Unveiling Lyman Continuum photon escape mechanisms of local galaxies with SOFIA

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K22358
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0204:Astronomy, earth and planetary science, and related fields
• Research Institution: University of Tsukuba
• Principal Investigator: Hashimoto Takuya 筑波大学, 数理物質系, 助教 (40870887)
• Project Period (FY): 2020-09-11 – 2023-03-31
• Keywords: 赤外線天文学 / 銀河形成進化 / 近傍銀河 / 電離光子 / SOFIA

Outline of Final Research Achievements

The goal of this study was to make an observational connection between the far-infrared emission line luminosity ratio ([OIII]88μm/[CII]158μm) of galaxies and the physics of ionized photon escape. Far-infrared data of nearby galaxies were obtained by the principal investigator using the SOFIA telescope. By combining the data with archival data of nearby galaxies as well, we have identified the characteristics of objects with high [OIII]88μm/[CII]158μm. Furthermore, we succeeded in deriving an empirical law linking the luminosity ratio to the ionizing photon escape rate, and applied it to distant galaxies. We showed that distant galaxies were prone to cosmic reionization. The paper was accepted and later published (Ura & Hashimoto et al. 2023 ApJ).

Free Research Field

天文学

Academic Significance and Societal Importance of the Research Achievements

宇宙再電離現象とは、宇宙誕生後およそ2-10億年に起きた宇宙空間の最後の相転移を指す。未解明な部分が多く、現代天文学におけるフロンティアの一つである。とくに重要な課題の一つが、遠方銀河の電離光子脱出率の推定である。これは測定自体が難しいため、従来の研究では、銀河の紫外線や可視光の光学特性と電離光子脱出率を結びつける試みが主流であった。本研究では、近年のALMA望遠鏡の成果を時宜よく鑑みて、遠赤外線の特性と電離光子脱出率の関係に着目した点で学術的意義が高い。本研究の成果は、今後、ALMAやJWSTを用いた遠方銀河の研究成果を解釈する上で、土台になると期待される。