Archive by Author | oiwei

Radio Galaxy Zoo searches for Hybrid Morphology Radio galaxies (HyMoRS): #hybrid

First science paper on hybrid morphology radio galaxies found through Radio Galaxy Zoo project has now been submitted!

hybrid_blogfig1 In the paper we have revised the definition of the hybrid morphology radio galaxy (HyMoRS or hybrids) class. In general, HyMoRS show different Fanaroff-Riley radio morphology on either side of the active nucleus, that is FRI type on one side and FRII on the other side of their infrared host galaxy. But we found that this wasn’t very precise, and set up a clear definition of these sources, which is:

”To minimise the misclassification of HyMoRS, we attempt to tighten the original morphological classification of radio galaxies in the scope of detailed observational and analytical/numerical studies undertaken in the past 30 years. We consider a radio source to be a HyMoRS only if

(i) it has a well-defined hotspot on one side and a clear FR I type jet on the other, though we note the hotspots may `flicker’, that is their brightness may be rapidly variable (Saxton et al. 2002), and, in the case the radio source has a very prominent core or is highly asymmetric,

(ii) its core prominence does not suggest strong relativistic beaming nor its asymmetric radio structure can be explained by differential light travel time effects. ”

Based on this we revised hybrids reported in scientific literature and found 18 objects that satisfy our criteria. With Radio Galaxy Zoo during the first year of its operation, through our fantastic RadioTalk, you guys now nearly doubled this number finding another 14 hybrids, which we now confirm! Two examples from the paper are below:

We also looked at the mid-infrared colours of hybrids’ hosts. As explained by Ivy in our last RGZ blog post (, the mid-infrared colour space is defined by the WISE filter bands: W1, W2 and W3, corresponding to 3.4, 4.6 and 12 microns, respectively.

The results are below:


For those of you interested in seeing the full paper, we will post a link to freely accessible copy once the paper is accepted by the journal and is in press! 🙂

Fantastic job everyone!
Anna & the RGZ science team

First Radio Galaxy Zoo paper has been submitted!

The project description and early science paper (results from Year 1) for the Radio Galaxy Zoo project has been submitted!


authorlist1We find that the RGZ citizen scientists are as effective as the science experts at identifying the radio sources and their host galaxies.

Based upon our results from 1 year of operation, we find the RGZ host galaxies reside in 3 primary loci of mid-infrared colour space.  The mid-infrared colour space is defined by the WISE filter bands: W1, W2 and W3, corresponding to 3.4, 4.6 and 12 microns; respectively.

Approximately 10% of the RGZ sample reside in the mid-IR colour space dominated by elliptical galaxies, which have older stellar populations and are less dusty, hence resulting in bluer (W2-W3) colours. The 2nd locus (where ~15% of RGZ sources are found) lies in the colour space known as the `AGN wedge’, typically associated with X-ray-bright QSOs and Seyferts. And lastly, the largest concentration of RGZ host galaxies (~30%) can be found in the 3rd locus usually associated with luminous infrared galaxies (LIRGs).  It should be noted that only a small fraction of LIRGs are associated with late-stage mergers.  The remainder of the RGZ host population are distributed along the loci of both star-forming and active galaxies, indicative of radio emission from star-forming galaxies and/or dusty elliptical (non-star-forming) galaxies. See the figure below for a plot of these results.

blog_fig2Caption to figure WISE colour-colour diagram, showing sources from the WISE all-sky catalog (colourmap), 33,127 sources from the 75% RGZ catalog (black contours), and powerful radio galaxies (green points) from (Gürkan et al. 2014). The wedge used to identify IR colours of X-ray-bright AGN from Lacy et al. (2004) & Mateos et al. (2012) is overplotted (red dashes). Only 10% of the WISE all-sky sources have colours in the X-ray bright AGN wedge; this is contrasted with 40% of RGZ and 49% of the Gürkan et al. (2014) radio galaxies. The remaining RGZ sources have WISE colours consistent with distinct populations of elliptical galaxies and LIRGs, with smaller numbers of spiral galaxies and starbursts.

