We posted briefly about the 227th meeting of the American Astronomical Society, which several members of the Galaxy Zoo science team attended last week. I wanted to share a little bit more about the research that we presented, and the experiences we had at the meeting.
Kyle Willett (Postdoc, University of Minnesota)
I presented a poster on the data release of the Galaxy Zoo: Hubble project. While it’s been a couple of years since we formally finished the classifications for GZH, we’ve been working hard in the meantime on aggregating and calibrating the data; this includes two supplementary data sets that users helped classify in the newest interface. One of those sets were the images of galaxies processed with the FERENGI code in order to mimic their appearances at higher redshifts; these have been absolutely critical for the calibration/debiasing procedure we’re applying to the real Hubble galaxies. The second set of new images were the deeper images of galaxies in the GOODS north and south fields, completed early last year. We’re using these to analyze the effect of depth on morphologies, and seeing how the disk/clumpy fractions change with improved imaging.
AAS went well for me, and I got to talk about GZH with a number of new colleagues. I particularly liked having my poster between Melanie Galloway’s and Brooke Simmons’ — I got to point out GZH science results on one side and the next generation of even higher redshift galaxies on the other, which made for a very nice story to tell.
Melanie Galloway (PhD student, University of Minnesota)
Galaxy Zoo users probably know that there are two main types of galaxies: disks and ellipticals. There is a cool relationship between these shapes and their color: disks tend to be blue (which is an indicator of young stars), while almost all ellipticals appear red (which indicates the stars are old; “red and dead” is a term commonly used.) Astronomers believe that this relationship between color and shape implies that galaxies tend to be created as disks, and over their lifetimes, transform from young disks to old ellipticals. Data from Galaxy Zoo revealed that there are also red disk galaxies in the Universe, and right now it is not known how they fit into our current perception of galaxy evolution.
Mel used data from Galaxy Zoo: Hubble to tackle this question by analyzing how the fraction of red disks changed between now and 6 billion years ago. She found that this fraction was actually much higher in the past! This result probably means that red disks don’t tend to stay red disks, and may instead be a common phase of a typical galaxy’s evolution from blue disk to red elliptical.
Melanie Beck (PhD student, University of Minnesota)
At this year’s AAS conference, I presented work which focused on the relationship between galaxies’ masses and their sizes. In general, more massive galaxies are also physically larger (but not always!). However, the mass-size relationship is different for galaxies in the distant universe compared to those in the nearby universe. It’s also different between disk galaxies compared to ellipticals in that the sizes of elliptical galaxies grow much, much faster than those of disk galaxies but don’t seem to grow much in mass. To explain this behavior, models predict that disk galaxies must evolve into elliptical galaxies at a rate that mimics the growth rate of the ellipticals. These models predict that there should be many more elliptical galaxies of a particular size and mass in the nearby universe compared to disks. To test this, we need to keep track of the number of galaxies as a function of mass, size, and type (elliptical or disk) over a large period of time.
My initial work utilizes classifications from Galaxy Zoo 2 separated by Smooth or Features/Disk. All the galaxies in this catalog are considered to be in the local universe. Using sophisticated statistical techniques, I’m able to robustly determine the number of galaxies as a function of mass, size and type. Next I’m applying the same techniques to classifications from Galaxy Zoo: Hubble and Galaxy Zoo: CANDELS as these catalogs contain galaxies from the more and more distant universe. Once we have the analysis from all three we can compare the numbers of galaxies at each time and finally test those models!
Brooke Simmons (Postdoc and Einstein Fellow, UC San Diego)
AAS is always a hectic science bonanza, and presenting a poster is a way of slowing things down a bit: unlike a talk, which is over in 15 minutes or less, you get to have your results up all day. My poster was an introduction to the upcoming release of classifications for the high-redshift CANDELS galaxies, so it shows a basic overview of how the classifications work and an early science result about featureless disks at high redshift.
It was great to present 2 data releases side-by-side, with Kyle’s poster to my left, and it was even better to get to present the result of the volunteers’ efforts. Between these posters and the previous data releases for Galaxy Zoo, we’ve measured the shapes of hundreds of thousands of galaxies (actually, I think it’s over a million!) spanning the last 12 billion years of cosmic time.
The “green pea” galaxies were one of the first discoveries of the Galaxy Zoo; they were first noticed by several of our early volunteers, and appeared in a paper led by Carie Cardamone in 2009 (with over 100 citations so far!). They’ve been the subject of a great deal of follow-up research since then, much of which we’ve tried to follow on this blog.
