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arXiv 1402.7076astro-ph.GAastro-ph.CO
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银河系中特定恒星形成率的质量无关性

The Mass-Independence of Specific Star Formation Rates in Galactic Disks

Louis E. Abramson, Daniel D. Kelson, Alan Dressler, Bianca M. Poggianti, Michael D. Gladders, Augustus Oemler, Benedetta Vulcani

备注：
6 pages, 2 figures; Accepted to ApJL March 2014. ArXiv version updated to reflect changes made during refereeing; results unchanged
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摘要：

恒星形成速率/恒星质量关系（SFR“主序星”; ${\rm SFR}-M_*$）的斜率并不完全一致：特定恒星形成速率$({\rm SFR}/M_*)$与$M_*$有微弱但显著的反相关。在这里，我们证明，这种趋势可能只是反映了众所周知的增加隆起的质量分数-部分星系不形成恒星-与PDMATHAMO。使用大量的凸起/磁盘分解和SFR估计来自斯隆数字巡天，我们表明，重新归一化SFR磁盘恒星质量$({\rm sSFR_{\rm disk}\equiv SFR}/M_{*,{\rm disk}})$减少$M_*$的SF效率的$\sim0.25$ dex每dex的依赖，完全擦除它在一些子样本。定量地，我们发现$\log {\rm sSFR_{disk}}-\log M_*$有一个斜率$β_{\rm disk}\in[-0.20,0.00]\pm0.02$（取决于SFR估计和主序星定义）的恒星形成星系的$M_*\geq10^{10}M_{\odot}$和隆起质量分数$B/T\lesssim0.6$，一般与纯磁盘控制样本（$β_{\rm control}=-0.05\pm0.04$）。$\langle{\rm SFR}/M_{*,{\rm disk}}\rangle$（很大程度上）独立于恒星形成盘的宿主质量，这对从任何${\rm SFR}-M_*$关系中推断的星系演化方面都有很强的影响，包括：“质量淬火”（凸起增长）的表现，塑造恒星形成恒星质量函数的因素（低质量，盘主导星系的均匀$d\log M_*/dt$），以及恒星形成历史的多样性（${\rm SFR}(M_*,t)$的分散）。我们的研究结果强调了在观测和理论工作中需要将星系视为复合系统而不是综合质量。

英文摘要：

The slope of the star formation rate/stellar mass relation (the SFR "Main Sequence"; ${\rm SFR}-M_*$) is not quite unity: specific star formation rates $({\rm SFR}/M_*)$ are weakly-but-significantly anti-correlated with $M_*$. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions -- portions of a galaxy not forming stars -- with $M_*$. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass $({\rm sSFR_{\rm disk}\equiv SFR}/M_{*,{\rm disk}})$ reduces the $M_*$-dependence of SF efficiency by $\sim0.25$ dex per dex, erasing it entirely in some subsamples. Quantitatively, we find $\log {\rm sSFR_{disk}}-\log M_*$ to have a slope $β_{\rm disk}\in[-0.20,0.00]\pm0.02$ (depending on SFR estimator and Main Sequence definition) for star-forming galaxies with $M_*\geq10^{10}M_{\odot}$ and bulge mass-fractions $B/T\lesssim0.6$, generally consistent with a pure-disk control sample ($β_{\rm control}=-0.05\pm0.04$). That $\langle{\rm SFR}/M_{*,{\rm disk}}\rangle$ is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any ${\rm SFR}-M_*$ relation, including: manifestations of "mass quenching" (bulge growth), factors shaping the star-forming stellar mass function (uniform $d\log M_*/dt$ for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in ${\rm SFR}(M_*,t)$). Our results emphasize the need to treat galaxies as composite systems -- not integrated masses -- in observational and theoretical work.

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