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

Thanks to forum user milk_n_cookies for finding an appropriate galaxy for the holiday – the Turkey Galaxy:

(the legs are to the top left – click for a larger view)

Here is the Sloan Digital Sky Survey data for The Turkey Galaxy (official name SDSS J033009.27-011137.2).

Happy Thanksgiving to all of you, around the world – we are thankful for all the time you have shared with us as we have explored the universe together!

We have issued a press release describing the exciting simultaneous discovery of a significant population of red spiral galaxies by both the Galaxy Zoo and Space Telescope A901/902 Galaxy Evolution Survey (STAGES) projects. These unusual galaxies are found mainly in the outskirts of galaxy groups and clusters, and appear to be a missing link in the transformation of normal star-forming spirals to ‘red and dead’ early-types (lenticulars and ellipticals) in dense environments.You can see the press release here, and see the news on the BBC, and Wired. 

Hot on the heels of the acceptance of our initial paper looking at the environmental dependence of morphology and colour, here’s another one considering similar questions, but using a very different approach.

The first author is Ramin Skibba, a friend of the Galaxy Zoo team, who is an expert in a mysterious analysis tool called ‘mark correlation functions’. He’s calculated these using the Galaxy Zoo data and interpreted the results to help us understand how the morphology and colour of galaxies depend on their environment. This has confirmed many of the findings in our previous paper, and given us new insight into the processes responsible for transforming galaxies from blue to red and spiral to elliptical. Ramin will write a blog post, explaining his paper in more detail, soon.

The paper has just been submitted to our usual journal of choice, Monthly Notices of the Royal Astronomical Society. The submitted version will be available later in the week; we’ll post more then.

(For those counting, this is the 7th Galaxy Zoo paper to be submitted. So far, four have been accepted and we’re still working on the other two).

The wheels of science sometimes seem to turn very slowly. It was back in May when, after several months of work, we submitted a paper which investigates how the morphology and colour of galaxies varies depending on where in the universe they live. Earlier this week, exactly six months later, the paper was finally accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS).Along the way we have added a number of improvements requested during peer review, and others which were suggested to us by colleagues or we thought of after submission. The paper will now be sent to the publisher for typesetting, and should appear online before the end of the year (after we’ve given it a final proof read), and in print shortly after that.We wanted people to know about our work as soon as possible, both the Galaxy Zoo users and fellow astronomers, so we put the paper on a public scientific archive at the same time as submitting to the journal. We have updated that version to match the one which will appear in MNRAS. If you are feeling adventurous, you can get it here. A more approachable summary of the results can be found on this poster.

So why has it taken so long? Well, it hasn’t really. It usually takes at least a couple of months for a paper to go through the peer review process, and often longer for a lengthy paper like this one. This process involves the selection of an independent reviewer by the journal, who usually remains anonymous. They carefully read the paper and provide suggestions for changes to be made before publication. As the reviewer is usually very busy doing their own science, it generally takes a month before the reviewer sends their report. The authors then usually revise their paper based on the reviewer’s comments, and reply to the referee giving additional explanation and justification for any suggestions which were not acted upon. This exchange sometimes repeats a few times. If the reviewer recommends many changes, which take the authors a long time to get around to doing, a paper may spend over a year in review!

One unfortunate delay for our paper was that the first reviewer was rather more rigourously technical than most astronomers, and took a dislike to our slightly casual use of terms such as ‘independent’ in our title and abstract (the brief summary of the paper). This reviewer wanted us, unreasonably we believe, to rewrite our paper before they were willing to actually read it. Sometimes it happens that there is a mismatch between the paper’s intended readership and the chosen reviewer. We therefore asked the journal for a second opinion, to which they kindly agreed. The second reviewer was much more positive, and gave very useful suggestions for minor changes that have helped to improve the paper. We also made quite a few small changes that we had thought of while the paper was in review, and even tried to make the first referee happy by changing the title slightly. We are really happy with the resulting paper, but glad to have it finished with, so we can now concentrate on all the other exciting work we are doing. Stay posted!

We’re halfway through our second observing run to follow up overlapping-galaxy pairs (and it is still a lot warmer than that picture from Spain looks in the last blog entry!) . Anna and I arrived yesterday at Kitt Peak National Observatory southwest of Tucson, Arizona. She got here at lunchtime, and I didn’t make it until just after sunset because of a committee meeting in town. We’re using the 3.5-meter WIYN telescope (Wisconsin-Indiana-Yale-NOAO – it takes more than a village to build an observatory!), located at Kitt Peak National Observatory. As we did last April, we’re using a camera called OPTIC, which can be temperamental in the software and networking departments but can deliver very sharp images through tracking of atmospheric image motions right on the chip during an exposure. We’ve gotten several images as sharp as 0.5 arcseconds, which is not much bigger than a single SDSS image pixel. The combination of a larger telescope and much longer exposures let us measure features that the SDSS survey images only hint at.

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More good news for the Zoo arrived this week. As Bill prepares for our next observing run on top on Kitt Peak in Arizona, we received an email that we’ve been awarded time on the giant 30m radio dish of the IRAM observatory above Granada for not one, but two Zoo projects.  The first is the beginning of our campaign to make use of the beautiful catalogue of merging galaxies the Zoo provides, led by Daniel Darg here in Oxford. The second is the project the Zoo was originally designed for, teasing out the effect of black holes in star formation in ellipticals. Kevin and I have already had great success doing this with IRAM, but the ability of the Zoo to find nearby blue ellipticals will be of enormous value.

In both cases, we’ll be looking for the signature of carbon monoxide (CO) in the galaxies. That might sound obscure, but CO is actually the second most common molecule in the Universe. The most common is just hydrogen, H2, but that’s hard to detect so instead we go after CO. Once you know how much CO there is, there’s a well-established formula that gives you the star formation rate, something which we need to know if we’re going to understand how the galaxies are evolving.

We’re waiting for the final schedules to be drawn up, but it looks like at least one Zookeeper will be spending New Year up a mountain. Watch this space.

I created the Merger Checking (which now has over a million clicks), three Pea Hunts (All finished) and now an unofficial irregular galaxy classification. What started as 80 lines of Perl code is now 800 (about 50 of the original 80 lines still survive), but can now support almost any Galaxy Zoo mini-project.These mini-projects will never be as pretty as the main GZ sites, but they are quick to build, modify and use.

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A quick followup to last week’s announcement of my talk on the Zoo and Hanny’s Voorwerp – the PDF visuals and MP3 narration are now available online. Truth in advertising compels me to point out that we ended up not being able to record the talk live, so I redid the narration later. As best I can tell, this version was less entertaining than the one for a live audience (as well as being a good bit shorter). You also have to figure out when to page forward…