The star formation rates (SFRs) of low-metallicity galaxies depend sensitively on the gas metallicity, because metals are crucial to mediating the transition from intermediate-temperature atomic gas to cold molecular gas, a necessary precursor to star formation. We study the impact of this effect on the star formation history of galaxies. We incorporate metallicity-dependent star formation and metal enrichment in a simple model that follows the evolution of a halo main progenitor. Our model shows that including the effect of metallicity leads to suppression of star formation at redshift z 2 in dark halos with masses 1011 M ☉, with the suppression becoming near total for halos below ~109.5-1010 M ☉. We find that at high redshift, until z ~ 2, the SFR cannot catch up with the gas inflow rate (IR), because the SFR is limited by the free-fall time, and because it is suppressed further by a lack of metals in small halos. As a result, in each galaxy the SFR is growing in time faster than the IR, and the integrated cosmic SFR density is rising with time. The suppressed in situ SFR at high-z makes the growth of stellar mass dominated by ex situ SFR, meaning stars formed in lower mass progenitor galaxies and then accreted, which implies that the specific SFR (sSFR) remains constant with time. The intensely accreted gas at high-z is accumulating as an atomic gas reservoir. This provides additional fuel for star formation in 1010-1012 M ☉ halos at z ~ 1-3, which allows the SFR to exceed the instantaneous IR, and may enable an even higher outflow rate. At z 1, following the natural decline in IR with time due to the universal expansion, the SFR and sSFR are expected to drop. We specify the expected dependence of sSFR and metallicity on stellar mass and redshift. At a given z, and below a critical mass, these relations are predicted to be flat and rising, respectively. Our model predictions qualitatively match some of the puzzling features in the observed star formation history.
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机译：低金属星系的恒星形成率（SFR）敏感地取决于气体的金属性，因为金属对于介导从中温原子气体到冷分子气体（恒星形成的必要前体）的过渡至关重要。我们研究了这种效应对星系恒星形成历史的影响。我们在一个简单的模型中结合了依赖于金属性的恒星形成和金属富集，该模型遵循光晕主要祖先的演变。我们的模型表明，包括金属性的影响导致质量为1011 M dark的暗晕中红移z> 2时恒星形成的抑制，而对于〜109.5-1010 M below以下的晕，抑制作用几乎全部消失。我们发现，在高红移下，直到z〜2时，SFR才能赶上气体流入速率（IR），这是因为SFR受自由落体时间的限制，并且由于SFR中的金属缺乏进一步抑制了SFR。小光环。结果，在每个星系中，SFR的时间增长速度都快于IR，并且积分的SFR密度随时间增长。高z抑制的原位SFR使恒星质量的增长受原位SFR的支配，这意味着恒星在较低质量的祖先星系中形成然后再增生，这意味着特定SFR（sSFR）随时间保持恒定。高z处强烈积聚的气体积聚为原子气藏。这为z〜1-3处1010-1012 M☉晕中的恒星形成提供了额外的燃料，这使SFR超过了瞬时IR，并可能实现更高的流出速率。在z <1处，由于通用扩展导致IR随着时间自然下降，因此SFR和sSFR预计会下降。我们指定了sSFR和金属性对恒星质量和红移的预期依赖性。在给定的z且低于临界质量的情况下，预计这些关系将分别为平坦和上升。我们的模型预测定性地匹配了观测到的恒星形成历史中的一些令人费解的特征。
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