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

星系最初是如何形成的，以及它们在一生中是如何变化的，这是天体物理学中最不被理解的问题之一。这样的理解对于揭示我们的宇宙是如何进化的以及洞察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读。这个项目的重点是星系中的尘埃如何影响观测。尘埃基本上深刻地影响了星系的所有可观测诊断，例如它们的亮度和颜色、结构(圆盘、凸起)、颜色梯度和恒星质量估计。以前的工作表明，较亮的盘状星系往往比低光度星系遭受更多的尘埃衰减，其中心部分比外部遭受更多的尘埃吸收。然而，有两个关键问题仍然没有得到回答：(1)全球尘埃衰减-和衰减梯度-如何同时取决于整套相关参数(光度或恒星质量、恒星形成速度、密度或标度长度以及结构)？(2)尘埃衰减是如何作为星系参数的函数影响星系结构的常用测量方法？这个项目将通过收集本质上相似的星系(恒星质量、恒星形成率、密度、结构)的样本来研究这些问题。此外，首席研究员将领导一个合作努力，以扩大密歇根大学以学生为中心的有效教学方法的使用，并评估有效的以学生为中心的教学方法在密歇根大学本科生天文学入门课程中的影响(例如，基于探究的活动、讲座教程、思维对分享、诊断评估和学习分析)。这个项目还包括培训一名研究生，包括指导和教学技能；在这项研究项目的背景下发展本科生的研究技能；以及参与推广，包括在当地的一所小学。更严格地说，由于类似星系的样本是从随机角度观察的，而且边缘星系受到尘埃衰减的影响更大，研究光学性质如何随倾角变化使相对尘埃衰减能够作为星系参数的函数进行独立于模型的测量。然而，这关键取决于收集真正相似星系样本的能力，之前的许多工作至少使用了一些因尘埃衰减而产生偏差的选择标准。这导致高倾角成员和低倾角成员的样本并不真正相似，这种依赖于倾角的交叉样本污染显著影响关于尘埃衰减对星系参数的依赖的结论。研究人员工作的一个关键进展是，他们正在制定一套选择标准，使类似星系的样本能够以不受倾角偏差影响的方式组装。这一进展使得能够以前所未有的精度比较真正相似的星系样本的观测属性。因此，该项目的目标有两个：(1)使用广域近红外测量和这种与倾角无关的星系结构新测量方法，以一种与倾角无关的方式选择真正本质上相似的星系样本，这种方式达到了前所未有的程度。(2)利用这些样本以完整、公正、稳健和详细的方式测量尘埃衰减对所有相关星系参数的依赖关系，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属性的函数。调查人员将向公众发布他们的结构度量和其他测量目录。

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.