The mass of the Local Group (LG) is a crucial parameter for galaxy formation theories. However, its observational determination is challenging - its mass budget is dominated by dark matter which cannot be directly observed. To meet this end the posterior distributions of the LG and its massive constituents have been constructed by means of constrained and random cosmological simulations. Two priors are assumed - the LCDM model that is used to set up the simulations and a LG model,which encodes the observational knowledge of the LG and is used to select LG-like objects from the simulations. The constrained simulations are designed to reproduce the local cosmography as it is imprinted onto the Cosmicflows-2 database of velocities. Several prescriptions are used to define the LG model, focusing in particular on different recent estimates of the tangential velocity of M31. It is found that (a) different $v_{tan}$ choices affect the peak mass values up to a factor of 2, and change mass ratios of $M_{M31}$ to $M_{MW}$ by up to 20%; (b) constrained simulations yield more sharply peaked posterior distributions compared with the random ones; (c) LG mass estimates are found to be smaller than those found using the timing argument; (d) preferred MW masses lie in the range of $(0.6 - 0.8)\times10^{12} M_{\odot}$ whereas (e) $M_{M31}$ is found to vary between $(1.0 - 2.0)\times10^{12} M_{\odot}$, with a strong dependence on the $v_{tan}$ values used.
利用数值N体/流体动力学模拟方法，研究了在高红移的PopII GRBs（GRBIs）观测中，从不同初始质量函数（IMF）、产额和寿命的恒星星族中探测和区分PopIII星富集特征的可能性。PopIII和PopII的恒星形成制度，同时采用头重脚轻和Salpeter-like IMF的原始PopIII恒星形成。我们发现，部分GRBIIs托管在介质中以前丰富的PopIII星（PopIII为主）是模型独立的。典型的丰度比，如[Si/O] vs [C/O]和[Fe/C] vs [Si/C]，可以帮助从大质量和中等质量的PopIII恒星中分离富集，而低质量的第一颗恒星则与常规的PopII世代退化。拥有PopIII主导的GRBII的星系的性质对第一颗恒星质量的特定假设并不十分敏感。
Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. II. Dark and stellar mass concentrations for 13 nearby face-on galaxies
Constraining early-time dust formation in core-collapse supernovae
核心坍缩超新星（CCSNe）尘埃形成的理论模型预测在$\sim 1000$天内形成的喷出物尘埃的$\gtrsim 0.01$ M $_\odot$，与这些时期的观测结果之间存在严重的差异，这推断出更低的质量。我们证明，在光学薄的情况下，这些低尘埃质量是强大的，尽管显着的观测和模型的不确定性。对于11个观测良好的CCSNe样本，没有合理的模型达到$10^{-4}$ M $_\odot$以上的碳尘质量，或$\sim 10^{-3}$ M $_\odot$以上的硅酸盐质量。光学厚的模型可以容纳更大的尘埃质量，但尘埃必须聚集在一起，并有一个低（$<0.1$）覆盖分数，以避免与光学波长的数据冲突。这些值是不足以重现所观察到的红外通量，所需的覆盖率不仅不同SNe之间，但时代之间的同一对象。在协调大型尘埃质量与早期的CCSNe观测的困难，结合完善的检测超新星遗迹中的巨大尘埃质量，表明后期尘埃形成的机制是必要的。
