Radio Galaxy Zoo: what radio lobe shapes tell us about the mutual impact of jets and intergalactic gas
The following blogpost is from Stas Shabala about the Radio Galaxy Zoo paper led by his student, Payton Rodman, exploring the origin of asymmetries observed in a sample of Radio Galaxy Zoo radio galaxies.
Another Radio Galaxy Zoo paper has just been accepted for publication. “Radio Galaxy Zoo: Observational evidence for environment as the cause of radio source asymmetry” will shortly appear in Monthly Notices of the Royal Astronomical Society, and is already available on the preprint server (https://arxiv.org/abs/1811.03726). This paper, led by University of Tasmania undergraduate student Payton Rodman, looks at the properties of lobes in powerful radio galaxies. These lobes are inflated by a pair of jets, emerging in opposite directions from the accretion disk of the black hole at the centre of their host galaxy. Astronomers have known for a while that how big, bright or wide the radio lobes are depends on the properties of the intergalactic gas into which these lobes expand. Small, slow-growing lobes are usually found in galaxy clusters, while their large, rapidly expanding cousins tend to stay away from such dense environments. Radio lobes move about and heat intergalactic gas, and in this way they are thought to be responsible for regulating the formation of stars (by staving off the gravitational collapse of cold gas) in massive galaxies over the last eight billion years. Because of this, understanding how jets and lobes interact with their surroundings is important for understanding the history of the Universe. What complicates matters is that the mechanisms responsible for feeding the black hole and generating jets are also different in these two environments. So does nature or nurture determine what the lobes look like?
We decided to use the fact that all radio galaxies start out with two intrinsically identical jets propagating in opposite directions. If the two resultant lobes look different, this could only be due to the interaction with the surrounding gas – in other words, nurture. To test the nurture hypothesis, we used the first tranche of Radio Galaxy Zoo classifications. We selected all sources classified by citizen scientists to contain two clear radio lobes, and subjected this sample to a number of rigorous cuts on brightness, shape, redshift, and availability of environment information. Hot intergalactic gas is usually traced by X-ray observations, but these are unavailable for the majority of the sample. Instead, we used the clustering of optical galaxies from the Sloan Digital Sky Survey, which should be a good proxy for the underlying gas distribution. Then, for each radio galaxy, we compared the properties of the two radio lobes to how many galaxies were found near each of the lobes. We found a clear anti-correlation between the length of the radio lobe, and the number of nearby galaxies – in other words, shorter lobes have more galaxies surrounding them. These results were in excellent agreement with quantitative predictions from models (such as this hydrodynamic simulation made on the University of Tasmania’s supercomputer by PhD student Patrick Yates), which show that it is more difficult for lobes to expand into dense environments. The relationship between the luminosity of the lobes and galaxy clustering was much less clear, again consistent with models which predict a highly non-linear luminosity evolution as the lobes grow.
The excellent agreement between models and observations suggests that it is nurture, not nature, which determines lobe properties. It also opens up a new way of studying radio galaxy environments: though sensitive observations of optical galaxy clustering. With help from Zooites, we hope to expand this work to a much larger Radio Galaxy Zoo sample, which would allow us to probe the finer aspects of jet – environment interaction. Further afield, the ongoing GAMA Legacy ATCA Southern Survey (GLASS) project on the Australia Telescope Compact Array, as well as the Australian Square Kilometre Array Pathfinder EMU survey, will use this method to study the physics of black hole jets and the impact they have on their surroundings in a younger Universe.
On the 31 October 2018, Radio Galaxy Zoo published its first end-to-end machine learning system for “Classifying Radio sources Automatically using Neural networks” (ClaRAN). This paper is led by ClaRAN’s developer, Chen Wu, a data scientist at the International Centre for Radio Astronomy Research at the University of Western Australia (ICRAR/UWA), who repurposed the FAST-rCNN algorithm (used by Microsoft and Facebook) to classify radio galaxies. ClaRAN was trained on radio galaxies classified by Radio Galaxy Zoo and so recognises some of the most common radio morphologies that have been classified.
