I am very happy to present the results from the first published paper based on your classifications of the HST-CANDELS Images.
Galaxy Zoo: CANDELS combined optical and infrared imaging from the Hubble Space Telescope, which allows us to probe galaxies back to when the universe was only around 3 billion years old (early than we could do with optical HST images alone). So we are looking at galaxies whose light has taken over 10 billion years to reach us!
Our first area of research with this data is to look at disk and barred disk galaxies, as the title suggests…….
This work is based on an initial sample of 876 disk galaxies, which are from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). We want to explore what happens to barred disk galaxies beyond eight billion years ago, building on our work looking at the evolving bar fraction with Galaxy Zoo: Hubble.
When we began this work, we were unsure what we would find when looking so far back. From our Galaxy Zoo: Hubble work we had identified that 10% of disk galaxies hosted a galactic bar eight billion years ago, but beyond this our knowledge of disks was limited to a single simulation of disk galaxies. This simulation predicted that bars in disk galaxies were very rare beyond the epoch we had observed to, as the Universe would be to young for disk galaxies to
have settled down enough to form barred structures.
As Figure 1 shows, we actually find that roughly 10% of all disk galaxies host a bar, even back to when the Universe was only 3 billion years old! This is a very exciting result, as it shows that disk galaxies were able to settle at much earlier times than originally believed.
What we need to understand now is how do these disk galaxies form their bars? Could they be completely settled disk galaxies which have naturally formed bars, even during this epoch of violent galaxy evolution where galaxy mergers are more frequent? Or were these bars formed by a galaxy-galaxy interaction, as seen by some simulations? The answer could be one or the other, or most likely a combination of these two theories. Either way, we hope to explore this population of barred disk galaxies in greater detail over the coming months!
So there is a summary of the first Galaxy Zoo: CANDELS paper. If you would like to see this in more detail, please take a look at the paper here, and why not check out the RAS press release too! Thank you all for your hard work, and keep classifying!
Posted on behalf of Tom Melvin.
A paper that uses Galaxy Zoo: Hubble to study whether supermassive black holes are fueled by galaxy bars beyond the local universe has recently been accepted! The paper will be published in MNRAS, but for a short summary, here is the original blog post.
While preparing for more observations of the Galaxy Zoo giant AGN clouds (Voorwerpjes), this is a good time to introduce more complete ways of obtaining astronomical spectra. Traditionally, we’ve put a long slit in front of spectrographs, so we can measure everything along that line without worries about overlapping spectra of different objects or pieces of sky. In some cases, as with the optical fibers used by the Sloan Digital Sky Survey, we get the light summed within a circular aperture on the sky (with Sloan, from hundreds of different objects at each pointing of the telescope). But many of the things we want to understand are large and oddly shaped, so these approaches limit us to a very partial view (or to making many observations to cover everything of interest). Enter the Integral-Field Unit (IFU), which is any kind of device that lets us get the spectrum of every point in some region of the sky. They often use fiber optics to rearrange light from the object, so each small region of it comes out at a different place on what would otherwise be the spectrograph slit. After that it all becomes a software problem.
IFUs are becoming more common on large telescopes. We’ve gotten excellent data on some Voorwerpje systems with the unit on the 8-meter Gemini North telescope. Here’s a sample of raw data on UGC 11185. Each horizontal streak is the spectrum of an area 0.2 arcseconds square. The sampling, sensitivity, and image quality are superb, revealing multiple clouds of gas moving within a total span of almost 1000 km/s.
On the other hand, if we want to use its whole wavelength range, the Gemini device covers only 3.5×5 arcseconds of sky at once. I’m headed to the 3.5m WIYN telescope on Kitt Peak to use a complementary device called Hexpak, newly commissioned by instrument designer Matt Bershady of the University of Wisconsin (who I’ve been emailing about this since I learned of the project three years ago). This fiber bundle plugs into the multipurpose spectrograph kept in a climate-controlled room below the telescope, and combines small and densely-packed fibers in the middle (for things like galactic nuclei, small and bright with lots of structure) and large fibers near the edges (collecting a lot of signal from large diffuse surrounding material – sound familiar?). Matt and his team were able to get a short exposure through thin clouds of UGC 11185 as a feasibility test – here’s a piece of that raw data frame, showing the small central fiber and the larger surrounding ones (which show brighter night-sky airglow lines as well as more object signal; the bright [O III] lines and H-beta are near the middle, with wavelength increasing to the right for each spectrum). I hope to get a lot more data like this shortly.
