Merger Papers Accepted for Publication in MNRAS
Thanks for everyone’s work – both papers should soon be appearing in the Monthly Notices of the Royal Astronomical Society 🙂
Galaxy Zoo Paper on Dust in Spirals Submitted.
Before Kevin starts sending me friendly emails that I haven’t blogged about this yet, I want to announce the submission of the latest Galaxy Zoo paper (submitted to Monthly Notices on August 17th):
I’m delighted that I finally got this work submitted. Now I feel like I can properly call myself part of the Galaxy Zoo team. My first entry on the blog Blue Sky and Red Spirals was about this work, and you can also check out the scientific poster I made about it. I hinted several times over the past 8 months that we were very close to submission, so it’s great to be able to say it’s actually now in the referee process. I actually think this is one of the quickest papers I’ve ever written – only 10 months from when I started working on it, to submission of the paper. Fingers crossed for an equally smooth referee process.
Our main conclusions ended up being:
- Spiral galaxies are reddened as they become more inclined due to the presence of dust (this effect is explained in great detail in Blue Sky and Red Spirals)
- Spiral galaxies with large bulges are much redder than spiral galaxies with no/small bulges. This effect is larger than the dust reddening – face-on spirals with large bulges are redder than edge-on spirals with no bulge (on average).
- There is more dust reddening in spiral galaxies with small bulges than in those with large bulges.
- There is a peak in the dust content of spirals at moderate luminosities. Very luminous and very dim spirals both have less dust reddening. Very dim spirals are physically smaller, and make less dust than brighter ones. Very bright spirals usually don’t have a lot of recent star formation, and as dust is destroyed over time we may just be seeing that effect.
We compared the observed trends to a model published in 2004 (Tuffs etal. 2004: Attenuation of Stellar Light in Spiral Galaxies for the very keen!) and concluded that it works pretty well (especially considering how much you have to simplify a spiral galaxy to be able to model it), but there are some problems at the shortest wavelengths covered by SDSS – we see a lot less reddening there than the model predicts.
We finished by talking about the impact all these things have on galaxy surveys. It’s a fairly small effect, but because dust always dims galaxies that means that inclined spirals are often “left out” of samples which people use to study cosmology, or do galaxy evolution (just because you can’t see them, or they’re below a cut in brightness you needed to make). I don’t think I need to tell this crowd that spiral and elliptical galaxies are quite different objects, they also have different clustering properties. So if you preferentially leave out some of the spirals that could introduce some subtle biases, which when people are trying to use galaxy surveys to get percent level accuracy on cosmological parameters might actually start to matter!
Machine learning paper now available
Just a quick note that Manda’s submitted paper on machine learning is now available on astro-ph.
Galaxy Zoo paper on host galaxies of growing black holes submitted!
It’s usually me who is reminding people to go blog about paper submissions and acceptances, so it’s a bit embarassing that I forgot to remind myself last week to announce the submission of the latest Galaxy Zoo paper.
I’ve been working on it for a while, probably over a year. The paper took so long to finish because not only did we have to analyse a huge amount of data, it also took quite a while to figure out what it all meant. I kept producing new plots that showed trends that didn’t really make any sense to us. We therefore needed to take our time digesting what we saw and condensing it into a `readable’ paper. It still over 20 pages long and there are still many results for which we could only offer some speculation. It’s not an easy paper to summarise, so I will (for now) simply summarise it as: “the black hole growth in spiral and elliptical galaxies is due to completely different evolutionary scenarios.”
Or, as I will put it in my talk on Friday at the IAU Symposium on the black hole-galaxy connection:
The answer may depend on
(thanks to stellar on the forum!)
Unlike our previous papers, this is the first paper that we have decided to submit to the Astrophysical Journal. Now fingers crossed that the refereeing process goes well.
Latest Galaxy Zoo paper submitted!
Hi Everyone!
This is to announce the submission of a new galaxy zoo paper entitled “Reproducing Galaxy Morphologies Via Machine Learning”.
