盘状星系的内环：死的还是活的
Inner rings in disc galaxies: dead or alive
摘要：
在这封信中，我将“被动”内环与那些没有当前恒星形成的内环区分开来，以区别于那些经历了最近恒星形成的“主动”内环。我建立了一个附近星系的样本，从NIRS 0 S和S4 G调查中观察到近红外和中红外的内环。我使用了319个星系的档案远紫外（FUV）和Hα成像来诊断它们的内环是被动的还是主动的。我发现被动环只存在于早期盘状星系（-3<=T<=2）中。在这一阶段范围内，根据FUV和Hα指标，分别有21+-3%和28+-5%的环是被动的。根据FUV是被动的环根据Hα总是被动的，但反过来并不总是正确的。环形透镜形成被动环的30-40%，这是在级范围-3<=T<=2中在主动环中发现的环形透镜的分数的四倍。这与环的共振和流形起源是一致的，因为这两个模型都预测纯粹的恒星环比它们的恒星形成对应物更宽。在共振环的情况下，加宽可以至少部分地归因于环的溶解。如果大多数内环都有共振起源，我估计2亿年是它们溶解时间尺度的下限。这个时间尺度在内环半径处是一个轨道周期的量级。
英文摘要：
In this Letter, I distinguish "passive" inner rings as those with no current star formation, as distinct from "active" inner rings that have undergone recent star formation. I built a sample of nearby galaxies with inner rings observed in the near- and mid-infrared from the NIRS0S and the S4G surveys. I used archival far-ultraviolet (FUV) and Hα imaging of 319 galaxies to diagnose whether their inner rings are passive or active. I found that passive rings are found only in early-type disc galaxies (-3<=T<=2). In this range of stages, 21+-3% and 28+-5% of the rings are passive according to the FUV and Hα indicators, respectively. A ring that is passive according to the FUV is always passive according to Hα, but the reverse is not always true. Ring-lenses form 30-40% of passive rings, which is four times more than the fraction of ring-lenses found in active rings in the stage range -3<=T<=2. This is consistent with both a resonance and a manifold origin for the rings because both models predict purely stellar rings to be wider than their star-forming counterparts. In the case of resonance rings, the widening may be at least partly due to the dissolution of rings. If most inner rings have a resonance origin, I estimate 200Myr to be a lower bound for their dissolution time-scale. This time-scale is of the order of one orbital period at the radius of inner rings.
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