STARBENCH: the D-type expansion of an H II region

T.~G. Bisbas, T.~J. Haworth, R.~J.~R. Williams, J. Mackey, P. Tremblin, A.~C. Raga, S.~J. Arthur, C. Baczynski, T. Frostholm, S. Geen, T. Haugbølle, D. Hubber, I.~T. Iliev, R. Kuiper, J. Rosdahl, D. Sullivan, S. Walch, R. Wünsch, James Dale

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STARBENCH is a project focused on benchmarking and validating different star formation and stellar feedback codes. In this first STARBENCH paper we perform a comparison study of the D-type expansion of an H II region. The aim of this work is to understand the differences observed between the 12 participating numerical codes against the various analytical expressions examining the D-type phase of H II region expansion. To do this, we propose two well-defined tests which are tackled by 1D and 3D grid- and smoothed particle hydrodynamics-based codes. The first test examines the ‘early phase’ D-type scenario during which the mechanical pressure driving the expansion is significantly larger than the thermal pressure of the neutral medium. The second test examines the ‘late phase’ D-type scenario during which the system relaxes to pressure equilibrium with the external medium. Although they are mutually in excellent agreement, all 12 participating codes follow a modified expansion law that deviates significantly from the classical Spitzer solution in both scenarios. We present a semi-empirical formula combining the two different solutions appropriate to both early and late phases that agrees with high-resolution simulations to ≲ 2 per cent. This formula provides a much better benchmark solution for code validation than the Spitzer solution. The present comparison has validated the participating codes and through this project we provide a data set for calibrating the treatment of ionizing radiation hydrodynamics codes.
Original languageEnglish
Pages (from-to)1324-1343
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date25 Aug 2015
Publication statusPublished - 21 Oct 2015


  • hydrodynamics, methods: numerical, ISM: bubbles, H II regions, ISM: kinematics and dynamics, galaxies: ISM


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