16801

We propose to create a legacy map of the southern half of M31 in the optical and near ultraviolet (NUV). The Panchromatic Hubble Andromeda Southern Treasury (PHAST) will add virgul100 million stars to M31.s stellar photometry archive and cover regions of M31 that are structurally unique and more sensitive to the merger history than the northern disk mapped in the Panchromatic Hubble Andromeda Treasury (PHAT). These newly mapped regions include the intersections with M32 and the giant southern stream comma the split portion of the star forming ring comma and the southern bar. By providing age comma metallicity comma stellar mass comma and follow-up kinematics comma the resolved stellar photometry of these regions will be used for detailed comparisons to simulations comma including star formation history and population asymmetries as well as the orbits of M32 and the giant southern stream comma allowing us to distinguish between competing merger scenarios. Thus comma these measurements tightly constrain models of M31.s merger history and disk evolution. Furthermore comma the legacy value for such observations is undeniable M31 has been and will continue to be a centerpiece target for many NASA and ESA missions comma as well as for ground-based time-domain observations that could find extremely valuable events that require HST resolution for identifying precursors. These current and future data sets cover the entire galaxy comma and thus comma our coverage will increase the value of all past and future M31 observations. PHAST will complete a lasting baseline data set for this high-demand target that no other current or planned facility will be able to produce.

本研究拟构建仙女座星系（M31）南半部的光学与近紫外（NUV）遗留型巡天天图。泛色哈勃仙女座南部巡天（PHAST）将为M31的恒星测光数据库新增逾1亿颗恒星，并覆盖M31中结构独特、相较于泛色哈勃仙女座巡天（PHAT）已测绘的北部银盘区域对星系并合历史更为敏感的区域。本次新测绘的区域涵盖与M32的交界区域、巨型南部恒星流、恒星形成环的分裂区段以及南部棒状结构。通过获取恒星年龄、金属丰度、恒星质量及后续运动学数据，上述区域的分辨恒星测光结果将用于与各类数值模拟开展精细对比，涵盖恒星形成历史、天体族群空间不对称性，以及M32与巨型南部恒星流的轨道参数，从而帮助我们区分不同的竞争性并合假说。因此，这些测量结果将严格约束M31的并合历史与盘演化模型。此外，此类观测的遗留价值毋庸置疑：M31历来是且仍将是诸多美国国家航空航天局（NASA）与欧洲空间局（ESA）任务的核心观测目标，同时也是地面时域天文学观测的重点目标——后者可探测到极具科学价值的暂现源事件，而这类事件需要哈勃空间望远镜（HST）的高分辨率才能识别其前兆天体。当前与未来的各类观测数据集将覆盖整个M31星系，因此本次测绘将提升所有过往及未来M31观测数据的科学价值。PHAST将为这一受高度关注的观测目标构建一套持久的基准数据集，而当前及未来其他任何观测设施均无法生成此类数据集。