MOLECULAR GAS, CO, AND STAR FORMATION IN GALAXIES: EMERGENT EMPIRICAL RELATIONS, FEEDBACK, AND THE EVOLUTION OF VERY GAS-RICH SYSTEMS
MOLECULAR GAS, CO, AND STAR FORMATION IN GALAXIES: EMERGENT EMPIRICAL RELATIONS, FEEDBACK, AND THE EVOLUTION OF VERY GAS-RICH SYSTEMS
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星系中的分子气体、CO 和恒星形成：紧急经验关系、反馈和富含气体的系统的演化
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发表时间：
2009
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通讯作者：
P. Papadopoulos
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作者：
F. I. Pelupessy;P. Papadopoulos
我们在星系尺度的数值模拟中使用H1、H2气相和恒星耦合演化的时变模型来（1）检验Kennicutt-Schmidt（K-S）关系和H2-压力关系的出现，（2）探索一个现实的H2调节的星星形成配方，它带来了一个被忽视的、潜在重要的SF调节因子，（3）超越典型的星系环境（这些星系经验关系是针对这些环境推导的），以探索非常富含气体的星系的早期演化。在这项工作中，我们模型的低质量星系（M重子109 M嫌），同时纳入一个独立的治疗CO的形成和破坏，最重要的示踪分子的H2在星系中，沿着，为H2气体本身。我们发现，在各种星际介质（ISM）态、恒星分量及其反馈（T_（11）Gyr）之间达到动态平衡后，K-S和H_2-压力经验关系都能在星系中稳健地出现.这些关系的唯一显着的依赖似乎是CO衍生的（因此直接观察到的），这表明了强烈的依赖ISM金属丰度。H2调节的星星形成配方成功地再现了以前的数值模型的形态和定量方面，同时取消了星星形成效率参数。发现大部分H1 → H2质量交换发生在高度非平衡条件下，即使在典型的ISM环境中也需要时间依赖性处理。我们的动力学模型表明，CO分子可以是一个穷人，非线性，氢气示踪剂。最后，对于早期的演化阶段（T = 0.4 Gyr），我们发现真正的星星形成的显着和系统的偏差，从K-S关系，这是特别明显和延长的金属贫乏的系统预期。最大的此类偏差发生在气体非常丰富的星系中，其中全球星星形成率（SFR）可能与CO推导的K-S关系的预期偏差相差2.3 -4倍。这是特别重要的，因为在高红移的气体丰富的系统可能会出现具有异常高的SFR相对于其CO明亮的H2气藏。这表明在早期宇宙结构形成的模拟中，K-S关系作为星星形成的次网格物理学的元素可能存在严重的缺陷。
We use time-varying models of the coupled evolution of the H i, H2 gas phases and stars in galaxy-sized numerical simulations to (1) test for the emergence of the Kennicutt–Schmidt (K–S) and the H2–pressure relation, (2) explore a realistic H2-regulated star formation recipe which brings forth a neglected and potentially significant SF-regulating factor, and (3) go beyond typical galactic environments (for which these galactic empirical relations are deduced) to explore the early evolution of very gas-rich galaxies. In this work, we model low-mass galaxies (Mbaryon ⩽ 109 M☉), while incorporating an independent treatment of CO formation and destruction, the most important tracer molecule of H2 in galaxies, along with that for the H2 gas itself. We find that both the K–S and the H2–pressure empirical relations can robustly emerge in galaxies after a dynamic equilibrium sets in between the various interstellar medium (ISM) states, the stellar component and its feedback (T ≳ 1 Gyr). The only significant dependence of these relations seems to be for the CO-derived (and thus directly observable) ones, which show a strong dependence on the ISM metallicity. The H2-regulated star formation recipe successfully reproduces the morphological and quantitative aspects of previous numerical models while doing away with the star formation efficiency parameter. Most of the H i → H2 mass exchange is found taking place under highly non-equilibrium conditions necessitating a time-dependent treatment even in typical ISM environments. Our dynamic models indicate that the CO molecule can be a poor, nonlinear, H2 gas tracer. Finally, for early evolutionary stages (T ≲ 0.4 Gyr), we find significant and systematic deviations of the true star formation from that expected from the K–S relation, which are especially pronounced and prolonged for metal-poor systems. The largest such deviations occur for the very gas-rich galaxies, where deviations of a factor ∼3–4 in global star formation rate (SFR) can take place with respect to those expected from the CO-derived K–S relation. This is particularly important since gas-rich systems at high redshifts could appear as having unusually high SFRs with respect to their CO-bright H2 gas reservoirs. This points to a possibly serious deficiency of K–S relations as elements of the sub-grid physics of star formation in simulations of structure formation in the early universe.