First let me introduce myself as I am a newcomer to Galaxy Zoo. My name is Manda Banerji and I am a final year PhD student at University College London. I am interested in automated machine learning tools for morphological classification and became interested in comparing the classifications you all have worked on over the last couple of years to those produced by machine learning codes. So a couple of months back I started working with my PhD supervisor, Prof. Ofer Lahav, on using artificial neural networks to perform morphological classifications. The result has been this paper.
Basically what we have shown here is that using ~10% of the sample of objects that you have classified to train an artificial neural network, we are able to reproduce your classifications for the rest of the objects to an accuracy of greater than 90% provided we choose our neural network input parameters carefully.
There are of course caveats. A neural network is not as good as the human eye in recognizing unusual objects but by and large it does a decent job for the bulk of the galaxies. The most interesting result from this paper however was that if we limit our training sample to the brightest galaxies only and use these to classify fainter galaxies, this does not degrade our results. This means that using your visual classifications as a training set, we can use neural networks to accurately classify hundreds of millions of objects likely to become available over the next few years. These surveys will go considerably deeper and image fainter objects than in the Sloan Digital Sky Survey from which the Galaxy Zoo images were taken – therefore obtaining data for 100-1000 times more objects – and so your work has paved the way for accurate classifications with these future surveys too!
I hope to write another blog soon with a few more details on what we did and how the neural network works. Meanwhile, keep a look out for our paper. It has just been submitted to MNRAS and we eagerly await the referee’s reports!
The Peas are online
Our paper ‘Green Peas in Galaxy Zoo hits the public pre-print archive astro-ph today.  If you’d like to see the paper in full detail you can download it here
(click on PDF to get the full paper).
We’ve also summarized the science results and much of the process of writing the paper  in a separate blog post. Its now been accepted for publication in MNRAS, and we’ll keep you all up to date as it goes through the publication process.
Thanks!
Carie
Edit: Yale press release
The Story of the Peas: writing a scientific paper
Writing the Peas paper has been a great experience for me. I’m still new to the process; its only my 3rd paper and my first with Galaxy Zoo. Kevin and Jordan suggested that I use my experience here to talk a little bit about the process of writing a paper. Every time a paper is written the stages you go through can vary, but I’ll try to describe what we’ve been doing with the Peas paper over the last year. This is a separate perspective from the one Alice is putting together giving the history of the Peas on the Galaxy Zoo Forum.
Eleventh Galaxy Zoo paper submitted!
My colleagues and I are happy to say that the eleventh Galaxy Zoo paper has now been submitted to the journal Astronomy Education Review. The paper is called “Galaxy Zoo: Exploring the Motivations of Citizen Science Volunteers,” and the authors are myself, Georgia Bracey, Pamela, and Chris, Phil, Kevin, Alex, and Jan of the original Galaxy Zoo team. In addition to being the eleventh paper overall, it is also the first paper to study the Galaxy Zoo volunteer community – that is, you!
We are grateful for your collaboration with us even more than usual, because for this paper, you not only classified galaxies, but some of you agreed to give a half-hour of your time to participate in an instant message or phone interview.
As with all the other papers, this paper is being sent out by the journal’s editors to one or more anonymous “peer reviewers” – practicing education researchers who read the paper and recommend that the journal either accept or reject the paper, or (most commonly) request that the authors resubmit the paper after making some improvements. The process can sometimes go a few cycles of changing and resubmitting before the paper is finally accepted. This peer review process helps ensure that scientific studies meet quality standards as judged by the community.
You might have noticed that I haven’t talked about this research on the blog yet, as other team members have done with their research. I wish I could have shared more, but there was an important reason for saving all the explanation until after the paper was submitted. It is well-known in social science research that if the group being studied is aware of the study results, all sorts of unpredictable things can happen.
