缩小修正：具有环境依赖的IMF和SNIa数量的椭圆星系的恒星形成时标
Downsizing revised: Star formation timescales for elliptical galaxies with an environment-dependent IMF and number of SNIa
摘要：
以往对大质量椭圆（E）~星系的恒星平均金属丰度和[Mg/Fe]值的研究表明，它们的恒星形成时间很短，这与恒星星族合成（SPS）研究的估计和分级组装理论不一致。应用先前开发的化学演化程序GalIMF，它允许一个环境依赖的恒星初始质量函数（IMF）被应用在集成星系初始质量函数（IGIMF）理论，而不是一个不变的正则IMF，恒星形成时标（SFT）的E星系重新评估。该代码的独特之处在于它允许银河系范围内的IMF和相关的化学富集随着银河系物理条件的变化而演变。对于质量较大的E~星系，如果单位质量的Ia型超新星（SNIa）数目增加，则计算的SFT与独立的SPS结果一致。这是恒星形成率较高的星系产生更大质量的星团的自然结果，每个恒星产生更多的SNIa祖先。计算结果表明，具有恒星质量$\approx 10^{9.5} M_\odot$的E~星系具有最长的平均SFT $\approx2\,$ Gyr.大部分质量较大的E~星系形成得更快（SFT $\,\approx 1\,$ Gyr），导致被M~矮星和更大的动态质光比所支配，而质量较低的星系由于其较浅的潜力而更容易失去气体供应，因此也具有类似的短平均SFT。这项工作首次实现了化学富集和SPS建模之间的早期型星系的SFT的一致性，并导致更好地了解恒星形成环境如何影响每单位恒星质量形成的SNIa总数。
英文摘要：
Previous studies of the stellar mean metallicity and [Mg/Fe] values of massive elliptical (E)~galaxies suggest that their stars were formed in a very short timescale which cannot be reconciled with estimates from stellar population synthesis (SPS) studies and with hierarchical-assembly. Applying the previously developed chemical evolution code, GalIMF, which allows an environment-dependent stellar initial mass function (IMF) to be applied in the integrated galaxy initial mass function (IGIMF) theory instead of an invariant canonical IMF, the star formation timescales (SFT) of E galaxies are re-evaluated. The code's uniqueness lies in it allowing the galaxy-wide IMF and associated chemical enrichment to evolve as the physical conditions in the galaxy change. The calculated SFTs become consistent with the independent SPS results if the number of type Ia supernovae (SNIa) per unit stellar mass increases for more massive E~galaxies. This is a natural outcome of galaxies with higher star-formation rates producing more massive star clusters, spawning a larger number of SNIa progenitors per star. The calculations show E~galaxies with a stellar mass $\approx 10^{9.5} M_\odot$ to have had the longest mean SFTs of $\approx2\,$Gyr. The bulk of more massive E~galaxies were formed faster (SFT$\,\approx 1\,$Gyr) leading to domination by M~dwarf stars and larger dynamical mass-to-light ratios as observed, while lower-mass galaxies tend to lose their gas supply more easily due to their shallower potential and therefore also have similarly-short mean SFTs. This work achieves, for the first time, consistency of the SFTs for early-type galaxies between chemical-enrichment and SPS modelling and leads to an improved understanding of how the star formation environment may affect the total number of SNIa per unit stellar mass formed.
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