Today’s guest blogger is Raul Jimenez who collaborated with us on an exciting paper on the spin (clockwise vs. counter-clockwise) of spiral galaxies.

The rate at which galaxies transform gas into stars as a function of time gives astronomers insight into the way galaxies formed and evolved. By using the SDSS spectra  one can infer the past star formation history of a galaxy. We have been doing this using sophisticated statistical tools, take a look here. Much has been learned about the formation of galaxies using their star formation history, for example we know that the most massive  galaxies assemble their stars early on, about 1-2 Gyr after the big-bang while small  mass galaxies (100 to 1000 times smaller than the milky way) do it during the whole age of the universe. What we have done in our recent paper is to look at how the star formation history of galaxies correlates to  the rotation direction of galaxies as measured by the galaxy zoo project. What we have found is that  galaxies that had lots of star formation in the past do tend to rotate in the same direction in groups with lengths of about 10 to 20 Mpc.

Although this might sound surprising, it is not! If one reviews very old papers, almost 40-50 years ago, where people like Andrei Doroskievich worked out the way galaxies should rotate based on how they were formed in the past, one realizes that the correlation we have found arises naturally in these models of galaxy formation, so-called hierarchical models. What is happening is that in the past the cluster of galaxies was not yet formed and the spiral galaxies that the galaxy zoo has been classifying by morphology were  coming down the filamentary structure into the proto-clusters. Because the proto-cluster already contains the big elliptical galaxies, they  provide the same  “pull” on all the spiral galaxies in the filament.  So it is quite exciting to see this result from the galaxy zoo and the MOPED/VESPA catalogs. Now it is time to go back to theory and  numerical simulations and understand better what it means for galaxy formation and evolution. This is something we will do next.

The paper has been submitted to MNRAS, and the pre-print is available for download on astro-ph.

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Today’s guest blogger is Half65 from the forum:

More than a year and a half ago an Italian weekly newspaper announced the selling, along with the magazine, of the complete saga of Star Wars in DVD at a very good price. Due to the fact that I’m a sci-fi addict and that I love that saga I decided to buy it. The weekly newspaper is not one of my favourites and I bought it only for the DVD and put the magazine on a table. One day I decided to make a little order and I rediscovered the magazine and I began rapidly to take a look at the pages. Suddenly something attracted my sense and I discovered that inside there was an article about astronomical matters but also a brief part about a project to classify galaxies. Strange thing, I thought at that moment, and I supposed it was something similar to seti@home, could be useful but boring. But the computer was on, as usual, and near me and, absent-mindedly, I began to type in the weird URL, without WWW, with the zoo word mixed with galaxy. I didn’t know, at that time, that I was a few steps from addiction. I read the home page then I began to surf in the various links and then …. I arrived at the tutorial page. And bang. Those pictures were beautiful. In that period I was regaining my astronomy passion and I had began to watch the lecture of Prof. Alexei V. Filippenko of Berkley University on web-cast. I remained captured. I read it all carefully. I made all of the examples and then I tried the entry test. Incredibly my first attempt was successful. “And now.” I was lost in space. I began to classify and, at classification no. 283, had a terrible doubt. Anticlockwise?

“It’s not important!” was my first thought. “They request we don’t agonize over the picture.” I was just a click away from losing a great opportunity to become addicted to another fundamental part of the project: the Forum. “A Forum! I never participated in a forum before. Why start now?” I don’t know why but I pushed the forum button and bang (again). I believed that the forum was a sort of FAQ and when I discovered that it is not and that the solution to my problems was to enter a question and wait for an answer I was lost. “Nothing so difficult,” you can say. Yes.

But the forum was in English, which is not my language. But I gave it a try and I wrote a message in an unreadable blue. Don’t be afraid, I don’t want to bother you with the all story of what happened after that. But I must mention the first member that “talked” to me and said: “Hi welcome to the zoo! i see an anti-clock too, but could you please not use the blue writing? its making my eyes go funny (nothing to do with being past my bed time honest) happy hunting”. And it was fluffyporcupine. Bang (there is a lot in this story). Probably without that gentle approach I would have been out of business. And thanks to that I can know other incredible members.

Alice the most lovely moderator in the known part of the Universe.
Hanny the famous discoverer of “Hanny’s voorwerp”.
NGC3314 my overlapping guru.
waveney Waveney my Perl guru.
Edd the great Administrator.
weezerd my electronic brother.
ElisabethB the great asteroid hunter.
Elizabeth the voice from the other side of the Ocean.
Infinity the secret agent of the forum.