However, now that the study is over, we can and will gladly share our results. I’ll do that in a series of posts, first by giving a quick summary of what we found, then writing about the ethics of conducting research with people, then about ways to avoid bias in social science, and finally posting a detailed explanation of what we found in the study and what it means.
Now for the quick summary: based on our interviews, we identified 12 motivations that volunteers have given for participating in Galaxy Zoo – 12 reasons why people like you participate. These 12 reasons are:
| Motivation (the category name we used in the paper) | Description (what we said on the survey) |
| 1. Contribute | I am excited to contribute to original scientific research. |
| 2. Learning | I find the site and forums helpful in learning about astronomy. |
| 3. Discovery | I can look at galaxies that few people have seen before. |
| 4. Community | I can meet other people with similar interests. |
| 5. Teaching | I find Galaxy Zoo to be a useful resource for teaching other people. |
| 6. Beauty | I enjoy looking at the beautiful galaxy images. |
| 7. Fun | I had a lot of fun categorizing the galaxies. |
| 8. Vastness | I am amazed by the vast scale of the universe. |
| 9. Helping | I am happy to help. |
| 10. Zoo | I am interested in the Galaxy Zoo project. |
| 11. Astronomy | I am interested in astronomy. |
| 12. Science | I am interested in science. |
We included these motivations in an online survey that many of you took (thanks!), and we are now analyzing the results of that survey to find out which motivations are common and which are rare.
Knowing your motivations for participating will be greatly helpful to us and to other citizen science projects by helping us understand you better. As we understand what appeals to you about Galaxy Zoo, we can design future Zoos to meet those needs and wants. So, this research is helping us create the best Zoos we can create for you.
I really enjoyed doing the interviews, and going through all your forum responses. It’s clear that many of you have many different reasons for being a part of Galaxy Zoo, and many different and eloquent ways of expressing your reasons. A few of the reasons that you gave as part of the forum discussion stuck out in my mind. One of you said “just knowing how small you are is something that’s really hard to explain.” Another said “getting to know, at least a little, some fans and professionals in the GalaxyZoo community.” Another of you said “I’m so proud to be with You, the whole project, to be a part of something bigger than wars or politics. Because science and discovering the truth are the only things that matter.” And there were many, many others.
It’s been a real pleasure getting to know so many of your reasons for being a part of this great enterprise we call Galaxy Zoo, and we’re looking forward to continuing to work with all of you!
Fifth Galaxy Zoo paper accepted – Everything you've ever wanted to know about Blue Early-type galaxies!
The peer-review process can sometimes take quite some time. One of the major motivations for doing Galaxy Zoo was to find galaxies that don’t quite fit into the neat picture of blue spirals and red ellipticals, and so one of the early Galaxy Zoo papers that we submitted was on the blue early-types/ellipticals fond by you guys. We initially submitted it last June for publication in the journal Monthly Notices of the Royal Astronomical Society.
In the time between last June and now, we went through two revisions after getting comments from an anonymous referee, and the third revision will now appear in a future issue of MNRAS. The paper will appear on the pre-print archive astro-ph on Monday, but if you can’t wait, you can also download the PDF here (warning: 7.6 MB!). If you want to see just the cool pictures, here’s the most exciting one:Â
These are all blue early-type galaxies with ongoing star formation. In fact, all of these have star formation rates (the rate at which young stars are being born) of more than 5 solar masses per year. That means each of these is churning out more young, blue, hot stars than our Milky Way galaxy!
Thanks to all of you for your clicks. This paper wouldn’t have been possible without Galaxy Zoo, and as always, we do acknowledge you on the first page of the paper:
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Blue Sky and Red Spirals
This post is from Karen Masters at Portsmouth, who is working on red spirals….
