Stellar mass dependence of the 21-cm signal around the first star and its impact on the global signal

Toshiyuki Tanaka, Kenji Hasegawa, Hidenobu Yajima, Masato I.N. Kobayashi, Naoshi Sugiyama

Research output: Contribution to journalArticle

Abstract

The 21-cm signal in the vicinity of the first stars is expected to reflect properties of the first stars. In this study, we pay special attention to tracing the time evolution of the ionizing photons' escape fraction, which affects the distribution of neutral hydrogen, by performing radiation hydrodynamics (RHD) simulations resolving dense gas in a halo. We find that the radial profile of 21-cm differential brightness temperature is quite sensitive to the stellar and halo masses, which reflects the time evolution of the escape fraction. In the case of a less massive star, ionizing photons hardly escape from its host halo due to the absorption by dense halo gas, thus a deep 21-cm absorption feature at just outside the halo lasts a long time. Whereas, in the case of a massive star, escaped photons heat up the ambient intergalactic medium, resulting in a spatially extended 21-cm emission signature. Although individual signals are found to be undetectable with the Square Kilometre Array, our analysis using the results from the RHD simulations indicates that the properties of the first stars are imprinted on the 21-cm global signal: its amplitude depends not only on the cosmic star formation rate density, but also on the typical mass of the first stars due to the stellar-mass-dependent heating rate. Thus, we suggest that the initial mass function of the first stars is an essential factor in understanding the global signal.

Original languageEnglish
Pages (from-to)1925-1937
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume480
Issue number2
DOIs
Publication statusPublished - 2018 Oct

Keywords

  • Dark ages
  • First stars
  • Hydrodynamics
  • Intergalactic medium -H II regions
  • Radiative transfer
  • Radio lines: general
  • Reionization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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