New images for Galaxy Zoo from GAMA-KiDS!

Hello Zooniverse citizen scientists! We’re extremely excited to announce the release of a new dataset on Galaxy Zoo. For the past several months we’ve been working with scientific collaborators from the Galaxy And Mass Assembly Survey and the VST Kilo-Degree Survey. This blog post will give you a few details about these surveys, the new data set, and what we hope to achieve with Galaxy Zoo classifications.

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The Galaxy And Mass Assembly (GAMA) Survey is an international project to exploit the latest generation of ground and space-based survey facilities. Its aim is to study cosmology and galaxy formation and evolution from scales of thousands up to millions of light years across. The science goals include furthering our understanding of how the mass of stars within galaxies builds up over time, how and when do galaxies form their stars, how are those previous questions related to a galaxy’s environment, and at what epoch did star-formation and mass-build-up dominate? Visual morphologies from Galaxy Zoo will allow us to explore if, how, when, and where galaxies transition from one type into another, what impact this has on the formation of stars, and to look for new types of unique and interesting galaxies.

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The observations are from the Kilo-Degree Survey (KiDS) on the 2.6m VLT Survey Telescope (VST) located at the ESO Paranal Observatory in Chile. KiDS is a large optical imaging survey in the Southern sky designed to tackle some of the most fundamental questions of cosmology and galaxy formation of today. At the heart of KiDS lies the 300 million pixel camera OmegaCAM. Its instantaneous field of view is a full square degree and it was designed to provide extremely accurate measurements of the intrinsic shapes of faint, small galaxies.

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The 2.6m VLT Survey Telescope (VST), located at the ESO Paranal Observatory in Chile, is carrying out observations for the Kilo-Degree Survey (KiDS).

The scientific teams behind GAMA and KiDS have been working closely to put together this new set of images. Galaxies have been selected from a catalogue produced by the GAMA Survey and images have been constructed based on observations from KiDS. While some of these galaxies have already been looked at by Galaxy Zoo citizen scientists before using their Sloan Digital Sky Survey (SDSS) images, the improvement in the resolution and depth of KiDS images over SDSS imaging is remarkable. With this new GAMA-KiDS data set we hope to be able to study the very faintest structures within galaxies, as well as more accurately classify features which may have been missed before. Take a look at the image below to see how much clearer the new images are!

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This image compares SDSS images (on the left) with those from GAMA-KiDS (right) for three example galaxies: G107214, G298570 and G551505.  Our new images reveal a lot more detail!

We’re really excited about getting classifications for these new images, and we hope you are too! We’re more than happy to talk about any interesting galaxies you may come across and to answer any questions you may have. Until then, enjoy, and thank you for your help!

– by Dr Lee Kelvin, on behalf of the GAMA and KiDS teams

RGZ Team Spotlight: James Ansell

Hi everyone! I’m James and I’ve joined the RGZ team as a Communication/Engagement intern. I’m a PhD Candidate at the Australian National Centre for the Public Awareness of Science (CPAS) which is part of the Australian National University (ANU). I’m also a Sessional Academic (read: Tutor and marker) for a couple undergraduate courses covering things from ‘the Public Awareness of Science’ to ‘Science, Risk and Ethics’. And to pay the bills I work for the ANU in an administration role at (essentially) the Business School as well as a few other odd jobs.

But I am at heart an errant astronomer – having double majored in Astronomy/Astrophysics and Science Communications at the ANU for my B.Sci, graduating with Honours in 2015. I grew up in Alice Springs in the middle of Australia and had a purely spectacular night sky to look at. Something I only appreciated when I lived Brazil after graduating high school.

As part of my undergraduate studies I did dabbled a bit in some astronomy research. Firstly I did a project with Dr Charley Lineweaver (if you don’t know Charley, you should!) looking at the (surprisingly fuzzy) distinctions we make between objects in space e.g. planet, dwarf-planet, asteroid, moon. Let’s just say the project didn’t go where I thought it would.

Secondly, as part of an Astronomy Winter School I did research looking for ‘intergalactic stellar bridges’. Essentially chains of stars going from one galaxy to another which may have played a role in stellar formation in galaxies. I think. It was several years ago and the weather was against us when we went to do observations, so it didn’t go anywhere and my memory is pretty fuzzy on the details.

