从光晕到银河一号。气体调节器模型的动力学和隐含的宇宙sSFR历史
From haloes to Galaxies - I. The dynamics of the gas regulator model and the implied cosmic sSFR history
摘要：
我们探索的基本参数，驱动气体调节器模型，或浴缸模型内的恒星形成星系的基本属性的演变。在不假设星系处于平衡态的情况下，导出了星系关键性质演化的一般解析形式，即气体质量、恒星形成率、恒星质量、比恒星形成率、气体分数、气相金属丰度和恒星金属丰度。我们发现，所需的时间尺度达到平衡，τ_eq，这是由产品的恒星形成效率和质量负载因子，是核心参数，基本上是在控制所有关键星系属性的演变。大多数关键标度关系（如质量-SFR关系和质量-金属丰度关系）中的散射主要由τ_eq控制。最引人注目的是，预测的sSFR演化完全由tau_eq控制（除了宇宙时间）。虽然sSFR的精确演变取决于tau_eq，但sSFR历史对tau_eq的不同值很大程度上不敏感。在任何时期，最小和最大sSFR之间的差异小于四倍。预测的sSFR历史的形状简单地模仿了暗物质晕的比质量增加率（sMIR_DM），sSFR的典型值约为2*sMIR_DM，与典型的半解析模型（SAM）的预测非常一致，但两者都与观测到的sSFR历史有根本的不同。这清楚地表明，一些关键的过程是在两个典型的SAM和气体调节器模型失踪，我们暗示一些可能的罪魁祸首。我们强调的关键作用tau_eq控制的星系人口的演变，特别是对于气体丰富的低质量星系，是非常不可能生活在周围的平衡态在任何时代，这在很大程度上被忽略了在许多类似的研究。
英文摘要：
We explore the basic parameters that drive the evolution of the fundamental properties of star forming galaxies within the gas regulator model, or bathtub-model. We derive the general analytic form of the evolution of the key galaxy properties, i.e. gas mass, star formation rate (SFR), stellar mass, specific SFR, gas fraction, gas phase metallicity and stellar metallicity, without assuming that galaxies live in the equilibrium state. We find that the timescale required to reach equilibrium, tau_eq, which is determined by the product of star-formation efficiency and mass-loading factor, is the central parameter that is essentially in control of the evolution of all key galaxy properties. The scatters in most of the key scaling relations, such as the mass-SFR relation and mass-metallicity relation, are primarily governed by tau_eq. Most strikingly, the predicted sSFR evolution is controlled solely by tau_eq (apart from the cosmic time). Although the precise evolution of the sSFR depends on tau_eq, the sSFR history is largely insensitive to different values of tau_eq. The difference between the minimum and maximum sSFR at any epoch is less than a factor of four. The shape of the predicted sSFR history simply mimics that of the specific mass increase rate of the dark matter halos (sMIR_DM) with the typical value of the sSFR around 2*sMIR_DM, in good agreement with the predictions from typical Semi-Analytic Models (SAMs), but both are fundamentally different from the observed sSFR history. This clearly implies that some key process is missing in both typical SAMs and gas regulator model, and we hint at some possible culprit. We emphasize the critical role of tau_eq in controlling the evolution of the galaxy population, especially for gas rich low mass galaxies that are very unlikely to live around the equilibrium state at any epoch and this has been largely ignored in many similar studies.
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