Visualizing the decision trees for Galaxy Zoo
Today we’ve added a new tool that visualizes the full decision tree for every Galaxy Zoo project from GZ2 onward (GZ1 only asked users one question, and would make for a boring visualization). Each tree shows all the possible paths Galaxy Zoo users can take when classifying a galaxy. Each “task” is color-coded by the minimum number of branches in the tree a classifier needs to take in order to reach that question. In other words, it indicates how deeply buried in the tree a particular question is, a property that is helpful when scientists are analyzing the classifications.
Galaxy Zoo has used two basic templates for its decision trees. The first template allowed users to classify galaxies into smooth, edge-on disks, or face on disks (with bars and/or spiral arms) and was used for Galaxy Zoo 2, the infrared UKIDSS images, and is currently being used for the SDSS data that is live on the site. The second template was designed for high-redshift galaxies, and allows users to classify galaxies into smooth, clumpy, edge on disks, or face on disks. This template was used for Galaxy Zoo: Hubble (GZ3), FERENGI (artificially redshifted images of galaxies), and is currently being used by the CANDELS and GOODS images in GZ4. Although these final three projects ask the same basic questions, there are some subtle differences between them in the questions we ask about the bulge dominance, “odd” features, mergers, spiral arms, and/or clumps.
If you ever wanted to know all the questions Galaxy Zoo could possibly ask you, head on over to the new visualization and have a look!