A new paper on the Green Peas has just appeared in Nature, one of the most prestigious and widely-read journals in science. A truly international team of researchers (working in Ukraine, Czech Republic, Switzerland, France, Germany, and the United States) made observations of one green pea galaxy, known as J0925+1403, using an ultraviolet spectrograph on the Hubble Space Telescope. They were able to measure emission from what astronomers call “Lyman continuum” photons; this is light produced by massive stars that are solidly in the ultraviolet wavelengths.
The reason this is so important and interesting relates to one of the most fundamental steps in the history of the Universe that astronomers know of. The majority of matter in the Universe is hydrogen (formed shortly after the Big Bang), and much of it exists in diffuse clouds between galaxies, which is called the intergalactic medium. We know from observations that almost all of that hydrogen is currently ionized – that means instead of consisting of a neutral atom with one proton and one electron orbiting it, the average hydrogen atom between galaxies has had its electron stripped away from the proton. This is a big difference because neutral atoms interact with light differently than ionized atoms. If the hydrogen between galaxies were neutral, it would absorb much of the light coming from individual stars and galaxies, making a huge difference in our ability to observe distant objects.
It’s been known for years the Universe is currently ionized; however, about 700 million years after the Big Bang, we know that the Universe used to be neutral. That’s pretty well-established — however, there’s a great deal of debate about what caused the sudden reionization. Something must have produced large numbers of photons that traveled into the intergalactic medium and ionized all of the hydrogen fairly quickly. There have been lots of papers proposing different possible sources for this, including dwarf galaxies, active galactic nuclei, quasars, very early and massive stars, etc.
This new paper proposes that green pea galaxies could be responsible for re-ionizing the early Universe. The measurements from this paper show that at least one green pea galaxy is actively emitting photons with sufficient energy to ionize neutral hydrogen. Lots of galaxies can create such radiation, but one unique aspect of the peas is that the photons are escaping the galaxy where they’re being formed. Usually they’re absorbed by dust or gas clouds within the galaxy before they can affect the rest of the Universe. This is the first time that it’s been demonstrated to occur for a green pea galaxy.
The paper (Izotov et al. 2016) is available online. Nature has also published a nice summary at a slightly less technical level to accompany the article that I’d recommend – you can read that here. Please post if you have any questions or want to discuss more about what this means. We’re extremely excited that your discoveries are still yielding new and interesting science!
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.
We celebrated 8 years of Galaxy Zoo back in July, with this blog series of all things 8-like about Galaxy Zoo.
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.
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 arxiv.org.
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 authors.galaxyzoo.org.” 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.
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 data.galaxyzoo.org). 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!
As happens every winter, a large fraction of the world’s astronomers have migrated to a large convention center to share and talk about every aspect of research, outreach, education, and methods of astronomy. This is the biannual meeting of the American Astronomical Society: this winter, the 227th edition is being held in Kissimmee, Florida.
Several posters and talks will be on new research results from Galaxy Zoo data. These include:
- Becky Smethurst (Oxford) – giving a talk on her PhD dissertation research of the quenching history of galaxies and the role of active galactic nucleus (AGN) feedback. (119.04D; Tue)
- Melanie Beck (Minnesota) – a poster on the bivariate mass-size relation of galaxies as a function of morphology (342.38; Thu)
- Melanie Galloway (Minnesota) – a poster on the redshift evolution of the fraction of red disk galaxies, using GZ: Hubble data (342.40; Thu)
- Kyle Willett (Minnesota) – a poster on the upcoming release of the GZ: Hubble catalog (342.41; Thu)
- Brooke Simmons (UC San Diego) – a poster on the release of the GZ: CANDELS catalog (342.42; Thu)
In addition, there are several other abstracts that that use Galaxy Zoo data (although it may not always be the main focus), and several of our core team members (Chris, Kevin, Lucy, etc) are here, but talking about other aspects of their research.
It looks to be an exciting week, and we’ll try to blog and tweet more about the amazing things going on in astronomy right now. Check out more of what’s going on at #aas227!
Happy 2nd birthday to Radio Galaxy Zoo!
On Radio Galaxy Zoo’s 2nd birthday, we wish to thank you all for achieving more than 1.42 million classifications (~57.2 years of work)! That is an extra 20 years of classifications just in the last year. We are nearly at the halfway mark now so we are cheering you all on for the great effort and dedication that many of you have shown.
So what has the science team done in the last year with your classifications? Our first refereed paper has been published.
Anna Kapinska’s HyMoRS paper has been submitted for publication and we have another 3 papers on the sidelines in preparation and awaiting submission in the next few months.
And we have also submitted several proposals to conduct follow-up observations of the many interesting systems that you all have found!
Thank you all very much for your support again. We are most grateful for your help thus far. However, we still have more than half of our sample to classify. So we are seeking 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!