In addition, we will also be submitting our paper on Hybrid Morphology Radio Sources (HyMoRS) in the next few days so stay tuned!

As always, thank you all very much for all your help and support and keep up the awesome work!

Julie, Ivy & the RGZ science team

1 million classifications and beyond!

Huzzah! We have now broken through the 1 million mark with Radio Galaxy Zoo as of January 16, 2015. It has taken all of you ~13 months to do 40 years worth of cross-identifications. Well done and a huge thank you to every single one of you out there who helped us along.

A big shout-out to the winners of our 1 millionth classification milestone competition. The winners are: @planetari7, @ChrisMolloy, @leonie van vliet, @antikodon, @BOSSARD louis michel and @JF45456.   I will be e-mailing each of you soon.

My biggest thank you to every single Radio Galaxy Zooite who helped us get this far. We really could not have done this without you.


Ivy, Julie & the entire RGZ team

Happy 1st birthday Radio Galaxy Zoo!

Hurray! Radio Galaxy Zoo has reached its first anniversary!


A scrumptious cake model of an AGN made by Zookeeper Kevin’s students, Anna Weigel & Lia Sartori.

What a wonderful year it has been! In 1 year, we have completed ~30% of the project and  have reached nearly 1 million classifications! In celebration of our anniversary, we are announcing that we will offer some special prizes to the first few citizen scientist(s) who take us to the 1 millionth classification and beyond! The top prizes we have to offer include a signed copy of “Bang! — the complete history of the Universe” signed by Brian May & Chris Lintott, a black ICRAR T-shirt (in your size), a CSIRO water bottle, CSIRO mugs, 3D telescope bookmarks and some Zooniverse stickers.


First prize for the RGZooite who helps us reach 1 million classification gets a signed copy of “Bang!” !

Using the current number of classifications of 931,029 and assuming that each classification took 5 minutes, this translates to a continuous working time of nearly 9 years! If we assume that one can only classify continuously over a standard 40-hour work-week, it’d take more than 37 years to complete what you all have so kindly done in 1 year!

In addition to matching the radio jets with their black holes, we (the citizen scientists & the science team) are making  new discoveries of extreme types of radio galaxies. Just a few days after launch last year, @Dolorous_Edd and @antikodon discovered a very large nearby wide-angle tailed radio galaxy. They are currently working with Prof Rudnick and Prof Andernach on publishing their findings and analysis. Large teams of RGZ citizen scientists are also helping Dr Kapinska and Dr Mao with their search for Hybrids and S-DRAGNs, respectively!

Thank you all so very much for your support! We are most grateful for such a humbling effort by everyone. We hope that all of you have a wonderful holiday period and wishing you all a great upcoming year!

Best wishes, Ivy & Julie
(@ivywong & @42jkb)

RGZ Team Spotlight: Minnie Mao

Meet Minnie Mao, leading the study of spiral double radio lobe AGNs (or S-DRAGNs) for Radio Galaxy Zoo.

minnie_vlaHello! 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?

RGZ Team Spotlight: Julie Banfield

Meet Julie (aka @42jkb on RadioTalk), a project scientist on Radio Galaxy Zoo!

julieI’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!

Radio interferometry, Fourier transforms, and the guts of radio interferometry (part 2)

Today’s post is also from Dr Enno Middelberg and is the second part of two explaining in more detail about radio interferometry and the techniques used in producing the radio images in Radio Galaxy Zoo.

