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

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

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.