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Galaxy Zoo Highlights from 2015

Following on from the excellent summary of the hi-lights in 2015 for the Radio Galaxy Zoo project, here’s a similar post about results from Galaxy Zoo.

This year we collected 4,755,448 classifications on 209,291 different images of galaxies. You continue to amaze us with your collective efforts. Thank you so much for each and everyone of of these classifications.

The year started with Galaxy Zoo scientists at Mauna Kea observing galaxies, and reported in this wonderful series of blog posts by (former) Zooniverse developer Ed Paget.

Ed, Chris, Sandor, and Becky in front of the telescope

Ed, Chris, Sandor, and Becky on Mauna Kea.

We celebrated 8 years of Galaxy Zoo back in July, with this blog series of all things 8-like about Galaxy Zoo.

An 8 for our 8th birthday!

An 8 for our 8th birthday!

Back in May we finished collecting classifications on the last of our Hubble Space Telescope images. At the AAS in Florida this week, Kyle Willett and Brooke Simmons presented posters on the planned data releases for the classifications.

We both launched and finished classifying the first set of images of simulated galaxies from the Illustris Simulation (read more here: New Images for Galaxy Zoo: Illustris and here: Finished with First Set of Illustris Images). We also launched our first set of images from the DECaLS survey, which is using the Dark Energy Camera (New Images for Galaxy Zoo: DECaLS)

We also launched a new Galaxy Zoo side project – Galaxy Zoo Bars (one of the first projects built on the new Zooniverse Project Builder software), measuring bar lengths of galaxies in the distant Universe. The entire set were measured in less than a year, so thank you to any of you who contributed to that, and if you missed it don’t worry, we have plans for more special projects this year.

We launched a new web interface to explore the Galaxy Zoo classifications.

Screenshot of the Visualisation Tool

Screenshot of the Visualisation Tool

Our contributions to the peer reviewed astronomical literature continue. Papers number 45-48 from the team were officially published in 2015. They were:
– Galaxy Zoo: the effect of bar-driven fueling on the presence of an active galactic nucleus in disc galaxies, Galloway+ 2015.
– Galaxy Zoo: Evidence for Diverse Star Formation Histories through the Green Valley, Smethurst+ 2015.
– Galaxy Zoo: the dependence of the star formation-stellar mass relation on spiral disc morphology, Willett+ 2015.

You can access all 48 team papers using your classifications at the Zooniverse Publication Page. Remember that all Zooniverse papers published in the Monthly Notices of the Royal Astronomical Society – which includes most of the Galaxy Zoo papers – are available open access to any reader, and if we happen to publish elsewhere we always make the post-acceptance version available on the

All of our papers include a version of this acknowledgement to our classifiers: “The data in this paper are the result of the efforts of the Galaxy Zoo volunteers, without whom none of this work would be possible. Their efforts are individually acknowledged at” We all hope you all know how grateful we are for each and every one of your classifications.

This year saw publication of the first paper on Hubble observations of Voorwerpje systems accompanied by an HST press release.

Montage of Hubble images of Voorwerpjes

Montage of Hubble images of Voorwerpjes

One of those papers from (mostly) outside the GZ team discussed a rare examples of double radio sources from spiral hosts, something Radio Galaxy Zoo will find many more of: “J1649+2635: a grand-design spiral with a large double-lobed radio source”, Mao et al. 2015.

Another exciting thing about this year has been the number of papers from non team members using the classifications which are now public (see To date almost 300 astronomical papers have been written which cite the original description of Galaxy Zoo (Lintott et al. 2008) and the two data release papers so far (Lintott et al. 2011 for GZ1 and Willett et al. 2013 for GZ2) have 164 and 34 citations respectively. The number of papers in the Astrophysics Data System which contain the words “Galaxy Zoo” (which you can search in ADS Labs) is an astonishing 700 (409 for refereed publications).

These are just some of the high-lights I’ve pulled together. If I’ve missed your favourite feel free to add it in the comments below. All in all it’s been a great year. Here’s to an equally good 2016!

Radio Galaxy Zoo: conferencing in Italy (Day 4)

Final day of the conference. Still pro-pasta, but may have hit my personal limit on gelato and/or red wine.