Sorry I can’t mention all the members but that was my intention. And also I discovered a mad passion for topic=6732.0>overlapping galaxies, the Object of the Day and the Perl language. I’m able to participate to this project due to the patience and kindness of the members, especially with newbies (I’m still one). Learn English. Talk with real astronomers. Learn too much more and discovered that there was too much to learn. I was able to put together an Object of the Day collection and with them made little tour of the universe that could be visible with the last version of Google Earth. OK. STOP. I must finish now. Don’t be afraid if you don’t know English very well, if you have no degree, if you think that you can’t be of use to the project, that you can’t do the right thing, that you can’t do that. Stop thinking and go to the project and discover that even with a single classification you could be part of history.

Half65.

P.S.: This story was made with the kindness and essential help of Alice really the most lovely moderator in the known part of the Universe.

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This is from Dan Darg, a graduate student at Oxford, who’s been working on the mergers:

The mergers paper is finally out and will be quite a tour de force. We are confident Galaxy Zoo is the largest visually examined parent sample from which any merger sample has ever been derived and we were able to put together ~3000 merging systems. By contrast, a decade or so ago, a sample with 20 mergers would have been considered a `large’ sample. Galaxy Zoo has thus enabled us to examine several of the key properties of merging galaxies. These include their colours, (stellar) masses, environment, star-formation rates and AGN activity.



The paper is quite long but should be fairly readable to a general audience. I begin in section 1 by an overview of the issues that concern mergers in modern astrophysics and previous methods to find them. This gives us a means to contrast and compare the Galaxy Zoo method which we believe has several advantages.

In section 2 I describe the construction of our catalogue of ~3000 mergers. Here you can see exactly how your votes were used to find the most robust merging systems and is well worth a read (especially if you want to see what issues arose and what we’ll try to overcome in the Galaxy Zoo 2 project).



In section 3 we start to look at results, starting with colour-magnitude digrams since these are the most direct things we detect when we look at pretty much anything in astronomy, i.e. how much and what colour light is coming from mergers. We compared the light with that from a randomly select “control” sample of galaxies taken from SDSS and found that our mergers have a wider spread in colour! In particular, we found a lot of very “blue” looking galaxies in mergers. This can be interpreted to mean that mergers involve (or bring about) new star formation.



We then found some useful results in section 4. Firstly, we estimated the fraction of galaxies in the local universe involved in a major merger. This sort of thing has been sought a lot in modern research and our figure, 1-3%, is very much in the range of expectation. We also were able to estimate something new though, namely, the fraction of spiral to elliptical galaxies in mergers. No other empirical study to date has been able to do this. Interestingly, we found more spirals in mergers than ellipticals compared with the global population!



In section 5 and 6 we studied the environments and stellar masses of our merging galaxies and found that our merging galaxies tended to occupy slightly denser environments and, ellipticals in particular in mergers, seemed to be more massive than their control counterparts.



In section 7 we studied the spectra of our mergers in order to figure which ones had Active Galactic Nuclei, which ones are producing lots of new stars and which ones are inactive. All of these processes and properties are important to our understanding of how galaxies form and evolve and our paper will hopefully provide the impetus for lots of new projects that seek to answer these questions.



Many thanks to all you all for pressing that “merger” button! Lots of interesting science is coming out of it!



Dan


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Today’s guest blogger is Thomas J from the Galaxy Zoo forum.
My interest in astronomy goes back almost as far as I remember. I recall, after dinner with my grandparents one afternoon, my father sitting down and telling me about the Big Bang. I was amazed at the concept and my interest was piqued, although at the time, I didn’t really understand it. If I am totally honest, I understand it little more today! I should really say that, at that age, it was more of an interest in ‘space’ diluted with plenty of science fiction. After all, it’s much easier for a child to comprehend ‘Flash Gordon and the Mud Men’ than the angular separation of galaxies. I did, however, own a large hard back book on astronomy which I would read in bed almost every night.

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Today’s guest blogger is veteran forum member Geoff Roynon.

My interest in the night sky (and astronomy) goes back to the late 1950s when I was growing up in South Africa and we were blessed with dark skies. I soon learned to spot the Southern Cross and Orion and various other “star shapes” in the night sky. We also saw some of the early satellites going by overhead so this must have been 1958/59.

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