ON RADIATION PRESSURE IN STATIC, DUSTY H II REGIONS

被引:177
作者
Draine, B. T. [1 ]
机构
[1] Princeton Univ Observ, Princeton, NJ 08544 USA
基金
美国国家科学基金会;
关键词
dust; extinction; H II regions; infrared: ISM; ISM: bubbles; ISM: structure; radio continuum: ISM; ULTRACOMPACT HII-REGIONS; RADIO-CONTINUUM; STAR-FORMATION; MILKY-WAY; COMPACT; EXTINCTION; EVOLUTION; GALAXIES; GRAINS; VLA;
D O I
10.1088/0004-637X/732/2/100
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Radiation pressure acting on gas and dust causes H II regions to have central densities that are lower than the density near the ionized boundary. H II regions in static equilibrium comprise a family of similarity solutions with three parameters: beta, gamma, and the product Q(0)n(rms); beta characterizes the stellar spectrum, gamma characterizes the dust/gas ratio, Q(0) is the stellar ionizing output (photons/s), and n(rms) is the rms density within the ionized region. Adopting standard values for beta and gamma, varying Q(0)n(rms) generates a one-parameter family of density profiles, ranging from nearly uniform density (small Q(0)n(rms)) to shell-like (large Q(0)n(rms)). When Q(0)n(rms) greater than or similar to 10(52) cm(-3) s(-1), dusty H II regions have conspicuous central cavities, even if no stellar wind is present. For given beta, gamma, and Q(0)n(rms), a fourth quantity, which can be Q(0), determines the overall size and density of the H II region. Examples of density and emissivity profiles are given. We show how quantities of interest-such as the peak-to-central emission measure ratio, the rms-to-mean density ratio, the edge-to-rms density ratio, and the fraction of the ionizing photons absorbed by the gas-depend on beta, gamma, and Q(0)n(rms). For dusty H II regions, compression of the gas and dust into an ionized shell results in a substantial increase in the fraction of the stellar photons that actually ionize H (relative to a uniform-density H II region with the same dust/gas ratio and density n = n(rms)). We discuss the extent to which radial drift of dust grains in H II regions can alter the dust-to-gas ratio. The applicability of these solutions to real H II regions is discussed.
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页数:12
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