Measuring the effects of dust attenuation on the luminosities and morphologies of disk galaxies

星系最初是如何形成的，以及它们在整个生命周期中是如何变化的，这是天体物理学中最不为人所知的问题之一。这样的理解对于揭示我们的宇宙是如何进化的，并深入了解我们银河系的起源是必要的。许多项目都以解开这些谜团为中心，并依赖于对观察结果的解释。这个项目关注的是星系中的尘埃如何影响观测。尘埃基本上深刻地影响着所有可观测星系的诊断，比如它们的亮度和颜色、结构（盘状、凸起）、颜色梯度和恒星质量估计。先前的研究表明，较明亮的盘状星系往往比低光度星系遭受更多的尘埃衰减，并且它们的中心部分比外部部分遭受更多的尘埃吸收。然而，两个关键问题仍未得到解答：(1)全球尘埃衰减和衰减梯度如何同时依赖于整套相关参数（光度或恒星质量、恒星形成速率、密度或尺度长度和结构）？(2)作为星系参数的函数，尘埃衰减对常用的星系结构测量有怎样的影响？该项目将通过收集本质上相似的星系样本（恒星质量、恒星形成率、密度、结构）来研究这些问题。此外，首席研究员将领导一项合作努力，以扩大密歇根大学本科天文学入门课程中以学生为中心的有效教学法的使用和评估影响（例如，探究式活动，讲座辅导，思维配对分享，诊断评估和学习分析）。该项目还包括对一名研究生的培训，包括指导和教学技能；本研究项目背景下大学生科研技能的培养；参与外展活动，包括在当地一所小学。从技术上讲，因为类似星系的样本是从随机角度观察的，而边缘上的星系受尘埃衰减的影响更大，研究光学特性如何随倾角变化，可以独立于模型测量相对尘埃衰减作为星系参数的函数。然而，这关键取决于收集真正相似星系样本的能力，而且许多先前的工作至少使用了一些受尘埃衰减影响的选择标准。这导致样品的高低倾角成员并不真正相似，这种依赖于倾角的交叉样本污染严重影响了尘埃衰减对星系参数依赖性的结论。研究人员工作的一个关键进展是，他们正在开发一套选择标准，使类似星系的样本能够以不受倾斜偏差影响的方式组装。这一进展使我们能够以前所未有的精度比较真正相似星系样本的观测特性。因此，该项目的目标是双重的：(1)使用广域近红外巡天和这种新颖的与倾角无关的星系结构测量方法，以一种从未实现过的与倾角无关的方式，选择真正本质上相似的星系样本。(2)利用这些样本完整、无偏、稳健和详细地测量尘埃衰减对所有相关星系参数的依赖性，首次测量尘埃衰减对基于sdss的星系结构测量的影响，并首次测量尘埃衰减的径向梯度作为星系性质的函数。调查人员将向公众公布他们的结构指标和其他测量数据。

Precisely how galaxies initially form and how they change throughout their lifetimes are among the least understood problems in astrophysics. Such understanding is necessary to uncover how our Universe evolved and to gain insight into the origin of our own Milky Way Galaxy. Many projects are centered on unraveling these mysteries and depend on interpreting observations. This project focuses on how dust in galaxies affects observations. Dust profoundly affects essentially all of the observable diagnostics of galaxies, such as their brightnesses and colors, structures (disks, bulges), color gradients and stellar mass estimates. Previous work demonstrated that more luminous disk galaxies tend to suffer more dust attenuation than low-luminosity galaxies and that their central parts suffer more dust absorption than their outer parts. Yet, two critical questions remain unanswered: (1) How does global dust attenuation---and attenuation gradients---depend simultaneously on the entire set of relevant parameters (luminosity or stellar mass, star formation rate, density or scale length, and structure)? (2) How in detail are commonly-used measures of galaxy structure affected by dust attenuation as a function of galaxy parameters? This project will study these questions by assembling samples of intrinsically similar galaxies (stellar mass, star formation rate, density, structure).In addition, the principle investigator will lead a collaborative effort to widen the use and assess the impact of effective student-centered pedagogy in University of Michigan introductory undergraduate astronomy classes (e.g., inquiry-based activities, lecture tutorials, think-pair share, diagnostic assessments and learning analytics). This project also involves training of a graduate student, including mentorship and teaching skills; the development of undergraduate research skills in the context of this research project; and involvement in outreach, including in a local elementary school.More technically, because the samples of similar galaxies are viewed from random angles and edge-on galaxies are much more strongly affected by dust attenuation, studying how the optical properties vary with inclination enables a model-independent measurement of relative dust attenuation as a function of galaxy parameters. However, this crucially depends on the ability to assemble samples of truly similar galaxies, and many previous works use at least some selection criteria that are biased by dust attenuation. This results in samples where the high and low inclination members are not truly similar, and this inclination-dependent cross-sample contamination significantly affects conclusions about the dependence of dust attenuation on galaxy parameters. A critical advance of the investigators' work is that they are developing a set of selection criteria that enables the assembly of samples of similar galaxies in a manner that is unaffected by inclination bias. This advance enables the comparison of the observed properties of samples of truly similar galaxies with unprecedented accuracy. Therefore, the goals of this project are two-fold: (1) To use wide-area near-infrared surveys and this novel inclination-independent measures of galaxy structure to select samples of truly intrinsically similar galaxies in a way that is independent of inclination to a degree never before achieved. (2) To use these samples to measure the dependence of dust attenuation on all relevant galaxy parameters in a complete, unbiased, robust and detailed manner to measure for the first time the effects of dust attenuation on SDSS-based measures of galaxy structure and to measure for the first time the radial gradients in dust attenuation as a function of galaxy properties. The investigators will release their catalogues of structural metrics and other measurements to the public.