ORCID Profile
0000-0002-4597-1906
Current Organisations
CSIRO Astronomy and Space Science
,
Western Sydney University
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Astronomical and Space Sciences | Cosmology and Extragalactic Astronomy | Astronomical and Space Instrumentation | Astronomy And Astrophysics | Stellar Astronomy and Planetary Systems | Broadband Network Technology | Macromolecular and Materials Chemistry | Antenna Technology | Chemical Sciences Not Elsewhere Classified | Digital Systems | Earth Sciences Not Elsewhere Classified | Navigation And Position Fixing | Information Systems | Instruments And Techniques | Information Systems Organisation | Communications Technologies | Galactic Astronomy | Global Information Systems | Physical Sciences Not Elsewhere Classified
Expanding Knowledge in the Physical Sciences | Physical sciences | Higher education | Information processing services | Technological and organisational innovation | Solar-photoelectric | Chemical sciences | Integrated circuits and devices | Scientific instrumentation | Expanding Knowledge in Technology | Information services not elsewhere classified |
Publisher: Oxford University Press (OUP)
Date: 02-05-2023
Abstract: We present MeerKAT L-band (886–1682 MHz) observations of the extended radio structure of the peculiar galaxy pair PKS 2130−538 known as the ‘Dancing Ghosts’. The complex of bending and possibly interacting jets and lobes originate from two active galactic nuclei hosts in the Abell 3785 galaxy cluster, one of which is the brightest cluster galaxy. The radio properties of the PKS 2130−538 – flux density, spectral index, and polarization – are typical for large, bent-tail galaxies. We also investigate a number of thin extended low surface brightness filaments originating from the lobes. South-east from the Dancing Ghosts, we detect a region of low surface brightness emission that has no clear origin. While it could originate from the Abell 3785 radio halo, we investigate the possibility that it is associated with the two PKS 2130−538 hosts. We find no evidence of interaction between the two PKS 2130−538 hosts.
Publisher: Elsevier BV
Date: 04-2022
Publisher: Oxford University Press (OUP)
Date: 06-1984
Publisher: American Astronomical Society
Date: 19-09-2014
Publisher: Oxford University Press (OUP)
Date: 09-12-2019
Abstract: We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.
Publisher: Oxford University Press (OUP)
Date: 13-11-2018
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: EDP Sciences
Date: 23-07-2012
Publisher: EDP Sciences
Date: 04-2022
DOI: 10.1051/0004-6361/202142048
Abstract: Context. The Shapley Supercluster (⟨ z ⟩≈0.048) contains several tens of gravitationally bound clusters and groups, making it an ideal subject for radio studies of cluster mergers. Aims. We used new high sensitivity radio observations to investigate the less energetic events of mass assembly in the Shapley Supercluster from supercluster down to galactic scales. Methods. We created total intensity images of the full region between A3558 and A3562, from ∼230 to ∼1650 MHz, using ASKAP, MeerKAT and the GMRT, with sensitivities ranging from ∼6 to ∼100 μJy beam −1 . We performed a detailed morphological and spectral study of the extended emission features, complemented with ESO-VST optical imaging and X-ray data from XMM-Newton . Results. We report the first GHz frequency detection of extremely low brightness intercluster diffuse emission on a ∼1 Mpc scale connecting a cluster and a group, namely: A3562 and the group SC 1329–313. It is morphologically similar to the X-ray emission in the region. We also found (1) a radio tail generated by ram pressure stripping in the galaxy SOS 61086 in SC 1329–313 (2) a head-tail radio galaxy, whose tail is broken and culminates in a misaligned bar (3) ultrasteep diffuse emission at the centre of A3558. Finally (4), we confirm the ultra-steep spectrum nature of the radio halo in A3562. Conclusions. Our study strongly supports the scenario of a flyby of SC 1329–313 north of A3562 into the supercluster core. This event perturbed the centre of A3562, leaving traces of this interaction in the form of turbulence between A3562 and SC 1329–313, at the origin of the radio bridge and eventually affecting the evolution of in idual supercluster galaxies by triggering ram pressure stripping. Our work shows that minor mergers can be spectacular and have the potential to generate diffuse radio emission that carries important information on the formation of large-scale structures in the Universe.