Ivy, Julie & RGZ team
We’re really excited to report that, with your help, the first batch of galaxy images from the Illustris simulation was finished last week! While we still have plenty of images still available to be classified (both from Illustris and DECaLS), I wanted to explain again how the images are being sorted in Galaxy Zoo and show some of the very early results we’re getting from your classifications.
The galaxies we selected from Illustris were a really big set – after eliminating galaxies which were likely to be too small or dim for accurate visual identification (we did this by filtering on the mass of the galaxies), we had over 110,000 images. In designing this phase of Galaxy Zoo, though, we wanted to try and prioritize the order of the images being shown so that we could do some early science projects along the way, rather than waiting many months for the entire data set to be finished before we started our analysis. This first set of Illustris data included 10,832 images, which were classified a total of more than 430,000 times by Galaxy Zoo volunteers.
One of the main questions we wanted to answer was: “How is the apparent morphology of a galaxy affected by the angle at which it’s viewed?” This is an important one – for observations of the real Universe, we can’t change the position of our telescope relative to the objects we’re looking at. If a galaxy is edge-on, for example, we’re really limited in being able to determine if there’s a bar, how many spiral arms there are, etc. In Illustris, though, we can change the viewing angle in the simulation! As a result, we might hypothesize that all edge-on disks should be identifiable as spiral or S0 galaxies at all the other viewpoints.
Here’s a quick test I’ve run of that. Using the set of collated classifications that just finished from Illustris, I looked for unique galaxies that were classified as “edge-on disks” from at least 1 of the 4 viewing angles that we have data for. Then I looked at the GZ classifications for the other viewing angles to see if they were still edge-on. Results:
Very close to what we expect! Only about 10% of galaxies had any edge-on classifications; of those, almost all of them are classified as face-on at every other angle (the big bump at N=1 in this plot). The exceptions are where the disk is aligned with two of the virtual cameras — then, we see it as edge-on twice and face-on twice. Since the cameras are oriented like they’re at points of a pyramid with the galaxy at the center, geometry tells us we should expect a typical disk to be edge-on for 0 cameras most of the time, 1 sometimes, 2 very rarely, and never 3 or 4. Just what we see!
We’re excited to be starting on the analysis phase and are, as always, extremely thankful for your help.
Just a quick reference to a piece that came out in Currents, the newsletter of the National Optical Astronomy Observatory (NOAO) in the US. They included a short piece on the classifications from the new images in DECaLS, a survey which is being co-led by NOAO staff and carried out at their southern observing site in Chile. This followed a longer piece in their September newsletter on the first data release for DECaLS, which includes more details on the tremendous capabilities of the new survey. Good reads if you have a moment!
A quick update: Galaxy Zoo volunteers have already provided more than 750,000 classifications of DECaLS images. We’re completely done with about a quarter of the first data release, and all the images have enough early classifications that we’re starting on preliminary analysis soon. As always, thanks to everyone for your interest and help!
I think the most common question/comment we’ve been seeing for classifiers of the simulated Illustris galaxies is along the lines of: “What’s the blue stuff?”
It’s a great question. Let’s talk about it in more detail.
The short answer is that the blue regions are the simulations’ method of reproducing the light emitted by young stars. A star’s lifetime generally scales as a function of its mass – the more massive the star is when it’s first formed, the hotter it is and the faster it burns fuel. Emission from hotter objects will tend to be bluer (ie, produce more photons at shorter wavelengths) compared to less massive stars. These are trends we see in optical images of stars in galaxies, including naked-eye views and composite color images. The exact color depends on the filters being used as well as processing of the images – that’s the difference between images you may have seen of star-forming regions being pink in some images and blue in others, such as those in Illustris.
A couple more specific questions that we’ve received:
What’s causing the blue colors in the galaxies? Are they caused by individual atomic or molecular lines that we can see in the spectra?
Volunteers who worked on the original GZ green peas project might be familiar with the term “nebular emission” – individual, narrow lines caused by ionized or hot gas surrounding stars, or whether they’re the result of the broadband colors of the stars themselves. The GZ-Illustris images use a stellar population model that only computes the broadband colors, due to some issues with unrealistic green images caused by the interaction of the codes that deal with both the emission lines and effects of dust. The model we’re using – based on work by Bruzual & Charlot (2003) – omits the emission lines for that reason. However, we’ve made extensive comparisons of the two sets of images and find that they agree very well for our scientific goals, including the morphology classifications.
How should visual morphology classifiers deal with the star-forming regions? Ignore them and look at the underlying stellar populations? Treat them as part of the galaxy? Something else?
