Galaxy Zoo meets CANDELS

As we discussed in this previous post, classifying a galaxy into morphological categories can tell us a lot about its structure. We often want to have classifications of large numbers of galaxies in order to  compare various properties (such as color, mass, star formation rates, etc.) with morphology. However, visual classifications can be very time consuming and classifying large samples (thousands of galaxies or more) can be a daunting prospect for any individual. In 2007 two astronomers, Kevin Schawinski and Chris Lintott, had a unique idea for how to deal with this problem - involve the general public in classifying galaxies - and Galaxy Zoo was born.

For the original Galaxy Zoo project, over one hundred thousand volunteers signed up to classify nearly one million galaxies from the Sloan Digital Sky Survey (SDSS). These volunteers determined whether each of the galaxies was a spiral or an elliptical and if it was a spiral whether it was rotating clockwise, counter-clockwise, or viewed edge on. Galaxy mergers and image artifacts were also options that the classifiers could select. Not only did these citizen scientists quickly take to classifying galaxies, they had fun and learned a lot about galaxies in the process. The Galaxy Zoo webpage hosts a forum where volunteers can post about interesting objects they find and discuss their classifications. One of the exciting aspects of having all of these galaxies looked at individually was the ability to identify rare and unique objects that had not been seen before, such as Hanny's Voowerp. These classifications have provided an incredible data set for Galaxy Zoo scientists and a number of publications have resulted from this tremendous effort.

The Galaxy Zoo project was further expanded with the start of Galaxy Zoo 2, which included a much more detailed look at a subset of galaxies, and Galaxy Zoo Hubble, which asks volunteers to classify galaxies imaged with the Hubble Space Telescope in a number of deep fields. Last month, Galaxy Zoo relaunched in its latest incarnation and now includes reprocessed SDSS images along with HST images from CANDELS. These new images have been discussed in great detail on the Galaxy Zoo blog. This is a unique and exciting project for CANDELS because now galaxies at high redshift with near-infrared data will be classified alongside SDSS galaxies by many people to produce a fantastic data set of classifications.

A sampling of colorized CANDELS galaxies that are in the newly relaunched Galaxy Zoo

We worked together closely with the Galaxy Zoo team to produce images for the website. Astronomers are used to analyzing images taken with a specific filter, or one very narrow portion of the spectrum. As such, these images are scientifically very useful, but we must look at images taken in different filters in order to study various galaxy properties. The beautiful color astronomical images that you are probably used to seeing combine several of these filters together. Since CANDELS images are taken in the near-infrared, which is not visible to the human eye, visible colors are assigned to the different near-infrared filters. These images are thus false-colored, but these colors represent real physical properties. The pictures above highlight what some of these CANDELS galaxies look like in color as they are being classified by volunteers.

Since the success of Galaxy Zoo, a number of other Citizen Science projects have begun. Collectively, these projects are a part of the Zooniverse and include things such as finding planets around other stars, studying the surface of the moon, and investigating the history of the Earth's climate. There are a number of interesting projects that anyone out there can contribute to. We hope you explore some of these while you are exploring Galaxy Zoo and looking at CANDELS galaxies!