We had only a half day for the final day of the Bologna workshop on extragalactic radio surveys. After a tasty conference dinner at the historic Palazzo Re Enzo, we devoted the morning to AGN physics. This is the counterpart to the sessions we had on star formation in galaxies on Monday; almost all continuum radio emission that we detect in individual galaxies is either due to a thermal component from star formation or synchrotron and free-free emission that’s produced in some way by the central supermassive black hole, known as an active galactic nucleus (AGN).

Leith Godfrey (ASTRON) gave a really neat talk on “remnant” radio galaxies, which refers to galaxies that still have active radio emission from the heated plasma in distant lobes, but for which we don’t see the jet because the black has shut down its active phase some time ago (in our observed frame). We can identify these remnants both via morphology (big radio lobes with no jet or core) and through their radio spectra – energy losses from the particles cause a characteristic curved shape which you see if you plot frequency vs. radio flux density. Leith has been doing statistical studies of remnants, finding that less than 1% of bright radio sources are in a dying phase. This is interesting since the number of sources we observe constrains the timescales on which radio galaxies die. It also points toward certain physical properties – there are strong adiabatic losses after the jet switches off, but the lobes seem to remain very high-pressured compared to their environments right up until the end of their lives.

Marisa Brienza (ASTRON) gave the talk immediately following on a new remnant, named BLOB1, that she and her team just detected with LOFAR. LOFAR, a low-frequency array located in the Netherlands and other European countries, is just ramping up full operations, but will be a hugely powerful instrument for increasing the size of these samples over the next decade.

Example of a new radio remnant, named BLOB1, detected with the LOFAR telescope at 137 MHz. From Brienza et al. (2015).

Example of a new radio remnant, named BLOB1, detected with the LOFAR telescope at 137 MHz. From Brienza et al. (2015).

After several more talks, Mike Garrett (ASTRON/Leiden) gave some closing remarks on the conference, including some summaries of what had been discussed and where he thought the future of extragalactic radio sources was going. I was really stoked that RGZ was one of the first results that he specifically cited as being important; Mike mentioned both citizen science and new distributed software routines as being crucial for dealing with the potentially billions of new celestial sources that telescopes will detect in the next decade. The role of citizen scientists in radio astronomy may change – I’ve talked to scientists at this conference about someday doing tasks other than morphology identification, for example – and we’ll definitely have to increase the interplay between the citizen science datasets and machine learning algorithms to maximize our survey results. But, as Mike said on his final slide, the present state of radio surveys is very bright indeed, and we have every reason to think that the best is yet to come.

It’s been a fantastic workshop, and I’m grateful to the conference organizers for accepting my talk and offering financial assistance, the American Astronomical Society for covering my travel costs, and the NSF for partially supporting my work on RGZ at the University of Minnesota. Looking forward to a day or so of sightseeing this weekend, but I’m inspired to get back to work next week and continue being part of such a vibrant scientific community.

Radio Galaxy Zoo: conferencing in Italy (Day 2)

Yesterday was the second day of the workshop in Bologna on extragalactic radio surveys, where I’m attending and gave a talk on Radio Galaxy Zoo. We had three major blocks of talks yesterday: one on galaxy evolution, one on cosmology, and the final one on exploiting synergies between radio telescopes.

Galaxy evolution is a big topic, and one that drives a lot of the science behind both Galaxy Zoo and Radio Galaxy Zoo. Several of the talks really highlighted the importance of having multiwavelength data, in addition to what we learn from the radio (this is one of our main goals identifying the optical counterpart in our project). A couple of the most famous deep fields which have been studied in radio were discussed, including the VLA-COSMOS study, GOODS-North, and the Hubble Deep Field.

Poster showing the field and some zoomed-in sources from the VLA-COSMOS project.

Poster showing the entire field and some zoomed-in radio sources from the VLA-COSMOS project.

Data from new telescopes, like the low-frequency LOFAR, are yielding some exciting results. One interesting result was the fact that lower-mass galaxies more commonly hosted active galactic nuclei (AGN) seen in the radio in the early Universe, at redshifts of 1 < z < 2. Galaxies with higher masses, however, had about the same fraction of radio-loud AGN at this time. It’s interpreted as being the result of more galaxies accreting matter in what’s known as “cold” or “radiative mode”, thanks to the increase in the supply of cold gas available to galaxies at earlier times (Wendy Williams, U. Hertfordshire).

