東京大学 · 物理学・天文学
Umeda教授の研究室は、宇宙初期期の再電離時代における中性水素の状態や銀河の形成メカニズムを、ジェームズ・ウェッブ宇宙望遠鏡（JWST）の高精度分光観測データを基に解明することを主眼としています。特に、Lyαのダムピングウェイブ吸収を用いた中性水素率やイオン化バブルの測定を通じて、再電離の進行状況を定量的に評価しています。また、極もくもくな金属貧乏銀河における高イオン化線の起源や、初期宇宙に存在する赤みがかった活発銀河核（LRDs）の物理的メカニズムについても、非熱的放射体やガス包囲モデルを用いて解明を進めています。
Figures are computed from collected data and may differ slightly.
Abstract We present volume-averaged neutral hydrogen fractions x H I and ionized bubble radii R b measured with Ly α damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by the CEERS, GO-1433, DDT-2750, and JADES programs and obtain a sample containing 27 bright UV-continuum ( M UV < −18.5 mag) galaxies at 7 < z < 12. We construct four composite spectra binned by redshift and find the clear evolution of the softening break toward high r
Abstract Strong high-ionization lines such as He ii of young galaxies are puzzling at high and low redshift. Although recent studies suggest the existence of nonthermal sources, whether their ionizing spectra can consistently explain multiple major emission lines remains a question. Here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (EMPGs) that show strong He ii λ 4686. We parameterize the ionizing spectra composed of a blackbody and power-la
We present volume-averaged neutral hydrogen fractions $x_{\rm \HI}$ and ionized bubble radii $R_{\rm b}$ measured with Ly$α$ damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by CEERS, GO-1433, DDT-2750, and JADES programs, and obtain a sample containing 27 bright UV-continuum ($M_{\rm UV}<-18.5~{\rm mag}$) galaxies at $7
Abstract We present luminosity functions (LFs) and angular correlation functions (ACFs) derived from 18,960 Ly α emitters (LAEs) at z = 2.2−7.3 over a wide survey area of ≲24 deg 2 that are identified in the narrowband data of the HSC-SSP and CHORUS surveys. Confirming the large sample with 241 spectroscopically identified LAEs, we determine Ly α LFs and ACFs in the brighter luminosity range down to 0.5 L ⋆ , and confirm that our measurements are consistent with previous studies but offer signif
Abstract Little Red Dots (LRDs) newly discovered with JWST are active galactic nuclei (AGNs) that may represent black hole (BH) growth at the earliest cosmic epochs. These sources show puzzling features unlike typical AGNs, including red optical continua, weak hot-dust emission, and a lack of detectable X-rays. Previously, LRDs have often been interpreted as dust-reddened AGNs, leading to severe inconsistencies with the luminosity and BH mass densities inferred for previously known AGNs over 0 &
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