The role of galactic wind recycling represents one of the largest unknowns in galaxy evolution, as any contribution of recycling to galaxy growth is largely degenerate with the inflow rates of first-time infalling material, and the rates with which outflowing gas and metals are driven from galaxies. We present measurements of the efficiency of wind recycling from the EAGLE cosmological simulation project, leveraging the statistical power of large-volume simulations that reproduce a realistic galaxy population. We study wind recycling at the halo scale, i.e. gas that has been ejected beyond the halo virial radius, and at the galaxy scale, i.e. gas that has been ejected from the ISM to at least $\approx 10 \, \%$ of the virial radius (thus excluding smaller-scale galactic fountains). Galaxy-scale wind recycling is generally inefficient, with a characteristic return timescale that is comparable or longer than a Hubble time, and with an efficiency that clearly peaks at the characteristic halo mass of $M_{200} = 10^{12} \, \mathrm{M_\odot}$. Correspondingly, the majority of gas being accreted onto galaxies in EAGLE is infalling for the first time. At the halo scale, the efficiency of recycling onto haloes differs by orders of magnitude from values assumed by semi-analytic galaxy formation models. Differences in the efficiency of wind recycling with other hydrodynamical simulations are currently difficult to assess, but are likely smaller. We are able to show that the fractional contribution of wind recycling to galaxy growth is smaller in EAGLE than in some other simulations. We find that cumulative first-time gas accretion rates at the virial radius are reduced relative to the expectation from dark matter accretion for haloes with mass, $M_{200} < 10^{12} \, \mathrm{M_\odot}$, indicating efficient preventative feedback on halo scales.

中文翻译：

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鹰模拟中的银河流入和风循环率

银河风循环的作用代表了星系演化中最大的未知数之一，因为循环对星系生长的任何贡献在很大程度上会随着第一次落入物质的流入速率以及流出气体和金属被驱离的速率而退化。星系。我们展示了来自 EAGLE 宇宙学模拟项目的风循环效率的测量结果，利用了再现现实星系群的大容量模拟的统计能力。我们研究了光环尺度上的风循环，即已经喷射到光环维里半径之外的气体，以及在星系尺度上，即从 ISM 喷射到至少 $\approx 10 \, \%$ 的气体维里半径（因此不包括较小规模的银河喷泉）。银河规模的风能回收通常效率低下，具有与哈勃时间相当或更长的特征返回时间尺度，并且效率在特征晕质量 $M_{200} = 10^{12}\, \mathrm{M_\odot}$ 处明显达到峰值。相应地，大多数吸积到 EAGLE 星系中的气体是第一次下落。在晕尺度上，再循环到晕圈的效率与半解析星系形成模型假设的值相差几个数量级。风能回收效率与其他流体动力学模拟的差异目前难以评估，但可能较小。我们能够证明，EAGLE 中风回收对星系增长的部分贡献比其他一些模拟中要小。