The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
The stellar masses, mean ages, metallicities, and star formation histories of galaxies are now commonly estimated via stellar population synthesis (SPS) techniques. SPS relies on stellar evolution calculations from the main sequence to stellar death, stellar spectral libraries, phenomenological dust models, and stellar initial mass functions (IMFs). The present work is the first in a series that explores the impact of uncertainties in key phases of stellar evolution and the IMF on the derived physical properties of galaxies and the expected luminosity evolution for a passively evolving set of stars. A Monte-Carlo Markov-Chain approach is taken to fit near-UV through near-IR photometry of a representative sample of low- and high-redshift galaxies with this new SPS model. Significant results include the following: 1) including uncertainties in stellar evolution, stellar masses at z~0 carry errors of ~0.3 dex at 95% CL with little dependence on luminosity or color, while at z~2, the masses of bright red galaxies are uncertain at the ~0.6 dex level; 2) either current stellar evolution models, current observational stellar libraries, or both, do not adequately characterize the metallicity-dependence of the thermally-pulsating asymptotic giant branch phase; 3) conservative estimates on the uncertainty of the slope of the IMF in the solar neighborhood imply that luminosity evolution per unit redshift is uncertain at the ~0.4 mag level in the K-band, which is a substantial source of uncertainty for interpreting the evolution of galaxy populations across time; 4) The more plausible assumption of a distribution of stellar metallicities, rather than a fixed value as is usually assumed, can have significant effects on the interpretation of colors blueward of the V-band. (ABRIDGED)
Fifty Years of IMF Variation: The Intermediate-Mass Stars
我跟踪历史的银河系场星和疏散星团IMF的恒星计数估计，集中在被忽视的质量范围从1到15 M ${_\odot}$。普遍认为国际货币基金组织具有普遍性，这似乎是没有根据的质量范围。最近的两个估计场星IMF使用不同的方法和样品给出的值的平均对数斜率$Γ$之间的-1.7和-2.1之间的质量范围为1.1至4 M ${_\odot}$。两个较老的估计之间的2和15 M ${_\odot}$严重不同意，在这个范围内的领域国际货币基金组织基本上是未知的恒星计数。尽管有许多详细的研究，即使是使用均匀数据和简化程序的研究，并且只包括具有显著质量范围的星团，但在此质量范围内的疏散星团IMF之间的$Γ$的变化也没有减少。这些星团变化\textit{might}可能是由于采样、系统误差、恒星演化不确定性、动力学演化和未分辨双星的综合影响。如果是这样，那么聚类数据与普遍的IMF一致，但也与相当大的变化一致。聚类数据不允许估计平均IMF或$Γ$，因为平均值取决于加权程序和其他效应的选择。如果集群IMF的扩散超过了上面列出的影响，那么真正的IMF变化一定会发生，而到目前为止，这种变化并不太依赖于所研究的物理条件。在观测和模拟中看到的恒星形成过程的复杂性表明，可能会有很大的实现差异，在这种情况下，单个集群IMF将部分是恒星形成过程中进化偶然性的产物，而感兴趣的函数是IMF参数的概率分布。
Theoretical arguments and indirect observational evidence suggest that the stellar initial mass function (IMF) may evolve with time, such that it is more weighted toward high mass stars at higher redshift. Here we test this idea by comparing the rate of luminosity evolution of massive early-type galaxies in clusters at 0.02<z<0.83 to the rate of their color evolution. A combined fit to the rest-frame U-V color evolution and the previously measured evolution of the M/L_B ratio gives x~-0.3 for the logarithmic slope of the IMF in the region around 1 Solar mass, flatter than the present-day value…
我们提出了一个空间分辨比较的恒星质量和总质量的表面分布的9个早期类型的星系。这些星系是斯隆透镜ACS巡天（或SLACS; Bolton et al. 2006）的一个子集。通过探索再现透镜图像的像素化质量模型来获得总质量分布。恒星质量分布是由适合透镜星系光度学的星族综合模型导出的。还计算了非线性-主要是模型退化。恒星可以解释内部区域的所有质量。事实上，萨尔彼得IMF在内部区域提供了太多的恒星质量，因此似乎被排除在外。暗物质在半光半径处变得重要，并在更大的半径处变得越来越占主导地位。恒星和黑暗的成分是紧密对齐的，但实际的椭圆度是不相关的。最后，我们试图直观地总结的结果，渲染的密度，恒星与黑暗的比例，和不确定性作为假彩色地图。
