The delayed formation of dwarf galaxies

Jeremy V. Kepner, Arif Babul, David N. Spergel

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


One of the largest uncertainties in understanding the effect of a background UV field on galaxy formation is the intensity and evolution of the radiation field with redshift. This work attempts to shed light on this issue by computing the quasi-hydrostatic equilibrium states of gas in spherically symmetric dark matter halos (roughly corresponding to dwarf galaxies) as a function of the amplitude of the background UV field. We integrate the full equations of radiative transfer, heating, cooling, and nonequilibrium chemistry for nine species: H, H+, H-, H2, H2+, He, He+, He++, and e-. As the amplitude of the UV background is decreased, the gas in the core of the dwarf goes through three stages characterized by the predominance of ionized (H+), neutral (H), and molecular (H2) hydrogen. Characterizing the gas state of a dwarf galaxy with the radiation field allows us to estimate its behavior for a variety of models of the background UV flux. Our results indicate that a typical radiation field can easily delay the collapse of gas in halos corresponding to 1 σ cold dark matter perturbations with circular velocities of less than 30 km s-1.

Original languageEnglish (US)
Pages (from-to)61-68
Number of pages8
JournalAstrophysical Journal
Issue number1 PART I
StatePublished - 1997

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Diffuse radiation
  • Galaxies: Formation
  • Galaxies: Halos
  • Radiative transfer


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