Publisher: Cambridge University Press (CUP)
Date: 1988
Publisher: EDP Sciences
Date: 23-12-2010
Publisher: Oxford University Press (OUP)
Date: 14-08-2012
Publisher: EDP Sciences
Date: 12-2017
DOI: 10.1051/0004-6361/201730449
Abstract: It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 h of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, M mol = 2.0 ± 0.2× 10 11 M ⊙ , extended, ~40 kpc, CO(1–0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at z CO = 2.1478, is a clumpy, massive disk galaxy, M ∗ ~ 5 × 10 11 M ⊙ , which lies 250 kpc in projection from MRC 1138−262 and is a known H α emitter, named HAE229. This source has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO(1–0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a s le of cluster members at z 0.4 thatare detected in low-order CO transitions, with a similar s le of sources drawn from the field. We confirm findings that the CO-luminosity and full-width at half maximum are correlated in starbursts and show that this relation is valid for normal high- z galaxies as well as for those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results suggest that environment does not have an impact on the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping do not operate efficiently in (proto)clusters.
Publisher: Sissa Medialab
Date: 29-05-2015
DOI: 10.22323/1.215.0103
Publisher: Oxford University Press (OUP)
Date: 06-1981
Publisher: Elsevier BV
Date: 07-2013
Publisher: American Astronomical Society
Date: 14-10-2020
Publisher: Oxford University Press (OUP)
Date: 14-02-2014
Publisher: Oxford University Press (OUP)
Date: 14-01-2014
Publisher: American Astronomical Society
Date: 18-01-2017
Publisher: Springer Science and Business Media LLC
Date: 03-1987
DOI: 10.1038/326012A0
Publisher: American Astronomical Society
Date: 10-06-2003
DOI: 10.1086/374862
Publisher: Oxford University Press (OUP)
Date: 20-05-2014
DOI: 10.1093/MNRAS/STU576
Publisher: Oxford University Press (OUP)
Date: 15-08-1994
Publisher: IOP Publishing
Date: 11-09-2019
Publisher: Cambridge University Press (CUP)
Date: 10-2016
DOI: 10.1017/S1743921316012825
Abstract: The tens of millions of radio sources to be detected with next-generation surveys pose new challenges, quite apart from the obvious ones of processing speed and data volumes. For ex le, existing algorithms are inadequate for source extraction or cross-matching radio and optical/IR sources, and a new generation of algorithms are needed using machine learning and other techniques. The large numbers of sources enable new ways of testing astrophysical models, using a variety of “large-n astronomy” techniques such as statistical redshifts. Furthermore, while unexpected discoveries account for some of the most significant discoveries in astronomy, it will be difficult to discover the unexpected in large volumes of data, unless specific software is developed to mine the data for the unexpected.
Publisher: Oxford University Press (OUP)
Date: 16-06-2007
Publisher: Elsevier BV
Date: 11-1997
DOI: 10.1038/KI.1997.454
Publisher: American Astronomical Society
Date: 02-2002
DOI: 10.1086/324383
Publisher: American Astronomical Society
Date: 20-11-1998
DOI: 10.1086/306373
Publisher: IOP Publishing
Date: 14-02-2019
Publisher: American Astronomical Society
Date: 06-1995
DOI: 10.1086/175818
Publisher: Cambridge University Press (CUP)
Date: 1990
Publisher: Elsevier BV
Date: 2021
Publisher: Cambridge University Press (CUP)
Date: 2001
Publisher: IOP Publishing
Date: 09-09-2019
Publisher: Oxford University Press (OUP)
Date: 07-1992
Publisher: American Astronomical Society
Date: 07-09-2023
Publisher: Cambridge University Press (CUP)
Date: 09-2011
DOI: 10.1017/S1743921312009519
Abstract: The Far-Infrared Radio Correlation (FRC) is the tightest and most universal correlation known among global parameters of galaxies. Here we present the results of our investigation of the 70 μm FRC of starforming galaxies in the Extended Chandra Deep Field South (ECDFS) out to z 2. In order to quantify the evolution of the FRC we used both survival analysis and stacking techniques, which gave similar results. We also calculated the FRC using total infrared luminosity and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within 0.22) over the redshift range 0 - 2. We see no evidence for evolution in the FRC at 70 μm, which is surprising given the many factors that are expected to change this ratio at high redshifts.