The purpose of ClaRAN is to reduce the number of radio sources that require human visual classification so that future Radio Galaxy Zoo projects will have fewer “boring” sources, thereby increasing the chances of real discoveries by citizen scientists. ClaRAN (and its future cousins) are crucial for future surveys such as the EMU survey which is expected to detect ~70 million radio sources (using the Australian Square Kilometre Array Pathfinder telescope). While Radio Galaxy Zoo has made visual source classifications much more efficient, we will still need to reduce the total survey sample size to a sample for visual inspection that is less than 1% of the 70 million sources.
How does ClaRAN work? ClaRAN inspects both the radio and coordinate-matched infrared overlay in the same fashion as RGZ Zooites, and then determines the radio source component associations in a similar fashion to the RGZ Data Release 1 (DR1) catalogue. As ClaRAN is still in its prototype stage (–analogous to the capabilities of a toddler), it only understands 3 main classes of radio morphologies — sources which have 1-, 2- or 3- separate radio components. ClaRAN was trained to understand these three different radio morphologies through seeing examples of all three classes from the
RGZ DR1 catalogue. The animated gif in the figure below (from the ICRAR press release) describes how ClaRAN “sees” the example radio galaxy.
As we look towards the future, we look forward to teaching ClaRAN some of
the more complex and exotic radio galaxy structures. For that to happen, we need to assemble much larger samples of more complex radio morphology classifications. With your support of Radio Galaxy Zoo, I am sure that we will get there.
Fun fact: did you know that some of the more obscure bugs in the RGZ DR1 catalogue processing was actually found through training ClaRAN? This is because ClaRAN is a good learner and will learn all the small details that we didn’t initially notice. We only discovered these bugs through some of the funny answers that we got out of some of the early testing of ClaRAN.
Thank you very much again to all our Radio Galaxy Zooites for your support. More information on the ICRAR press release for ClaRAN can be found via this link: https://www.icrar.org/claran/
Help vote for Radio Galaxy Zoo Gems!
At the Galaxy Zoos (both at Galaxy Zoo & Radio Galaxy Zoo), we are fizzling with excitement as we prepare for observations using the Advanced Camera for Surveys instrument on board the Hubble Space Telescope. These new Hubble maps will have greater resolution than those that we have from the Sloan Digital Sky Server.
As mentioned by Bill’s blogpost, we have been allocated fewer observing slots than our full list of candidates. Therefore, we invite all of you to help shape the observing priorities of our current target list. You will help determine which host galaxies would gain the most from these Hubble observations (and thus have highest priorities on the target list).
The main science targets specific to these Hubble observations are the host galaxies of Green Double Radio-lobed Active Galactic Nuclei (Green DRAGN — pronounced Green Dragon) and Spiral Double
Radio-lobed Active Galactic Nuclei (S-DRAGN).
Green DRAGN — The prominent green appearance in these DRAGN host galaxies come from the strong [OIII] emission line that dominate the emission in the Sloan r-band. Therefore, these galaxies appear very green in a Sloan 3-colour (g,r,i) image due the lack of equivalently-strong emission in the Sloan g– and i– bands (the blue- and red- filters, respectively). The Green Pea galaxies (Cardamone et al 2009) from the original Galaxy Zoo project are a class of green galaxies that appear to be dominated
by star formation. On the other hand, the Green Bean galaxies (Schirmer et al 2013) are thought to consists of quasar light echoes (eg Galaxy Zoo’s Hanny’s Voorwerp). However, the original Green Bean population show little to no emission at radio wavelengths.
In Radio Galaxy Zoo, we have found a population of Green Bean-like galaxies which host bright radio lobes. Therefore, what sort of feedback are galaxies getting from these “radio-active” Green DRAGNs and how do they relate to the other green galaxies and our understanding of galaxy evolution? Figure 1 shows an example of a Green DRAGN that also happened to be a Hybrid Morphology Radio Galaxy
found by Radio Galaxy Zoo and published by team scientist Anna Kapinska in collaboration with citizen scientist Ivan Terentev (see blogpost on their paper).
Spiral DRAGN — Typically, radio galaxies with big radio jets and lobes are hosted by early-type galaxies. Spiral galaxies are often thought to not be “mature” or massive enough to host giant radio lobes. However, a few S-DRAGNs have been found in the past by our very own Bill Keel (Keel et al 2006, see Figure 2) and Minnie Mao (Mao et al 2015). To shed light on this rare phenomena,
we seek your help through Radio Galaxy Zoo and this observing programme to assemble a more statistically significant number of this rare class of objects. Figure 2 shows a combined HST and VLA map of the S-DRAGN
published by Bill in 2006.