Elsewhere, the European Southern Observatory has commissioned an enormous IFU, and the Sloan team has rebuilt their fiber bundles so that each one now makes multiple IFUs which can be placed on many galaxies at a time – this part of the Sloan survey extension is known as MANGA. Then there is the Spanish-led CALIFA project for hundreds of galaxies, which has publicly released data for their first two subsets. Then there are SAURON (whose data ca be tamed in software by GANDALF) and the upgrade of SCORPIO-2 and more… Swimming in data as we sift for knowledge, I am reminded of this anonymous computer error message in haiku form:
Out of memory.
We wish to hold the whole sky
but we never will.
First off, the science team for Radio Galaxy Zoo wants to thank our volunteers for their continued clicks, discussion on Talk, and continued participation in the project. As of today, we have 892,582 classifications on RGZ and over 45,000 subjects completed from the FIRST-SDSS sample. We absolutely could not do this without you, and we’re working hard on turning the data into interesting science.
We want to let you know of some particular galaxies that will be appearing slightly more often in the interface. One of the things I’ve been working on for Radio Galaxy Zoo over the last month is finding better and smarter ways of combining clicks from independent classifiers into the “final answer” for each galaxy. For past Zooniverse projects, we’ve been able to do this using relatively simple methods – users are weighted a little bit by their consistency with other volunteers, but the final data product is mostly just the vote fractions for various tasks. However, the task in RGZ is a bit more complex, and the simpler methods of combining classifications are proving very difficult. In order to accurately combine the information each volunteer gives us, we need to establish a bit more common ground than we currently have.
To calibrate the clicks across all citizen scientists, we need to look at galaxies that the same people have done. The science team has started this by labeling the correct morphologies (to the best of our abilities) for a smaller, “gold standard” sample. We use these as seed weights in our data reduction – that lets us calibrate users who have done the gold standard galaxies. These results are propagated outward to the full sample by looking at other galaxies done by both calibrated and uncalibrated users, and so on. Kind of like pulling ourselves up by the bootstraps. :)
What we’re missing right now, though, are galaxies that lots of citizen scientists have jointly classified. Since each galaxy is retired after 20 people classify it, the chances of seeing a particular galaxy is pretty low. Some members of the science team, including myself, recently sat down with a sample of 100 galaxies taken from a combination of random selection and ones you’ve identified on Talk as having interesting or non-trivial morphologies (bent jets, triple systems, giants, no IR counterparts, etc). These is what we’d like to use for calibration. However, only about a dozen users so far have done enough of this sample to give us enough data for calibration.
So, in order to help the accuracy of the data pipeline, we’ve chosen 20 “gold standard” galaxies that will eventually be shown to all volunteers. They won’t all be in one bunch (you should see one every five subjects or so) and you shouldn’t see any galaxies that you’ve classified before. We’ll label the galaxies on Talk – look for the hashtag #goldstandard. I hope that another positive outcome will be users getting to discuss interesting features in galaxies that they haven’t come across before. After you’ve done all 20 galaxies in the sample, your future classifications will be randomly selected as usual.
Please let us know on Talk if you have any questions about this, and I’ll be happy to discuss it further. Thanks again for all of your help – we hope this will let us produce a more accurate RGZ product and science papers in the coming year!
Meet Minnie Mao, leading the study of spiral double radio lobe AGNs (or S-DRAGNs) for Radio Galaxy Zoo.
Hello! My name is Minnie and I am a VLA postdoc at NRAO in Socorro, NM. Astronomers use a lot of acronyms, and often are not very creative with telescope names/ VLA stands for ‘Very Large Array’, which is where some of the Radio Galaxy Zoo radio images come from!
I did my PhD at the University of Tasmania with Ray Norris (yup, THE Ray Norris), Jim Lovell, and Rob Sharp. We used optical data cross-matched with radio data from the ATCA (Australia Telescope Compact Array, where the rest of the RGZ radio images come from) to determine how galaxies have changed across cosmic time. A large chunk of the PhD was spent staring at images of radio galaxies, classifying their morphology, and determining their counterparts in optical/infrared images. While this can be a lot of fun, the Universe is rather large so I am glad I can now share this job with the wonderful zoo-ites!
One of my primary reasons for being involved in RGZ is because I am excited for the day when radio images become as familiar to people as optical images. To this end I hope you enjoy RGZ, because really, what is more fun than peering far back into the nether-reaches of the Universe?
