Effects of galactic fountains and delayed mixing in the chemical evolution of the Milky Way
Effects of galactic fountains and delayed mixing in the chemical evolution of the Milky Way
复制标题
银河喷泉和延迟混合对银河系化学演化的影响
DOI：
--
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
U.S.A.
中科院分区：
文献类型：
--
作者：
E. Spitoni;F. Matteucci;S. Recchi;G. Cescutti;A. B. D. D. Astronomia;U. Trieste;Italy.;Inaf Trieste;I. O. Astronomy;V. University;A. D. O. Physics;Astronomy;U. California;U.S.A.
上下文大多数星系化学演化模型都采用瞬时混合近似（IMA）。这种假设可能是不现实的，因为存在化学不均匀性，虽然目前的银河系化学演化模型可以重现IMA下的大多数观测约束。目标。本文的目的是测试是否放松这种近似在一个详细的化学演化模型可以改善或恶化的协议与观察。为了做到这一点，我们研究了两个可能的原因放松的瞬时混合：i）“银河喷泉时间延迟效应”和ii）“金属冷却时间延迟效应”。方法.我们考虑了大质量恒星化学富集的各种星系喷泉时间延迟。然后，我们测试了时间延迟的浓缩从所有质量的恒星，由于气体冷却的范围在0.5-1 Gyr。结果我们发现，银河喷泉的影响是可以忽略不计的，如果一个平均的时间延迟为0.1 Gyr，在以前的论文中建议，假设。较长的时间延迟会产生结果差异，但这是不现实的。我们还发现，在磁盘中的O丰度梯度是不受银河喷泉。只有当我们采用依赖于金属丰度的恒星产额时，金属冷却时间延迟才对化学丰度的演化产生强烈的影响。相反，如果采用根据太阳化学成分计算的产额，则产生的影响可以忽略不计，就像银河喷泉延迟的情况一样。结论.通过银河喷泉模型，延迟只考虑大质量恒星和只在磁盘中的IMA的松弛，不影响化学演化结果。与金属相关的产额和从晕相开始的所有恒星化学富集的时间延迟相结合，反而产生与观测不同的结果。
Context. The majority of galactic chemical evolution models assumes the instantaneous mixing approximation (IMA). This assumption is probably not realistic, as indicated by the existence of chemical inhomogeneities, although current chemical evolution models of the Milky Way can reproduce the majority of the observational constraints under the IMA. Aims. The aim of this paper is to test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigated two possible causes for relaxing of the instantaneous mixing: i) the “galactic fountain time delay effect” and ii) the “metal cooling time delay effect”. Methods. We considered various galactic fountain time delays for the chemical enrichment from massive stars. We then tested a time delay in the enrichment from stars of all masses due to gas cooling in the range 0.5–1 Gyr. Results. We found that the effect of galactic fountains is negligible if an average time delay of 0.1 Gyr, as suggested in a previous paper, is assumed. Longer time delays produce differences in the results but they are not realistic. We also found that the O abundance gradient in the disk is not affected by galactic fountains. The metal cooling time delays produce strong effects on the evolution of the chemical abundances only if we adopt stellar yields depending on metallicity. If, instead, the yields computed for the solar chemical composition are adopted, negligible effects are produced, as in the case of the galactic fountain delay. Conclusions. The relaxation of the IMA by means of the galactic fountain model, where the delay is considered only for massive stars and only in the disk, does not affect the chemical evolution results. The combination of metal dependent yields and time delay in the chemical enrichment from all stars starting from the halo phase, instead, produces results at variance with observations.