Radio Galaxy Zoo (RGZ) is an internet crowdsourced citizen science project that seeks to locate supermassive black holes in distant galaxies.[1][2] It is hosted by the web portal Zooniverse. The scientific team want to identify black hole/jet pairs and associate them with the host galaxies. Using a large number of classifications provided by citizen scientists they hope to build a more complete picture of black holes at various stages and their origin.[3][4] It was initiated in 2010 by Ray Norris in collaboration with the Zooniverse team, and was driven by the need to cross-identify the millions of extragalactic radio sources that will be discovered by the forthcoming Evolutionary Map of the Universe survey. RGZ is now led by scientists Julie Banfield and Ivy Wong.[5] RGZ started operations on 17 December 2013,[3] and ceased collecting new classifications on 1 May 2019.[6]
RGZ has published five scientific studies (May 2018).
i) Radio Galaxy Zoo: host galaxies and radio morphologies derived from visual inspection. (November 2015)[1][8]
The abstract begins: "We present results from the first twelve months of operation of Radio Galaxy Zoo, which upon completion will enable visual inspection of over 170,000 radio sources to determine the host galaxy of the radio emission and the radio morphology."[1] It then explains that RGZ "uses 1.4GHz radio images from both the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and the Australia Telescope Large Area Survey (ATLAS) in combination with mid-infrared images at 3.4μm from the Wide-field Infrared Survey Explorer (WISE) and at 3.6μm from the Spitzer Space Telescope."[1] Its aims are that when complete, RGZ will measure the relative populations and properties of host galaxies; processes that might also provide an avenue for finding radio structures that are rare and extreme.[1]
On the International Centre for Radio Astronomy Research (ICRAR) website, an article from September 2015 named "Volunteer black hole hunters as good as the experts" explains how citizen scientists are as good as professionals at RGZ's tasks.[9] The research team tested trained citizen scientists and ten professional astronomers using a hundred images to help quantify the quality of the data gathered. As the initial results were published, facts and figures from RGZ became available. More than 1.2 million radio images have been looked at, which enabled 60,000 radio sources to be matched to their host galaxies: "A feat that would have taken a single astronomer working 40 hours a week roughly 50 years to complete."[9]
Radio Galaxy 3C 83.1B an example of a Wide-angle Tail Radio Galaxy
ii) Radio Galaxy Zoo: discovery of a poor cluster through a giant wide-angle tail radio galaxy. (May 2016)[10][11]
The abstract begins: "We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project." It continues to explain that the analysis of 2MASX J08231289+0333016's surrounding environment indicates that it is within a poor cluster. Radio morphology suggests that, firstly, "the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster" and secondly that "the source may have had two ignition events of the active galactic nucleus with 10^7yrs in between."[10] These suggestions reinforce the idea that there is an association between RGZ J082312.9+033301 and the newly discovered poor cluster.[10]
On The Conversation website in an article "How citizen scientists discovered a giant cluster of galaxies", Ray Norris writes about the above study.[5] He explains that two Russian citizen scientists (CSs), Ivan Terentev and Tim Matorny, were participating in RGZ when they noticed something odd with one of the radio sources. It became clear that the radio source the two CSs had found "was just one of a line of radio blobs that delineate a C-shaped “wide angle tail galaxy” (WATG)." Lead scientist Julie Banfield explained that this was "something that none of us had even thought would be possible."[5]
WATGs are rare objects that are formed when jets of electrons from black holes, usually seen to be straight, are bent into a C shape by intergalactic gas. This characteristic shape is "a sure sign that there is intergalactic gas, signifying a cluster of galaxies, the largest known objects in the universe."[5] The WATG discovered by Terentev and Matorny is one of the largest known and has led to the cluster being named after them. "This cluster, more than a billion light years away, contains at least 40 galaxies, marking an intersection of the sheets and filaments of the cosmic web that make up our universe."[5] Clusters, despite their importance, are hard to find but the use of WATGs might be a way of finding more: However WATGs are rare.