In a previous post I have explained how the similarity of the electric field at two antennas’ locations is related to the Fourier transform of the sky brightness. Unfortunately, we’re not quite there (yet). You may have heard about sine and cosine functions and know that they are one-dimensional. Images, and the sky brightness distribution, however, are two-dimensional. So how can we imagine a two-dimensional Fourier transform? In this case, we have to combine 2D waves with various frequencies, amplitudes, and orientations into one image. We can make a comparison with waves on a lake. Just like a sine or cosine wave, a water wave has an amplitude and a frequency, but in addition it also has an orientation, or a direction in which it travels. Now let us think of a few people sitting around a pond or lake. Everyone kneels down to generate waves which then propagate through the water. Let us further assume that the waves are not curved, but that the crests and valleys are parallel lines. Now all these waves, with properly chosen frequencies, amplitudes, and directions will propagate into the center of the pond, where the waves interfere. With just the right parameters, the interference pattern can be made to look like a 2D image. In a radio interferometer, every two telescopes make a measurement which represents the properties of such a wave, and all waves combined then can be turned into an image. Let me point out that the analogy with the lake is taking things a little bit too far: since the water waves keep moving across the lake, a potential image formed by their intererence will disappear quite quickly, but I hope you get the point about interfering 2D waves.

To illustrate this further I have made a little movie. Let us assume that the radio sky looks just like Jean Baptiste Joseph Fourier (top left panel in the movie). I have taken this image from Wikipedia, cropped it to 128×128 pixels, and calculated its Fourier transform. The Fourier transform is an image with the same dimensions, but the pixels indicate the amplitude, phase and frequency of 2D waves which, when combined, result in an image. Then I have taken an increasing number of pixels from this Fourier transform (which ones is indicated at the top right), calculated which 2D waves they represent (bottom right), and incrementally added them into an image (bottom left). At the beginning of the movie, when only few Fourier transform pixels are used, the reconstructed Mr. Fourier is barely recognizable, with 50 Fourier pixels added, one begins to identify a person, and with an increasing number of waves added, the image more and more resembles the input image. You should play it frame by frame, in particular at the beginning, when the changes in the reconstructed image are large. In radio interferometry, Mr. Fourier’s image is what we want (how does the sky look like?), but what we get is only the pixels shown in the upper right image. Each of these pixels, all by itself, provides information as illustrated in the bottom  right, but all together, they yield an image such as in the bottom left image. And the more pixels we measure, the more accurate the image becomes.

So in summary: a radio interferometer makes measurements of the similarity of the electric field at two locations, and the degree of similarity represents the Fourier transform of the sky radio brightness for the two antennas in that instant. Astronomers then reconstruct the sky brightness from all these measurements taken together – that’s also why the technique is called “synthesis imaging”, or “aperture synthesis”. And if you’ve kept reading until here without having your brain turn to mush – congratulations! This is typically the subject of lectures for advanced physics students. I’ve been learning about radio interferometry now for more than 15 years and am still discovering new and interesting bits.

Radio interferometry, Fourier transforms, and the guts of radio interferometry (Part 1)

Today’s post comes from Dr Enno Middelberg and is the first part of two  explaining in more detail about radio interferometry and the techniques used in producing the radio images in Radio Galaxy Zoo.


I have written in an earlier post about the basic idea of how to increase the resolution of a radio telescope: use many telescopes, separated by kilometers, and observe the same object with all. Here is a little more information about how this works.

At the very heart of an interferometer is the van Cittert-Zernike theorem: it essentially states that the degree of similarity of the electric field at two locations is a measure of the Fourier transform of the sky brightness distribution. Now that’s a big bite to swallow, but let me explain it in less confusing words: the electric field is all we can measure – radio waves are electromagnetic waves, and radio telescopes are sensitive to the electric field. Now we can build a radio telescope in a way that it produces as its output a voltage which is proportional to the electric field which the antenna receives from, e.g., a galaxy. Much of the signal will be noise from our own Milky Way, the atmosphere and the electronics which amplify the feeble signals, but a tiny little bit of the signal will be caused by radio waves from space, and both antennas will receive a little bit of these. Now suppose we have two telescopes separated by 1 km or so, and both telescopes produce such voltages which contain a little bit of this signal. The voltages are digitised and the two data streams are fed into a correlator. The correlator is a computer which takes the two data streams and calculates their correlation coefficient, which is an indicator for their similarity. If the two data streams have nothing in common (for example, because an unexperienced PhD student pointed the two antennas in different directions 🙂 ) then the correlation coefficient will be zero, which is to say that they are not similar at all. However, if the two telescopes point at the same source, the data streams will have a few bits in common, and the correlator spits out a correlation coefficient which is not zero. This is our measurement!

