Hydrodynamic Simulations of Galaxy Formation. II. Photoionization and the Formation of Low-Mass Galaxies

1995/10/31 by Anne A. Thoul, David H. Weinberg · 21 citations
Engineering · Physics and Astronomy · #Astronomy and Astrophysical Research #Baryon #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Helium #Ionization #Photoionization #Photoionization mode #Space Technology and Applications #Ultraviolet #astro-ph

paper · pdf · doi:10.1086/177446

published as Astrophys.J.465:608,1996 · 22 pages, uuencoded compressed postscript with figures. Submitted to ApJ. Latest version also available at http://cfata2.harvard.edu/thoul/papers.html

arxiv created 1995/10/31 · openalex publication_date 1996/07/01 · arxiv updated 2011/08/17 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

Photoionization by the high-redshift ultraviolet radiation background heats low- density gas before it falls into dark matter potential wells, and it eliminates the neutral hydrogen and singly ionized helium that dominate cooling of primordial gas at temperatures of 10^4-10⁵^ K. We investigate the influence of photoionization on galaxy formation using high-resolution simulations with a one-dimensional, spherically symmetric, Lagrangian hydrodynamics/gravity code. We find that the presence of a photoionizing background suppresses the formation of galaxies with circular velocities v_circ_ <~ 30 km s^-1^ and substantially reduces the mass of cooled baryons in systems with circular velocities up to v_circ_ ~ 50 km s^-1^. Above v_circ_ ~ 75 km s^-1^, photoionization has no significant effect. Photoionization exerts its influence primarily by heating gas before collapse; the elimination of line cooling processes is less important. We discuss the implications of these results for hierarchical theories of galaxy formation.

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