THE QUENCHED MASS PORTION OF STAR-FORMING GALAXIES AND THE ORIGIN OF THE STAR FORMATION SEQUENCE SLOPE
THE QUENCHED MASS PORTION OF STAR-FORMING GALAXIES AND THE ORIGIN OF THE STAR FORMATION SEQUENCE SLOPE
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DOI：
10.3847/1538-4357/834/1/39
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发表时间：
2016-11
期刊：
影响因子：
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通讯作者：
Z. Pan;Xianzhong Zheng;X. Kong
中科院分区：
文献类型：
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作者：
Z. Pan;Xianzhong Zheng;X. Kong
在观测上，一个巨大的盘状星系可以拥有一个像静止星系一样不活跃的凸起部分。据推测，恒星形成星系（SFG）中的淬灭成分是星星形成主序星（MS）在高质量时具有浅斜率的原因。在本文中，我们提出了一个玩具模型来量化淬火的质量部分SFG（fQ）在固定的恒星质量（M*）和调和MS的斜率在低和高质量的制度。在这个模型中，每个SFG是由一个星形成加上淬火组件。恒星形成组分的质量（MSF）与星星形成速率（SFR）之间存在一个关系式，其中αSF <$1.0。猝灭分量对恒星质量有贡献，但对SFR没有贡献。因此，可以根据观察到的MS斜率α与αSF的偏离来量化fQ。采用Whitaker等人报道的红移依赖的MS斜率，我们探索了z = [0.5，2.5]上关系的演化。我们发现类银河系的SFG（with）在z = 2.25时通常具有fQ = 30%-40%，而在z = 0.75时该值迅速上升到70%-80%。还讨论了低质量区域中出现的α 1.0 MS斜率的起源。我们认为，在这种情况下，大多数低质量的SFG停留在“稳定阶段”的星星形成阶段。在这个阶段，SFR主要由恒星反馈调节，而不受猝灭机制的显著影响，因此在宇宙时间内大致保持不变。该方案成功地产生了α = 1.0 MS斜率，以及在低质量下观察到的从z = 2.5到z = 0的MS演变。
Observationally, a massive disk galaxy can harbor a bulge component that is comparably inactive as a quiescent galaxy. It has been speculated that the quenched component contained in star-forming galaxies (SFGs) is the reason why the star formation main sequence (MS) has a shallow slope at high masses. In this paper, we present a toy model to quantify the quenched mass portion of SFGs (fQ) at fixed stellar mass (M*) and to reconcile the MS slopes in both the low- and the high-mass regimes. In this model, each SFG is composed of a star-forming plus a quenched component. The mass of the star-forming component (MSF) correlates with the star formation rate (SFR) following a relation SFR , where αSF ∼ 1.0. The quenched component contributes to the stellar mass but not to the SFR. It is thus possible to quantify fQ based on the departure of the observed MS slope α from αSF. Adopting the redshift-dependent MS slope reported by Whitaker et al., we explore the evolution of the relations over z = [0.5, 2.5]. We find that Milky Way-like SFGs (with ) typically have an fQ = 30%–40% at z ∼ 2.25, whereas this value rapidly rises up to 70%–80% at z ∼ 0.75. The origin of an α ∼ 1.0 MS slope seen in the low-mass regime is also discussed. We argue for a scenario in which the majority of low-mass SFGs stay in a “steady-stage” star formation phase. In this phase, the SFR is mainly regulated by stellar feedback and not significantly influenced by the quenching mechanisms, thus remaining roughly constant over cosmic time. This scenario successfully produces an α ∼ 1.0 MS slope, as well as the observed MS evolution from z = 2.5 to z = 0 at low masses.