Galaxy Zoo inspires! Not just science, but also art. For the latest music video created by a poster on the forum, check out this link (youtube.com). Thanks, newo57!

With the first Galaxy Zoo paper submitted (kudos to Kate and Anze!), we’d like to describe to you what happens next. What’s scientific publishing all about? How does it work? If you’ve followed the blog and the forum, you have a pretty good idea of the first part of the scientific process: discovery!

We set out on the Galaxy Zoo project in part to test whether spiral galaxies in different parts of the sky somehow have spins that align, as has been claimed by earlier work. Kate and Anze have commented on the motivation for this work and blogged about how we did find an effect, were startled by it and so started the bias test to understand it. Kate and Anze used the bias test data to show conclusively that in the case of Galaxy Zoo it was an effect with the observers and that the universe isn’t mad.

This is one of the amazing and unique things about science. Good scientists spend most of their time arguing against the effects they see in their own data, to avoid falling into traps of seeing only what they expect to see. To see how unique and amazing this is, try to imagine a politician arguing against a piece of legislation s/he is sponsoring! This process of double, triple, and quadruple-checking one’s own work is a very important part of science.

Once we were convinced that we really understood what is going on, we could then write up our conclusions in the form of a scientific paper. Steven wrote here about the process of writing a paper; Kate went through the same process Steven described. Over the past few weeks, she passed her paper around to the rest of the Galaxy Zoo team for comments. Kate’s paper has thus passed through the first check — her own examination of her results — and the second — amongst the team itself.

The next step in scientific research is to submit the paper to a journal. This has now happened, and the paper Land et al. (2008) (where “et al.” means “and the rest,” including YOU!!) has been submitted to the top UK journal Monthly Notices of the Royal Astronomical Society (MNRAS).

The editor of this journal will now select an anonymous referee who can comment on the scientific and technical merits of the paper. The referee is another astronomer or cosmologist whom the editor can ask for an expert assessment of the work. He or she will have a few weeks to read it, think about it, and then make a number of recommendations to the editor of the journal. There are three options. The referee can reject the paper outright. This generally happens very rarely, except in highly competitive top journals like Nature and Science. They can support publication of the paper, asking for only a few minor modifications. This also happens quite rarely, though! The most common outcome is for her to write a “referee report,” suggesting a number of modifications and ask for clarifications. The referee might have questions about some part of the analysis, suggest some alternative thoughts and ideas, or criticise the methodology. Sometimes referees can be hostile to a paper; but often, they are genuinely helpful and constructive.

After receiving the report, we get a few weeks to digest it and modify the paper according to the referee’s comments, and argue against the points raised that we disagree with. This process may repeat itself a number of times if the referee isn’t happy with our modifications, and so it can often take weeks and months for a paper to get to a decision by the editor (acceptance or rejection). If a referee is being particularly unreasonable, we can write to the editor requesting a new referee. In extreme circumstances, we could even choose to submit the paper to a different journal and hope for a more reasonable referee.

The whole process is generally known as peer review since the referee is a peer — a fellow scientist and expert in the field. If the paper is accepted, it will appear both in the online and print version of the journal after another few weeks or months. A paper accepted in such a journal is then considered peer-reviewed.

So, if Kate’s paper hasn’t yet been peer-reviewed why is the paper already “public”? It’s general practice in astrophysics to post papers as preprints on a web server called astro-ph. Astro-ph is updated daily to make all papers publicly accessible for anyone. Most people post their papers there when they submit them to journals so they are available immediately. Some wait till the paper is accepted. Thus, not everything on astro-ph is peer-reviewed! In fact, in cosmology, some like to submit preprints to astro-ph before submitting so to allow the community to comment before the draft is submitted to a journal.

It’s important to note that something said in a “peer-reviewed” paper isn’t necessarily true. The point of peer-review is to weed out obviously flawed paper whose logic has holes or whose data don’t support the conclusion. Knowing that a paper has been peer-reviewed should give you extra confidence that its results are believable - that means that an expert in the field has read through the paper and thinks its conclusions are believable.It’s really just the first step of proper “peer-review,” because the process continues. As the community of astrophysicists digests the paper, they too pass judgement on whetherthey consider the paper important and whether they believe the conclusion. Thus, in the years after publication, other astrophysicists might deem Land et al. (2008) a key paper and cite it in the future, commenting on it positively. Or they might disagree with it, but that would still be a sign that it was important enough to comment on. Or it might just fade into obscurity if astronomers don’t consider it important. That’s the historical legacy of a paper - and that’s the ultimate peer-review.