Galaxy Zoo: Are Bars Responsible for the Feeding of Supermasssive Black Holes Beyond the Local Universe?
Supermassive black holes are thought to reside in the centers of most galaxies. These massive objects can produce powerful jets of energy that may significantly influence the evolution of their host galaxies. While we believe that black holes have an important role in galaxy evolution, a crucial unknown aspect about black holes is how they are fueled and turn into active galactic nuclei (AGN).
Among the proposed black hole fueling processes, bar-driven secular evolution is among the most popular. Bars are linear structures of stars that stretch across the centers of galaxies. They are theorized to fuel black holes by driving gas from the outskirts of galaxies into the very centers, where supermassive black holes lie.
Previous studies have tested whether bars can fuel black holes by examining whether there is an excess of bars among AGN hosts compared to non-AGN hosts. For the most part, those works found that there was not a significant enhancement of bars among AGN hosts, leading them to conclude that bars do not fuel black holes. But almost all these previous works were limited to the local universe, i.e., in the present, where the number of AGN is the lowest across cosmic time.
In this work, we investigate whether there is an excess of bars among AGN hosts beyond the local universe, i.e., in the distant past, up to 7 billion years ago. In this epoch, the number of AGN hosts is much higher, giving us a better glimpse of the identity of the black hole fueling mechanism. To conduct this experiment, we created two samples: 1) a sample of AGN hosts and 2) a carefully constructed control sample of non-AGN hosts that are matched to the AGN hosts. In order to create the largest samples possible, our experiment utilized three of the most popular extragalactic surveys: AEGIS, COSMOS, and GOODS-S. With these samples, we used the Galaxy Zoo: Hubble bar classifications to identify barred galaxies. Below is a gallery of 6 sets of AGN and their corresponding control galaxies, 2 sets from each survey.
Our main results are shown in the figure below. We have two probes of bar presence—bar fraction (left) and bar likelihood (right)—for the AEGIS, COSMOS, and GOODS-S surveys.
We find no statistically significant enhancement in the bar fraction or the bar likelihood in AGN hosts (green squares) compared to the non-AGN hosts (purple triangles). Our results, combined with previous works at the local universe, indicate that bars are not the primary fueling mechanism for supermassive black hole growth for the last 7 billion years. Moreover, given the growth of supermassive black holes over cosmic time, our results imply that bars are not directly responsible for the buildup of at least half the local supermassive black hole mass density.
Therefore, although among the most popular fueling mechanisms, it seems that bars do not fuel black holes. However, this result does narrow the search for the real black hole fueling mechanism.
At a conceptual level the formation of radio galaxies is pretty simple. According to a basic picture first introduced in the 1970s, a supermassive black hole in the center of a galaxy generates a symmetric pair of oppositely directed, high speed jets or beams of hot, ionized gas as a by-product of energy released or stored from matter falling onto the black hole. Those jets drill holes in the atmosphere of the galaxy and then even far beyond, dumping energy, excavating cavities and possibly entraining gas into the jets and cavities along the way. The jets carry magnetic fields and high energy electrons. Those electrons, spiraling in the magnetic fields light up the jets and the cavities they excavate in the radio band through a process called synchrotron emission.
While calculations based on this cartoon picture can correctly predict a few properties of radio galaxies, anyone who has looked at the images in Radio Galaxy Zoo can see that there must be a whole lot more to the story. Radio galaxies at best have only a rough bilateral symmetry with respect to their host galaxies. Furthermore, no two radio galaxies look alike, and most look pretty complicated; some could only be described as messy. In fact, the physics of radio galaxy formation is really very complex for a whole bunch of reasons that range from inherent instabilities in the dynamics of a fast jet, to the reality that the jets are not steady at the source. Furthermore, the surrounding environments are themselves messy, dynamic and sometimes even violent. All of these influences have impact on the appearances of radio galaxies.
The other side of the coin is that, if they can be understood, these complications may improve opportunities to decipher both the formation processes of the jets as well as the conditions that control their development and dissipation as they penetrate their environments. One part of piecing this puzzle together is expanding our awareness of all the things radio galaxies do, as well as when and where they do what they do. That’s what Radio Galaxy Zoo is about.
On the other hand, to go beyond the cartoon picture of what we see we also have to develop much more sophisticated and realistic models of the phenomena. This is very challenging. Because the detailed physics is so complex (messy!), astronomers have come to depend increasingly on large computer simulations that solve equations for gas dynamics with magnetic fields and high energy electrons. Pioneering gas dynamical simulations of jets in the 1980s already played an important role in confirming the value of the jet paradigm and helped to refine it soon after it was introduced.