Publisher: Springer Netherlands
Date: 2005
Publisher: Oxford University Press (OUP)
Date: 11-12-2014
Publisher: Oxford University Press (OUP)
Date: 17-08-2020
Abstract: Cross-matching catalogues from radio surveys to catalogues of sources at other wavelengths is extremely hard, because radio sources are often extended, often consist of several spatially separated components, and often no radio component is coincident with the optical/infrared host galaxy. Traditionally, the cross-matching is done by eye, but this does not scale to the millions of radio sources expected from the next generation of radio surveys. We present an innovative automated procedure, using Bayesian hypothesis testing, that models trial radio-source morphologies with putative positions of the host galaxy. This new algorithm differs from an earlier version by allowing more complex radio-source morphologies, and performing a simultaneous fit over a large field. We show that this technique performs well in an unsupervised mode.
Publisher: Oxford University Press (OUP)
Date: 31-12-2016
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2019.49
Abstract: We present a detailed analysis of the radio galaxy PKS $2250{-}351$ , a giant of 1.2 Mpc projected size, its host galaxy, and its environment. We use radio data from the Murchison Widefield Array, the upgraded Giant Metre-wavelength Radio Telescope, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to model the jet power and age. Optical and IR data come from the Galaxy And Mass Assembly (GAMA) survey and provide information on the host galaxy and environment. GAMA spectroscopy confirms that PKS $2250{-}351$ lies at $z=0.2115$ in the irregular, and likely unrelaxed, cluster Abell 3936. We find its host is a massive, ‘red and dead’ elliptical galaxy with negligible star formation but with a highly obscured active galactic nucleus dominating the mid-IR emission. Assuming it lies on the local M – $\\sigma$ relation, it has an Eddington accretion rate of $\\lambda_{\\rm EDD}\\sim 0.014$ . We find that the lobe-derived jet power (a time-averaged measure) is an order of magnitude greater than the hotspot-derived jet power (an instantaneous measure). We propose that over the lifetime of the observed radio emission ( ${\\sim} 300\\,$ Myr), the accretion has switched from an inefficient advection-dominated mode to a thin disc efficient mode, consistent with the decrease in jet power. We also suggest that the asymmetric radio morphology is due to its environment, with the host of PKS $2250{-}351$ lying to the west of the densest concentration of galaxies in Abell 3936.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-08-2019
Abstract: Fast radio bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Nonrepeating FRB observations have had insufficient positional accuracy to localize them to an in idual host galaxy. We report the interferometric localization of the single-pulse FRB 180924 to a position 4 kiloparsecs from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from those of the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.
Publisher: Cambridge University Press (CUP)
Date: 2011
DOI: 10.1017/S1743921311012713
Abstract: For more than 50,000 years, Indigenous Australians have incorporated celestial events into their oral traditions and used the motions of celestial bodies for navigation, time-keeping, food economics, and social structure. In this paper, we explore the ways in which Aboriginal people made careful observations of the sky, measurements of celestial bodies, and incorporated astronomical events into complex oral traditions by searching for written records of time-keeping using celestial bodies, the use of rising and setting stars as indicators of special events, recorded observations of variable stars, the solar cycle, and lunar phases (including ocean tides and eclipses) in oral tradition, as well as astronomical measurements of the equinox, solstice, and cardinal points.
