The metallicity of galaxy disks: Infall versus outflow
The metallicity of galaxy disks: Infall versus outflow
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DOI：
10.1086/508913
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发表时间：
2007-04-01
影响因子：
4.9
通讯作者：
Dalcanton, Julianne J.
中科院分区：
文献类型：
--
作者：
Dalcanton, Julianne J.
气体吸积（流入）和风（流出）都会改变星系的金属丰度和气体比例，降低有效产量。在旋转速度小于120 km/s的星系中，低的有效产额被广泛解释为由于超新星驱动的风在特征星系质量以下开始，但气体吸积也是一个可行的解释。然而，这里提出的计算证明：（1）富含金属的流出是唯一的机制，可以显着降低有效产量，但只有气体丰富的系统;（2）这几乎是不可能的，以减少一个气体贫乏的系统的有效产量，无论有多少气体损失或吸积;（3）任何后续的星星形成驱动的有效产量回到封闭的盒子值。因此，只有气体丰富的系统与低星星形成率（如矮不规则星）可以产生和维持低有效产量。因此，在低质量星系中看到的有效产额下降是由于这些星系的气体丰富和低星星形成率，这是由于它们的表面密度完全低于肯尼库特SF阈值。额外的计算证实，通过风损失的重子质量分数只会随着星系质量的变化而变化，在任何质量尺度下都没有急剧上升，并且不需要超过15%的重子已经被任何质量的星系损失。因此，超新星反馈不太可能有效地从低质量盘星系中移除大量气体。此外，金属损失和星系质量之间的依赖性是足够弱的大质量星系主导的IGM的金属富集。本文中的计算为任何任意的化学演化历史提供了极限情况，如附录中所证明的。
Both gas accretion (infall) and winds (outflow) change a galaxy's metallicity and gas fraction, lowering the effective yield. Low effective yields in galaxies with rotation speeds < 120 km s(-1) have been widely interpreted as due to the onset of supernova-driven winds below a characteristic galaxy mass, but gas accretion is also a viable explanation. However, calculations presented here prove that (1) metal-enriched outflows are the only mechanism that can significantly reduce the effective yield, but only for gas-rich systems; (2) it is nearly impossible to reduce the effective yield of a gas-poor system, no matter how much gas is lost or accreted; and (3) any subsequent star formation drives the effective yield back to the closed-box value. Thus, only gas-rich systems with low star formation rates (such as dwarf irregulars) can produce and maintain low effective yields. The drop in effective yield seen in low-mass galaxies is therefore due to these galaxies' gas richnesses and low star formation rates, which result from their surface densities falling entirely below the Kennicutt SF threshold. Additional calculations confirm that the fraction of baryonic mass lost through winds varies only weakly with galaxy mass, shows no sharp upturn at any mass scale, and does not require that > 15% of the baryons have been lost by galaxies of any mass. Supernova feedback is therefore unlikely to be effective for removing large amounts of gas from low-mass disk galaxies. In addition, the dependence between metal loss and galaxy mass is sufficiently weak that massive galaxies dominate metal enrichment of the IGM. The calculations in this paper provide limiting cases for any arbitrary chemical evolution history, as is proven in an Appendix.