The Chemical Abundance Structure of the Inner Milky Way: A Signature of “Upside-down” Disk Formation
The Chemical Abundance Structure of the Inner Milky Way: A Signature of “Upside-down” Disk Formation
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内银河系的化学丰度结构：“颠倒”的圆盘形成的标志
DOI：
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发表时间：
2016
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影响因子：
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通讯作者：
J. Holtzman
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作者：
Jenna K C Freudenburg;D. Weinberg;M. Hayden;J. Holtzman
我们提出了一个内星系中恒星分布的模型，由Hayden等人（H15）测量为与中平面垂直距离的函数。厚盘形成的“颠倒”的情况下，其中的恒星形成的气体层的厚度合同作为恒星质量的磁盘的增长，我们结合联合收割机一个简单的处方，其中的恒星分布的标度高度线性下降，从到超过时间尺度tc，保持不变，单区化学演化。我们假设一个线性指数的星星形成历史。利用星星形成效率时间尺度、外流质量负荷因子和，该模型再现了观测到的内盘星轨迹和H15在、和测量的金属丰度分布函数（MDF）。模型参数的实质性变化导致与H15数据的不一致;例如，模型分别在高和低时与观察到的H15数据相匹配或不匹配。推断的尺度高度演化，与zh（t）下降的时间尺度在大的回望时间，有利于倒置形成的动力学加热的最初薄恒星人口作为主要机制调节磁盘厚度。我们的short-tc模型的失败表明，任何模型中，厚盘的形成是一个离散的事件将不会再现连续的依赖性的H15发现的介子。我们的方案的内部磁盘的演变可以测试未来的测量分布和年龄金属丰度分布。
We present a model for the distribution of stars in the inner Galaxy, , measured as a function of vertical distance from the midplane by Hayden et al. (H15). Motivated by an “upside-down” scenario for thick disk formation, in which the thickness of the star-forming gas layer contracts as the stellar mass of the disk grows, we combine one-zone chemical evolution with a simple prescription in which the scale-height of the stellar distribution drops linearly from to over a timescale tc, remaining constant thereafter. We assume a linear-exponential star formation history, . With a star formation efficiency timescale , an outflow mass-loading factor , , and , the model reproduces the observed locus of inner disk stars in and the metallicity distribution functions (MDFs) measured by H15 at , , and . Substantial changes to model parameters lead to disagreement with the H15 data; for example, models with or fail to match the observed MDF at high- and low- , respectively. The inferred scale-height evolution, with zh(t) dropping on a timescale at large lookback times, favors upside-down formation over dynamical heating of an initially thin stellar population as the primary mechanism regulating disk thickness. The failure of our short-tc models suggests that any model in which thick disk formation is a discrete event will not reproduce the continuous dependence of the MDF on found by H15. Our scenario for the evolution of the inner disk can be tested by future measurements of the -distribution and the age–metallicity distribution at .