Those early simulations were, however, seriously limited by available computer power and computational methods. In important ways the structures they made did not really look much like actual radio galaxies. At best they were too grainy. At worst important physics had to be left out, including the processes that actually produce the radio emission. This made it hard to know exactly how to compare the simulations with real radio galaxies. Thankfully, rapid improvements in both of those areas have led recently to much more realistic and detailed simulations that are starting to look more like the real thing and can be used to better pin down what is actually going on.
Our group at the University of Minnesota has been involved for some years now in pushing forward the boundaries of what can be learned about radio galaxies from simulations. I illustrate below some of the lessons we have learned from these simulations and some of the complex radio galaxy environments that it is now possible to explore through simulations. Each of these simulations was part of the work carried out by a student as part of their PhD training.
The jets responsible for radio galaxy formation propagate at speeds that can be a significant fraction of the speed of light. They are almost certainly supersonic. These properties lead to several related behaviors that are illustrated in Figure 1. It turns out that the flows within such a jet tend periodically to expand and then to contract. As they do so they form a sequence of shocks along the jet. These are visible in the figure. The jet also creates a sonic boom or bow shock in front as it moves forward. A close look at the jet in this figure also reveals that the jet actually does not remain straight as it moves forward. The end of the jet turns out to be unstable, so soon after launch begins to ‘flap’ or wobble. As a result the end of the jet tends to jump around, enlarging the area of impact on the ambient medium.
Many radio galaxies form inside clusters of galaxies, where the ambient medium is highly non-uniform and stirred up as a result of its own, violent formation. This distorts and bends the radio structures. At the same time the energy and momentum deposited by the jets creates cavities in the cluster gas that lead to dark holes in the thermal X-ray emission of the cluster. Figure 2 illustrates some of these behaviors for a simulated radio galaxy formed at the center of a cluster. Even though the source of the radio galaxy is at rest, there are fast gas motions in the cluster gas that obviously deflect the radio galaxy jets. ‘Mock’ radio images representing synchrotron emission by high energy electrons in the magnetic field carried by the jets are shown on the right in the figure at two times. At the same two times mock images of thermal X-rays are shown to the left. The X-ray images have been processed to exaggerate the dark cavities produced by the jets. Note that each image spans about 700 kpc or 2 million light years.
Quite a few radio galaxies in clusters are not made by galaxies anchored in the cluster center, but are hosted by galaxies moving through the cluster. This is especially common in clusters that are in the process of merging with another cluster. In that case the host galaxy can be moving very fast, and even supersonically with respect to its local, ambient medium. Then the radio jets can be very strongly deflected into ‘tails’ by an effective cross wind and eventually disrupted. Figure 3 illustrates the mock synchrotron emission from such a simulated radio galaxy. The abruptness of jet bending depends on the relative speed of the jet with respect to its internal sound speed and the relative speed of the host galaxy through its ambient medium with respect to the sound speed of that medium. So, when strongly bent jets are seen in a radio galaxy it is a strong clue that the motion of the galaxy is supersonic in relation to its environment. When multiple tailed radio galaxies are found in a given cluster it provides potentially valuable information about the dynamical condition of the cluster, since a relaxed cluster ought not to have many galaxies moving at supersonic speeds through the cluster gas.
Even more complex motions between the host galaxies and the ambient gas are possible. Those can sometimes lead to really exotic-looking radio structures. One beautiful example of this is the radio source 3C75 in the merging cluster Abell 400. Evidently two massive galaxies have become gravitationally bound into a binary system with a separation of about 7 kpc. The orbital period should be around 100 Myr. The pair also appears to be moving together supersonically through the ambient medium. Each of those galaxies has formed radio jets. If it were not for the binary the expected outcome might resemble the situation pictured in Figure 3. However, the binary motions cause each of the two galaxies to oscillate in its motion and this causes the radio jets to develop more complex, twisted shapes before they disrupt into tails. Figure 4 illustrates a preliminary effort to simulate this dynamics. The image on the right shows the real 3C75, where pink is the radio emission (VLA) and blue is thermal X-rays (Chandra). The image on the left traces the distribution of gas expelled by each of the two galaxies in the binary system. This simulation seems to capture the general character of the dynamical situation responsible for 3C75.