Outside of academia, I was involved in the ANU Black Hole Society (the Astronomy Club), the ANU Physics Society and the Science Communication Society. Also I absolutely love the TV series Cosmos, both the Carl Sagan original which I saw as a teenager and then the Neil deGrasse Tyson remake from a few years ago.

Since my astronomy research didn’t turn out particularly well, I ended up going down the science communication route. I’ve since done research looking into the effects of fictional doctors on young people’s perceptions of healthcare, factors affecting the uptake of vaccinations in Australia and the relationship between people’s perceptions of ‘Superfoods’ and their health behaviours. But I do miss the Astronomy and Astrophysics side of things so I’m super excited to be able to combine my two interests as part of the Radio Galaxy Zoo team.

(Also for some random fun facts about me – I used to host a music program on a Canberra community radio station, I founded the Canberra pop-culture festival ‘GAMMA.CON’ which is basically our local Comic-Con and I fly Hot Air Balloons with the ACT branch of the Scout Association.)

I’ll be hanging around in the forums under the name ‘JRAnsell’ and am keen to hear from you – if you’ve got questions about RGZ specifically or astronomy more broadly let me know! You can also hit me up on Twitter @radiogalaxyzoo or at radiogalaxyzoo@gmail.com.

Galaxy Zoo relatives at AAS meeting – Hubble does overlapping galaxies

Among the results being presented at this week’s meeting of the American Astronomical Society in Texas (near Dallas) is this poster presentation on the status of the STARSMOG project. This program, a “snapshot” survey using the Hubble Space Telescope, selected targets from a list of overlapping galaxy pairs with spiral members and very different redshifts, so they are not interacting with each there and likely to be more symmetric. The source list includes pairs from Galaxy Zoo (about 60%) and the GAMA (Galaxy And Mass Assembly) survey. These data will allow very extensive analysis; this presentation reads more like a movie trailer in comparison, highlighting only a few results (primarily from the master’s thesis work by Sarah Bradford).

Among the highlights are:

Sharp outer edges to the location of dust lanes in spiral disks.

Distinct dust lanes disappearing for galaxies “late” in the Hubble sequence (Scd-Sd-Sdm-Sm, for those keeping track), maybe happening earlier in the sequence when there is a bar.

The dust web – in the outer disks of some spirals, we see not only dust lanes following the spiral pattern, but additional lanes cutting almost perpendicular to them. This is not completely new, but we can measure the dust more accurately with backlighting where the galaxy’s own light does not dilute its effects.

A first look at the fraction of area in the backlit regions with various levels of transmitted light. This goes beyond  our earlier arm/interam distinction to provide a more rigorous description of the dust distributions.

Bars and rings sweeping adjacent disk regions nearly free of dust (didn’t have room for a separate image on that, although the whole sample is shown in tiny versions across the bottom)

Here is a PNG of the poster. It doesn’t do the images justice, but the text is (just) legible.

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The shoulder of Giants

To stand on the shoulder of giants, we first have to find them.   In Radio Galaxy Zoo, we are of course referring to the hunt for Giant Radio Galaxies.  These Giants can provide us with valuable insights into the environment in which they reside as well as the evolution of radio AGN.   In this post, I will present a summary of the highlights that Heinz A. has reported on RGZ’s search for Giants in 2016.

As of late September 2016, RGZ citizen scientists have uncovered at least 313 Giant candidates which are larger than 1 Mpc in projected size.  Of the 313, 201 are new discoveries made by RGZ!  Of course, follow-up observations and further verification checks are required.  However, this is still fantastic job and no small feat by the team.  A big thank you goes to RG Zooite Antikodon & Dolorous_Edd for paving the way again and discovering ~78% of these Giant candidates.  To put things into perspective, if one wanted to extract a list of Giants from the NASA Extragalactic Database (NED; a well-known archive used by professional astronomers) one would find only 55 objects tagged as Giant Radio Galaxies!  This is partly due to the fact that in publications such objects are not always explicitly labelled as such.  Here is Heinz’s table comparing the properties of the published Giants versus the newly-discovered RGZ candidates :

Property Published New RGZ candidates
Number 231 201
Median redshift 0.26 0.57
Median linear size (Mpc) 1.3 1.18
Number (size> 2 Mpc) 29 6

It is clear that RGZ is leading the pack in collating and cataloguing these unusual radio galaxies.  With our upcoming observing run using the Gemini-North 8-meter telescope in Hawaii, we will be following up several of these candidates.

