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arXiv 1408.2640astro-ph.GA
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银河系生态系统:气体含量,流入和流出

Galaxy Ecosystems: gas contents, inflows and outflows

Zhankui Lu, H. J. Mo, Yu Lu

摘要:

我们使用一组星系冷气质量分数和气相金属丰度的观测数据来约束质量在$10^{11} M_{\odot}$到$10^{12} M_{\odot}$之间的晕所承载的中央星系中气体的含量、流入和流出。高红移星系中的气体含量是通过结合Lu et al.(2014)的经验恒星形成历史和恒星形成模型得到的,该模型将恒星形成速率与星系中的冷气体质量联系起来。我们发现,自$z = 2$以来,无论采用哪种恒星形成模型,低质量星系中的重子总质量都远小于普适重子质量分数。气相金属丰度的演变数据要求在$z\lesssim 2$下的净金属流出,并且金属负载因子被约束为约$0.01$,或约金属产率的$60\%$。基于银河外流比星际介质和早期喷出的物质更富含金属的假设,我们能够对净吸积率和净质量外流率的上限提出严格的限制。上限强烈表明,在$z < 2$的低质量星系的气相金属丰度和气体质量分数的演变是不兼容的强流出。我们推测,低质量星系的低恒星形成效率是由于一些预防性的过程,防止气体吸积到星系摆在首位。

英文摘要:

We use a set of observational data for galaxy cold gas mass fraction and gas phase metallicity to constrain the content, inflow and outflow of gas in central galaxies hosted by halos with masses between $10^{11} M_{\odot}$ to $10^{12} M_{\odot}$. The gas contents in high redshift galaxies are obtained by combining the empirical star formation histories of Lu et al. (2014) and star formation models that relate star formation rate with the cold gas mass in galaxies. We find that the total baryon mass in low-mass galaxies is always much less than the universal baryon mass fraction since $z = 2$, regardless of star formation model adopted. The data for the evolution of the gas phase metallicity require net metal outflow at $z\lesssim 2$, and the metal loading factor is constrained to be about $0.01$, or about $60\%$ of the metal yield. Based on the assumption that galactic outflow is more enriched in metal than both the interstellar medium and the material ejected at earlier epochs, we are able to put stringent constraints on the upper limits for both the net accretion rate and the net mass outflow rate. The upper limits strongly suggest that the evolution of the gas phase metallicity and gas mass fraction for low-mass galaxies at $z < 2$ is not compatible with strong outflow. We speculate that the low star formation efficiency of low-mass galaxies is owing to some preventative processes that prevent gas from accreting into galaxies in the first place.

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