A couple weeks ago, I talked about the Voorwerp (”object”), the strange blue object that Hanny posted to the Galaxy Zoo forum. She asked if anyone knew what it was, and we sure didn’t. Part of the problem was that we didn’t have a spectrum for it, so it could have been literally anywhere from right next door in our galaxy to the edge of the universe. Our colleague Bill Keel took a spectrum, which he posted about here in the blog, and found that the Voorwerp is associated with the galaxy above it. We’ve since been looking around for other colleagues that can help us figure out what the Voorwerp is.

Thanks to Matt Jarvis, who was observing at the 4.2m William Herschel Telescope in La Palma, we’ve been able to get some better images. The William Herschel Telescope is bigger than the telescope that gathers images for the Sloan Digital Sky Survey (SDSS is 2.4 m; WHT is 4.2 m), and the images that Matt took are longer exposures, so we can see fainter features in them. The conditions were also quite good (good “seeing” in astronomer’s lingo) and so the image has very good resolution (it’s “sharper”) as the atmosphere didn’t blur things too badly.

So what kind of data did we get? We got three images in filters very similar to the SDSS ones. We got a g, r and i-band image. Those correspond roughly to green, red and infra-red for human eyes. Just to make things confusing though, we colour g in blue, r in green and i in red to stay consistent with the SDSS/GZ images. Without further ado, here are the original SDSS and new WHT images:

Original SDSS image

New WHT image

The WHT image is rotated with respect to the SDSS image; look at the orientation of the galaxy and the Voorwerp to see how they compare. Once you mentally rotate the images so they match, you can see clearly that the Voorwerp is quite a lot bigger than we initially thought, because so much of it was too faint to be visible in the SDSS image. This immediately makes us want to get an even deeper g-band (blue colour) image to see just how much bigger it is! For that, we will probably go to the world’s largest telescopes such as ESO’s Very Large Telescopes, Gemini or Keck.

To give you an idea just how big the Voorwerp is by now, look at the spiral galaxy next to it. This galaxy is a very massive spiral galaxy, likely as big or bigger than our own Milky Way! That’s really, really big!

If you look at the new WHT image of the Voorwerp, you can also see a huge, gaping hole. From the SDSS images, it wasn’t really clear whether the fuzzy structure there was anything real, but the WHT image makes it clear that this is a genuine hole. Again, just to put it into proportion, that hole has a diameter of something like 10 000 light-years. We have no good idea of what could punch such a large hole. One possibility is that a massive burst of star formation occurred there, causing a string of powerful supernova explosions, causing an expanding bubble. Such holes presumably caused by supernovae have been seen in other galaxies, but as far as we know, nothing anywhere near this size.

In his last post, Bill mentioned that the spectrum of the Voorwerp showed some very odd emission lines, in particular Helium II (HeII) and Neon V. HeII only really appears in spectra when there is something really hot around to excite the gas - something hotter than the hottest star. This could be an active galactic nucleus(i.e. gas falling into a supermassive black hole, and heating up as it falls), or perhaps some high velocity shocks. We’re busy analysing the spectrum to understand better what’s going on here.

By a luck coincidence, the Voorwerp turned out to be at a redshift where the HeII line “redshifted” into a common narrow-band filter. Such a filter blocks all light except in a very narrow wavelength range, and so lets us take an image focusing only on those areas which are emitting light in that wavelength range. Below is the image of the Voorwerp in the wavelength range of the HeII line:

The Voorwerp in HeII

The HeII emission clearly comes from a good chunk of the whole Voorwerp (again,a deeper image might show even more), so whatever is exciting the gas in the Voorwerp seems to do it over quite a large volume.

What’s next? We really still have no idea of what the Voorwerp really is. The more data we take on it, the stranger it gets. Many of us are busy trying to convince friends of ours on observing runs to take observations of the Voorwerp so we can figure out what it is.

That’s how an observational science like astrophysics works: you find something new, you don’t know what it is, so you take more data to try and understand it better and form some hypothesis about what’s actually going on and then you confirm it with more data. But we’re still at the very start of this process. The mystery deepens… *cue scary music.

‘Anyone?‘ asked Hanny from the Galaxy Zoo Forum. She came across a weird blue blob that none of us could really make any sense of. It’s right next to a rather massive galaxy that might be a spiral or a somewhat disturbed galaxy.

A highly scientific illustration.

At first, we had no clue. The mystery blob didn’t have a spectrum, so we couldn’t tell much about it at all. It could be in our Milky Way, it could be as distant as that big galaxy, or it could even be at the edge of the universe. Bill Keel enhanced the SDSS image a bit (see below) to reveal the intricate structure of what became known as ‘Hanny’s Voorwerp’ (object).