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FIRST image of an example of one of the largest known Giant Radio Galaxy J1102+1345

My warmest congratulations again to the Giants Team! Keep up the fantastic work. After all, we still have a third of RGZ to complete and I am sure more Giant candidates will be discovered in 2017.  More information can be found at the Giant team’s RadioTalk Discussion thread.

 

 

 

There be S-DRAGNs!

This end-of-year post is written by Jean Tate, an RGZ citizen scientist and associate science team member who is providing us with the 2016 update on her team’s hunt for more Spiral Double Radio-lobe AGNs — SDRAGNs.   My warmest congratulations again to the SDRAGN Team!  I will be sure to look out for more SDRAGN news in 2017.  More information can be found at the SDRAGN team’s RadioTalk Discussion thread.

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A small band of intrepid scientists – citizen and regular – have been hunting SDRAGNs for quite some time now.  These strange beasts were mythical, until 1998 when one was spotted above the Antipodes (it goes by the highly memorable name of 0313-192 … not).  Since then a dozen or so other Spiral galaxies which host Double Radio lobes (and which have Active Galactic Nuclei; SDRAGN, get it?) have been bagged. With thousands of sharp-eyed citizen scientists, RGZ is an ideal place to look for more.

It has been relatively easy to find  SDRAGN candidates – two known ones were flagged by RGZooites, who were quite unaware of their status – but rather more challenging to turn candidates into certainties; for example, chance alignments can appear very convincing. Anyway, from ~a thousand “possibles”, the SDRAGN team picked ten really promising ones, and is now writing up a paper on them (actually, while doing some final checks, two of the ten turned out to be imposters; never mind, there are dozens more good candidates for a second paper).  Curiously, one of the most difficult questions was (and still is) “is this really a spiral?”

jtsdragnThe figure above shows J1649+26, an SDRAGN published by Minnie M. in 2015 (URL Link to her paper).  The red contours represent the double radio lobes emanating from the supermassive black hole of this galaxy.

You can see some of the SDRAGN candidates in RGZ Talk, by searching for the hashtag #SDRAGN (some will also have the hashtag #spiral; many candidates do not have either hashtag). If you find an SDRAGN candidate, please include the #SDRAGN hashtag in your comment.

New Hubble+Gemini results – history of fading AGN

Just in time to brighten our holiday season, we got word that the Astrophysical Journal has accepted out next paper on the Voorwerpje clouds around fading active galactic nuclei (AGN). The full paper is now linked on the arXiv preprint server.

This time, we concentrated on the clouds and what they can tell us about the history of these AGN. To do this, we worked pixel-by-pixel with the Hubble images of the clouds in the H-alpha and [O III] emission lines, augmented by a new (and very rich) set of integral-field spectroscopy measurements from the 8-meter Gemini North telescope, velocity maps from the Russian 6-meter telescope, and long-slit spectra from the 3-meter Shane telescope at Lick Observatory.

To examine the history of each AGN, our approach was that the AGN had to be at least bright enough to ionize the hydrogen we see glowing at each point at the time the light reaching that point was given off. Certainly we can’t expect each piece of the cloud to absorb all the deep-UV radiation, so this is a lower limit. Two external checks, on quasars unlikely to have faded greatly and on the Teacup AGN which has had detailed modeling done from spectra, suggests that the very brightest pixels at each radius absorb comparable fractions of the ionizing radiation. This gives confidence that we can track at least the behavior of a single object, underestimating its brightness by a single factor, if we look at the upper envelope of all pixels in the H-alpha images. We hoped this would be feasible all the way back to the original Hubble proposal to look at Hanny’s Voorwerp. Here is a graphic from the new paper comparing our AGN in this way. The distance in light-years at each point corresponds to the time delay between the AGN and cloud, and the curve labelled “Projection” shows how much one of these points would change if we view that location not perpendicular to the light but at angles up to 30 degrees each way. To be conservative, the plot shows the data corresponding to the bottom of this curve (minimum AGN luminosity at each point).agnhistories-sm

The common feature is the rapid brightness drop in the last 20,000 years for each (measured from the light now reaching us from the nuclei). Before that, most of them would not have stood out as having enough of an energy shortfall to enter our sample. Because of smearing due the large size of the clouds, and the long time it takes for electrons to recombine with protons at such low densities, we would not necessarily see the signature of similar low states more than about 40,000 years back.