Cosmology is probably being a bit underrepresented at this conference, since we only had three talks in this session. A lot of the focus was on how detecting very large samples of galaxies (both in radio continuum, like the FIRST and ATLAS surveys in RGZ data, as well as looking at spectral lines like the 21-cm hydrogen line) constrain our cosmological models. Different parameters for both dark energy and dark matter make specific predictions for how populations of galaxies evolve, including their numbers, distributions of sizes and masses, and geometrical arrangement. You can also test cosmology through gravitational lensing at radio wavelengths. It’s promising, but very challenging compared to how it’s done in optical wavelengths due to difficulties in fitting shapes in the raw visibility data (Prina Patel, U. Western Cape).

One of the talks I found really interesting (and new to me) was by Emma Storm, from GRAPPA/U. Amsterdam. She gave a great presentation on how radio observations explore the nature of dark matter. While we don’t know a huge amount about the nature of the dark matter particle, one prominent theory predicts that when they collide, the particles annihilate and produce other particles in the Standard Model that we can directly observe (like pions and gamma rays). If that’s so, then these annihilations would also produce charged particles like electrons and positrons; when those particles are accelerated in magnetic fields, they emit synchrotron radiation, which we detect in the radio. So by looking for radio emission in objects that we expect to be dominated by dark matter (like galaxy clusters), scientists can constrain the parameters of their dark matter models, particularly things like the cross-section. The signal this would produce is expected to be diffuse and weak, though; Emma’s work doesn’t detect radio emission in many clusters, but places important upper limits on the amount that could be there within the detection limits.

Limits on dark matter annihilation cross sections as a function of the particle's mass. Each curve is an upper limit based on radio observations of a galaxy cluster (from Storm et al. 2013).

Limits on dark matter annihilation cross sections as a function of the particle’s mass. Each curve is an upper limit based on radio observations of a galaxy cluster (from Storm et al. 2013).

The last session of the day dealt with synergy and commensality. I normally hate things that sound like business-speak buzzwords, but in this case it is really important – we have a number of new radio telescopes coming online now or in the next several years, such as ALMA in Chile, LOFAR in Europe, and the Square Kilometer Array in Australia and South Africa. It’s quite important to plan the capabilities and designs of each so that we don’t repeat work unnecessarily, maximize the scientific output, and try to make the data and results available to as many people as possible.

Halfway over already! You can also follow what some of the other people have been discussing at the conference at the hashtag #radsurveys15.

Rocks… In… Spaaaaaace

You know those odd features in some SDSS images that look like intergalactic traffic lights?

examples of asteroids in SDSS images

Stop! Asteroid Time.

They aren’t intergalactic at all: they’re asteroids on the move in our own solar system. They move slowly compared to satellite trails (which look more like #spacelasers), but they often move quickly enough that they’ve shifted noticeably between the red, green, and blue exposures that make up the images in SDSS/Galaxy Zoo. When the images from each filter are aligned and combined, the moving asteroid dots its way colorfully across part of the image.

These objects are a source of intense study for some astronomers and planetary scientists, and the SDSS Moving Object Catalog gives the properties of over 100,000 of them. Planetary astronomer Alex Parker, who studies asteroids, has made a video showing their orbits.

I find their orbits mesmerizing, and there’s quite a lot of science in there too, with the relative sizes illustrated by the point sizes, and colors representing different asteroid compositions and families. There’s more information at the Vimeo page (and thanks to Amanda Bauer for posting the video on her awesome blog).

One of the most common questions we receive about asteroids from Galaxy Zoo volunteers is whether there will ever be a citizen science project to find them. So far, as the catalog linked above shows, the answer has been that computers are pretty good at finding asteroids, so there hasn’t been quite the need for your clicks… yet. There are some asteroids that are a little more difficult to spot, and those we’d really like to spot are quite rare, so stay tuned for a different answer to the question in the future. And in the meantime, enjoy the very cool show provided by all those little traffic lights traversing their way around our solar system.

