Journal Article

The 21-cm signature of early relic H <span class="smallCaps">ii</span> regions

Midori Tokutani, Naoki Yoshida, S. Peng Oh and Naoshi Sugiyama

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 2, pages 777-780
Published in print May 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI:
The 21-cm signature of early relic H ii regions

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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.

Keywords: intergalactic medium; cosmology: theory; early Universe

Journal Article.  3262 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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