Galaxy Zoo’s special exhibition of merging galaxies
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: May 19, 2008

Since Galaxy Zoo opened its gates almost a year ago, over 125,000 armchair astronomers have visited the online menagerie and made around 40,000,000 individual classifications of elliptical, spiral and merging galaxies. Now the team are appealing to the public to review their set of possible merging galaxies in order to answer some long standing questions about the weird and wonderful world of interacting galaxies.

As with any zoo the oddest creations provide the greatest thrill, and Galaxy Zoo is no exception. From the original classifications, the results of which were recently submitted to peer reviewed journals, a fantastic set of merging galaxies have been identified. The Galaxy Zoo team are now relying on the public to review the set of possible merging galaxies, in order to make sure the team have as many true merger candidates as possible, therefore maximising the pool of scientific data to work with. The results will help to answer some of the long standing questions surrounding the importance and frequency of merging galaxies.

In theoretical simulations, astronomers have found that the merger of spiral galaxies can create an elliptical galaxy, and that an elliptical can become a spiral by accretion of further stars and gas during its lifetime. Since Edwin Hubble first devised the galaxy classification system, which divided galaxies into two main categories – rugby ball shaped ‘elliptical’ galaxies and whirlpool like ‘spiral’ galaxies – there has been controversy among scientists about how these two principal types are even connected in the global understanding of galaxy formation and evolution. By classifying some of these images visitors are helping astronomers to understand the structure of the Universe and how galaxies form and evolve.

Left: Spiral galaxy NGC 3227 interacts with dwarf elliptical galaxy NGC 3226. Right: Spiral galaxies NGC 3395 and NGC 3396.

Left: Spiral galaxies NGC 3786 and NGC 3788. Right: Arp 188, the Tadpole Galaxy, which has suffered a massive interaction in the past, caused by the barely discernible galaxy located at the bottom right of Arp 188.

Above: NGC 5257 and 5258 join arms as they collide. These images are from the Sloan Digital Sky Survey and show different examples of merging galaxies, conforming to the Galaxy Zoo working definition of a merger that is ‘anything that has a disturbed morphology and is the product of two or more galaxies.’ Images: Sloan Digital Sky Survery, www.sdss.org.

The work of the Galaxy Zoo team, and of the interested public, is far from done: Galaxy Zoo 2’s development is well under way, which will see a much more detailed classification system of the brightest galaxies in the Sloan Digital Sky Survey, an ambitious astronomical survey which is systematically mapping a quarter of the entire sky. Even further down the line we will see Galaxy Zoo 3 with brand new data. The ultimate goal of Galaxy Zoo is to perform a census of the one million galaxies captured by the Sloan Digital Sky Survey.

To find instructions on how to contribute to the Galaxy Zoo survey, including an interactive tutorial to teach you how to classify the galaxies, visit www.galaxyzoo.org, but be warned, it’s highly addictive!

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