Using Space Warps to Discover and Weigh Galaxies

A mosaic of the Space Warps spotter's guide.

John Wheeler once summarized General Relativity as “Matter tells space how to curve, and space tells matter how to move.” While that is a handy description, and while there have been many textbooks written, lectures given and websites constructed to explain this, the quote itself doesn’t address what happens to the light streaming through the universe as it encounters the warped space curved by matter.

A useful visualization.The simple answer is: it curves too, and Einstein’s equations provide predictions for exactly how it works. In fact, observations of the bending of starlight around the Sun were one of the first implemented tests of General Relativity, and it passed with flying colors. On the scale of the Universe, the Sun isn’t that massive, but it’s massive enough to bend the light just a little, and by exactly the amount the equations predicted.

Those equations say that more matter in the same place is more likely to produce a strong lens effect, distorting and magnifying a background source. So what happens when you have a *lot* of matter, say, in a big galaxy or a cluster of galaxies?

a) an Einstein cross (credit: NASA/ESA); b) an example from the Space Warps dataset; c) a known lens in CANDELS that Galaxy Zoo users spotted.

From left to right: a) an Einstein cross (credit: NASA/ESA); b) an example from the Space Warps dataset; c) a known lens in CANDELS that Galaxy Zoo users spotted.

Some pretty impressive configurations, which are rare but which humans are best at finding — hence Space Warps, the Zooniverse’s newest project and our astronomical project sibling. Co-lens-experts Phil Marshall and Aprajita Verma joined us during this hangout to describe how they use gravitational lenses to weigh galaxies. In particular, they can tell the difference between Dark Matter and “matter that’s dark” — the former being the exotic particles that are very different from stars and gas and planets and people, and the latter being normal matter that isn’t bright, such as brown dwarf “stars” that never actually ignited.

Note: Google+ was feeling a bit out of sorts, so the first minute or so of the broadcast was cut off, during which time Bill Keel showed us the first known image of a gravitational lens, from 1903. We went on to talk about all of the above, and more besides, including the importance of simulated lenses, why the images Space Warps uses are specially tuned to help us find lenses, and how the science team (which includes citizen scientists from Galaxy Zoo!) plan to turn our clicks into discoveries.

(or download the podcast mp3 here)

Notice my swapping of pronouns to “we” — I’m not on the Space Warps science team, but I’ve done nearly 100 classifications now myself! I can’t wait to see the results start to come in from this project.


Meet our new sibling project: Space Warps, where you can help find rare and spectacular gravitational lenses. Many citizen scientists took part in building this project, and it’s already proven very popular just in its first day! But the science team still needs your help.

Project leads Phil Marshall and Aprajita Verma will be joining us tomorrow on our live Hangout to talk in more detail about gravitational lenses and what they want to achieve with the Space Warps project. Please join us, and have a look at in the meantime!

Space Warps

Hooray! Space Warps is live, and the spotters are turning up in numbers. Check out the site at – there’s a few little bugs that Anu, Surhud  and the dev team are ironing out, but basically it’s looking pretty good! Thanks very much to everyone who’s helped out in the last few months – your feedback has been very useful indeed in designing a really nice, easy to use website that hopefully will enable many new discoveries. And to all of you who are new to Space Warps – welcome!

If you’re feeling really keen, why don’t you come and hang out in the discussion forum at We’re starting to tag images to help organise them, and the more interesting conversations we have there, the more useful it will be for the newer volunteers. And of course, you can vote on the candidates spotted by other people…

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Update: Peas are a Mess!

Hi all,

About two weeks ago, a group of astronomers led by Ricardo Amorin posted a new paper on the peas to astro-ph. They used the giant Gran Telescopio Canarias (GranTeCan or GTC) to take really high-quality spectra of some of the peas. What they find is amazing, but not entirely unexpected. We already knew from Carie Cardamone’s paper that the peas are extremely intense starbursts, that is, they form more stars relative to their mass than any other kind of galaxy in the nearby universe. Now, Amorin et al. show that they are a real mess:

A GTC spectrum of a pea from Amorin et al. (arXiv:1207.0509) zoomed in on the Halpha emission line. The Halpha line comes from gas ionised by the powerful radiation from very young stars. The high-resolution spectrum clearly shows that the single Halpha line is actually due to several different components.

