Astronomy and Astrophysics Evolution of Photoionization and Star Formation in Starbursts and H Ii Galaxies
Astronomy and Astrophysics Evolution of Photoionization and Star Formation in Starbursts and H Ii Galaxies
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星暴和 H Ii 星系中光电离和恒星形成的天文学和天体物理学演化
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发表时间：
2001
期刊：
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通讯作者：
M. Fioc
中科院分区：
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作者：
E. Moy;B. Rocca;M. Fioc
我们使用我们的演化合成模型P‘EGASE(Fioc&Rocca-Volmerange 1997,2000)与光电离程序Cloudy(Ferland 1996)相结合，相干地分析了恒星爆发和H II星系的恒星和星云能量分布。这项研究的创新之处在于将恒星爆发的演化和金属性与宿主星系过去的恒星形成历史联系起来。消光和几何效应对发射线和连续体的计算与金属丰度是一致的。我们将我们的模型预测与≈750H II区和恒星爆发的观测样本进行了比较。当拟合[O III]λ4363/[O III]λ5007，[O I]λ6300/Hα，[S II]λλ6716,6731/Hα，[N II]λ6584/Hα和[O III]λ5007/Hβ时，最显著的特征是U中的发散随金属丰度Z的增加而减小。不需要额外的电离光子源--冲击或隐藏的活动星系核。在贫金属的H II星系中观察到的高水平激发需要非常年轻的群体(≤3 Myr)，而恒星爆发核星系(SBNG)与更大的年龄范围(≤5 Myr)是一致的。颜色(B−V、V−R)和等效宽度与发射线比率一致。即使对于小口径观测，也需要一个潜在的总体。这种演化的布居不仅使连续谱变红，稀释了发射线的等效宽度，而且还参与了电离过程。它对线路比的主要影响是在猝发停止时保持高水平的激励。模型结合了哈勃序列星系典型的底层群体和年龄在0到8 Myr之间的瞬时恒星爆发，与所有数据都令人满意地吻合。
We analyze coherently the stellar and nebular energy distributions of starbursts and H ii galaxies, using our evolutionary synthesis model, P ´ EGASE (Fioc & Rocca-Volmerange 1997, 2000), coupled to the photoion-ization code CLOUDY (Ferland 1996). The originality of this study is to relate the evolution and the metallicity of the starburst to the past star formation history of the host galaxy. Extinction and geometrical effects on emission lines and continua are computed in coherency with metallicity. We compare our model predictions to an observed sample of ≈ 750 H ii regions and starbursts. When fitting [O iii] λ4363 /[O iii] λ5007 , [O i] λ6300 /Hα, [S ii] λλ6716,6731 /Hα, [N ii] λ6584 /Hα and [O iii] λ5007 /Hβ, the most striking feature is the decreasing spread in U with increasing metallicity Z. High-U objects systematically have a low metallicity while low levels of excita-tion happen at any Z. The best fits of emission line ratios are obtained with a combination of a high-and a low-ionization components. No additional source of ionizing photons – shocks or hidden AGN – is needed. The high level of excitation observed in metal-poor H ii galaxies requires a very young population (≤ 3 Myr), while starburst nuclear galaxies (SBNGs) are consistent with a wider range of age (≤ 5 Myr). Colors (B − V , V − R) and equivalent widths are fitted in coherency with emission line ratios. An underlying population is needed, even for small-aperture observations. This evolved population not only reddens the continuum and dilutes the equivalent width of the emission lines, but also participates in the ionization process. Its main effect on line ratios is to maintain a high level of excitation when the burst stops. Models combining underlying populations typical of Hubble sequence galaxies and instantaneous starbursts with ages between 0 and 8 Myr agree satisfactorily with all the data.