What will we use our merger data for?

Mergers are really interesting since they are the main process by which the universe evolves its galaxy population and creates more and more massive galaxies. Additionally, the collision between two galaxies involves ALOT of energy. This energy gets transferred into compressive forces when clouds of gas in the galaxies collide and collapse into violent bursts of star formation. Understanding how all the stars in the universe form is a really important aspect of a full understanding of the cosmos and so mergers help us understand some of the key observations made in modern astronomy. We also want to know what fractions of mergers involve spirals and how many are ellipticals, what is the typical mass ratio between merging galaxies and whether or not mergers tend to happen in clusters or not.

Another important contribution mergers can make is help us understand the formation of Active Galactic Nuclei (AGN). Mergers and, more generally, galaxies with disturbed morphologies often turn out to be Ultra-Luminous-Infra-Red Galaxies (ULIRGs) which are themselves interesting because they tend to host AGNs. An AGN is thought to be a Super Massive Black Hole that sits at the centre of a galaxy and produces vast quantities of radiation as matter falls into it (this is called ‘accretion onto a black hole’). AGNs produce vast amounts of light that far out strips that emitted by all the stars in its galaxy combined. Also, they sometimes produce dramatic jets of matter that fly out at relativistic speeds. Alot is still unknown about the mechanism that produces these jets and so AGN and their formation is a hot-topic of research. Distant quasar galaxies are thought to be AGN and tell us much about the formation of the first galaxies in the universe. The more we know about AGN and how they form, the more we can know about some of the distant events near the beginning of the universe. Specific properties of AGN can be probed by examining the spectra that they produce and we hope to apply these tests to all of the good mergers that we find.

I posted a request yesterday afternoon for help in sorting out a set of possible mergers; as the developers are busy with Zoo 2, I just posted a set of lists. Clunky, and annoying, but I’d hoped people would still be able to help out. By the end of last night, forum member Waveney had built us a proper interface. You’ll find the address at the end of the instructions below.

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One of the most impressive aspects of Galaxy Zoo has been the way we’ve been able to use the data in all sorts of unexpected ways. Whether it’s finding overlapping galaxies or strange blue blobs it’s become obvious that there is a lot more to all of your efforts than just elliptical vs spiral. When we were putting together the site, we didn’t give much thought to the many galaxy mergers in the catalogue; as far as the primary science goals went they were mostly just contaminants in our data set.It quickly became obvious that we had the chance to assemble a large and interesting set of mergers and learn more about why, where and how these beautiful collisions occur; conducting the first investigation into this is Daniel Darg who’s based here in Oxford.

He’s already got interesting results, but we’d like his paper to be as comprehensive as possible and that means including as many mergers as we can find. Everything which has a weighted vote of more than 60% in the merger category has proved to be a true merger, but now we need for help to have a closer look at those which have a vote between 40% and 60% in this category. We’re keen to get on with this, so rather than wait for Zoo 2 we thought we could ask for your help here. To find out how, read on below.

Update : New, easier classification system available : See this post.

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