先天还是后天？SDSS星系中特定恒星形成率分布的线索
Nature or nurture? Clues from the distribution of specific star formation rates in SDSS galaxies
摘要：
这项工作研究了调节附近星系中特定恒星形成率（SSFR）的主要机制，并将该数量的两个代理--\Ha的等效宽度和$(u-r)$颜色--与其他物理特性相互关联（质量、金属丰度、环境、形态、和存在密切的同伴）在一个样本的$\sim82500$星系提取的斯隆数字巡天（SDSS）。在颜色等效宽度平面中存在一个相对紧密的“老化序列”，这有利于这样一种设想，即气体向恒星的长期转化（即“自然”）是瞬时SSFR的主要物理驱动力，也是从“化学原始”（贫金属和强烈的恒星形成）状态逐渐过渡到“化学演化”（富金属和被动演化）系统的主要物理驱动力。然而，环境因素（即“养育”）也很重要。在该领域，星系可能会暂时受到离散的“淬火”和“复兴”事件的影响，但这种事件在概率意义上几乎没有统计意义，我们没有发现任何证据表明星系相互作用是平均而言，恒星形成的主要驱动力。虽然视觉分类的合并倾向于显示系统较高的EW（H $α$）和蓝色的$(u-r)$颜色为一个给定的光度，大多数星系与高SSFR有不确定的形态，这可能是由于内部或外部的过程。场星系的早期和晚期形态类型是一致的逐渐“老化”的情况下，没有明显的签名突然减少的SSFR。相比之下，恒星的形成显着减少，有时完全淬火在一个短的时间尺度在密集的环境中，许多对象被发现在一个'淬火序列'中的颜色等效宽度平面。
英文摘要：
This work investigates the main mechanism(s) that regulate the specific star formation rate (SSFR) in nearby galaxies, cross-correlating two proxies of this quantity -- the equivalent width of the \Ha\ line and the $(u-r)$ colour -- with other physical properties (mass, metallicity, environment, morphology, and the presence of close companions) in a sample of $\sim82500$ galaxies extracted from the Sloan Digital Sky Survey (SDSS). The existence of a relatively tight `ageing sequence' in the colour-equivalent width plane favours a scenario where the secular conversion of gas into stars (i.e. `nature') is the main physical driver of the instantaneous SSFR and the gradual transition from a `chemically primitive' (metal-poor and intensely star-forming) state to a `chemically evolved' (metal-rich and passively evolving) system. Nevertheless, environmental factors (i.e. `nurture') are also important. In the field, galaxies may be temporarily affected by discrete `quenching' and `rejuvenation' episodes, but such events show little statistical significance in a probabilistic sense, and we find no evidence that galaxy interactions are, on average, a dominant driver of star formation. Although visually classified mergers tend to display systematically higher EW(H$α$) and bluer $(u-r)$ colours for a given luminosity, most galaxies with high SSFR have uncertain morphologies, which could be due to either internal or external processes. Field galaxies of early and late morphological types are consistent with the gradual `ageing' scenario, with no obvious signatures of a sudden decrease in their SSFR. In contrast, star formation is significantly reduced and sometimes completely quenched on a short time scale in dense environments, where many objects are found on a `quenched sequence' in the colour-equivalent width plane.
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