Title: Exploring the stellar populations of backsplash galaxies Show Chinese title

Title: 探索回溅星系的恒星群体

Abstract: Backsplash galaxies are those that traverse and overshoot cluster cores as they fall into these structures. They are affected by environment, and should stand out in contrast to the infalling population. We target galaxies in the vicinity of clusters (R>R200) and select a sample in projected phase space (PPS), from the compilation of Sampaio et al. based on SDSS data. We present a statistical analysis, comparing two regions in PPS, with the same projected distance to the cluster but different velocity. The analysis relies on the presence of variations in the stellar population content of backsplash galaxies. We find a lower limit in the fractional contribution of ~5% with respect to the general sample of infalling galaxies at similar group-centric distance when using single line strength analysis, or ~15-30% when adopting bivariate distributions. The stellar populations show a subtle but significant difference towards older ages, and a higher fraction of quiescent galaxies. We also compare this set with a general field sample, where a substantially larger difference in galaxy properties is found, with the field sample being consistently younger, metal poorer and with a lower fraction of quiescent galaxies. Noting that our "cluster" sample is located outside of the virial radius, we expect this difference to be caused by pre-processing of the infalling galaxies in the overall higher density regions. Show Chinese abstract

Abstract: 回溅星系是指那些在落入这些结构时穿越并超过星团核心的星系。它们受到环境的影响，并且应该与正在落向星团的星系群体形成对比。 我们针对位于星团附近的星系（R>R200）进行目标定位，并从Sampaio等人基于SDSS数据编纂的数据集中选择样本，使用投影相空间（PPS）进行选择。 我们展示了统计分析，比较了PPS中的两个区域，这两个区域具有相同的投影距离到星团，但速度不同。 该分析依赖于回溅星系的恒星群体含量存在变化的事实。 当我们使用单线强度分析时，我们发现相对于具有相似群中心距离的一般落向星团的星系样本，回溅星系的分数贡献有一个下限，约为5%，或者当采用双变量分布时，约为15-30%。 恒星群体显示出微妙但显著的老化趋势，以及更高的休眠星系数。 我们将这一组与一般场样本进行了比较，在场样本中发现了星系属性上更为显著的差异，场样本普遍更年轻，金属含量更低，并且休眠星系数较低。 考虑到我们的“星团”样本位于超越了引力半径的位置，我们预计这种差异是由落向星团的星系在总体密度更高的区域经历的预处理造成的。