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arXiv 2109.02684astro-ph.GA
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恒星形成星系中弥漫电离气体(DIG):孔径效应对局部HII区的影响

The diffuse ionized gas (DIG) in star-forming galaxies: the influence of aperture effects on local HII regions

F. Mannucci, F. Belfiore, M. Curti, G. Cresci, R. Maiolino, A. Marasco, A. Marconi, M. Mingozzi, G. Tozzi, A. Amiri

摘要:

弥散电离气体(DIG)对星系的星云发射有贡献,导致发射线通量比与HII区域产生的通量比有很大不同。通过比较[SII] 6717,31在附近星系HII区的定点观测和更遥远星系的积分光谱,最近有人声称DIG也可以深刻影响明亮的恒星形成星系的发射,并且必须对观测到的线比进行大的校正,以恢复HII区的真正贡献。在这里,我们表明,而不是DIG对恒星形成星系的综合光谱的影响是低于在以前的工作中假设的。事实上,孔径效应对附近HII区域光谱的影响在很大程度上是观测到的差异的原因:当使用足够大的孔径提取局部HII区域的光谱时,同时仍然避免DIG,观测到的线比与更遥远的星系相同。这一结果与使用强线方法测量金属丰度高度相关。

英文摘要:

The Diffuse Ionized Gas (DIG) contributes to the nebular emission of galaxies, resulting in emission line flux ratios that can be significantly different from those produced by HII regions. Comparing the emission of [SII]6717,31 between pointed observations of HII regions in nearby galaxies and integrated spectra of more distant galaxies, it has been recently claimed that the DIG can also deeply affect the emission of bright, star-forming galaxies, and that a large correction must be applied to observed line ratios to recover the genuine contribution from HII regions. Here we show instead that the effect of DIG on the integrated spectra of star-forming galaxies is lower than assumed in previous work. Indeed, aperture effects on the spectroscopy of nearby HII regions are largely responsible for the observed difference: when spectra of local HII regions are extracted using large enough apertures while still avoiding the DIG, the observed line ratios are the same as in more distant galaxies. This result is highly relevant for the use of strong-line methods to measure metallicity.

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