About Me
Nice to meet you. 初めまして。I'm Hiroya Umeda. 梅田滉也です。
Astronomer & Ph.D. Candidate
I'm in currently a Ph.D. candidate in the University of Tokyo, Department of Physics. My main research interests are cosmic reionization and galaxy evolution. I work in the observational cosmology group in ICRR. My advisor is Prof. M. Ouchi.
- NASA/ADS: author:"Umeda, Hiroya"
- Group Website: ICRR/ObsCos Group
- Position: 2nd year Ph.D. candidate
I'm enjoying my life right now. How about you?
Research
I mainly work on cosmic reionization and galaxy formation. I work with optical/near-infrared data obtained with Subaru, JWST, etc...
Cosmic Reionization and Galaxy Formation
Cosmic reionization is the last phase change of our universe that ended around redshit 5. With the onset of the first light (i.e., stars, galaxies), ionizing photons produced by baryonic structures ionize the intergalactic neutral hydrogen gas. This cosmic scale astrophysical phenomenon thus imprints the formation of the first stars as well as the evolution of cosmic structures. My goal is to fully capture this cosmological event in the context of structure formation via observations.
Galaxy Continuum Damping Wing Analysis with JWST
Using James Webb Space Telecope, we detect redshift evolution of galaxy spectrum shape around Lyman break. The softening of the break feature at the higher redshift suggest the increasing Lyα optical depth due to the cosmic reionization.
CV
Education
Ph.D. Course
2023 -
the University of Tokyo, Tokyo, Japan
Advisor: Prof. M. Ouchi
Major: Physics
Master of Science
2021 - 2023
the University of Tokyo, Tokyo, Japan
Advisor: Prof. M. Ouchi
Thesis: "Cosmic Reionization History and Sources Probed by Optical Imaging and Spectroscopy with the Subaru Telescope"
Bachelor of Science
2017 - 2021
the University of Tokyo, Tokyo, Japan
Major: Physics
Paper
First Author
- Umeda et al., Probing the Cosmic Reionization History with JWST: Gunn-Peterson and Lya Damping Wing Absorption at 4.5< z < 13, submitted to ApJ, 2025.
- Umeda et al., SILVERRUSH. XIV. Lya Luminosity Functions and Angular Correlation Functions from ~20,000 Lya Emitters at z~2.2-7.3 from upto 24 deg2 HSC-SSP and CHORUS Surveys: Linking the Postreionization Epoch to the Heart of Reionization, ApJS, 277, 37, 24, 2025.
- Umeda et al., JWST Measurements of Neutral Hydrogen Fractions and Ionized Bubble Sizes at z = 7 − 12 Obtained with Lyα Damping Wing Absorptions in 27 Bright Continuum Galaxies, ApJ, 971, 124, 16, 2024.
- Umeda et al., EMPRESS. VII. Ionizing Spectrum Shapes of Extremely Metal-Poor Galaxies: Uncovering the Origins of Strong HeII and the Impact on Cosmic Reionization, ApJ, 930, 37, 14, 2022.
Co-Authored
- Hatano, Ouchi, Umeda et al., EMPRESS. XIV. Strong High Ionization Lines of Young Galaxies at z = 0 - 8; Ionizing Spectra Consistent with the Intermediate Mass Black Holes with M_BH~10^3-10^6 M_sun, 2023arXiv230502189H, ApJ, 966, 170, 14, 2024.
- Harikane, Nakajima, Ouchi, Umeda et al., Pure Spectroscopic Constraints on UV Luminosity Functions and Cosmic Star Formation History From 25 Galaxies at z = 8.61 - 13.20 Confirmed with JWST/NIRSpec, 2023arXiv230406658H
- Kikuta, Ouchi, Shibuya, Liang, Umeda et al., SILVERRUSH. XIII. A Catalog of 20,567 Lyα Emitters at z = 2 - 7 Identified in the Full-depth Data of the Subaru/HSC-SSP and CHORUS Surveys, ApJS, 268, 24, 21, 2023.
and more...
Conferences
Talks (Total 24)
- Escape of Lyman Radiation from Galactic Labyrinths, OAC, Crete, Greece, Apr, 2025
- First Galaxies: Building blocks of galaxies across, U Oxford, Oxford, U.K., Apr, 2025
- Kochel CLAW, Kochel, Germany, Sept, 2024
- First Stars VII, Flatiron Institute, New York, U.S., May, 2024
- ELT Science in Light of JWST, UCLA, Los Angeles, U.S., Dec, 2023
- Resolving the Extragalactic Universe with ALMA & JWST, U Waseda, Tokyo, Japan, Nov, 2023
- Understanding Epoch of Reionization, Sexten Center for Astrophysics, Sesto, Italy, Mar, 2023
- SAZERAC SIPS: Early Galaxy Formation Near and Far, Online, Dec, 2021
Posters (Total 2)
- FoPM Symposium, U Tokyo, Tokyo, Japan, Feb, 2023
- The 52nd Saas-Fee Advanced Course, Le Diablerets, Switzerland, Mar, 2023
Seminars (Total 10)
- Galaxies Group Discussion seminar, KICC, Cambridge, U.K., Oct, 2024
- Coffee Talk, U Edinburgh, Edinburgh, U.K., Oct, 2024
- Seminar Talk, U Heidelberg, Heidelber, Germany, Sept, 2024
- Seminar Talk, UCSC, Santa Cruz, U.S., May, 2024
Contact
Inquiries on my research are always welcome! Please let me know your name and position in the email.
Location:
Rm #511, University of Tokyo, ICRR, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-0882, Japan
Email:
ume_at_icrr.u-tokyo.ac.jp
Call:
63127 (Internal)