Publisher: MDPI AG
Date: 28-10-2021
Abstract: 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 companion, may indicate that the environment is important in creating the ORC phenomenon, possibly because of an increased ambient density or magnetic field.
Publisher: Oxford University Press (OUP)
Date: 09-1988
Publisher: Oxford University Press (OUP)
Date: 07-1986
Publisher: Oxford University Press (OUP)
Date: 25-06-2012
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.41
Abstract: The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together $60+$ programs recorded 20 000 h producing 146 papers to date. In 2016, the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper, we review the major results from the prior operation of the MWA and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes but also include ideas for directions outside these categories.
Publisher: Cambridge University Press (CUP)
Date: 1998
Publisher: Oxford University Press (OUP)
Date: 08-01-2021
Abstract: We present observations of a region of the Galactic plane taken during the Early Science Program of the Australian Square Kilometre Array Pathfinder (ASKAP). In this context, we observed the scorpio field at 912 MHz with an uncompleted array consisting of 15 commissioned antennas. The resulting map covers a square region of ∼40 deg2, centred on (l, b) = (343.5°, 0.75°), with a synthesized beam of 24 × 21 arcsec2 and a background rms noise of 150–200 μJy beam−1, increasing to 500–600 μJy beam−1 close to the Galactic plane. A total of 3963 radio sources were detected and characterized in the field using the caesar source finder. We obtained differential source counts in agreement with previously published data after correction for source extraction and characterization uncertainties, estimated from simulated data. The ASKAP positional and flux density scale accuracy were also investigated through comparison with previous surveys (MGPS, NVSS) and additional observations of the scorpio field, carried out with ATCA at 2.1 GHz and 10 arcsec spatial resolution. These allowed us to obtain a measurement of the spectral index for a subset of the catalogued sources and an estimated fraction of (at least) 8 per cent of resolved sources in the reported catalogue. We cross-matched our catalogued sources with different astronomical data bases to search for possible counterparts, finding ∼150 associations to known Galactic objects. Finally, we explored a multiparametric approach for classifying previously unreported Galactic sources based on their radio-infrared colours.
Publisher: Informa UK Limited
Date: 12-2012
Publisher: Oxford University Press (OUP)
Date: 18-05-2018
Publisher: Oxford University Press (OUP)
Date: 25-11-0088
Publisher: American Astronomical Society
Date: 06-07-2011
Publisher: Oxford University Press (OUP)
Date: 1995
Publisher: EDP Sciences
Date: 12-2016
Publisher: Springer Science and Business Media LLC
Date: 12-2011
Publisher: Elsevier BV
Date: 1999
Publisher: American Astronomical Society
Date: 17-10-2016
Publisher: Cambridge University Press (CUP)
Date: 11-2010
DOI: 10.1017/S1743921310010896
Abstract: Special Session 5 on Accelerating the Rate of Astronomical Discovery addressed a range of potential limits to progress: paradigmatic, technological, organizational, and political. It examined each issue both from modern and historical perspectives, and drew lessons to guide future progress. A number of issues were identified which may regulate the flow of discoveries, such as the balance between large strongly-focussed projects and instruments, designed to answer the most fundamental questions confronting us, and the need to maintain a creative environment with room for unorthodox thinkers and bold, high risk, projects. Also important is the need to maintain historical and cultural perspectives, and the need to engage the minds of the most brilliant young people on the planet, regardless of their background, ethnicity, gender, or geography.
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.41
Abstract: The Rapid ASKAP Continuum Survey (RACS) is the first large-area survey to be conducted with the full 36-antenna Australian Square Kilometre Array Pathfinder (ASKAP) telescope. RACS will provide a shallow model of the ASKAP sky that will aid the calibration of future deep ASKAP surveys. RACS will cover the whole sky visible from the ASKAP site in Western Australia and will cover the full ASKAP band of 700–1800 MHz. The RACS images are generally deeper than the existing NRAO VLA Sky Survey and Sydney University Molonglo Sky Survey radio surveys and have better spatial resolution. All RACS survey products will be public, including radio images (with $\\sim$ 15 arcsec resolution) and catalogues of about three million source components with spectral index and polarisation information. In this paper, we present a description of the RACS survey and the first data release of 903 images covering the sky south of declination $+41^\\circ$ made over a 288-MHz band centred at 887.5 MHz.