On the National Radio Astronomy Observatory website, Matorny and Terentev commented on their discovery. “I am still amazed and feel more motivated to look for stunning new radio galaxies,” Matorny said.[12] Terentev added, “I got a chance to see the whole process of science … and I have been a part of it!”[12]
iii) Radio Galaxy Zoo: A Search for Hybrid Morphology Radio Galaxies. (December 2017)[13]
The abstract begins: "Hybrid morphology radio sources are a rare type of radio galaxy that display different Fanaroff-Riley classes on opposite sides of their nuclei." The authors explain that RGZ has enabled them to discover 25 new candidate hybrid morphology radio galaxies (HyMoRS). These HyMoRS are at distances between redshifts z=0.14 and 1.0. Nine of the host galaxies have previous spectra and include quasars and a rare Green bean galaxy. It states: "Although the origin of the hybrid morphology radio galaxies is still unclear, this type of radio source starts depicting itself as a rather diverse class."[13] The abstract ends:"While high angular resolution follow-up observations are still necessary to confirm our candidates, we demonstrate the efficacy of the Radio Galaxy Zoo in the pre-selection of these sources from all-sky radio surveys, and report the reliability of citizen scientists in identifying and classifying complex radio sources."[13]
In an article on the ARC Centre of Excellence for All-Sky Astrophysics CAASTRO website named "Citizen scientists bag a bunch of 'two-faced' galaxies", the author explains the findings of the above study.[14] The lead scientist is Anna Kapinska with CS Ivan Terentev named second. Kapinska's team have been looking for rare types of galaxies named Hybrid Morphology Radio Galaxies (HyMoRS). These show galaxy characteristics that are combined, rather than distinct. The article states: "Finding more HyMoRS helps us understand what kind of galaxy can turn out this way, and what gives them their unusual properties. Knowing that, in turn, helps us better understand how all galaxies evolve."[14]
The first recognised HyMoRS was discovered in 2002 and since then 30 more. RGZ near doubled the discoveries by adding 25 more. Galaxies with black holes that produce jets are often "divided into two classes, Fanaroff-Riley I and Fanaroff-Riley II (or FR I and II). FR I galaxies have jets that fade away as they extend outwards, while FR II galaxies have jets that end in a bright, strongly-emitting region (a ‘hotspot’)."[14] Explanations include the behaviour of the central black hole, different densities of matter in the surrounding environment or simply illusions because of different distances.[14]
iv) Radio Galaxy Zoo: Cosmological Alignment of Radio Sources (November 2017)[15]
In November 2017, a team led by Omar Contigiani published a paper in Monthly Notices of the Royal Astronomical Society studying the mutual alignment of radio sources.[15] Using data drawn from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and TIFR GMRT Sky Survey (TGSS), they investigate the most powerful radio sources, namely the largest elliptical galaxies emitting plasma-filled jets. The abstract begins: "We study the mutual alignment of radio sources within two surveys, FIRST and TGSS. This is done by producing two position angle catalogues containing the preferential directions of respectively 30059 and 11674 extended sources distributed over more than 7000 and 17000 square degrees."[15] The FIRST sample sources were identified by participants in RGZ, while the TGSS sample was the result of an automated process. Marginal evidence of local alignment is found in the FIRST sample, which has a 2% probability of being by chance. This supports other recent research by scientists using the Giant Metrewave Radio Telescope. The abstract ends: "The TGSS sample is found to be too sparsely populated to manifest a similar signal." Results suggest that there is a relative alignment present at cosmological distances.[15]
v) Radio Galaxy Zoo: Compact and extended radio source classification with deep learning (May 2018).[16]
In May 2018, Lukic and team published a study in Monthly Notices of the Royal Astronomical Society concerning machine learning techniques. The abstract begins: "Machine learning techniques have been increasingly useful in astronomical applications over the last few years, for example in the morphological classification of galaxies."[16]
Gems of the Galaxy Zoos (ZooGems)
During the next two years, up to 105 RGZ objects will be observed with the Hubble Space Telescope (HST) as a result of Program 15445, whose P.I. is William Keel.[17][18] The program's abstract begins: "The classic Galaxy Zoo project and its successors have been rich sources of interesting astrophysics beyond their initial goals. Green Pea starbursts, AGN ionization echoes, dust in backlit spirals, AGN in pseudobulges, have all seen HST followup programs."[17] As a result of NASA 'gap fillers' initiative, it is hoped that significant scientific progress can be made by HST observations of a total of 304 objects, which have been chosen by voters using a Zooniverse custom-made interface.[17] Keel stated: "Each one of them might not be enough for an individual study, but when you put them all together it adds up to an interesting study."[18]
Gems of the Galaxy Zoos finished in September 2023 after imaging 193 of the 300 candidates. Many of the images can be viewed on Wikimedia Commons.