We could also improve another measure of the AGN history – the WISE satellite’s mid-infrared sky survey gave us more accurate measure of these objects’ infrared output. That way, we can tell whether it is at least possible for the AGN to be bright enough to light up the gas, but so dust-blocked in our direction that we underestimate their brightness. The answer in most cases is “not at all”.

New data brought additional surprises (these objects have been gifts that just keep on giving). The Gemini data were taken with fiber-optic arrays giving us a spectrum for each tiny area 0.2 arcseconds on a side (although limited to 3.5×5 arc second fields), taken under extraordinarily steady atmospheric conditions so we can resolve structures as small as 0.5 arc second. We use these results to see how the gas is ionized and moves; some loops of gas that earlier looked as if they were being blown out from the nuclei are mostly rotating instead. Unlike some well-studied, powerful AGN with giant emission clouds, the Voorwerpje clouds are mostly just orbiting the galaxies (generally as part of tidal tails), being ionized by the AGN radiation but not shoved around by AGN winds. This montage shows the core of NGC 5972 seen by these various instruments, hinting at the level of mapping allowed by the Gemini spectra (and helping explain why it took so long to work finish the latest paper).ngc5972-hst-gmos-bta

Work on the Voorwerpjes continues in many ways. Galaxy Zoo participants still find possible clouds (and the moderators have been excellent about making sure we see them). There is more to be learned from the Gemini data, while X-ray observatories  are gradually bringing the current status of the AGN into sharper focus. A narrowband imaging survey from the ground can pick out fainter (and sometimes older) clouds. Colleagues with expertise in radio interferometry are addressing questions posed by the unexpected misalignments of optical and radio structures in some of our galaxies. Finally, the new DECaLS and Pan-STARRS survey data will eventually bring nearly the whole sky into our examination (for a huge range of projects, not just AGN history).

Once again, thanks to all who have helped us find and unravel these fascinating objects!

Happy 3rd birthday Radio Galaxy Zoo!

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In 2016, you have all contributed to more than 16 years of continuous classification and our project is now two-thirds of its way to completion and what a year it has been!

The biggest science news coming out of Radio Galaxy Zoo this year will have to be the official publication of the Matorny-Terentev cluster of galaxies, (RGZ-CL J0823.2+0333) –named after two of our super-Zooites who discovered the Giant Wide-Angle Tail galaxy (shown in white contours to the left, Banfield et al 2016).   We have also made great progress across several RadioTalk projects such as the Giants, the Spiral-DRAGNs, the Green DRAGNs and the HyMoRS.    Therefore, we will be providing more detailed updates from the team leaders in the coming weeks so please stay tuned for more exciting Radio Galaxy Zoo science highlights from 2016.

Our science team has also been evolving and this year, we bade farewell to Kyle W. and Chris S. who are pursuing new adventures and we sincerely thank them for all the fish.  We also saw the arrival and departure of Tim F., our ANU outreach student who worked with Julie and we hope that you have enjoyed his blog posts earlier this year.

This year, the RGZ science team welcomes Meg Schwamb from Gemini Observatory (who helped with the Chinese translation of RGZ) and Jean Tate, the first RGZ citizen scientist to become an associate member of the RGZ science team.  Meg will be helping us with the upcoming RGZ follow-up observations using the Gemini telescope.

We also have a new student joining our team and working with Julie in the coming year. Meet James L.,  a PhD Candidate in Science Communication at the Australian National Centre for the Public Awareness of Science. He completed his Bachelor of Science (Hons) in 2015 at the Australian National University with a double major in Astronomy/Astrophysics and Science Communication.  I am sure that you’ll hear more from James himself in the coming year.

Thank you all very much for your support again. We are most grateful for your help thus far. To finish the remaining third of the project, we seek your help in the coming days, months & year to complete this monumental task.

