EAPSI: Determining Disk Galaxy Evolutionary State through Spatially-Resolved Gas Mass Fractions

EAPSI：通过空间分辨气体质量分数确定盘星系演化状态

• 批准号: 1613857
• 负责人: Zachary Pace
• 金额: $ 0.54万
• 依托单位: Pace Zachary J
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-15 至 2017-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1613857&HistoricalAwards=false
• 关键词: EAPSI; Determining; Disk; Galaxy; Evolutionary

Current research in galaxy formation and evolution seeks to answer one main question: how did the heterogeneous universe we observe--with its vast tracts of virtually-empty space between immensely compact islands of stars and hot gas--form from an overwhelmingly homogeneous beginning, the Big Bang? This is indicated robustly in individual galaxies by the gas mass fraction, the percentage of mass contained in both hot plasma and cool atomic & molecular hydrogen--as opposed to mass contained in stars. A small gas fraction indicates--in general--an evolved system with reduced capacity for forming new stars, while a large gas fraction suggests the potential for large star formation and metal-enrichment of the interstellar medium. In collaboration with Prof. Yanmei Chen (Nanjing University: Nanjing, Jiansu, China), the PI will construct statistically-robust estimates of stellar mass, and compare to his existing measurements of spatially-resolved gas mass. The radial variation of gas mass fraction will be compared with estimates of total galaxy mass, star formation rate, and galaxy environment density.In the new era of integral-field spectroscopic surveys (such as MaNGA, SAMI, and CALIFA), responsive, robust, and cheap methods of stellar-continuum fitting are necessary counterparts to large, nightly datastreams. Most methods of stellar-mass estimation are computationally costly, and do not take advantage of modern advances in statistics and machine learning. Prof. Yanmei Chen has developed a method of fitting the stellar continuum, which relies on the one-off principal-component analysis (PCA) of a library of single stellar population (SSP) models, which yields order-of-magnitude improvements in compute time and will enable the use of larger, more flexible SSP libraries. The PI has obtained a set of fully-theoretical SSP models, with a spectral resolution exceeding that of MaNGA. Such SSPs include near-IR features like the CaII triplet (necessary for breaking the age-metallicity degeneracy), and improve on existing models of the thermally-pulsating asymptotic giant branch (TP-AGB). Combining the high-resolution stellar library with Chen's PCA code (translated by the PI from IDL to Python) will yield measurable improvements in resolved stellar-mass estimates. When paired with resolved total gas mass (HI + H2), estimated using new optical-spectroscopic methods (rather than from expensive, radio-band follow-up), a census of stars and gas in nearby galaxies will result. These single-source estimates of galaxy evolutionary state will improve current knowledge of galactic chemical evolution and mass assembly, and place the Milky Way in a cosmic context.This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Ministry of Science and Technology of China.

目前对星系形成和演化的研究试图回答一个主要问题：我们观察到的异质宇宙-在恒星和热气体的极其紧凑的岛屿之间有大片虚拟空间-是如何从一个极其均匀的开始形成的，大爆炸？这在单个星系中通过气体质量分数，即热等离子体和冷原子分子氢中所含质量的百分比-而不是恒星中所含的质量-得到了有力的证明。一般来说，小的气体部分表明一个演化的系统形成新恒星的能力降低，而大的气体部分表明有可能形成大的星星和星际介质中的金属富集。在与Yanmei Chen教授（南京大学：中国江苏省南京市）的合作中，PI将构建恒星质量的可靠估计，并与他现有的空间分辨气体质量的测量结果进行比较。气体质量分数的径向变化将与星系总质量、星星形成率和星系环境密度的估计值进行比较。在积分场光谱测量的新时代（如MaNGA、SAMI和CALIFA），响应灵敏、鲁棒且廉价的恒星连续体拟合方法是大型夜间数据流的必要对应物。大多数恒星质量估计方法的计算成本很高，并且没有利用统计学和机器学习的现代进步。Yanmei Chen教授开发了一种拟合恒星连续体的方法，该方法依赖于单恒星种群（SSP）模型库的一次性主成分分析（PCA），该方法在计算时间上有数量级的改进，并将使更大，更灵活的SSP库的使用成为可能。PI已经获得了一组完全理论化的SSP模型，其光谱分辨率超过了MaNGA。这样的SSP包括近红外特征，如CaII三重态（打破年龄-金属丰度简并性所必需的），并改进了现有的热脉动渐近巨星分支（TP-AGB）模型。将高分辨率恒星库与Chen的PCA代码（由PI从IDL翻译为Python）相结合，将在解决恒星质量估计方面产生可衡量的改进。当与使用新的光学光谱方法（而不是昂贵的无线电波段后续方法）估计的总气体质量（HI + H2）配对时，将导致对附近星系中恒星和气体的普查。这些对星系演化状态的单源估计将改善目前对星系化学演化和质量组装的认识，并将银河系置于宇宙背景中。该奖项隶属于东亚和太平洋夏季研究所计划，支持美国研究生的夏季研究，由NSF和中国科学技术部共同资助。