Exploring the Galaxy: 3-Dimensional Structure and Stellar Streams

Harvard University, Cambridge MA

Investigators

Abstract

The investigators have used the Pan-STARRS-1 survey (PS1) of nearly 1 billion stars to map the dust and gas in our galaxy. Based on the colors of these stars, the investigators have pioneered a method to very accurately measure the dust and gas in the spiral arms of our galaxy. Dust reddens starlight, for the same reason that sunsets are red. Astronomers use this map to determine distances to various objects, and to correct for the effects of dust on their data. The investigators will expand their first work, over the northern sky, using a new southern sky survey to map the 3-dimensional (3-D) structure of the entire galaxy. The investigator has a plan for improving the accuracy of their map, through averaging the data in a new way. All maps will be publicly released and will provide a legacy dataset of enormous value for 3-D reddening estimates, stellar stream searches, and other Galactic structure work. They will be available to the general public via the World-Wide Telescope interface, which has over 10 million unique users. In the process of creating the first-generation 3-D dust map the investigator has identified technical improvements, such as spatial regularization, that would enhance the quantitative reliability of the map. Rather than computing each pixel of the map independently, the next map will combine information from neighboring pixels to stabilize the fit and allow smaller pixels (both angle and distance) with lower noise. The new map will also incorporate detailed information on the observational selection function and Galactic priors to make possible an estimate of the number of stars of every type in every volume element. Inclusion of proper motions and parallaxes from Gaia will stabilize the 3-D fit and increase the fidelity of the map. Timely data releases spur the advancement of knowledge, and the investigator has a strong record of data releases date back to the first dust maps. The first-generation 3-D map has already resulted in the release of a molecular cloud distance catalog. The integrated (along each line of sight) map has been tested against emission-based maps and found to agree well. The improved "second-generation" maps of dust and stars proposed herein will be a powerful probe of Galactic structure, and may lead to discoveries of new tidal streams, disk warps, and other features that help us understand Galactic dynamics. Additionally these maps will provide a foundation for the longer-term goal of a direct calculation of the 6-D radiation field (amount of radiation at every place, in every direction, at every energy).