Eight years and eight different types of galaxy images

One of the wonderful things we’ve been able to do with Galaxy Zoo over the years is to use the same site to classify many different types of images of the sky. These include surveys that come from a range of telescopes, both on the ground and in space, images at a range of wavelengths, and covering different areas of the sky. We need these different sets of images because they drive the wide variety of scientific questions that the science team studies using galaxy morphology. As part of our celebration of eight years of Galaxy Zoo, I wanted to highlight the different datasets we’ve been able to classify over the years.

Sloan Digital Sky Survey (Legacy Sample)

The bulk of the data used in both the original Galaxy Zoo and Galaxy Zoo 2 projects. These images were taken by the SDSS telescope, located in the mountains of New Mexico, and provided almost 900,000 individual galaxies that volunteers helped to classify.

Spiral galaxies from SDSS and Galaxy Zoo (Lintott et al. 2008)

COSMOS (Hubble Space Telescope)

The Cosmological Evolution Survey (COSMOS) was a dedicated campaign to image the same 2-square-degree field of the sky with more than a dozen telescopes, from radio through X-ray. 86,314 images of galaxies in the COSMOS field taken with Hubble were classified as part of the Galaxy Zoo: Hubble project.

Unbarred spiral galaxies from COSMOS and classified in GZ: Hubble. From Melvin et al. (2014).

CANDELS (Hubble Space Telescope)

The Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) was the largest project in the history of Hubble, with the equivalent of more than four straight months of observing time. Using the near-infrared WFC3 camera, Hubble image some of the earliest massive galaxies, formed only 2-3 billion years after the Big Bang. 49,555 images from CANDELS were classified in Galaxy Zoo from 2012-2013.

Disk galaxies in GZ:CANDELS, including those without bars (top row) and those with bars (bottom row). From Simmons et al. (2014).

UKIDSS (infrared images)

The United Kingdom Infrared Telescope, located near the summit of Mauna Kea in Hawai’i, carried out a large survey at infrared wavelengths, ranging from 1 to 3 microns. This survey (UKIDSS) allows us to compare morphologies of the same galaxies between optical and infrared, probing the effects of galactic dust and different stellar populations. 70,503 galaxies from UKIDSS have been classified by Galaxy Zoo volunteers.

A spiral galaxy with dust lanes, seen in both the optical (SDSS; left) and the infrared (UKIDSS; right).

FERENGI (artificially-redshifted)

One of the critical issues with all Galaxy Zoo data has been calibration of the morphologies we measure, especially in distant galaxies where small and/or faint images can affect the accuracy of classifications. Using a piece of software called FERENGI, we artificially processed SDSS images to make them appear as if they were much further away, and we’re using those classifications to calibrate the data from Hubble. This included 6,624 images of galaxies at a range of distances and brightnesses.

An SDSS image of a barred spiral, artificially processed to appear as if it were at a variety of distances.

GOODS (Hubble Space Telescope)

The Great Observatories Origins Deep Survey (GOODS) is another multi-wavelength survey of the sky, focusing on data from NASA’s flagship space telescopes of Hubble, Chandra, and Spitzer (plus others). We not only study high-redshift galaxies using GOODS data in Galaxy Zoo, but also measure how increasing the sensitivity of the images can change the apparent morphology. 11,157 GOODS images have been classified in Galaxy Zoo at both shallow and deep imaging depths.

Comparison of the GOODS images classified in Galaxy Zoo. The left shows shallower images with only 2 sets of exposures; the right shows the deeper images with 5 sets of exposure.

Flipping spiral galaxies

One of the very first Galaxy Zoo papers addressed a fundamental question: are spiral galaxies in the Universe more likely to spin clockwise, counterclockwise, or equally likely in both directions? To measure this, we used images of spiral galaxies that were artificially flipped, which helped us correct for a psychological bias in the human brain that exhibits a slight preference for counterclockwise spins.

Images of four spiral galaxies, both as the originals (top) and horizontally flipped (bottom).

Single-band SDSS (ugriz)

The latest new set of data used SDSS galaxies again. Instead of making the “color” images that we’ve used before, however, Galaxy Zoo volunteers were asked to classify images from the five individual filters in SDSS, spanning light from the near-ultraviolet to the near-infrared. This will allow us to better measure how morphology can change as a function of observing wavelength, and determine which physical processes in the galaxy are responsible for the light that defines how we measure the shapes.

Single-band filter images of galaxies from the SDSS.

More to come soon. Thanks again for all your help with what we’ve done so far!!!