Observed variations in the H II region luminosity function (H II LF) seen in spiral arm versus interarm regions, and different galactic Hubble type, can be explained simply by evolutionary effects and maximum number of ionizing stars per cluster. We present Monte Carlo simulations of the H II LF, drawing the number of ionizing stars (N*) from a power-law distribution of constant slope, and the stellar masses from a Salpeter initial mass function with an upper mass limit of 100 M⊙. We investigate the evolution of the H II LF, as determined by stellar main-sequence lifetimes and ionizing luminosities, for a single-burst case and continuous creation of the nebular population. Shallower H II LF slopes measured for the arms of spiral galaxies can be explained as a composite slope, expected for a zero-age burst population, whereas the interarm regions tend to be dominated by evolved rich clusters described by a single, steeper slope. Steeper slopes in earlier-type galaxies can be explained simply by a lower maximum N* cutoff found for the parent OB associations. The form of the H II LF can reveal features of the most recent (10 Myr) star formation history in nearby galaxies.
展开▼
机译：在旋臂对臂间区域观察到的H II区域光度函数（H II LF）的变化，以及不同的星系哈勃类型，可以通过进化效应和每个星团的最大电离星数简单地解释。我们提出了H II LF的蒙特卡罗模拟，从恒定斜率的幂律分布中得出电离星的数量（N *），从质量上限为100M⊙的Salpeter初始质量函数中提取恒星质量。我们调查了H II LF的演变，这由恒星主序列寿命和电离发光度确定，适用于单爆发情况和连续创建的星云种群。可以为旋涡星系的臂测得的较浅的H II LF斜率可以解释为零年龄猝发人口所期望的复合斜率，而臂间区域则倾向于由单个较陡的斜率描述的演化的富集团占主导地位。早期类型星系中的更陡的坡度可以通过为母体OB关联找到的较低的最大N *截止值简单解释。 H II LF的形式可以揭示附近星系中最新（10 Myr）恒星形成历史的特征。
展开▼