The five different SDSS bands (g,u,r,i,z), note the intricate structure in the g-band image.

The object seems to be very bright in the g-band image and virtually absent in the others. This led us to think that it must be an emission line object, i.e. an object which emits most of its light only in very specific atomic transitions. This usually means that what we are seeing is ionised gas, rather than stars. Still, it could be anything. Bill Keel kindly also obtained a multi-colour image with the 0.9m SARA telescope at Kitt Peak. The three colours here are much closer to what human eyes would see, so as Bill pointed out, it’s actually much more appropriate to call it the mystery *green* blob.

BVR image from the SARA telescope.

We’ve managed to contact a friend of ours who is currently observing at the 4.2m William Herschel telescope in La Palma and convinced him to take a spectrum of the Voorwerp for us. It shows us that the Voorwerp is…. *drumroll* at the same distance as the big galaxy. This implies that it’s really rather huge and luminous.What does all this mean? What is the Voorwerp? That’s not too clear yet. We have to properly analyse the spectrum to understand what exactly is going on. It’s likely forming stars at a huge rate, ionising lots of gas and making it shine. We’re also trying to get a deeper image to see if there’s evidence of an interaction between the big galaxy and the Voorwerp.So what’s next? We’ll have to do a lot of work to understand this mystery blob better. Right now, the Voorwerp is only slightly less mysterious than when we started, but I have a feeling that it’s going to be really good fun figuring out what is really happening here. It also shows the power of Galaxy Zoo and of having you guys go through the images by eye. If Hanny hadn’t spotted it and asked, we’d never have known about it!

Hey all, as some of you know, I’m working on the blue ellipticals in Galaxy Zoo. I’ve been working on the formation and evolution of elliptical galaxies ever since I started my PhD. In many ways, they’re the most interesting galaxy type out there because they never really want to come out “right” in simulations. They are rather enigmatic objects and we’re not sure how they form.

They *appear* to be completely quiescent - i.e. not forming any stars* - but more recent work by our group has shown that that’s not entirely true. We used the GALEX ultraviolet space telescope to look for small amounts of hot, blue young stars in elliptical galaxies and to our surprise found them to be very common!

It turns out that it’s just too hard to really disentangle such small populations of young stars against the background of really old stars. Unfortunately, this idea that elliptical galaxies are all old and have no young stars in them led some people to specifically *exclude* any galaxies that might have young stars in them from the elliptical class. So our discovery from the ultraviolet data led us to search for more of these elliptical galaxies with young stars in them.

We knew that the only way to find them was my making our own catalogue of ellipticals where we would *not* throw out things that look like ellipticals but had the blue colours or spectra indicating young stars.

I did classify 50 000 galaxies from the SDSS by eye in a week, dividing galaxies into ellipticals vs. everything else; once I was done, I checked to see what was left. And lo and behold, there was a small but significant population of *very* blue elliptical galaxies! This project of course led to Galaxy Zoo, since 50 000 may sound a lot, but it’s only a tiny fraction of the 1 million in SDSS. So now with all the classifications from all you guys (thanks so much!), I’ve been able to study blue ellipticals in much more detail.

Here’s what I did: I selected a redshift (distance) range and a limit in absolute magnitude (luminosity - how bright the galaxies actually are) to create a “volume-limited” sample. That’s a sample where I know that I’ve got all galaxies down to a certain luminosity limit in a certain volume. That’s important when you want to compare numbers (e.g. blue vs. red ellipticals), because blue and red galaxies can have different luminosities, and we must compare apples to apples.

I already knew from earlier tests that your classifications are absolutely awesome, but when I pulled up the images of those galaxies that you classified as “elliptical” that also had very blue colours, I was amazed. Here they were! Blue ellipticals, lots of them!

So with this incredible sample in my hands, I started work on a paper. In Chris’s words, it’s a “classic astronomy paper” because we’re doing nothing fancy, but simply report what we find. The most important finding (I think) is that blue ellipticals exist (i.e. they aren’t misclassified spirals) and that they aren’t super-rare, but make up ~5% of the elliptical population.

We’ve also measured their star formation rates in a variety of ways and the measured rates make them by far the highest ever reported for ellipticals. We have some ellipticals with star formation rates of over 50 solar masses per year. To compare, our own Milky Way only manages about 3 per year!

Here are some example images (click for a larger view):

What’s next? I am still polishing the text and we’re doing some comparisons to a simulation. After that, I will circulate the draft with the other team members again for a final round of comments and then it’s probably good to submit to a journal.