I just wanted to add a link to a post by Zooniverse Technical Director Arfon Smith over on the Zooniverse blog:
Please go there to read it.
This development means coders can “fork” their own versions of the Galaxy Zoo code and help (for example) translate the site into other languages, providing another way for people to contribute to the great science coming out of Galaxy Zoo.
Way back in August I gave a evening (public) plenary talk about “The Zoo of Galaxies” at the 28th General Assembly of the International Astronomical Union. I wrote a couple of blog posts about it at the time (here and a bit more here). Just this week I got word that the video is now available, so here it is:
To go with this I have also posted the “proceedings” (a write-up based on my talks) which will be appearing in the 16th Volume of “Highlights of Astronomy”. This is available on the arxiv. It’s not supposed to be a transcript as such, but if you watch both the video and read this I think you’ll see they’re quite similar.
Just a quick note to point out a new paper based on Galaxy Zoo classifications appeared on the arxiv this morning (and just accepted to MNRAS): The Differing Star Formation Histories of Red and Blue Spirals and Ellipticals, by Rita Tojeiro et al.
In this work we took samples of galaxies split by their morphological classifications (from you all, and actually going back to the original Galaxy Zoo project) as well as by their optical colour. With the help of an Ogden Trust undergraduate summer student (Joshua Richards) we then compiled the average star formation histories of these samples, based on fits of star formation models to the Sloan Digital Sky Survey spectra of the galaxies (previously published and called VESPA, or “VErsatile SPectral Analysis” by Rita).
Our main result was that red spirals differ in their star formation histories from blue spirals only in the last billion years or less. We also find that blue ellipticals have very similar star formation histories to blue spirals. We show some results about the dust and metal (astronomers metal) content of the galaxies as well. I think it’s a nice project and I’m very happy to see it finally finished and published.
Thanks again for the classifications.
The relaunch of Galaxy Zoo doesn’t only include the fantastic new images from the CANDELS survey on Hubble Space Telescope, but also includes over 200,000 new local galaxies from the Sloan Digital Sky Survey. We’ve had a lot of questions about where these galaxies came from and why they weren’t put into earlier versions of Galaxy Zoo, so I thought I’d write a bit about these new images.
The Sloan Digital Sky Survey Project (SDSS) is currently in its 3rd phase (SDSS-III). You can read all about the history of SDSS here, and here, but briefly SDSS-I (2000-2005) and SDSS-II (2005-2008) took images of about a quarter of the sky (which we often refer to as the SDSS Legacy Imaging), and then measured redshifts for almost 1 million galaxies (the “Main Galaxy Sample”, which was the basis of the original Galaxy Zoo and Galaxy Zoo 2 samples; plus the “Luminous Red Galaxy” sample) as well as 120,000 much more distant quasars (very distant galaxies visible only as point source thanks to their actively accreting black holes).
Following the success of this project, the Sloan Digital Sky Survey decided they wanted to do more surveys, and put together a proposal which had four components (BOSS, SEGUE2, MARVELS and APOGEE – see here). To meet the science goals of these projects they realised they would need more sky area to be imaged. This proposal was funded as SDSS-III and started in 2008 (planned to run until 2014). The first thing this new phase of SDSS did was to take the new imaging. This was done using exactly the same telescope and camera (and methods) as the original SDSS imaging. They imaged an area of sky called the ”Southern Galactic cap”. This is part of the sky which is visible from the Northern Hemisphere, but which is out the Southern side of our Galaxy’s disc. It totals about 40% of the size of the original SDSS area, brining the total imaging area up to about 1/3rd of the whole sky. The images in it were publicly released in January 2011 as part of the SDSS Data Release 8 (DR8 – so we sometimes call it the DR8 imaging area).
We have selected galaxies from this area which meet the criteria for being included in the original Galaxy Zoo 2 sample (for the experts – the brightest quarter of those which met Main Galaxy Sample criteria). Unfortunately in this part of the sky there is not systematic redshift survey of the local galaxies, so we will have to rely on other redshift surveys (the most complete being the 2MASS Redshift Survey) to get redshifts for as many of these galaxies as we can. We still think we’ll get a lot more galaxies and, be able to make large samples of really rare types of objects (like the red spiral or blue ellipticals). Another of our main science justifications for asking you to provide us with these morphologies was the potential for serendipitous discovery. Who knows what you might find in this part of the sky. The Violin Clef Galaxy is in the DR8 imaging area and featured heavily in our science team discussions of if this was a good idea or not.
