Cluster mass dependent truncation of the upper IMF: evidence from observations and simulations
C. Clarke, Th. Maschberger
备注：
8 pages, 4 figures; To appear in "UP: Have Observations Revealed a Variable Upper End of the Initial Mass Function?", Astronomical Society of the Pacific Conference Series
We attempt to evaluate whether the integrated galactic IMF (IGIMF) is expected to be steeper than the IMF within individual clusters through direct evaluation of whether there is a systematic dependence of maximum stellar mass on cluster mass. We show that the result is sensitive to observational selection biases and requires an accurate knowledge of cluster ages, particularly in more populous clusters. At face value there is no compelling evidence for non-random selection of stellar masses in low mass clusters but there is arguably some evidence that the maximum stellar mass is anomalously low (compared with the expectations of random mass selection) in clusters containing more than several thousand stars. Whether or not this effect is then imprinted on the IGIMF then depends on the slope of the cluster mass function. We argue that a more economical approach to the problem would instead involve direct analysis of the upper IMF in clusters using statistical tests for truncation of the mass function. When such an approach is applied to data from hydrodynamic simulations we find evidence for truncated mass functions even in the case of simulations without feedback.
The Pristine HeII Emitter near GN-z11: Constraining the Mass Distribution of the First Stars
Università degli Studi di Firenze（佛罗伦萨大学）；INAF/Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔奇天文台）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；Department of Physics and Astronomy, University College London（伦敦大学学院物理与天文系）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Scuola Normale Superiore（比萨高等师范学院）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）
Evidence of a non universal stellar Initial Mass Function. Insights from HST optical imaging of 6 Ultra Faint Dwarf Milky Way Satellites
利用HST/ACS深空观测资料，我们证明了6颗超暗矮银河系卫星（UFD）的亚太阳恒星初始质量函数（IMF）比银河系盘的IMF更接近底光。我们的数据具有约0.45 M $_{\odot}$的质量下限，而上限是$\sim 0.8$ M $_\odot$，由这些旧的、金属贫乏的系统的关断质量设定。如果用单一幂律公式表示，我们得到的IMF斜率比$-2.3$的“Salpeter”值要小，范围从狮子座IV的$-1.01$到牧夫座I的$-1.87$。这种偏差的重要性取决于星系，通常为95%或更高。当建模为对数正态分布时，IMF拟合的峰值质量比银河系盘中的峰值质量更大，然而，特征系统质量（$\sim0.22$ M $_{\odot}$）的银河系盘值仅在68%的显著性下被排除，并且仅针对样本中的一些UFD。我们发现，IMF的斜率与星系的平均金属丰度，并在较小的程度上，与速度色散和总质量。观测到的相关性的强度受到观测恒星数量中的散粒噪声的限制，但未来的天基任务，如JWST和WFIRST，都将增加可以详细研究的矮银河系卫星的数量，以及对单个星系的观测深度。
Impact of initial mass function on the chemical evolution of high-redshift galaxies
Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universität Heidelberg（海德堡大学天体物理中心理论天体物理研究所）；Interdiszipliäres Zentrum für Wissenschaftliches Rechnen, Universität Heidelberg（海德堡大学跨学科科学计算中心）；INFN-Padova（帕多瓦意大利国家核物理研究所）；Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova（帕多瓦大学伽利略·伽利莱物理与天文系）；INAF - Osservatorio Astronomico di Padova（帕多瓦天文台意大利国家天体物理研究所）；Department of Astronomy, University of Texas, Austin（德克萨斯大学奥斯汀分校天文学系）；Weinberg Institute for Theoretical Physics, University of Texas, Austin（德克萨斯大学奥斯汀分校温伯格理论物理研究所）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森尼天体物理中心）；Radcliffe Institute for Advanced Studies at Harvard University（哈佛大学拉德克利夫高等研究院）
