out a 300-night multi-band imaging survey of the high-latitude sky. The survey
includes three layers: the Wide layer will cover 1400 deg in five broad
bands (), with a point-source depth of . The
Deep layer covers a total of 26~deg in four fields, going roughly a
magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter
still in two pointings of HSC (a total of 3.5 deg). Here we describe the
instrument, the science goals of the survey, and the survey strategy and data
processing. This paper serves as an introduction to a special issue of the
Publications of the Astronomical Society of Japan, which includes a large
number of technical and scientific papers describing results from the early
phases of this survey.Comment: 14 pages, 7 figures, 5 tables. Corrected for a typo in the
coordinates of HSC-Wide spring equatorial field in Table
Growth of quantum three-dimensional structure of InGaAs emitting at ~1 µm applicable for a broadband near-infrared light source
We obtained a high-intensity and broadband emission centered at ~1 µm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduced misfit dislocations. However, under certain growth conditions for the In concentration and growth temperature, the growth mode of the InGaAs layer can be transformed from two-dimensional to 3D growth. We found the optimal conditions to obtain a broadband emission from 3D structures with a high intensity and controlled center wavelength at ~1 µm. This method offers an alternative approach for fabricating a broadband near-infrared light source for telecommunication and medical imaging systems such as for optical coherence tomography
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