We have to finish this priority selection by the 16th February 2018. So, please help vote now by clicking here. We have uploaded the targets in batches of 24 and so please click on all the batches for a view of the full target list. A handy tip for inspecting these images is to ensure that your screen brightness is adjusted to its maximum because many of the host galaxy features can be very faint.
We thank Radio Galaxy Zooites, Jean and Victor, for their immense help with assembling the priority selection project interface. You can track what Hubble is observing by proceding to the Hubble archive link or the Hubble Legacy Archive interface here.
The following blogpost is from Anna Kapinska about the Radio Galaxy Zoo paper that she published recently with Radio Galaxy Zooite, Ivan Terentev on the first sample of candidate Hybrid Morphology Radio Sources (HyMoRS) from the 1st year of Radio Galaxy Zoo results.
Radio Galaxy Zoo scores another scientific publication! The paper ‘Radio Galaxy Zoo: A search for hybrid morphology radio galaxies’ has been published today in the Astronomical Journal. First of all congratulations to everyone, and what wonderful work from all our citizen scientists and the science team! Special thanks go to Ivan Terentev, one of our very active citizen scientists, whose persistent work on finding and collecting HyMoRS in a discussion thread on RadioTalk (link) without doubt earned the second place in the author list of this paper. But of course the publication wouldn’t be possible without all our volunteers, and special thanks are noted in the paper (check out the Acknowledgements on page 14):
“This publication has been made possible by the participation of more than 11,000 volunteers in the Radio Galaxy Zoo Project. Their contributions are acknowledged at http:// rgzauthors.galaxyzoo.org. We thank the following volunteers, in particular, for their comments on the manuscript or active search for candidate RGZ HyMoRS on RadioTalk: Jean Tate, Tsimafei Matorny, Victor Linares Pagán, Christine Sunjoto, Leonie van Vliet, Claude Cornen, Sam Deen, K.T. Wraight, Chris Molloy, and Philip Dwyer.”
But what are HyMoRS? HYbrid MOrphology Radio Sources, HyMoRS or hybrids for short, are peculiar radio galaxies that show atypical radio morphologies. That is, radio galaxies which we can resolve in our observations come in two principal flavours: 1) FRI – type; and 2) FRII-type — named after two scientists who introduced this classification back in 1974, Berney Fanaroff and Julia Riley [link to paper].
Traditionally, FRIs and FRIIs are distinguished by different morphologies observed in radio images, where on the one hand we have archetypal FRIIs showing powerful jets that terminate in so-called hotspots (can be spotted in right panel of Figure 1 as two white bright spots at the ends of the jets), while on the other there are FRIs with their jets often turbulent and brightest close to the host galaxy and its supermassive black hole (left panel of Figure 1). HyMoRS are hybrids, they show both morphologies at the same time, that is they look like FRI on one side and FRII on the other side. Figure 2 shows two examples of the new HyMoRS candidates that Radio Galaxy Zoo identified in this latest paper.
How are HyMoRS formed? We still don’t have a very clear answer to this question. The thing is that there may be many reasons why one radio galaxy would have so radically different looking jets. One possibility is that the medium in which the jets travel through (the space around) is different on each side of the galaxy. In this case the FRI morphology could form if the medium is dense or clumpy for one jet, while FRII morphology could form if the medium is smoother or less dense on the other side for the second jet (but watch this space for more work from our science team). But there are also other options. For example, we may simply see the radio galaxy in projection, or we are observing rare events of a radio galaxy switching off, or switching off and on again. The more HyMoRS we know of, the better we can study them and pinpoint the scenarios of how they form.
For example, the science team at the University of Tasmania has produced a simulation of jets from an FRII-type radio galaxy located in the outer regions of a cluster (~550 kpc from the centre) and expanding in a non-uniform cluster environment. The jet on one side propagates into a much denser medium than the jet on the other side. The jets are very powerful (10^38 Watts) and the total simulation time is 310 Myr. The movies display the density changes associated with the jet expansion. Credit goes to Katie Vandorou, Patrick Yates and Stas Shabala for this simulation (link to simulation).