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 03-2016
DOI: 10.1093/MNRAS/STW186
Publisher: American Astronomical Society
Date: 10-01-2002
DOI: 10.1086/324281
Publisher: American Astronomical Society
Date: 25-03-2011
Publisher: Elsevier BV
Date: 12-2016
Publisher: American Astronomical Society
Date: 29-10-2014
Publisher: Cambridge University Press (CUP)
Date: 1990
DOI: 10.1017/S1323358000023420
Abstract: A survey of the optical spectra of IRAS galaxies, made with the AAT, has shown that the majority have strong emission lines. Ratios of the emission lines have been plotted on the Veilleux-Osterbrock diagram ([O III]/H β against [N II]/H α ) this shows that the IRAS galaxies comprise several classes. In our s le the majority appear to be starburst galaxies, but Seyfert, Liner and narrow-line galaxies are also represented. Co-added spectra of the galaxy classes are presented. On the basis of optical spectroscopy, it appears that the starburst phenomenon is capable of generating luminosities exceeding 10 12 L ⊙ .
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 24-04-2006
Publisher: Cambridge University Press (CUP)
Date: 2009
DOI: 10.1017/S1743921311002122
Abstract: The traditional cultures of Aboriginal Australians include a significant astronomical component, which is usually reported in terms of songs or stories associated with stars and constellations. Here we argue that the astronomical components extend further, and include a search for meaning in the sky, beyond simply mirroring the earth-bound understanding. In particular, we have found that traditional Aboriginal cultures include a deep understanding of the motion of objects in the sky, and that this knowledge was used for practical purposes such as constructing calendars. We also present evidence that traditional Aboriginal Australians made careful records and measurements of cyclical phenomena, and paid careful attention to unexpected phenomena such as eclipses and meteorite impacts.
Publisher: American Astronomical Society
Date: 10-01-1997
DOI: 10.1086/310434
Publisher: Oxford University Press (OUP)
Date: 06-08-2021
Abstract: We present a comprehensive multifrequency catalogue of radio sources behind the Large Magellanic Cloud (LMC) between 0.2 and 20 GHz, gathered from a combination of new and legacy radio continuum surveys. This catalogue covers an area of ∼144 deg2 at angular resolutions from 45 arcsec to ∼3 arcmin. We find 6434 discrete radio sources in total, of which 3789 are detected at two or more radio frequencies. We estimate the median spectral index (α where Sv ∼ να) of α = −0.89 and mean of −0.88 ± 0.48 for 3636 sources detected exclusively at two frequencies (0.843 and 1.384 GHz) with similar resolution [full width at half-maximum (FWHM) ∼40–45 arcsec]. The large frequency range of the surveys makes it an effective tool to investigate Gigahertz Peak Spectrum (GPS), Compact Steep Spectrum (CSS), and Infrared Faint Radio Source (IFRS) populations within our s le. We find 10 GPS candidates with peak frequencies near 5 GHz, from which we estimate their linear size. 1866 sources from our catalogue are CSS candidates with α & −0.8. We found six candidates for High Frequency Peaker (HFP) sources, whose radio fluxes peak above 5 GHz and no sources with unconstrained peaks and α & 0.5. We found optical counterparts for 343 of the radio continuum sources, of which 128 have a redshift measurement. Finally, we investigate the population of 123 IFRSs found in this study.
