How does radiative feedback from an ultraviolet background impact reionization?

Emanuele Sobacchi, Andrei Mesinger

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


An ionizing ultraviolet background (UVB) inhibits gas accretion and photoevaporates gas from the shallow potential wells of small, dwarf galaxies. During cosmological reionization, this effect can result in negative feedback: suppressing star formation inside HII regions, thus impeding their continued growth. It is difficult to model this process, given the enormous range of scales involved. We tackle this problem using a tiered approach: combining parametrized results from single-halo collapse simulations with large-scale models of reionization. In the resulting reionization models, the ionizing emissivity of galaxies depends on the local values of the reionization redshift and the UVB intensity.We present a physically motivated analytic expression for the average minimummass of star-forming galaxies, M̄min, which can be readily used in modelling galaxy formation. We findthat UVB feedback: (i) delays the end stages of reionization by δz ≲ 0.5; (ii) results in a more uniform distribution of HII regions, peaked on smaller scales (with large-scaleionization power suppressed by 10s of per cent) and (iii) suppresses the global photoionization rate per baryon by a factor of ≲2 towards the end of reionization. However, the impact is modest, since the hydrodynamic response of the gas to the UVB occurs on a time-scale comparable to reionization. In particular, the popular approach of modelling UVB feedback with an instantaneous transition in Mmin, dramatically overestimates its importance.UVB feedback on galaxies does not significantly affect reionization unless: (i) molecularly cooled galaxies contribute significantly to reionization; or (ii) internal feedback processes strongly couple with UVB feedback in the early Universe. Since both are considered unlikely, we conclude that there is no significant self-regulation of reionization by UVB feedback.

Original languageEnglish
Pages (from-to)3340-3348
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - 1 Jan 2013
Externally publishedYes


  • Evolution - galaxies
  • Formation - galaxies
  • Galaxies
  • High-redshift - cosmology
  • Theory - early universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'How does radiative feedback from an ultraviolet background impact reionization?'. Together they form a unique fingerprint.

Cite this