We wish you all a wonderful holiday period and a great upcoming year!

Cheers,

Ivy, Julie & RGZ team

 

 

Ferengi-2 Images Launched!

Hey volunteers! This is Mel G from the Minnesota science team, and I’m excited to announce the launch of the second set of FERENGI images on Galaxy Zoo today!

Some of you may remember classifying the first batch of FERENGI images back in 2013. For new volunteers, or experienced volunteers who need a refresher, FERENGI is a code that takes an image of a nearby galaxy and produces a new, simulated image of what that galaxy would look like if it was actually much farther away. 288 galaxies that were already classified by Galaxy Zoo volunteers were selected to be “ferengified” in that first sample; from these, 6,624 images were created of these galaxies at different distances and brightnesses. With your help, all images were classified and used to measure how distance affects classifications, which enabled us to debias and finally release the Galaxy Zoo: Hubble catalog just last month!

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original SDSS galaxy + 4 ferengified images at increasing distances

Recently, I found another use for these FERENGI classifications as I worked on my project on red disk galaxies, which will go into my PhD thesis to be completed this summer (coming up soon, yikes!). For this project I’ve been using data from Galaxy Zoo: Hubble to study the transformation of star-forming disk galaxies into non star-forming (aka “dead”) ellipticals between now and 6 billion years ago. Part of this research involves tracking the galaxy colors over time, which are indicators of whether the galaxies are still forming stars or not. A common way to distinguish star-forming galaxies from dead galaxies is to use a color-color diagram (this blog post goes into the details quite well, for the interested!). The short version is that galaxies in the upper-left of this plot, the “red sequence”, are no longer forming stars, and the lower-right portion, the “blue cloud”, are still producing lots of new stars. Typically the blue cloud is full of disk galaxies and the red sequence is full of ellipticals, but that statement is not 100% true;  there are actually quite a few disk galaxies mixed in with ellipticals up in the red sequence. We think these might represent a “transition” stage between blue/active disks and red/passive ellipticals, and studying how this population evolves with time will tell us more about how the shutting down of star formation is related to the morphological transformation.

What does this have to do with FERENGI? Well, detecting disk galaxies at high redshift is pretty hard – as we learned during the data reduction of the GZH catalog. Using raw Galaxy Zoo classifications, disks tend to be classified very similarly to ellipticals if they are very far away, so the number of disks we count is probably smaller than the true value. Using the FERENGI data, however, we can predict how many disks we should be detecting as a function of distance, and use that information to adjust the numbers of disks we count in the real Hubble data! The catch is that since galaxies with different colors tend to look a little different on average, it’s important to measure this incompleteness for both the red sequence and the blue cloud galaxies. Here comes the problem: in the original FERENGI sample,only 44 of the 300 galaxies have color data, leaving only 9 red sequence and 36 blue cloud galaxies to study. Unfortunately those numbers are too small to get a good measurement!

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color-color plots of the original and Ferengi-2 samples

So, as a sequel to the original FERENGI project, and as motivation to take proper measurements of red disks over time for my thesis, I’ve created FERENGI-2: a new set of FERENGI images from 936 galaxies. Each has been ferengified to 8 different distances, producing a total of 7,488 images that I need your help classifying. As you can see in the color-color plots here, these classifications will allow me to measure incompleteness for 388 galaxies in the red sequence (previously only 9) and 548 galaxies in the blue cloud (previously 36). This increase in data is huge, and will help not only the completion of my thesis, but many future projects that benefit from debiasing of Hubble data. Thanks again for your help!

Galaxy Zoo CANDELS

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We submitted the Galaxy Zoo CANDELS paper in May. Now, after some discussion with a very helpful referee, the paper is accepted! I hope our volunteers are as thrilled as I was to get the news. It happened within days of the Galaxy Zoo: Hubble paper acceptance. Hurray!

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Spot the typo! (No, just kidding.) (Well, sort of. There is one, but it’s not easy to find and it’s pretty inconsequential.) This is not quite the longest paper I’ve ever written, but it is the longest author list I’ve ever been at the top of. It includes both Galaxy Zoo and CANDELS scientists. And the volunteers are acknowledged too, in that first footnote. A lot of people did a lot of work to bring this together.

