Presentation #341.13 in the session “Galaxy Quenching”.
Nearly all current classification systems for galaxies are iterations of the early one provided by Edwin Hubble in 1926. Hubble used the optical appearance of galaxy images on photographic plates to divide the galactic zoo into three general classes: spirals, ellipticals, and irregulars. Galaxy colors are a reflection on the types of stars found in them. Big, massive stars undergo thermonuclear fusion rather quickly, so they are bright and hot, and blue. Lower mass stars are more commonly found but are typically identified by their cooler temperature and are therefore a fainter red color. Therefore, it is a simple conclusion that red regions of a galaxy are old with cooler stars and blue portions are young and the stars there are newly formed. The differences between these two regions create a bi-modality within the color distribution of galaxies. The region in between is dubbed the “Green Valley”. Previous attempts have tried to place the Green Valley as the quantitative divider between red and blue galaxies based on color. Interest in galaxy evolution and the morphological classification of galaxies has led to crowd-sourced astronomy projects such as Galaxy Zoo. Our goal is to examine the structural differences within galaxies that fall in the Green Valley, and what allows them to remain there as opposed to one of the extreme of red or blue. In one theory, thicker bars at the centers of galaxies allow for a larger distribution of gas, which then leads to more star formation and therefore more longevity of the galaxy itself. We will examine bar structures and other common morphological characteristics within Green Valley galaxies to test which of these characteristics play a major role in galaxy evolution. We plan to do this by cross-referencing characteristics that typically identify galaxies as red, blue, or green, with compiled Galaxy Zoo for the Galaxy And Mass Assembly Survey data. Which morphological characteristics are prevalent in the Green Valley? Which are not? How does the Green Valley population’s appearance compare to that of blue, star-forming galaxies?