Here we propose a step-by-step guide to reproduce a compact elliptical galaxy search which resulted in a Science magazine publication. This guide exploits Virtual Observatory desktop applications such as TOPCAT, VOSpec and Aladin, and uses the RCSED catalog data.
Galaxies exhibit a bimodal distribution in the optical color-magnitude space with a narrow "red sequence" populated by mostly early-type galaxies and a broad "blue cloud" containing star-forming objects. Researchers from Harvard and Paris Observatory added the near ultraviolet (NUV-r) color to it and discovered a tight relation in the 3D color-color-magnitude space smoothly continuing from the "blue cloud" to the "red sequence". Followed by the majority of galaxies, it can be used as a powerful classification tool, as well as a new distance estimator for intermediate redshifts that requires a minimal set of observables.
By mining the RCSED database, astronomers have added 195 rare compact elliptical galaxies to only 25 known before. Most of the newly discovered objects were in galaxy clusters, but 11 were free fliers ejected by gravitational slingshot effect from their birth places, the team reported in Science.