If you’d like to read the paper, it’s publicly available as a pre-print now and will be published at some point soon in the Monthly Notices of the Royal Astronomical Society. The pre-print version is the accepted version, so it should only differ from the eventual published paper by a tiny bit (I’m sure the proof editor will catch some typos and so on).

The paper may be a little long for a casual read, so here’s an overview:

  • We collected 2,149,206 classifications of 52,073 subjects, from 41,552 registered volunteers and 53,714 web browser sessions where the classifier didn’t log in. In the analysis we assumed each of those unique browser sessions was a separate volunteer.
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Most subjects have 40 classifications apiece, although some were retired early from active classification and others were classified further, until about 80 volunteers per galaxy had told us what they thought.

  • The raw consensus classifications are definitely useful, but we also weighted the classifications using a combination of “gold standard” data and consensus-based weighting. That is, classifiers were up- or down-weighted according to whether they could tell a galaxy apart from a star most of the time, and then the rest of the weighting proceeded in the same way it has for every other GZ dataset. No surprise: the majority of volunteers are excellent classifiers.
  • 6% of the raw classifications were from 86 classifiers who both classified a lot and gave the same answer (usually “star or artifact”) at least 98% of the time, no matter what images they saw. We have some bots, but they’re quite easy to spot.
  • Even with a pretty generous definition of what counts as “featured”, less than 15% of galaxies in the relatively young Universe that this data examines have clear signs of features. Most galaxies in the data set are relatively smooth and featureless.
  • Galaxy Zoo compares well with visual classifications of the same galaxies done by members of the CANDELS team, despite the fact that the comparison is sometimes hard because the questions they asked weren’t the same as what we did. This is, of course, a classic problem when comparing data sets of any kind: to some extent it’s always apples-vs-oranges, and the devil is in the details.
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We devote an entire section of the paper to comparing with the CANDELS-team classifications (from Kartaltepe et al. 2015, which we abbreviate to K15 in the paper). The bottom line: the classifications generally agree, and where they don’t we understand why. Sometimes it’s because there’s interesting science there, like mergers versus overlaps. The greyscale shading is a 2-D histogram; the difference in the blue versus red points is in which axis was used to separate the galaxy into bins so that the average trends could be computed.

  • By combining Galaxy Zoo classifications with multi-wavelength light profile fitting — where we fit a 2D equation to the distribution of light in a galaxy, the properties of which correlate pretty well with whether a galaxy has a strong disk component — we’ve identified a population of likely disk-dominated galaxies that also completely lack the features that are common in disk galaxies in the nearby, more evolved Universe. These disks don’t have spiral arms, they don’t have bars, they don’t have clumps. They’re smooth, but they are disks, not ellipticals. They tend to be a bit more compact than disk galaxies that do have features, even though they’re at the same luminosities. They’re also hard to identify using color alone (which echoes what we’ve seen in past Galaxy Zoo studies of various different kinds of galaxies). You really need both kinds of morphological information to reliably find these.
  • The data is available for download for those who would like to study it: data.galaxyzoo.org.

With the data releases of Galaxy Zoo: Hubble and Galaxy Zoo CANDELS added to the existing Galaxy Zoo releases, your combined classifications of over a million galaxies near and far are now public. We’ve already done some science together with these classifications, but there’s so much more to do. Thanks again for enabling us to learn about the Universe. This wouldn’t have been possible without you.

Galaxy Zoo: Hubble – data release and paper accepted!

I’m incredibly happy to report that the main paper for the Galaxy Zoo: Hubble project has just been accepted to the Monthly Notices of the Royal Astronomical Society! It’s been a long road for the project, but we’ve finally reached a major milestone. It’s due to the efforts of many, including the scientists who designed the interface and processed the initial images, the web developers who managed our technology and databases, more than 80,000 volunteers who spent time classifying galaxies and discussing them on the message boards, and the distributed GZ science team who have been steadily working on analyzing images, calibrating data, and writing the paper.

The preprint for the Galaxy Zoo: Hubble paper is available here. The release of GZH also syncs up with the publication of the Galaxy Zoo: CANDELS catalog, led by Brooke Simmons; she’ll have a blog post up later today, and the GZC paper is also available as a preprint.