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.
A radio galaxy is a galaxy with giant regions of radio emission extending well beyond its visible structure. These energetic radio lobes are powered by jets from its active galactic nucleus. They have luminosities up to 1039 W at radio wavelengths between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process. The observed structure in radio emission is determined by the interaction between twin jets and the external medium, modified by the effects of relativistic beaming. The host galaxies are almost exclusively large elliptical galaxies. Radio-loud active galaxies can be detected at large distances, making them valuable tools for observational cosmology. Recently, much work has been done on the effects of these objects on the intergalactic medium, particularly in galaxy groups and clusters.
Messier 87 is a supergiant elliptical galaxy in the constellation Virgo that contains several trillion stars. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.
Catalina Sky Survey is an astronomical survey to discover comets and asteroids. It is conducted at the Steward Observatory's Catalina Station, located near Tucson, Arizona, in the United States.
NGC 6397 is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752. It is located about 7,800 light-years from Earth, making it one of the two nearest globular clusters to Earth. The cluster contains around 400,000 stars, and can be seen with the naked eye under good observing conditions.
The Giant Metrewave Radio Telescope (GMRT), located near Narayangaon, Pune in India, is an array of thirty fully steerable parabolic radio telescopes of 45 metre diameter, observing at metre wavelengths. It is the largest and most sensitive radio telescope array in the world at low frequencies. It is operated by the National Centre for Radio Astrophysics (NCRA), a part of the Tata Institute of Fundamental Research, Mumbai. It was conceived and built under the direction of Govind Swarup during 1984 to 1996. It is an interferometric array with baselines of up to 25 kilometres (16 mi). It was recently upgraded with new receivers, after which it is also known as the upgraded Giant Metrewave Radio Telescope (uGMRT).
Amy J. Barger is an American astronomer and Henrietta Leavitt Professor of Astronomy at the University of Wisconsin–Madison. She is considered a pioneer in combining data from multiple telescopes to monitor multiple wavelengths and in discovering distant galaxies and supermassive black holes, which are outside of the visible spectrum. Barger is an active member of the International Astronomical Union.
Christopher John Lintott is a British astrophysicist, author and broadcaster. He is a Professor of Astrophysics in the Department of Physics at the University of Oxford, and, since 2023, Gresham Professor of Astronomy at Gresham College, London. Lintott is involved in a number of popular science projects aimed at bringing astronomy to a wider audience and is also the primary presenter of the BBC television series The Sky at Night, having previously been co-presenter with Patrick Moore until Moore's death in 2012. He co-authored Bang! – The Complete History of the Universe and The Cosmic Tourist with Moore and Queen guitarist and astrophysicist Brian May.
NGC 4639 is a barred spiral galaxy located in the equatorial constellation of Virgo. It was discovered by German-born astronomer William Herschel on April 12, 1784. John L. E. Dreyer described it as "pretty bright, small, extended, mottled but not resolved, 12th magnitude star 1 arcmin to southeast". This is a relatively nearby galaxy, lying approximately 72 million light-years away from the Milky Way. It is a companion to NGC 4654, and the two appear to have interacted roughly 500 million years ago. NGC 4639 is a member of the Virgo Cluster.
