Dynamical Mass and Heating of Galaxy Disks

天体物理学中的一个长期问题是了解星系在其一生中是如何形成和发展的。这样的理解对于揭示我们的宇宙是如何进化的以及洞察我们银河系的起源是必要的。了解星系形成和演化的一个重要方面是研究通过星系的恒星和气体的作用观察到的星系盘状系统的运动和结构。这个项目揭示了今天星系盘的质量组装和动力学演化的考古记录，揭示了恒星运动和恒星种群之间的关系。这一基础研究项目将在一所公立大学进行，在那里，进步和发现与教学和培训相结合，面向广大和多样化的受众。拟议的项目通过以下方式广泛传播知识并实现科学和技术素养：(1)通过启动关于新的WIYN天文台仪器的科学项目，加强研究和教学基础设施。(2)星系动力学和光谱仪仪器的STEM课程开发将与基础研究交织在一起，这是PI持续的教职职责的一部分。(3)未来STEM劳动力的研究生和本科生培训将包括天文观测、数据分析、仪器调试、数据挖掘和协作研究。(4)将开发、实施和评估有关光纤及其在社会中的使用的教育工具，作为我们的空间空间推广设施的一个公共项目的一部分，目标是学龄儿童和成人。(5)为期四年的关于银河系和外部星系的系列讲座将与这一教育项目相联系，向公众介绍光纤天文测量的专业知识。该项目的主要目标是将气体和恒星的自转和速度弥散的相对幅度与恒星的年龄和丰度结合起来，用作计时器，以探索过去4-6个回转周期中圆盘的动态加热。这类似于银河系开创性研究中用分解的恒星进行的测量，尽管这里的分辨率更粗，但广泛应用于一个具有代表性的星系样本，其晕质量范围很大。这项研究利用了WIYN 3.5米望远镜上的一个新的积分场单元(IFU)和第四代斯隆数字巡天中正在进行的一次大型IFU测量。这项工作的主要结果将是回答这样一个问题：恒星质量光比的明显变化是由于恒星初始质量函数的变化，恒星演化后期的不确定性，还是假设的亮和暗物质分布的细微差别。该方法通过显式地将盘状恒星群中的垂直梯度绑定到自洽的动力学模型中，从而能够准确地测量盘状质量。通过这样做，这项研究确定了最近的圆盘加热率如何依赖于星系的属性和环境，从而限制了这种现象的天体物理来源(S)。该项目校准了一种通过气体和恒星之间的不对称漂移来测量恒星速度分散的方法，这是几十年前在银河系中发现的一种相关的动力学现象，现在可以在外部星系中测量到。该方法将应用于当前一代附近星系的积分场光谱测量数据，并在高红移时应用。这个项目的更广泛的影响包括：(1)用分光光度计时器确定螺旋盘的垂直加热率是新颖的，并建立了宇宙中最大耗散结构中恒星密度分布的具体图景。(2)恒星和气体运动学的差异与恒星群年龄的耦合为估计恒星群的动力学质量和校准恒星群的质光比提供了一种新的手段。(3)校准质量光比对恒星演化的后期阶段、恒星形成将重子锁定在恒星中的效率以及暗晕的内部密度分布施加了严格的限制。

A longstanding problem in astrophysics is to understand how galaxies form and develop throughout their lifetimes. Such understanding is necessary to uncover how our Universe evolved and to gain insight into the origin of our own Milky Way Galaxy. One important aspect of understanding galaxy formation and evolution is the study of the motion and structure of a galaxy's disk system as observed through the action of the stars and gas of the galaxy. This project uncovers the archaeological record of mass-assembly and dynamical evolution of today's galaxy disks, revealed by relations between stellar motions and stellar populations. This basic research project will be conducted at a public University, where advances and discovery are combined with teaching and training to a large and diverse audience. The proposed project broadly disseminates knowledge and achieves scientific and technical literacy in these ways: (1) Research and teaching infrastructure will be enhanced by launching science projects on a new WIYN Observatory instrument. (2) STEM course development on galaxy dynamics and spectrograph instrumentation will intertwine with basic research as part of the PI's on-going faculty duties. (3) Graduate and undergraduate training of the future STEM workforce will include astronomical observations, data analysis, instrument commissioning, data mining, and collaborative research. (4) Educational tools on fiber-optics and their use in society will be developed, implemented, and assessed as part of a public project in our Space Place outreach facility, targeted at school-age students and adults. (5) A four-year lecture series on the Milky Way and external galaxies will be connected to this educational project, presenting expert knowledge on fiber-optic astronomical surveys to the public.The projects's primary objective is to couple the relative amplitude of rotation and velocity dispersion of gas and stars with stellar ages and abundances, used as chronometers, to probe the dynamical heating of disks over the past 4--6 Gyrs. This is analogous to what is being measured with resolved stars in ground-breaking studies of the Milky Way, here albeit more coarsely resolved yet broadly applied to a representative galaxy sample over a wide range in halo mass. This study is leveraged by a new integral-field unit (IFU) on the WIYN 3.5-m telescope and a large IFU survey being undertaken in the fourth generation of the Sloan Digital Sky Survey.A primary outcome of this work will be to answer the question of whether apparent variations in stellar mass-to-light ratios are due to changes in the stellar initial mass function, uncertainties in the late phases of stellar-evolution, or subtleties in the assumed distribution of luminous and dark matter. The approach enables accurate measurements of disk mass by explicitly tying the vertical gradients in disk stellar populations into a self-consistent dynamical model. In so doing, the study determines how recent disk heating-rates depend on galaxy properties and environment, thereby constraining the astrophysical source(s) of this phenomenon. The project calibrates a method for measuring stellar velocity dispersions via the asymmetric drift between gas and stars, a related dynamical phenomenon discovered decades ago in the Milky Way and now measurable in external galaxies. The method will be applied to the current generation of integral-field spectroscopic survey data on nearby galaxies and has application at high redshift. The broader implications of this project include the following: (1) Determining the vertical heating rate of spiral disks using spectrophotometric chronometers is novel and establishes a concrete picture of the stellar density profile in the largest dissipational structures in the universe. (2) Coupling differences between stellar and gas kinematics with stellar population ages provides a new means for estimating dynamical mass and calibrating the mass-to-light ratios of stellar populations. (3) Calibrating mass-to-light ratios places stringent constraints on late phases of stellar evolution, the efficiency with which star-formation locks baryons into stars, and the inner density profiles of dark halos.