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The first page of the project description and data release paper for Galaxy Zoo: Hubble (Willett et al. 2016).

Galaxy Zoo: Hubble began in 2010; it was the first work of GZ to move beyond the images taken with the Sloan Digital Sky Survey (SDSS). We were motivated by the need to study the evolution and formation of galaxies billions of years ago, in the early days of the Universe. While SDSS is an amazing telescope, it doesn’t have the sensitivity or resolution to make a quality image of a typical galaxy beyond a redshift of about z=0.4 (distances of a few billion parsecs). Instead, we used images from the Hubble Space Telescope, the flagship and workhorse telescope of NASA for the past two decades, and asked volunteers to help us classify the shapes of galaxies in several of Hubble’s largest and deepest surveys. After more than two years of work, the initial set of GZH classifications were finished in 2012 and the site moved on to other datasets, including CANDELS, UKIDSS, and Illustris.

So why has it taken several years to finish the analysis and publication of the data? The reduction of the GZH data ended up being more complicated and difficult than we’d originally anticipated. One key difference lies in our approach to a technique we call debiasing; these refer to sets of corrections made to the raw data supplied by the volunteers. There’s a known effect where galaxies that are less bright and/or further away will appear dimmer and/or smaller in the images which are being classified. This skews the data, making it appear that there are more elliptical/smooth galaxies than truly exist in the Universe. With SDSS images, we dealt with this by assuming that the nearest galaxies were reliably measured, and then deriving corrections which we applied to the rest of the sample.

In Galaxy Zoo: Hubble, we didn’t have that option available. The problem is that there are two separate effects in the data that affect morphological classification. The first is the debiasing issue just mentioned above; however, there’s also a genuine change in the populations of galaxies between, say, 6 billion years ago and the present day. Galaxies in the earlier epochs of the Universe were more likely to have clumpy substructures and less likely to have very well-settled spiral disks with features like bars. So if we just tried to correct for the debiasing effect based on local galaxies, we would have explicitly removed any of the real changes in the population over cosmic time. Since those trends are exactly what we want to study, we needed another approach.

Our solution ended up bringing in another set of data to serve as the calibration. Volunteers who have classified on the current version of the site may remember classifying the “FERENGI” sample. These were images of real galaxies that we processed with computer codes to make them look like they were at a variety of distances. The classifications for these images, which were completed in late 2013, gave us the solution to the first effect; we were able to model the relationship between distance to the galaxy and the likelihood of detecting features, and then applied a correction based on that relationship to the real GZH data.

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Top: Example of a galaxy image processed with FERENGI to make it appear at a variety of distances. Bottom: Calibration curves based on FERENGI data that measure the effect of distance on morphological classification. From Willett et al. (2016).

The new GZH data is similar in format and structure to the data release from GZ2. The main product is a very large data table (113,705 rows by 172 columns) that researchers can slice and dice to study specific groups of galaxies with morphological measurements. We’re also releasing data from several related image sets, including experiments on fading and swapping colors in images, the effect of bright active galactic nuclei (AGN), different exposure depths, and even a low-redshift set of SDSS Stripe 82 galaxies classified with the new decision tree. All of the data will be published in electronic tables along with the paper, and are also downloadable from data.galaxyzoo.org. Our reduction and analysis code is available as a public Github repository.

The science team has already published two papers based on preliminary Galaxy Zoo: Hubble data. This included a paper led by Edmond Cheung (UCSC/Kavli IPMU) that concluded that there is no evidence connecting galactic bars and AGN over a range of redshifts out to z = 1.0. Tom Melvin (U. Portsmouth) carefully examined the overall bar fraction in disks using COSMOS data, measuring a strong decrease in bar fraction going back to galaxies 7.8 billion years ago. We’re now excited to continue new research areas, including a project led by Melanie Galloway (U. Minnesota) on the evolution of red disk galaxies over cosmic time. We hope GZH will enable a lot more science very soon from both our team and external researchers, now that the data are publicly released.

A massive “thank you” again to everyone who’s helped with this project. Galaxy Zoo has made some amazing discoveries with your help in the past eight years, and now that two new unique sets of data are openly available, we’re looking forward to many more.