How rare are HyMoRS? We actually don’t really know, and this is because so far there are very few complete surveys of these radio galaxies. Current estimates indicate that they may be comprising less than 1% of the whole radio galaxy population. We are hoping that with Radio Galaxy Zoo and the new-generation telescopes we will be able to finally pin down the HyMoRS population. And our paper is definitely one big step towards that aim. It’s very exciting as with the fantastic efforts of RGZ we now have 25 new HyMoRS candidates — this could possibly double the numbers on known hybrids!”
So well done everyone and let’s keep up the fantastic work! We couldn’t have done it without you 🙂
Anna, Ivan & the coauthors on this latest paper
The official open access refereed paper can now be found at http://iopscience.iop.org/article/10.3847/1538-3881/aa90b7
The article can also be downloaded from: http://arxiv.org/abs/1711.09611
A CAASTRO story with embedded animation is now available at: http://www.caastro.org/news/2017-hymors
The following blogpost is from Omar Contigiani about the Radio Galaxy Zoo paper that he published recently on the cosmic alignment of radio sources.
In the Radio Galaxy Zoo an incredible variety of creatures can be found — as our citizen scientists might know by now, radio sources in the sky can have all sorts of shape and sizes. The most powerful among them are plasma-filled jets emitted by the some of the largest elliptical galaxies in existence. Because of their precise structure, anyone can associate orientations to these sources by simply looking at the directions the jets point at.
Recently, our scientists have been looking at the directional properties of these fascinating beasts. If a particular source points in a direction, is it possible that its neighbours also tend to do the same? Because the distances between adjacent objects are (quite literally) astronomical, it seems intuitive to assume that the relative orientations should be random. However, nature always finds subtle ways to mess with our intuition and it turns out that this is currently an open question in astronomy. Thanks to Radio Galaxy Zoo’s numerous (almost two million) image classifications, the team was able to report the most precise measurement of this effect to date. The results are available in a scientific article published in Monthly Notices of the Royal Astronomical Society this November.
The analysis performed in the study suggests that relative alignment of radio sources is present on distances which are dubbed as cosmological. This is because only phenomena related to the history of the Universe as a whole are known to be connected to such large scales.
While this is an exciting step towards an answer, formulating any conclusive statement about this alignment and the reasons behind it appears to be difficult. What drives this effect? Is it related to a shared history or environment? More science needs to be done and more galvanising discoveries are waiting for us just around the corner.
Once again, without the contributions made by our volunteers all over the world, we would not have been so successful in our endeavours. A big thank you to all our Radio Galaxy Zooites!
However, we have only reached 74% of our classification target. Head to Radio Galaxy Zoo to become involved and you will be contributing to real science being done today and may be co-authoring another great discovery with us!
Meet Francesco de Gasperin, an associate science team member (since 2015) who is very interested in the classifications resulting from Radio Galaxy Zoo
I am a VENI fellow at the Leiden University in the Netherlands. My research is mainly based on developing and exploiting new technologies in radio-astronomy to study active galactic nuclei (AGN), galaxy clusters, galaxies and ultimately everything which emits radio waves. I am part of the LOFAR collaboration and most of my time is invested in the commissioning of this new radio-telescope. I am now leading the effort to calibrate the low band antennas of LOFAR to observe the sky at decameter wavelength. Our plan is to ultimately produce the lowest frequency radio survey ever done.
I did my PhD at the Max Planck Institute for Astrophysics in Munich on a thesis titled: “The impact of radio-emitting supermassive black holes on their environment: the LOFAR view of the Virgo cluster”. During my master I also worked for the Planck mission, a satellite designed to study the Cosmic Microwave Background (CMB) – the relic radiation from the Big Bang.
What has Francesco and his student, Omar Contigiani done lately ?
Is the orientation of radio galaxies totally random? Or is it driven by the large scale structure where galaxies are embedded in? Recently, some works on small regions of the sky claimed an intrinsic alignment of radio sources. This is in line with the observed alignment between quasar jets and the surrounding large scale structure at higher redshifts.
With the help of the RGZ we are now able to identify the orientation of a very large number of radio galaxies. This allows us to expand these studies to unprecedented scales, moving from regions of few square degrees to around 10 thousands.
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|
|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.
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.
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.
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?”
The 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.
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!
Ivy, Julie & RGZ team
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