Emission lines in early-type galaxies: active nuclei or stars?
Emission lines in early-type galaxies: active nuclei or stars?
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早期型星系中的发射线：活动核还是恒星？
DOI：
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发表时间：
2011
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通讯作者：
U.S.A.
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作者：
A. C. U. D. Torino;Italy Space Telescope Science Institute;Baltimore.;U.S.A.
我们从斯隆数字巡天（SDSS）中选择了27244个附近的红色巨型早期星系（RGE）。在其光谱的大部分（53%）中，检测到[O III]λ5007发射线，其等效宽度（EW）分布强烈聚集在~0.75 A附近。绝大多数的这些RGE，它是可能的，以获得发射线比（约占一半的样品）显示的值的LINER的特性。发射线和恒星连续体之间的密切联系表明，恒星过程是RGE中大部分电离光子的最可能来源，而不是活动核。特别是，所观察到的EW和光学线的比例是一致的模型，其中的光电离来自热演化的恒星的预测。由超新星或恒星喷出物驱动的冲击也可能有助于电离预算。少数，约4%的星系显示出的发射线的等效宽度是样本中值的1.22倍。仅在其中发现了类似塞弗特的光谱。此外，该亚组中有40%具有射电对应物，而其余样本中这一比例仅为6%。这些特征表明它们的发射线可能起源于活动星系核。发射谱线诊断图没有显示活动星系核子集和样品其他成员之间的区别，因此它们不是建立电离光子的主要来源的有用工具，这是更好地预测发射谱线的EW。
We selected 27 244 nearby, red, giant early-type galaxies (RGEs) from the Sloan Digital Sky Survey (SDSS). In a large fraction (53%) of their spectra the [O III]λ5007 emission line is detected, with an equivalent width (EW) distribution strongly clustered around ~0.75 A. The vast majority of those RGEs for which it is possible to derive emission line ratios (amounting to about half of the sample) show values characteristic of LINERs. The close connection between emission lines and stellar continuum points to stellar processes as the most likely source of the bulk of the ionizing photons in RGEs, rather than active nuclei. In particular, the observed EW and optical line ratios are consistent with the predictions of models in which the photoionization comes from hot evolved stars. Shocks driven by supernovae or stellar ejecta might also contribute to the ionization budget. A minority, ~4%, of the galaxies show emission lines with an equivalent width that is a factor of ≳2 greater than the sample median. Only among them are Seyfert-like spectra found. Furthermore, 40% of this subgroup have a radio counterpart, compared to ~6% of the rest of the sample. These characteristics argue in favor of an AGN origin for their emission lines. Emission lines diagnostic diagrams do not reveal a distinction between the AGN subset and the other members of the sample, and consequently they are not a useful tool for establishing the dominant source of the ionizing photons, which is better predicted by the EW of the emission lines.