1999/08/07 by Tetsu Kitayama, Satoru Ikeuchi · 76 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Active galactic nucleus #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Chemistry #Cosmic ray #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Intergalactic medium #Ion #Ionization #Lyman limit #Optics #Photoionization #Photon #Physics #Quasar #Radiative transfer #Redshift #Reionization #Star formation #astro-ph
paper · pdf · doi:10.1086/308296
published in The Astrophysical Journal 529(2), 615-634 (IOP Publishing) · 38 pages, 16 figures, accepted for publication in ApJ
arxiv created 1999/08/07 · openalex publication_date 2000/02/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The effects of the ultraviolet (UV) background radiation on the formation of subgalactic clouds are studied by means of one-dimensional hydrodynamical simulations. The radiative transfer of the ionizing photons caused by the absorption by H I, He I, and He II, neglecting the emission, is explicitly taken into account. We find that the complete suppression of collapse occurs for the clouds with circular velocities typically in the range V c ~ 15-40 km s -1 and the 50% reduction in the cooled gas mass with V c ~ 20-55 km s -1 . These values depend most sensitively on the collapse epoch of the cloud, the shape of the UV spectrum, and the evolution of the UV intensity. Compared with the optically thin case, previously investigated by Thoul & Weinberg in 1996, the absorption of the external UV photons by the intervening medium systematically lowers the above threshold values by Δ V c ~ 5 km s -1 . Whether the gas can contract or keeps expanding is roughly determined by the balance between the gravitational force and the thermal pressure gradient when it is maximally exposed to the external UV flux. Based on our simulation results, we discuss a number of implications on galaxy formation, cosmic star formation history, and the observations of quasar absorption lines. In the Appendix, we derive analytical formulae for the photoionization coefficients and heating rates, which incorporate the frequency/direction-dependent transfer of external photons.