The Halpha emission lines of the peas, once studies at high resolution and signal-to-noise, show that they are actually composed of several different lines. The Halpha line is generated by the powerful ionising radiation from young, massive stars hitting the surrounding gas. The multiple lines mean that the peas have several chunks of gas and stars moving at large velocities relative to each other.

This makes sense from what we know from the few peas that have nice Hubble images.

Hubble image of a pea galaxy (Amorin et al. (arXiv:1207.0509)) showing that it actually consists of multiple components; it’s a real mess!

The multiple Halpha lines are almost certainly from these multiple components and suggest that the gas (and stars) in the peas are effectively a turbulent mess. Some of those clumps whiz past each other at over 500 km/sec. Yes, km/sec. Some of the Halpha lines are also broadened suggesting that really energetic events are occurring inside those star-forming clumps, such as multiple supernova remnants or powerful Wolf-Rayet stars.

You can get the full paper as PDF or other formats here on arxiv.

Another Galactic Twin

It seems that finding our Milky Way’s twin has become a bit of an industry these days.

NASA/ESA have got in on the act today, releasing a press release about their favourite twin of the Milky Way, NGC 1073 and the below absolutely gorgeous Hubble Space Telescope image they’ve taken of it: Classic Portrait of a Barred Spiral.

Hubble image of NGC 1073: another possible Milky Way twin. Credit: NASA/ESA

And it does look a lot like what we think the Milky Way looks like – except perhaps for having slightly less tightly wound arms.

An artists impression of our Galaxy. Credit: NASA/JPL-Caltech/Robert Hurt (SSC-Caltech)

You might remember, back in September I posted a guest blog by Portsmouth A-level student, Tim Buckman, who spent his summer with us at Portsmouth finding the Galaxy Zoo galaxy we thought was most like the Milky Way: “A Summer Spent Finding our Galactic Twin “. His project in turn was inspired in part by an ESO press release about spiral galaxy NGC 6744 which was claimed to be a twin for the Milky Way (A Postcard from Extragalactic Space).

NGC 6744 – the previously proposed clone. Credit: ESO.

NGC 6744 is quite a lot more massive than our Milky Way however, so I thought we could do better with SDSS and Galaxy Zoo. Tim applied some mass cuts, then used your classifications to find a face-on 4 armed spiral which he thought matched the maps of the Milky Way (which has a bar, but perhaps a rather weak one which might not be obvious in the types of images we used for Galaxy Zoo).

Tim’s Milky Way clone based on your Galaxy Zoo classifications

I was interested to notice last month that one of the most popular press releases from the AAS this year was about finding a sample of galaxies like our Milky Way and using them to estimate what the colour of the Milky Way would be (BBC Article: Milky Way’s True Colours; AAS abstract it’s based on: What is the Color of the Milky Way?), especially interesting to me as it turns out the Milky Way might be on it’s way to being a red spiral (as has been suggested before, e.g. by Mutch, Croton, Poole (2011), or see New Scientist article about this paper: Milky Way Faces Midlife Crisis), which you might remember I’ve done a bit of work on! ;)

Today’s NASA/ESA release has already been picked up by the BBC: Hubble Snaps Stunning Barred Spiral Galaxy Image (they’d already used “Striking View of Milky Way Twin” on NGC 6744), and covers it as Hubble Telescope Spies Milky Way Galaxy Twin.

For Galaxy Zoo people, it should be of interest that the press release also says:

Some astronomers have suggested that the formation of a central bar-like structure might signal a spiral galaxy’s passage from intense star-formation into adulthood, as the bars turn up more often in galaxies full of older, red stars than younger, blue stars.

Well those astronomers are us – Galaxy Zoo results on bars, based on your classifications have shown that bars are more common in redder discs. Thanks again for the classifications which allowed us to do that work.

GZ1 used for the fractions of early-types in clusters

We’re happy to report that we have once again used your (now public) GZ1 classifications to find an interesting result.

We use the classifications in a study we just submitted to MNRAS (or see the arXiv entry for a copy) looking at the observed fractions of early-type galaxies (and spiral galaxies), in groups and clusters of galaxies.

