We present an analysis of the intracluster light in the Frontier Field Cluster MACS J1149.5+2223 (z=0.544), which combines new and archival Hubble WFC3/IR imaging to provide continuous radial coverage out to 2.8 Mpc from the brightest cluster galaxy. Employing careful treatment of potential systematic biases and using data at the largest radii to determine the background sky level, we reconstruct the surface brightness profile out to a radius of 2 Mpc. This radius is the largest to which the intracluster light (ICL) has been measured for an individual cluster. Within this radius, we measure a total luminosity of 1.5e13 Lsun for the brightest cluster galaxy plus ICL light. From the profile and its logarithmic slope, we identify the transition from the brightest cluster galaxy to ICL at r~70 kpc. Remarkably, we also detect an inflection in the profile centered in the 1.2-1.7 Mpc (0.37-0.52 r200m) radial bin, a signature of an infall caustic in the stellar distribution. Based upon the shape and strength of the feature, we interpret it as potentially being at the splashback radius, although the radius is smaller than theoretical predictions. If this is the splashback radius, then it is the first such detection in the ICL and the first detection of the splashback radius for an individual cluster. Similar analyses should be possible with the other Frontier Field clusters, and eventually with clusters from the Euclid and Roman missions.
Locations of Accretion Shocks around Galaxy Clusters and the ICM properties: insights from Self-Similar Spherical Collapse with arbitrary mass accretion rates
First Sardinia Radio Telescope detection of the Sunyaev-Zel'dovich effect at 18.6 GHz
Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文系）；INAF-Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；INAF, Istituto di Radio Astronomia（意大利国家天体物理研究所无线电天文研究所）；Dipartimento di Fisica e Astronomia, Università degli Studi di Padova（帕多瓦大学物理与天文系）
Searching for Highly Magnified Stars at Cosmological Distances: Discovery of a Redshift 0.94 Blue Supergiant in Archival Images of the Galaxy Cluster MACS J0416.1-2403
Dark matter under the microscope: Constraining compact dark matter with caustic crossing events
一个星系团就像是一个宇宙望远镜，在背景星系的上方，但也像是一个透镜缺陷的宇宙显微镜。透镜焦散线的发散放大增强了透镜质量内存在的子结构的微透镜效应。当移动的背景光源在穿过这些焦散时变亮和消失时，可以访问精细尺度结构。最近在星系团MACSJ1149.5+2223的爱因斯坦半径附近发现了一颗遥远的透镜恒星（Kelly et al. 2017），这使得通过超临界的星系团物质柱达到太阳下质量微透镜的机会非常难得。在这里，我们将这些观测结果与高分辨率的光线跟踪模拟进行比较，其中包括由观测到的星团内星光和可能对最近观测到的LIGO事件负责的原始黑洞所设置的恒星微透镜。我们探索不同的方案与微透镜从群内介质和黑洞，包括原始的，并研究策略，利用这些独特的路线。我们发现，最好的约束在小质量制度的紧凑的暗物质的分数可以得到在集群内介质中发挥的作用可以忽略不计的区域。这种新的透镜现象应该是广泛的，可以在适度红移的透镜星系中检测到，这样光度距离就不会对检测单个放大恒星造成阻碍。连续的{ \it哈勃太空望远镜}监测几个这样的最佳弧将得到前所未有的致密物体的质谱，这有助于揭示暗物质的性质。