And interesting things are already being found in just a week of clicks. The new Talk interface is a great additional place for us to discuss the interesting things that can be found in the sky.
For example this great system with tidal tails and a Voorwerpjie:
and an oldie (but a goodie) in the beautiful galaxy pair of NGC 3799 and NGC 3800 (NGC 3799 in the centre, NGC 3800 just off to the upper right):
and just this morning I discovered the discussion of this really unusual looking possible blue elliptical (IC 2540):
There are also rather more artifacts and odd stuff going on in these new images than I think we saw in the SDSS Legacy sample (from GZ1 and GZ2). Remember these are completely new images you are looking at. It really is true that no-one has looked at these in this level of detail (or perhaps ever) before. The original sample had a sanity check at some level, since when GZ1 ran the majority of the sample had already been targeted by SDSS for redshifts (so someone had to plug a fibre into a plate for each galaxy). In this new imaging all that has happened is that a computer algorithm was run to detect likely galaxies and set the scale of the image you see. Sometimes that mistakes stars, satellite trails, or parts of galaxies for galaxies. Always classify the central object in the image, and help us clean up this sample by using the star/artifact button.
And you can enjoy these odd images too. I like this collection of “GZ Pure Art” based on just odd things/artifacts classifier “echo-lily-mai” thought were pretty. If you get confused by anything please join us on Talk, or the Forum where someone will help you identify what it is you’re seeing.
I’m back in the UK, so I thought it would be nice to give an update on the Chinese coverage of Galaxy Zoo resulting from the big talk I gave in Beijing at the 28th General Assembly of the International Astronomical Union. As you know, I was invited to give one of four “Invited Discourses” at that meeting, on the topic of “A Zoo of Galaxies”. The powerpoint slides of my talk are available online. I still don’t know where/if the video of the talk has appeared online, so will update more on that soon.
As I mentioned before, an abstract of my talk (and a picture of me and one of my favourite galaxies) appeared on the front page of the first edition of “Inquiries of Heaven” (the IAU Daily Newspaper for the meeting).
The talk also attracted a small amount of interest from Chinese press.
Kevin already posted the information that Xinhua (sort of the Chinese version of Reuters) covered it here: Astronomy Project Hunts for Chinese Helpers, (or the Chinese version); since this a news feed it got picked up by a variety of Chinese newspapers.
I was also interviewed for “Amateur Astronomer” (a Chinese astronomy magazine). Here’s the first page of the article they sent me.
I’ve given a couple of public talks recently on results on galaxy evolution from Galaxy Zoo (at the Hampshire Astronomical Group, and the Winchester Science Festival) and one of the things I like to point out is the quantity and variety of science results we’re getting out. To illustrate that I made the below wordl of words appearing in the abstracts of all the peer reviewed science papers the Galaxy Zoo science team have put out.
This is based on the 30 papers about astronomical objects submitted up until July 2012. I just missed Brooke’s first financial reform paper submitted by a day or two, and I love that this was out of date just as soon as I made it.
I realise I should sort out things like per cent – percent, and galaxy, Galaxy, galaxies technically being the same thing. But still I think it’s interesting to look out.
I’m delighted to announce that the latest paper based on Galaxy Zoo classifications was accepted to appear in the Monthly Notices of the Royal Astronomical Society earlier this week, and appears on the arxiv this morning (link).
Usually there is a long delay between submission and acceptance of papers (something Kevin discussed on this blog in “What Happens Next – Peer Review“), but in this case the initial referee report came back after 2 days, and the paper was accepted only 2 weeks after the first submission so I never got time to post to the arxiv or write a blog post about it before it was accepted! This was certainly the smoothest and fastest referee process I’ve been through.
Here’s the title page.
So what was new about this paper was that we combined information on the morphologies (whether or not the spiral galaxies had bars) with information on the amount of atomic hydrogen gas the galaxies contained and and our main result was that galaxies with more atomic gas in them, are less likely to have a bar.
