Trends and characteristics of severe road traffic injuries in children: a nationwide cohort study in Japan

Purpose: The purpose of this study was to evaluate temporal trends of characteristics of severe road traffic injuries in children and identify factors associated with mortality using a nationwide database in Japan. Methods: We performed a retrospective analysis of Japan Trauma Data Bank (JTDB) from 2004 to 2018. We included patients with traffic injuries under the age of 18 who were hospitalized. The primary outcome was in-hospital mortality. We evaluated trends in characteristics and assessed factors associated with in-hospital mortality using a logistic regression analysis. Results: A total of 4706 patients were analyzed. The most common mechanism of injury was bicycle crash (34.4%), followed by pedestrian (28.3%), and motorcycle crash (21.3%). The overall in-hospital mortality was 11.2%. We found decreasing trends in motorcycle crash and in-hospital mortality and increasing trends in rear passenger seats in cars over the 15-year period. The following factors were associated with in-hospital mortality: car crash (aOR 1.69, 95%CI 1.18–2.40), pedestrian (aOR 1.50, 95%CI 1.13–1.99), motorcycle crash (aOR 1.42, 95%CI 1.03–1.95) [bicycle crash as a reference]; concomitant injuries to head/neck (aOR 5.06, 95%CI 3.81–6.79), thorax (aOR 2.34, 95%CI 1.92–2.87), abdomen (aOR 1.74, 95%CI 1.29–2.33), pelvis/lower-extremity (aOR 1.57, 95%CI 1.23–2.00), spine (aOR 3.01, 95%CI 2.02–4.43); and 5-year increase in time period (aOR 0.80, 95%CI 0.70–0.91). Conclusions: We found decreasing trends in motorcycle crash and in-hospital mortality, increasing trends in rear passenger seats in cars over the 15-year period, and factors associated with in-hospital mortality such as type of mechanisms and concomitant injuries. Strengthening child road safety measures, particularly for rear passenger seats in vehicles, is imperative to enhance our dedication to injury prevention.The version of record of this article, first published in European Journal of Trauma and Emergency Surgery, is available online at Publisher’s website: https://doi.org/10.1007/s00068-023-02372-

Displacement-noise-free interferometeric gravitational-wave detector using unidirectional neutrons with four speeds

For further gravitational wave (GW) detections, it is significant to invent a technique to reduce all kinds of mirror displacement noise dominant at low frequencies for ground-based detectors. The neutron displacement-noise-free interferometer (DFI) is one of the tools to reduce all the mirror displacement noise at lower frequencies. In this paper, we describe a further simplified configuration of a neutron DFI in terms of neutron incidence direction. In the new configuration, neutrons enter the interferometer with unidirectional incidence at four speeds as opposed to two bidirectional incidences of opposite directions at two speeds as reported previously. This simplification of the neutron DFI is significant for proof-of-principle experiments

EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with ∼1.0\sim 1.0 (Fe/O)⊙_\odot and 0.020.02 (O/H)⊙_\odot : Possible Traces of Super Massive (>300M⊙>300 M_{\odot}) Stars in Early Galaxies

We present element abundance ratios and ionizing radiation of local young low-mass (~$10^{6}$ 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$^{-1}$), 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$\beta$ 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$\beta$ ratios are explained by the past existence of super massive ($>$300 M_sun) stars, which may evolve into intermediate-mass black holes ($\gtrsim$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.

A Search for Lyman alpha Emitters at Redshift 3.7

We present the results of a survey for emission-line objects based on optical intermediate-band ($\lambda_{\rm c}$ = 5736 \AA ~ and $\Delta\lambda$ = 280 \AA) and broad-band ($B$, $V$, $R$, and $i^\prime$) observations of the Subaru/XMM-Newton Deep Field on the 8.2 m Subaru telescope with the Subaru Prime Focus Camera, Suprime-Cam. All the data were obtained during the guaranteed time observations of the Suprime-Cam instrument. The intermediate-band image covered a sky area with 10\minpoint62 \times 12\minpoint40 \approx 132 arcmin$^2$ in the Subaru/XMM-Newton Deep Field (Ouchi et al.). Using this image, we have found 23 emission-line sources whose observed emission-line equivalent widths are greater than 250 \AA. Their optical multicolor properties indicate that six emission-line sources are Ly$\alpha$ emitters at $z \approx$ 3.7 ($\Delta z \approx 0.22$). They are either intense starburst galaxies or active galactic nuclei like quasars at $z \approx$ 3.7. Two more emission-line sources may also be Ly$\alpha$ emitters at $z \approx$ 3.7 although their multicolor properties are marginal. Among the remaining 15 emission-line objects, eight objects appear strong emission-line galaxies at lower redshift; e.g., [O {\sc ii}] $\lambda$3727 emitters at $z \approx 0.54$, H$\beta$ at $z \approx 0.18$, or [O {\sc iii}]$\lambda$5007 emitters at $z \approx 0.15$. The remaining seven objects are unclassified because they are too faint to be detected in broad-band images. We discuss observational properties of these strong emission-line sources. In particular, our data allow us to estimate the star formation density at $z \approx 3.7$ for the first time.Comment: Accepted for publication in AJ;14 pages, 26 figures (all figures are JPEG file

EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?

We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$\alpha$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed H$\alpha$ flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{\rm rot}$) of 5--23 km s$^{-1}$ smaller than the velocity dispersions ($\sigma_{0}$) of 17--31 km s$^{-1}$, indicating dispersion-dominated ($v_{\rm rot}/\sigma_{0}=0.29-0.80<1$) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of $f_{\rm gas}\simeq 0.9-1.0$. Comparing our results with other H$\alpha$ kinematics studies, we find that $v_{\rm rot}/\sigma_{0}$ decreases and $f_{\rm gas}$ increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-$z$ ($z\sim 7$) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at $z\sim 7$.Comment: Submitted to ApJ; After revisio

Clustering of Lyman Break Galaxies at z=4 and 5 in The Subaru Deep Field: Luminosity Dependence of The Correlation Function Slope

We explored the clustering properties of Lyman Break Galaxies (LBGs) at z=4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z=4 and 5. More luminous LBGs have a steeper correlation function. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions for LBGs predicted by this mock catalog were found to be almost consistent with the observation. Moreover, the overall correlation functions of LBGs were reproduced reasonably well. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark haloes had steeper and larger-amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the slope of the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity-dependence of the angular correlation function, if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs (abridged).Comment: 16 pages, 17 figures, Accepted for publication in ApJ, Full resolution version is available at http://zone.mtk.nao.ac.jp/~kashik/sdf/acf/sdf_lbgacf.pd