Now that we’ve that out of the way, we need to talk about Fourier transforms. The van Cittert-Zernike theorem states that the correlation coefficient is a measure for the Fourier transform of the sky brightness. Now what is a Fourier transform? The Fourier transform is an ingenious way of representing a mathematical function with a sum of sine and cosine functions. That is, if I take a large number of sine and cosine functions with various (but carefully selected!) frequencies and amplitudes, then their sum will be an accurate representation of another function, for example a square wave or a sawtooth. Check out the Wikipedia page on Fourier series (which are related to Fourier transforms, but easier to understand), which has a number of nice animations to illustrate this, such as this one:

You can also play with Paul Falstad’s Java applet to see how to construct functions using sine and cosine waves interactively – very instructive! In part 2 of this post I will explain how astronomers use 2D Fourier transforms to assemble images of the radio sky.


Radio Galaxy Zoo is now available in Chinese!

We’re pleased to announce that Radio Galaxy Zoo has been 
translated to traditional character Chinese. Many thanks
to the Zooniverse’s Chris Snyder for getting all the technical
things set up for the translation to go live and Mei-Yin Chou
at Academia Sinica’s Institute of Astronomy & Astrophysics
(ASIAA) for helping verifying the translation. What follows
is an announcement describing Radio Galaxy Zoo and the translation
in traditional character Chinese and then in English: 電 波星系動物園[中 文版]歡 迎你的加入!在此我們欣然宣佈本計畫中文版開始啟用。
感謝中央研究院天文及天文物理研究所 Dr. Meg Schwamb (Meg是 參與Planet
Hunters 和Planet Four計 畫的科學家)以 及天文推廣團隊成員黃珞文協助,
將英文內容翻譯轉換為繁體中文。在 許多星系核心深處其實隱匿著一些超大質量的黑洞,
時仍可看得到從星系核心噴出的巨大噴流。由 電波波段看到的天空和在「可見光」
波段所看到的(可見的意思就是人類肉眼所看得到的),此兩種景象有時大異其 趣。
或有時這些噴流的外觀是筆直的直線,有時卻 是一團、只有單邊而非雙邊對稱、
電波噴流和團塊影像,它們需要和所屬的宿主星系做成匹配。因 此,我們邀請你加入我們的行列,
再將它 們和紅外圖像進行比較及匹 配,這麼一來,在你的協助下,
噴流和宿主星系間本來付之闕如的關聯 性,未來將可建立成形。

Image Welcome to Radio Galaxy Zoo (Chinese)! It is with great
pleasure that we announce the launch of the Chinese version
of our project. We are very grateful to Dr Meg Schwamb
(from Planet Hunters and Planet Four) and Lauren Huang from
Academia Sinica’s Institute of Astronomy & Astrophysics
(ASIAA) for their help with translating our project from
English to traditional Chinese characters. Supermassive black holes (~several hundred million times
the mass of our Sun) lie deep in the cores of many galaxies.
And though we cannot directly see these black holes, we do
sometimes see the huge radio jets originating from the galaxy
cores. Galaxies in the radio sky can look quite different from
the one seen in the optical wavelengths by instruments such
as our own eyes. Some galaxies do not have any central radio
emission but only radio jet(s) emanating outwards. Sometimes
these jets are straight but at other times, they can be blobby,
one-sided or bent. With very large all-sky radio surveys, we
have many hundreds of thousands of radio jets and blobs that
need to be matched to their host galaxies. Therefore we invite you to see the Universe as you have never
seen before and help us map the radio sky by matching the radio
jets and filaments to the galaxies (as seen in the infrared images) from
whence they came.