arXiv 1611.046982016-11-15astro-ph.GA

恒星形成星系的淬灭质量部分和恒星形成序列斜率的起源

The quenched mass portion of star-forming galaxies and the origin of the star formation sequence slope

Zhizheng Pan, Xian Zhong Zheng, Xu Kong

备注：: 9 pages, 5 figures, accepted for puplication in the ApJ
DOI：: 10.3847/1538-4357/834/1/39

摘要：

在观测上，一个巨大的盘状星系可以拥有一个像静止星系（QG）一样不活跃的凸起部分。据推测，恒星形成星系（SFG）中包含的淬灭成分是恒星形成主序（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，以量化淬火的质量部分SFG（$f_{\rm Q}$）在固定的恒星质量（$M_{\ast}$）和调和的MS斜率在低和高质量的制度。在这个模型中，每个SFG由一个星形成和一个淬灭组成。恒星形成组分的质量（$M_{\rm SF}$）与恒星形成速率（SFR）之间的关系为SFR $\propto M_{\rm SF}^{α_{\rm SF}}$，其中$α_{\rm SF}\sim 1.0$。猝灭分量对恒星质量有贡献，但对SFR没有贡献。因此，可以基于观察到的MS斜率$α$与$α_{\rm SF}$的偏离来量化$f_{\rm Q}$。采用由\citet{Whitaker 2014}报道的红移依赖的MS斜率，我们探索了$z=[0.5,2.5]$上的$f_{\rm Q}-M_{\ast}$关系的演化。我们发现Milky Way质量SFG（具有$M_{\ast}\approx 10^{10.7}M_{\odot}$）通常在$z\sim 2.25$处具有$f_{\rm Q}=30\%-40\%$，而在$z\sim 0.75$处该值迅速上升至$70\%-80\%$。的$α\sim 1.0$ MS斜率的起源中看到的低质量制度进行了讨论。我们认为，大多数低质量的SFG停留在一个“稳定阶段”的恒星形成阶段的情况。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，因此在宇宙时间内保持大致恒定。这种情况下成功地产生了$α\sim 1.0$ 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。

英文摘要：

Observationally, a massive disk galaxy can harbor a bulge component that is comparably inactive as a quiescent galaxy (QG). 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 ($f_{\rm Q}$) at fixed stellar mass ($M_{\ast}$) and to reconcile the MS slopes both in the low and the high mass regimes. In this model, each SFG is composed by a star-forming plus a quenched component. The mass of the star-forming component ($M_{\rm SF}$) correlates with the star formation rate (SFR) following a relation SFR $\propto M_{\rm SF}^{α_{\rm SF}}$, where $α_{\rm SF}\sim 1.0$ . The quenched component contributes to the stellar mass but does not to the SFR. It is thus possible to quantify $f_{\rm Q}$ based on the departure of the observed MS slope $α$ from $α_{\rm SF}$. Adopting the redshift-dependent MS slope reported by \citet{Whitaker 2014}, we explore the evolution of the $f_{\rm Q}-M_{\ast}$ relations over $z=[0.5,2.5]$. We find that Milky-Way mass SFGs (with $M_{\ast}\approx 10^{10.7}M_{\odot}$) typically have a $f_{\rm Q}=30\%-40\%$ at $z\sim 2.25$, whereas this value rapidly rises up to $70\%-80\%$ at $z\sim 0.75$. The origin of an $α\sim 1.0$ 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 keeping roughly constant over cosmic time. This scenario successfully produces an $α\sim 1.0$ MS slope, as well as the observed MS evolution from $z=2.5$ to $z=0$ at low masses.

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