ORCID Profile
0000-0003-4985-0201
Current Organisation
University of Tsukuba
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Astronomical Society
Date: 04-2022
Abstract: We present two bright galaxy candidates at z ∼ 12–13 identified in our H -dropout Lyman break selection with 2.3 deg 2 near-infrared deep imaging data. These galaxy candidates, selected after careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 μ m, a flat continuum at 2–5 μ m, and nondetections at .2 μ m in the available photometric data sets, all of which are consistent with a z 12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4 σ [O iii ] 88 μ m line at z = 13.27, in agreement with its photometric redshift estimate. The number density of the z ∼ 12–13 candidates is comparable to that of bright z ∼ 10 galaxies and is consistent with a recently proposed double-power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z ∼ 4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z ∼ 10–13. Combined with recent studies reporting similarly bright galaxies at z ∼ 9–11 and mature stellar populations at z ∼ 6–9, our results indicate the existence of a number of star-forming galaxies at z 10, which will be detected with upcoming space missions such as the James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88 z 3.52 by using the spatial distribution of more than a million Ly α -emitting galaxies over a total target area of 540 deg 2 . The catalog comes from contiguous fiber spectra coverage of 25 deg 2 of sky from 2017 January through 2020 June, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Ly α -emitting galaxy (LAE) identifications and 123,891 [O ii ]-emitting galaxies at z 0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift ( z 0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, [O ii ] and Ly α line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within Δ z 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE s le has an r -band continuum counterpart down to a limiting magnitude of r ∼ 26.2 mag (AB) indicating that an LAE search of similar sensitivity to HETDEX with photometric preselection would miss nearly half of the HETDEX LAE catalog s le. Data access and details about the catalog can be found online at hetdex.org/ . A copy of the catalogs presented in this work (Version 3.2) is available to download at Zenodo doi: 10.5281/zenodo.7448504 .
Publisher: American Astronomical Society
Date: 12-2022
Abstract: The primordial He abundance Y P is a powerful probe of cosmology. Currently, Y P is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ( .1 Z ⊙ ) galaxies (EMPGs) having reliable He/H measurements with He i λ 10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor (0.1–0.4 Z ⊙ ) galaxies with reliable He/H estimates, we obtain Y P = 0.2370 − 0.0034 + 0.0033 by linear regression in the (He/H) − (O/H) plane, where we increase the number of EMPGs from three to eight anchoring He/H of the most metal-poor gas in galaxies. Although our Y P measurement and previous measurements are consistent, our result is slightly (∼1 σ ) smaller due to our EMPGs. Including the existing primordial deuterium D P measurement, we constrain the effective number of neutrino species N eff and the baryon-to-photon ratio η showing ≳1–2 σ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of the electron neutrino ξ e , as well as N eff and η , to vary. We obtain ξ e = 0.05 − 0.02 + 0.03 , N eff = 3.11 − 0.31 + 0.34 , and η × 10 10 = 6.08 − 0.06 + 0.06 from the Y P and D P measurements with a prior of η taken from Planck Collaboration et al. Our constraints suggest a lepton asymmetry and allow for a high value of N eff within the 1 σ level, which could mitigate the Hubble tension.
Publisher: American Astronomical Society
Date: 07-2023
Abstract: We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098 Z ⊙ ) and low stellar masses (10 4.7 –10 7.6 M ⊙ ). Taking deep medium/high-resolution ( R ∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H α emission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed H α flux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities ( v rot ) of 5–23 km s −1 smaller than the velocity dispersions ( σ 0 ) of 17–31 km s −1 , indicating dispersion-dominated ( v rot / σ 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 gas ≃ 0.9–1.0. Comparing our results with other H α kinematics studies, we find that v rot / σ 0 decreases and f gas increases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high- z ( z ∼ 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 observations at z ∼ 7.
Publisher: American Astronomical Society
Date: 12-2021
Abstract: We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Ly α emitting galaxies between 1.88 z 3.52, in a 540 deg 2 area encompassing a comoving volume of 10.9 Gpc 3 . No preselection of targets is involved instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.
Location: Japan
No related grants have been discovered for Ken Mawatari.