This is a tough one. Many galaxies have the “blobby” star-forming regions but others have nicer looking disk or spiral distributions. Our analysis suggests is that this is a pretty tight function of the total star formation rate (higher SFR = more realistic looking features). We suggest that users treat them as part of the galaxy; it might lead to some odd results in lower mass galaxies, but we expect they should trace each other very well for the more massive galaxies. If you see geometry that’s distinctly different from a well-formed spiral disk or elliptical, don’t be hesitant to click the “Anything Odd” or “Other” buttons – that’s one of the simplest ways in which we can measure the unusual effects of the blue regions, given the constraints of our classification scheme.
The distribution of the blue blobs is often disconnected and/or in unusual shapes compared to Sloan. What determines the spatial distribution of the star forming regions?
This results from the extremely discrete sampling of the density of stars in the images. Stars can only form in “chunks” of about 1 million solar masses, instead of the more typical small clusters and regions that we know exist in the real Universe. Moreover, these chunks have their light spread over a significant fraction of ~1 kpc (which is pretty big, compared to a typical galaxy radius of ~20 kpc), and so they often won’t look much like real star-forming regions. This, coupled with the lack of dust, leads to what you see in the GZ images.
Thanks as always to everyone for your help. Please post here or on Talk if you have more questions!
This post was written with the help of researchers Gregory Snyder (Space Telescope Science Institute) and Paul Torrey (MIT/Caltech), who worked extensively on the development of Illustris and the generation of the mock images for Galaxy Zoo.
This post was written with the help of Sugata Kaviraj, senior lecturer at the University of Hertfordshire in the UK. Sugata has been a member of the GZ science team for several years and is leading our analysis of tidal debris in the DECaLS images.
One of the biggest changes to the questions we’re asking for the new DECaLS images asks users to help us classify galaxies that are either merging and/or exhibiting “tidal debris”. While mergers have been part of Galaxy Zoo since our very first classifications, tidal debris is looking for something more specific, which the new DECaLS data is particularly suited for.
In astronomy, “tides” are a type of force exerted on an object by the effect of gravity. Specifically, it refers to the gravitational force exerted by one body on another – since the force exerted by gravity depends on the distance to the object (specifically, it’s proportional to the inverse square of the distance), the nearer side of the object will feel a stronger force than the farther side of the object. On Earth, the differential force caused (mostly) by the gravity of our Moon acts on the liquid in the oceans, causing the rise and fall in sea levels each day.
When the object is a solid body (like a planet or moon), tidal forces can strain and compress the body, resulting in internal heat and sometimes driving geological activity. A galaxy isn’t a solid body, but composed of individual stars/gas clouds/dark matter particles bound within its own gravitational field. When a galaxy is subjected to tidal forces, it pulls the galaxy apart, causing irregularities in shape that can take many forms depending on the magnitude and direction of the forces involved.
One of the main reasons we want to identify tidal features specifically is to make better measurements of the merger history of galaxies. A complication is that the event of merging with a galaxy isn’t an instantaneous event – depending on the relative masses, velocities, and orientations of the merging galaxies, tidal forces strip out long tails of stars and gas from the galactic centers.
The Mice (NGC 4676): colliding galaxies with tails of stars and gas distorted by tidal forces. Source: Hubblesite.org
Ultimately, the nuclei of the two galaxies will fully merge; if that happened sufficiently far in the past for the orbits of stars to relax, then it’s difficult for observers to determine if an elliptical galaxy today was the result of a merger.
Tidal debris features, however, are longer-lived signals of a merger sometime in a galaxy’s past. If we only asked about mergers, we’d be restricting the sample to galaxies that we’re lucky enough to observe “right in the act” of merging. By identifying the tidal debris as well, we can make a more complete census of galaxies that had a merger at some point in their past. One project that this is critical for is looking at the history of galaxy populations, and trying to figure out whether star formation and/or active black holes might be powered by merger events.
Since tidal debris features can be very faint (ie, having low surface brightnesses), the deeper DECaLS images that we’re currently classifying are much better at picking out these features than SDSS. That’s the main reason we’re focusing on trying to detect them in the current set of images.
Tidal debris can come in many different forms, including extended light, faint shells, dust lanes, or satellites in the process of being assimilated to clearly distorted galaxies which have presumably have had a recent interaction. The features can definitely be faint, but we’d like to ask that when you reach this question, please take a careful second look at the area around the main galaxy and see if you can spot anything. Examples are also available in the help text, and we hope that you’ll discuss features you’re not certain about with the moderators, scientists, and other volunteers in Talk.
Please let us know, here or on Talk, what questions you have. Thanks for your help in tackling a new and interesting scientific problem.
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.
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.