Understanding E+A galaxies

Definition

The "E" in "E+A" signifies an "elliptical type spectrum*" (and is sometimes replaced with "K" for "K-type spectrum") and the "A" signifies "A-type spectrum." This essentially means that there are older, redder stars (like "K"-type stars that are very common in "E"-lliptical galaxies) as well as newer, bluer stars (like "A"-type stars) present in the galaxy. The reason this is significant is because stars within galaxies are usually similar ages. Astronomers believe that events like major mergers between galaxies can cause "starbursts" (periods of star formation about 10-100x higher than normal star formation) where the mixing of gases within the galaxies combined with the kinetic energy of the merger forms a perfect breeding ground for new stars. The resultant galaxy still has the old stellar population present from the two original galaxies, while also housing these new, blue stars that formed in the merger! There are many ways a galaxy can undergo starburst, not just via mergers, and thus multiple ways that an E+A galaxy could form.

*You can think of a spectrum as the light signature of a galaxy. It is a graph that plots the amount of light being emitted at various wavelengths, ie. how much red light or blue light there is. These spectra can also help us gain insight into processes happening within the galaxy! For example, a dip in the amount of light being emitted around 656 nm can imply that there are no new stars being formed within the galaxy.

What can E+A galaxies tell us about their environments?

Our collaboration has been using the presence of E+A galaxies to understand and investigate galaxy evolution, galaxy properties, and cluster dynamics in various regions. Our research is focused on studying and virtualizing the presence of E+A galaxies in four main clusters: the Coma Cluster (Abell 1656), the Hercules Supercluster (SCl 160), the Leo Cluster (Abell 1367), and the Virgo Cluster (Abell 1689). In addition, members of our collaboration are focused on studying different types of E+A galaxies, including "blue," "green," and "gold" E+As, named for their optical color, as well as spiral and merger E+A galaxies.