But I want to back up a bit first and tell you about where we get this information on the atomic gas content, and why it might be interesting. As you might guess from the title of the paper it’s from something called the ALFALFA survey (and the new names in the author list for a Galaxy Zoo paper – Martha Haynes and Riccardo Giovanelli – are from Cornell University who are running this survey). Atomic hydrogen emits radio waves at a frequency of 1.4 GHz (or 21cm). This is detectable by a classic radio telescope (in what we call the “L”-band which makes up the second L of ALFALFA). In the case of ALFALFA, we use the Arecibo radio telescope (two of the “A”s in the acronym stand for Arecibo, the third is for array), which is the worlds biggest single dish radio telescope deep in the jungle of Puerto Rico.
ALFALFA is a massive survey which will map the location of atomic hydrogen over basically the whole sky visible to the Arecibo radio telescope. What’s neat about a survey for something which emits as a specific frequency is that you actually get a 3D map of where the hydrogen is – both redshift and sky position! Anyway, we made use of about 40% of the survey which is already complete, and which covers about 25% of the area of the sky in which the Galaxy Zoo galaxies are found (the Sloan Digital Sky Survey Legacy Area). Adding some cuts on how face-on the galaxies are so that the bars can be identified, and to make sure the sample contains the same size galaxies right through it’s volume we ended up with 2090 galaxies with both atomic hydrogen detections and bar classifications from you guys. This is an order of magnitude larger than any similar sample! So thanks.
Atomic hydrogen is the basic building block of galaxies (after dark matter). It represents the fuel for future star formation in a galaxy – a galaxy with a lot of atomic hydrogen could in principle make a lot of new stars. Many spiral galaxies have a lot of atomic hydrogen (with perhaps as much as 10 times as much mass in hydrogen as in stars!), while a typical elliptical galaxy has very little atomic gas, and so cannot form lots of new stars.
So our observation that bars are more likely to be found in spiral galaxies with less atomic gas supports our earlier ideas about bars possibly “killing” spirals (ie. helping to stop them form stars).
Of course it’s never quite that straightforward with galaxies. To start with correlation is not the same as causation, and to that we add that lots of things are correlated. We show some of that in the figure above. Bars are more likely in redder spirals which have more stars (“log Mstar” represents stellar mass in units relative to the mass of our Sun) and which also have less atomic gas. So the skeptical astronomer could say this has nothing to do with the gas content at all, just that the types/sizes of galaxies with less bars have more gas. To test that idea we measured the typical gas content of a spiral galaxy with a given number of stars, and from that we calculated how “deficient” or rich in atomic hydrogen any given galaxy was. Then we plotted the bar fraction against that. The convention in astronomy is to call how much less atomic hydrogen a galaxy has than normal it’s “HI deficiency” which gets bigger the less atomic hydrogen there is (from the people who brought you the magnitude scale!).
Anyway you can see we still see a clear trend, which demonstrates that it’s likely to be the atomic gas driving the correlation. Where a galaxy is richer in atomic hydrogen than normal it’s less likely to host a bar, and vice versa. Very atomic hydrogen rich galaxies which are massive and have bars are really quite rare!
Here are some examples of low and high mass galaxies which are gas rich or poor and with or without bars.
I made images of the whole sample we use available here.
At the end of the paper we put forward three possible explanations for the correlation, all of which fit in with the observations we presented. It’s possible that the bars are causing the atomic gas in galaxies to be used up faster – “killing” the galaxy. The bar does this by driving the gas to the centre of the galaxy where it gets denser, turns into molecular hydrogen and from that stars (but only in the centre). It’s also possible (based on dynamical studies of galaxies) that gas slows down the formation of a bar in a spiral galaxy, and/or destroys the bar. Finally it’s possible that as a galaxy interacts with its neighbours, a bar gets triggered and its gas gets stripped (ie. the correlation between the two is caused by an external process). We’ll need to do more work to figure out which of these (or which combination of them) is the most important.
To my mind the most interesting result was a hint that if a gas rich galaxy does (rarely) host a bar, it’s optically redder than similar galaxies without bars. It’s just possible that bars hold back infall of gas from the outer regions of a spiral galaxy and slow down star formation over all in that galaxy. That idea needs testing, but if it’s true it’s saying that an internal structure like a bar plays an important role in the global star formation history of a galaxy.
Anyway thanks again for the classifications!