When light travels through stuff it is scattered and absorbed. This is true of light passing through our atmosphere, and it is also true of light as it passes through galaxies. Light of different wavelengths is affected by this scattering and absorption in different ways. Bluer (or shorter wavelength) light is easier to scatter. The sky is blue on a cloudless day because the bluer light from the Sun is scattered out of the line of sight. This light “bounces around” off atoms and molecules in our atmosphere and eventually reaches our eye from some random direction – making the sky look blue. Obviously the light from the Sun itself appears slightly reddened by the same effect since the blue light is preferentially removed. At sunset or sunrise, when the Sun is close to the horizon the light from the Sun has to take a longer path through the atmosphere to get to us. More scattering takes place and the Sun appears redder than normal and makes a beautiful sight to see.
In spiral galaxies, the length of the path the light takes through the galaxy before it gets out and heads towards us depends on our viewing angle. When we see a spiral galaxy face-on the light has the shortest possible path out of the galaxy. By contrast, in an edge-on galaxy, the light must travel through most of the disk before getting out. We expect then that if scattering is important, edge-on galaxies will appear to be redder than face-on galaxies – for similar reasons that sunsets are red. The big question here though is “is scattering important”. Put another way we want to ask “are the disks of spiral galaxies transparent?”. We enjoy a fairly clear view of the extragalactic sky out of our spiral galaxy (the Milky Way), which suggested to early researchers than spiral galaxies probably were transparent. However it is also clear that there is a lot of “extinction due to dust” (our Astronomers terminology for the effect of scattering and absorption of light by particles in the inter-stellar medium) when we look towards the Galactic centre.
So what’s the problem of just looking at a bunch of spiral galaxies and seeing if they get redder as they get edge-on? Well nothing… except that you need to know you’re definitely looking at spirals, and you need to figure out how to measure how edge-on the spirals are. This of course is where Galaxy Zoo helps out so much. Thanks to you we now have an enormous number of visually classified unquestionably spiral galaxies. You even picked out the edge-on ones for us. We can also use the “axial ratios” (the ratio of the maximum dimension to the minimum dimension) of the galaxies from Sloan, which (with some assumptions about how thin the average galaxy is when it’s totally edge-on) gives an estimate of the exact angle of the galaxy’s orientation to us.
And what we’re finding is that spirals definitely get redder as they get more edge-on. So extinction due to dust is clearly important. Because Sloan measures the galaxies in 5 different wavelengths, we can make 4 Sloan colours (in Astronomy the colour is just the difference in the brightness in two different bands) and look at the relative amount of extinction with wavelength which provides information on the source of the scattering and absorption. We can also go to other surveys (for example UKIDSS which measures near-infra red light) to extend this further for some of the galaxies.
Extinction seems to be quite a hot topic lately with Sloan data, but what we have which other researchers don’t is the Galaxy Zoo classifications. They have to use other estimates of if the galaxy is a spiral or not, such as how concentrated the light is, or the exact details of the light profile. Neither is as simple or as reliable as having a human just look at the galaxy. Measuring the amount of extinction is important because it’s been largely neglected in studies using Sloan data up until now. The physical parameters of a galaxy ought not to depend on our viewing angle, but when researchers use colours and luminosities to estimate the star formation history or stellar mass of a spiral galaxy the answer will depend on viewing angle if extinction due to dust is not corrected for. More importantly, elliptical galaxies do not suffer from this effect, so if you compare the mean properties of ellipticals and spirals your answer will be biased by the effect of dust.
So most red spirals seem to be edge-on dusty star forming galaxies which would be normal blue spirals if seen face-on…. but this can’t explain all red spirals. We can still see a significant population of red face-on spirals, and by measuring the average amount of reddening we will even be able to pick out the edge-on spirals which would still be red if seen face-on.
I moved to Portsmouth in October and I was delighted to start working with the Galaxy Zoo team and data. I knew about the project (and even classified a handful of galaxies) before I moved here. I’m currently working on a short paper describing what I’ve told you about here and hope to have it submitted early in the New Year.
Merry Christmas!
Some example images:
A blue face-on spiral galaxy.
A red face-on spiral galaxy.
A red edge-on spiral galaxy.
Galaxy Zoo 