Detecting early galaxies through their 21-cm signature

Smadar Naoz*, Rennan Barkana

*Corresponding author for this work

Research output: Contribution to journalLetterpeer-review


New observations over the next few years of the emission of distant objects will help unfold the chapter in cosmic history around the era of the first galaxies. These observations will use the neutral hydrogen emission or absorption at a wavelength of 21 cm as a detector of the hydrogen abundance. We predict the signature on the 21-cm signal of the early generations of galaxies. We calculate the 21-cm power spectrum including two physical effects that were neglected in previous calculations. The first is the redistribution of the ultraviolet photons from the first galaxies due to their scattering off of the neutral hydrogen, which results in an enhancement of the 21-cm signal. The second is the presence of an ionized hydrogen bubble near each source, which produces a cut-off at observable scales. We show that the resulting clear signature in the 21-cm power spectrum can be used to detect and study the population of galaxies that formed just 200 Myr after the big bang.

Original languageEnglish
Pages (from-to)L63-L67
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - Mar 2008


  • Cosmology: theory
  • Galaxies: formation
  • Galaxies: high-redshift
  • Intergalactic medium
  • Radiative transfer


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