From this short set of simulation results it ought to be clear why many different kinds of radio galaxy structures are expected to form. It also ought to be apparent that we need better catalogs of what behaviors do exist in nature in order to see how to focus our simulation efforts and to establish what are the most important dynamical conditions in radio galaxy formation.
One of our scientists Prof. Ray Norris put the call out to the Radio Galaxy Zoo community for a hunt on spiral galaxies hosting powerful radio sources. The first known galaxy of this type is 0313-192, a galaxy much like our Milky Way and has left astronomers baffled.
Figure 1: 0313-192 The wrong galaxy from the Astronomy Picture of the Day. Credit: W. Keel (U. Alabama), M. Ledlow (Gemini Obs), F. Owen (NRAO, AUI, NSF, NASA.
Here is Prof. Norris’ post:
Keep an eye out for any hourglass sources that seem to be hosted by galaxies that look spiral in the infrared. These objects are incredibly rare in the local Universe (only 2 or 3 known) and we may not see any in Radio Galaxy Zoo, but if someone does find one, that would be worth writing a paper about (with the discoverer as co-author, of course). The rarity of radio-loud spirals is thought to be because the radio jets heat up and disrupt the gas in the spiral, switching off star formation, and turning the galaxy into a “red dead” elliptical. But we might find one or two where the jets have only just switched on and haven’t yet destroyed the spiral. See The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar for another example of this process in its very early stage. So keep your eyes peeled and yell out (very loudly) if you find one!
We are pleased to announce that the Radio Galaxy Zoo community has identified over a dozen potential candidates and we are in the process of following these up.
Have you seen any? Head over to Radio Galaxy Zoo to join in on the hunt and let us know what you find.
Meet Julie (aka @42jkb on RadioTalk), a project scientist on Radio Galaxy Zoo!
I’m a postdoctoral fellow at CSIRO Astronomy and Space Science in Australia. This is my first position after obtaining my PhD from the University of Calgary, Canada working on magnetic fields of radio galaxies. My first memories of astronomy and the wonders of the Universe were spending summer nights outside at campfires with my family staring up and counting the number of “shooting stars” we could see. It wasn’t until my second year of undergraduate studies at Western University in Ontario Canada that I considered doing astrophysical research; I was actually going through to be an airline pilot! I haven’t looked back at my decision to change into physics and astronomy and everyday I am amazed at the complexity and beauty of the Universe.
I spend my time researching magnetic fields and how important they are to radio galaxies. You can usually find me at the Australia Telescope Compact Array taking observations of all types of radio galaxies, sitting in front of a computer doing the exact same thing as Radio Galaxy Zoo, learning about life from my daughter, and educating myself on the wonderful country I now live in. I am excited about what Radio Galaxy Zoo has to offer the astronomical community and what the Universe will unfold for us through this project. Thank you for taking part!
Some colleagues and I successfully proposed for a symposium on citizen science at the annual meeting of the American Association for the Advancement of Science (AAAS) in San Jose, CA in February 2015. (The AAAS is one of the world’s largest scientific societies and is the publisher of the Science journal.) Our session will be titled “Citizen Science from the Zooniverse: Cutting-Edge Research with 1 Million Scientists.” It refers to the more than one million volunteers participating in a variety of citizen science projects. This milestone was reached in February, and the Guardian and other news outlets reported on it.
The Zooniverse began with Galaxy Zoo, which recently celebrated its seventh anniversary. Of course, Galaxy Zoo has been very successful, and it led to the development of a variety of citizen science projects coordinated by the Zooniverse in diverse fields such as biology, zoology, climate science, medicine, and astronomy. For example, projects include: Snapshot Serengeti, where people classify different animals caught in millions of camera trap images; Cell Slider, where they classify images of cancerous and ordinary cells and contribute to cancer research; Old Weather, where participants transcribe weather data from log books of Arctic exploration and research ships at sea between 1850 and 1950, thus contributing to climate model projections; and Whale FM, where they categorize the recorded sounds made by killer and pilot whales. And of course, in addition to Galaxy Zoo, there are numerous astronomy-related projects, such as Disk Detective, Planet Hunters, the Milky Way Project, and Space Warps.
We haven’t confirmed all of the speakers for our AAAS session yet, but we plan to have six speakers who will introduce and present results from the Zooniverse, Galaxy Zoo, Snapshot Serengeti, Old Weather, Cell Slider, and Space Warps. I’m sure it will be exciting and we’re all looking forward to it!