The Sciences

Galaxy Zoo!

Cosmic VarianceBy Risa WechslerJul 12, 2007 11:24 AM


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So, I've been in the throes of grant proposal writing, which as far as I can tell is the worst part of becoming a professor. As such, I've been ignoring as much of my email as humanly possible for the past week. Until I got an email from David Weinberg this afternoon, announcing to the SDSS (Sloan Digital Sky Survey) mailing list the arrival of a new web-based galaxy classification project, Galaxy Zoo. The project was started by some scientists with SDSS, including Alex Szalay and Bob Nichol, and others. They had a press release today, and it's already been covered by the BBC and was picked up by AP, so I think the website has gotten a bit hammered in the first day. The basic idea here is to harness the collective eyes and brains of the internet to visually classify galaxies by morphology. It turns out that galaxy mophologies are in some ways a lot easier to classify by eye than by computer, just like faces and other complex images. This is one reason that now that surveys include millions of galaxies, morphology studies have not been as popular as other classification schemes based on colors or spectral types. Apparently, galaxy zoo to the rescue! Here's the first thing I learned: looking at pictures of galaxies is a lot more fun than writing proposals to the NSF to get funding to think about galaxies. (Dear Galaxy Zoo: if I don't get a CAREER grant this year, I blame you!) There were tools to do this before, and I actually have managed to (finally) look at a bunch of these Sloan galaxies over the past few years (I'm a theorist who's never been observing, and normally I only look at fake galaxies in my computer -- or real galaxies labeled by just a couple of variables like luminosity and color instead of their infinite structural variety). But the fact that galaxyzoo gives you a goal for looking at each galaxy makes it totally addictive. Plus galaxies are just pretty awesome looking! Even better, each galaxy has a link directly back to the SDSS Sky Server, which has tons of other info about the galaxy, like a spectrum where available, 5 band magnitudes, etc. Personally, I found myself compelled to look at this information when perplexed about how to classify something. What's it's color? Is it star forming? What's is redshift? All there. (Really, it was all there in the Sky Server before, but this is a pretty cool interface to it because you start by wondering.) It turns out there's a lot of cool stuff in the Universe. In just a bit of classifying, I found a couple of cool galaxy interactions (click for more info):

A galaxy that to me looks like the cartwheel galaxy with bad seeing:

My main gripe about the site is that they've made the classification pretty simple, just allowing for 3 types of spirals, counterclockwise, clockwise, and edge on (none of which are really different types in the classical sense), elliptical galaxies, and mergers. What was I supposed to do with the cartwheel? And what about this bloby guy, which has whopping H-alpha and OII emission and the mysterious zwarning "NOT_GAL"? Clearly has no structure but I just couldn't bring myself to call it an elliptical.

Or these very nebulous beauties:

I kept wishing for a button that said "This one's interesting" or allowed me to choose from a menu, including things like "close pair", "blobby star forming thing", "scoop of neopolitan ice cream" or "i've got a green crayon". In all seriousness, I understand the simple scheme, but it does seem like there's a lot of potential here from a lot of eyes that won't be realized with it. I wonder whether a lot of this won't come from the classification statistics, though, i.e., probably many of the interested objects will have less consistent classifications than normal ellipticals or spirals. To be honest, I think I have exactly the wrong amount of knowledge to do this task effectively as designed -- I overanalyze it and think I must know what's going on, but am clearly just a clueless theorist. Turns out we're still trying to explain the two most basic parameters. Anyways, go check it out. A Universe of galaxies awaits at your fingertips!

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