Publisher: Oxford University Press (OUP)
Date: 04-2001
Publisher: American Astronomical Society
Date: 08-09-2020
Publisher: Oxford University Press (OUP)
Date: 23-10-2018
Publisher: American Astronomical Society
Date: 19-08-2013
Publisher: Springer-Verlag
Date: 2001
DOI: 10.1007/10854354_25
Publisher: Springer Berlin Heidelberg
Date: 1999
Publisher: Oxford University Press (OUP)
Date: 10-2018
Publisher: Oxford University Press (OUP)
Date: 19-03-2012
Publisher: Oxford University Press (OUP)
Date: 12-05-2021
Abstract: In the broad context of the Australian Square Kilometer Array Pathfinder (ASKAP) early-science phase and preparation for the related surveys, we report the first radio observations towards the Galactic plane. The targeted field was chosen to encompass the entire SCORPIO survey, one of the several pathfinder projects for the Evolutionary Map of the Universe survey planned with the ASKAP. The observations were carried out in 2018 January at a central frequency of 912 MHz, with 15 operational antennas, and covered a total area of about 40 square degrees in three different pointings. The final image has a resolution of 24.1 × 21.1 arcsec2 and a median rms of $541\\ \\mu \\mathrm{Jy\\ beam}^{-1}$. We were able to extract 3545 candidate sources, 75 per cent of them point sources. For a preliminary validation, a comparison with the 843 MHz Molonglo Galactic Plane Survey is presented. Although the present observations were obtained with the ASKAP only partially deployed, its unique capability to map complex sources, such as those inhabiting the Galactic plane, at different angular scales, is highlighted. Within the SCORPIO field all the previously classified H ii regions, Planetary Nebulae (PNe), and supernovae remnants (SNRs), previously known to be radio sources, were detected. We also report new radio detections from several H ii regions previously classified as ‘candidates’ or ‘radio quiet’ and from half of all the PNe in the SCORPIO field with robust classification. Most notably, we find numerous unclassified, extended sources which constitute a promising s le of candidates H ii regions and SNRs.
Publisher: Oxford University Press (OUP)
Date: 30-11-2020
Abstract: The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the ‘DeepDrill’ survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centred on 3.6 and 4.5 μm. These observations expand the area that was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field–South (ECDFS) field, the ELAIS-S1 field (ES1), and the XMM-Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate 5σ point-source depth of 2 μJy (corresponding to an AB magnitude of 23.1 sufficient to detect a 10$^{11} \\, \\mathrm{M}_{\\odot}$ galaxy out to z ≈ 5) in each of the two bands over a total area of $\\approx 29\\,$ deg2. The dual-band catalogues contain a total of 2.35 million sources. In this paper, we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the Shark semi-analytic model of galaxy formation. We also identify a population of sources with extremely red ([3.6]−[4.5] & .2) colours which we show mostly consists of highly obscured active galactic nuclei.
Publisher: Oxford University Press (OUP)
Date: 18-10-2012
Publisher: IOP Publishing
Date: 10-2012
DOI: 10.1086/668290
Publisher: American Astronomical Society
Date: 05-1989
DOI: 10.1086/185436
Publisher: Oxford University Press (OUP)
Date: 25-01-2014
Publisher: Oxford University Press (OUP)
Date: 02-07-2020
Abstract: We develop a new analysis approach towards identifying related radio components and their corresponding infrared host galaxy based on unsupervised machine learning methods. By exploiting Parallelized rotation and flipping INvariant Kohonen maps (pink), a self-organizing map (SOM) algorithm, we are able to associate radio and infrared sources without the a priori requirement of training labels. We present an ex le of this method using 894 415 images from the Faint Images of the Radio-Sky at Twenty centimeters (FIRST) and Wide-field Infrared Survey Explorer (WISE) surveys centred towards positions described by the FIRST catalogue. We produce a set of catalogues that complement FIRST and describe 802 646 objects, including their radio components and their corresponding AllWISE infrared host galaxy. Using these data products, we (i) demonstrate the ability to identify objects with rare and unique radio morphologies (e.g. ‘X’-shaped galaxies, hybrid FR I/FR II morphologies), (ii) can identify the potentially resolved radio components that are associated with a single infrared host, (iii) introduce a ‘curliness’ statistic to search for bent and disturbed radio morphologies, and (iv) extract a set of 17 giant radio galaxies between 700 and 1100 kpc. As we require no training labels, our method can be applied to any radio-continuum survey, provided a sufficiently representative SOM can be trained.