Recent work (De Lucia et al. (2011), which posted to the arxiv in September), used sophisticated semi
analytic models to determine the properties of galaxies found in massive
clusters in the Millennium Simulation. They identified elliptical galaxies
(or more accurately early-type galaxies) in the simulation, and found that the fraction these
galaxies, remained constant with cluster halo mass, over the range 10^14 to
10^14.8 solar masses. They compared their results with previous
observational studies which each contained less than 100 clusters.

With GZ1 we realised we could put together a much larger sample. We
used galaxies with GZ1 classifications, cross matched with cluster and
group catalogues, to compare the above results with almost 10 thousand
clusters. We found that the fraction of early-type galaxies is indeed
constant with cluster mass (see the included figure), and over a much larger range of 10^13 to 10^15
solar masses (with covers small groups of galaxies to rich clusters), than previously studied. We also found the well known result (to astronomers) that outside of groups and clusters, the fraction of early-type galaxies is
lower than inside of groups and clusters.

Plot showing the fraction of early-type galaxies (red lines) as a function of halo mass. We used two different halo mass catalogues, and the agreement between them is excellent. We also examine the fraction of spiral galaxies with halo mass (blue lines)

This work suggests that galaxies change from spiral to early-type when individual
galaxies join together to form small groups of galaxies, but that going from groups to rich clusters does not significantly change the morphologies of galaxies.

Without the GZ1 results at our finger-tips, this work, which was devised,
implemented, and written up in less than 2 months, would have taken much
longer to complete.

Thanks again for making the Zoo such a wealth of information,

Ben Hoyle (on behalf of Karen Masters, Bob Nichol, Steven Bamford, and Raul Jimenez)

Galaxy Zoo at the Durham Galaxy Evolution Conference

I think I won’t get in too much trouble if I say that in my opinion the event of summer 2011 for extragalactic astronomers was a massive international conference which took place in Durham, July 18th-22nd Galaxy Formation. You’ll be happy to know that Galaxy Zoo scientists were represented, with myself, Kevin, Ramin Skibba (who wrote one of the first Galaxy Zoo papers back in 2009), Vardha Bennert (who has done some HST followup for us, she’s profiled in the “She’s an Astronomer” series from 2009) and Boris Haussleur (see his blog posts about Hubble Zoo) all present.


400 Extragalactic Astronomers in Durham. That's me circled in orange, Ramin in pink and Boris in blue. Kevin and Vardha might be there somewhere but I've yet to spot them!

The moment of the conference for me was the first mention of Galaxy Zoo in the plenary talks – my work on the Galaxy Zoo 2 bars (see many blog posts!) was mentioned in a talk on the influence of internal evolution on galaxies (something we call “secular evolution” which bascially means the slow transformation of galaxies by material being moved around by the bars and/or spirals) which was given by Francoise Combes. I got so excited I took a picture of her slide, which you can also see in her talk pdf.

Francoise Combes talking about Galaxy Zoo results on bars

And here’s the slide so you can actually read it.

Francoise Combes's slide so you can actually read it


The red spirals also got a mention in a talk on gas in galaxies (by Luca Cortese – pdf unfortunately not uploaded at time of writing) where it was shown that at least half of them have very low NUV (near ultra-violet) emission for spiral galaxies. This is expected if as we think they are truly passive spirals with very little current star formation (which created NUV light).

Many of the slides for the talks, as well as the posters are available online (including mine, which for once wasn’t about my Galaxy Zoo work, but work with the new SDSS survey which is imaging 1.5 million galaxies at intermediate redshifts – unfortunately as fuzzy blobs, so no new objects for the Zoo from them!). There is also a plan to make video of the talks available. I’ll post an update about that when it happens.

Unfortunately I had to leave before Kevin and Vardha gave their talks on the Friday. Neither of them have posted their pdfs yet either. :(

Boris and Ramin had posters – also like me on their non-Galaxy Zoo work (Boris: Measuring the physical properties of galaxy components in modern multi-wavelength surveys, Ramin: Are Brightest Halo Galaxies Central Galaxies?).

It was a great conference and I had a wonderful time in Durham.


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