Galaxy Zoo is a crowdsourced astronomy project which invites people to assist in the morphological classification of large numbers of galaxies. It is an example of citizen science as it enlists the help of members of the public to help in scientific research.
Hanny's Voorwerp is a type of astronomical object called a quasar ionization echo. It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel while she was participating as a volunteer in the Galaxy Zoo project, part of the Zooniverse group of citizen science websites. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor.
Astroinformatics is an interdisciplinary field of study involving the combination of astronomy, data science, machine learning, informatics, and information/communications technologies. The field is closely related to astrostatistics.
Hercules A is a bright astronomical radio source in the constellation Hercules corresponding to the galaxy 3C 348.
Evolutionary Map of the Universe, or EMU, is a large project which will use the new ASKAP telescope to make a census of radio sources in the sky. EMU is expected to detect about 70 million radio sources. Most of these radio sources will be galaxies millions of light years away, many containing massive black holes, and some of the signals detected will have been sent less than half a billion years after the Big Bang, which created the universe 13.7 billion years ago. Unlike the NVSS, which mainly detected active galactic nuclei, the greater sensitivity of EMU means that about half the galaxies detected will be star-forming galaxies.
The Teacup galaxy, also known as the Teacup AGN or SDSS J1430+1339 is a low redshift type 2 quasar, showing an extended loop of ionized gas resembling a handle of a teacup, which was discovered by volunteers of the Galaxy Zoo project and labeled as a Voorwerpje.
In astronomy, an odd radio circle (ORC) is a very large unexplained astronomical object that, at radio wavelengths, is highly circular and brighter along its edges. As of 27 April 2021, there have been five such objects observed. The observed ORCs are bright at radio wavelengths, but are not visible at visible, infrared or X-ray wavelengths. This is due to the physical process producing this radiation, which is thought to be synchrotron radiation. Three of the ORCs contain optical galaxies in their centers, suggesting that the galaxies might have formed these objects.
ESO 383-76 is an elongated, X-ray luminous supergiant elliptical galaxy, residing as the dominant, brightest cluster galaxy (BCG) of the Abell 3571 galaxy cluster, the sixth-brightest in the sky at X-ray wavelengths. It is located at the distance of 200.6 megaparsecs from Earth, and is possibly a member of the large Shapley Supercluster. With a diameter of about 540.9 kiloparsecs, it is one of the largest galaxies known. It also contains a supermassive black hole, one of the most massive known with mass estimates varying from 2 billion M☉ to 28 billion M☉.
Gems of the Galaxy Zoos (Zoogems) was a gap-filler project which used the Hubble Space Telescope to take images of unusual objects found by volunteers classifying data from both Galaxy Zoo (GZ) and Radio Galaxy Zoo (RGZ). Between the HSTs' main observations, there is a short time that objects within that field of view can be imaged using gaps which last approximately 12 - 25 mins. The Zoogems project sought to use those small observation gaps to image 300 candidates taken from the two Zoos in order to better study and comprehend them. Starting observations in May 2018, HST Proposal 15445 had by the end of September 2023 imaged 193 of the 300 candidates with many of them having near 11 minute exposures.
↑ K.W. Willett (8 March 2016). Radio Galaxy Zoo: host galaxies and radio morphologies for large surveys from visual inspection. Conference: The Many Facets of Extragalactic Radio Surveys: Towards New Scientific Challenges, Bologna, October 2015. Proceedings of Science. pp.1–9. arXiv:1603.02645v1. Bibcode:2016arXiv160302645W.
1 2 The Scientific Team (December 2013). "Radio Galaxy Zoo website". Zooniverse. Archived from the original on 23 February 2018. Retrieved 21 March 2018.
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