Are Odd Radio Circles phoenixes of powerful radio galaxies?
Stanislav Shabala, Patrick Yates-Jones, Larissa Jerrim, Ross Turner, Martin Krause, Ray Norris, Baerbel Koribalski, Miroslav Filipovic, Larry Rudnick, Chris Power, Roland Crocker
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25 pages, 15 figures. Accepted for publication in PASA
Odd Radio Circles (ORCs) are a class of low surface brightness, circular objects approximately one arcminute in diameter. ORCs were recently discovered in the Australian Square Kilometre Array Pathfinder (ASKAP) data, and subsequently confirmed with follow-up observations on other instruments, yet their origins remain uncertain. In this paper, we suggest that ORCs could be remnant lobes of powerful radio galaxies, re-energised by the passage of a shock. Using relativistic hydrodynamic simulations with synchrotron emission calculated in post-processing, we show that buoyant evolution of remnant radio lobes is alone too slow to produce the observed ORC morphology. However, the passage of a shock can produce both filled and edge-brightnened ORC-like morphologies for a wide variety of shock and observing orientations. Circular ORCs are predicted to have host galaxies near the geometric centre of the radio emission, consistent with observations of these objects. Significantly offset hosts are possible for elliptical ORCs, potentially causing challenges for accurate host galaxy identification. Observed ORC number counts are broadly consistent with a paradigm in which moderately powerful radio galaxies are their progenitors.
The Odd Radio Circles are newly identified diffuse radio sources at ~1 GHz frequency, with edge-brightened nearly circular morphology, which is remarkably similar to supernova remnants although a physical association with previous population of Galactic supernova remnants is challenging due to detections of the Odd Radio Circles at high Galactic latitudes. Here, a serendipitous identification of a new source in a LOFAR 144 MHz image with similar morphology as that of Odd Radio Circles is reported. This is the first reported identification of an Odd Radio Circle at a very low frequency and with…
Odd Radio Circles or ORCs are recently discovered edge-brightened, low surface brightness circular radio sources. The progenitors and astrophysical processes responsible for their origins are presently debated. Some ORCs are host-less and some appear to be hosted in distant quiescent galaxies. Two plausible explanations consider ORCs as nearby supernova remnants with sizes a few hundred parsec in the intragroup medium of the local group of galaxies or alternatively shocked halos of a few hundred kpc extent around distant galaxies. The input shock energy required to create ORCs of a few hundred…
Odd Radio Circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift ($z ~ 0.2-0.6). Here we present detailed new MeerKAT radio images at 1284 MHz of the first ORC, originally discovered with the Australian Square Kilometre Array Pathfinder, with higher resolution (6 arcsec) and sensitivity (~ 2.4 uJy/bm). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarisation and spectral index maps. Based on these new data, we consider potential mechanis…
Odd Radio Circles (ORCs) are unexpected faint circles of diffuse radio emission discovered in recent wide deep radio surveys. They are typically about one arcmin in diameter, and may be spherical shells of synchrotron emission about a million light years in diameter, surrounding galaxies at a redshift of ~0.2-0.6. Here we study the properties and environment of the known ORCs. All three known single ORCs either lie in a significant overdensity or have a close companion. If the ORC is caused by an event in the host galaxy, then the fact that they tend to be in an overdensity, or have a close co…
A measurable fraction ($\sim8$ per cent) of recently discovered arcmin-size circular diffuse radio sources termed as Odd Radio Circles or ORCs can be supernovae remnants in the intragroup medium, within the local group and its immediate neighbour groups of galaxies. This estimate is based on the optical detection rate of the intragroup supernovae events in the nearby ($z \sim 0.1-0.2$) galaxy groups. A rate of about 5400 intragroup supernovae per million year is expected within the local and its immediate neighbour groups of galaxies. For a radio detectability period of about $10^{4}$ years, o…
The origin of arcmin-sized Odd Radio Circles (ORCs) found in modern all-sky radio surveys remain uncertain, with explanations ranging from starburst/AGN-driven shocks to supernova remnants (SNRs) in the low-density ambient medium. Using well-calibrated radio light curve models, we assess the possibility that ORCs are radio SNRs evolving in low ambient densities. Our models imply that ORCs 1-5 and J0624-6948 (near the LMC) as SNRs must be within 200 kpc and 100 kpc from the Sun respectively, given their observed flux densities and angular sizes. To be evolving in the circumgalactic medium of th…
Single- and double-headed odd radio circles in the LOFAR surveys
Hamburger Sternwarte, Universität Hamburg（汉堡天文台，汉堡大学）；Thüringer Landessternwarte（图林根州立天文台）；Universidad de Guanajuato（瓜纳华托大学）；Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München（慕尼黑大学物理学院大学天文台）；Department of Astronomy and Astrophysics, The University of Chicago（芝加哥大学天体物理学系）；ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所 ASTRON）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内克天文研究所）；Department of Physics, Astronomy and Mathematics, University of Hertfordshire（赫特福德郡大学物理、天文与数学系）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）
Cosmological Zoom-In Simulation of Odd Radio Circles as Merger-Driven Shocks in Galaxy Groups
Ludwig-Maximilians-Universität München（慕尼黑大学）；The University of Chicago（芝加哥大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Australia Telescope National Facility, CSIRO（澳大利亚望远镜国家设施，CSIRO）；Western Sydney University（西悉尼大学）
ASKAP EMU detection of an Odd Radio Circle (ORC) candidate: J094412-751016 (Anglerfish)
Western Sydney University（西悉尼大学）；Dominion Radio Astrophysical Observatory, Herzberg Astronomy & Astrophysics, National Research Council Canada（加拿大国家研究委员会赫茨伯格天体与天体物理学部多米农射电天文台）；Mizusawa VLBI Observatory, National Astronomical Observatory Japan（日本国立天文台水泽VLBI观测站）；INAF-Osservatorio Astrofisico di Catania（意大利国家天体物理研究所卡塔尼亚天文台）；Australia Telescope National Facility, CSIRO（澳大利亚望远镜国家设施，CSIRO）；Department of Physics, University of Wisconsin-Madison（威斯康星大学麦迪逊分校物理系）
ASKAP discovery of a pair of large radio bubbles: on the origin of odd radio circles
Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Research School of Astronomy and Astrophysics (RSAA), Australian National University（澳大利亚国立大学天文学与天体物理学研究学院）；INAF - Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；School of Physics, Henan Normal University（河南师范大学物理学院）；Department of Physics and Institute of Theoretical Physics, Nanjing Normal University（南京师范大学物理系和理论物理研究所）
We present the discovery of another Odd Radio Circle (ORC) with the Australian Square Kilometre Array Pathfinder (ASKAP) at 944 MHz. The observed radio ring, ORC J0102-2450, has a diameter of ~70 arcsec or 300 kpc, if associated with the central elliptical galaxy DES J010224.33-245039.5 (z ~ 0.27). Considering the overall radio morphology (circular ring and core) and lack of ring emission at non-radio wavelengths, we investigate if ORC J0102-2450 could be the relic lobe of a giant radio galaxy seen end-on or the result of a giant blast wave. We also explore possible interaction scenarios, for …
