2009/02/06 by Midori Tokutani, Naoki Yoshida, S. Peng Oh +1 · 6 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Brightness #Brightness temperature #Cosmic microwave background #Galaxies: Formation, Evolution, Phenomena #H II region #Ion #Ionization #Mean kinetic temperature #Physics #Radiative transfer #Radio Astronomy Observations and Technology #Radio telescope #Star formation #Stars #astro-ph.CO
paper · pdf · doi:10.1111/j.1365-2966.2009.14604.x
published in Monthly Notices of the Royal Astronomical Society 395(2), 777-780 (Oxford University Press) · 5 pages, 3 figures, accepted by MNRAS
arxiv created 2009/02/06 · openalex publication_date 2009/04/09 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We calculate the spin temperature and 21-cm brightness of early H ii regions around the first stars. We use outputs from cosmological radiation-hydrodynamics simulations of the formation and evolution of early H ii regions. In the pre-re-ionization era, H ii regions around massive primordial stars have diameters of a few kpc. The gas within the H ii regions is almost fully ionized, but begins recombining after the central stars die off. The relic H ii regions are then seen as bright emission sources in hydrogen 21 cm. We make brightness temperature maps of the H ii regions, accounting for radiative coupling with Lyman α photons in a simplified manner. The spin temperature in the relic H ii region is close to the gas kinetic temperature, generally several hundred to several thousand degrees. We show that the relic H ii region can be as bright as δTb∼ 100 mK in differential temperature against the cosmic microwave background for an angular resolution of subarcseconds. While individual early H ii patches will not be identified by currently planned radio telescopes, the collective fluctuations from early H ii regions might imprint signatures in the 21-cm background.