Title: Probing the Milky Way stellar and brown dwarf initial mass function with modern microlensing observations Show Chinese title

Title: 利用现代微透镜观测探测银河系恒星和褐矮星的初始质量函数

Abstract: We use recent microlensing observations toward the central bulge of the Galaxy to probe the overall stellar plus brown dwarf initial mass function (IMF) in these regions well within the brown dwarf domain. We find that the IMF is consistent with the same Chabrier (2005) IMF characteristic of the Galactic disk. In contrast, other IMFs suggested in the literature overpredict the number of short-time events, thus of very-low mass stars and brown dwarfs, compared with observations. This, again, supports the suggestion that brown dwarfs and stars form predominantly via the same mechanism. We show that claims for different IMFs in the stellar and substellar domains rather arise from an incorrect parameterization of the IMF. Furthermore, we show that the IMF in the central regions of the bulge seems to be bottom-heavy, as illustrated by the large number of short-time events compared with the other regions. This recalls our previous analysis of the IMF in massive early type galaxies and suggests the same kind of two-phase formation scenario, with the central bulge initially formed under more violent, burst-like conditions than the rest of the Galaxy. Show Chinese abstract

Abstract: 我们利用针对银河系中心凸起区域的最新微透镜观测，来探究这些区域中整体恒星加褐矮星初始质量函数（IMF）的情况，这些区域远在褐矮星范围内。 我们发现，IMF与银河系盘中特有的Chabrier（2005）IMF一致。 相反，文献中提出的其他IMF会高估短时事件的数量，因此高估了非常低质量恒星和褐矮星的数量，与观测结果相比。 这再次支持了褐矮星和恒星主要通过相同机制形成的建议。 我们表明，关于恒星和亚恒星领域不同IMF的声明，实际上是由于IMF参数化的错误所致。 此外，我们表明，凸起中心区域的IMF似乎更偏向于低质量端，这由与其它区域相比大量的短时事件所说明。 这使我们回想起之前对大质量早型星系中IMF的分析，并暗示了类似的两阶段形成情景，其中心凸起最初是在比银河系其他部分更加剧烈、爆发式的条件下形成的。