Publisher: Oxford University Press (OUP)
Date: 09-12-2022
Abstract: The SKA PAthfinder Radio Continuum Surveys (SPARCS) are providing deep-field imaging of the faint (sub-mJy) extragalactic radio source populations through a series of reference surveys. One of the key science goals for SPARCS is to characterize the relative contribution of radio emission associated with active galactic nucleus (AGN) from star formation (SF) in these faint radio source populations, using a combination of high sensitivity and high angular resolution imaging over a range of spatial scales (arcsec to mas). To isolate AGN contribution from SF, we hypothesize that there exists a brightness temperature cut-off point separating pure AGN from SF. We present a multiresolution (10–100 mas) view of the transition between compact AGN and diffuse SF through a deep wide-field EVN + e-MERLIN, multiple phase centre survey of the centre of the Northern SPARCS (SLOAN) reference field at 1.6 GHz. This is the first (and only) VLBI (+ e-MERLIN) milliarcsecond angular resolution observation of this field, and of the wider SPARCS reference field programme. Using these high spatial resolution (9 pc–0.3 kpc at z ∼ 1.25) data, 11 milliarcsec-scale sources are detected from a targeted s le of 52 known radio sources from previous observations with the e-MERLIN, giving a VLBI detection fraction of $\\sim 21{{\\ \\rm per\\ cent}}$. At spatial scales of $\\sim 9\\,$pc, these sources show little to no jet structure whilst at $\\sim 0.3\\,$kpc one-sided and two-sided radio jets begin to emerge on the same sources, indicating a possible transition from pure AGN emissions to AGN and SF systems.
Publisher: CSIRO Publishing
Date: 2014
DOI: 10.1071/EC14088
Publisher: EDP Sciences
Date: 23-05-2003
Publisher: American Astronomical Society
Date: 26-07-2023
Abstract: Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO J 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 z 2.1, namely MRC 0114-211 ( z = 1.41), MRC 0156-252 ( z = 2.02), and MRC 2048-272 ( z = 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1–0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large s le of high- z radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with r 2−1/1−0 and r 3−2/1−0 values ≲0.2. This could be part of the circumgalactic medium.
Publisher: Cambridge University Press (CUP)
Date: 1986
DOI: 10.1017/S1323358000026898
Abstract: The 1665 and 1667 MHz OH intensity towards Halley’s comet has been monitored during the period October 1985 to April 1986. The flux density variation during the course of the apparition roughly follows the predictions of Schloerb and Gerard (1985), although we find a systematically lower flux than they predicted. The relative intensities of these lines are approximately in the ratio expected for thermodynamic equilibrium.
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: American Astronomical Society
Date: 2001
DOI: 10.1086/318051
Publisher: EDP Sciences
Date: 26-02-2021
DOI: 10.1051/0004-6361/202039590
Abstract: Context. Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters. Aims. Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model. Methods. We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg 2 region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the Planck survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite. Results. We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii, r 200 . Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius, r 100 , of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift z = 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at σ . The Planck SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the in idual system level, including the surrounding warm-hot intergalactic medium distribution the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure.
Publisher: Oxford University Press (OUP)
Date: 11-05-1996
Publisher: Cambridge University Press (CUP)
Date: 1985
Publisher: IOP Publishing
Date: 09-09-2019
Publisher: Oxford University Press (OUP)
Date: 15-06-1995
Publisher: Cambridge University Press (CUP)
Date: 14-05-2010
DOI: 10.1017/S1743921310005302
Abstract: Commission 5 and its working groups have continued to operate at a high level of activity over the last three years. In an era when the volume of astronomical data generated by next-generation instruments continues to increase dramatically, and data centres and data tools become increasingly central to front-line astronomical research, the activities of Commission 5 are becoming even more significant. However, most of the activities of Commission 5 take place through its working groups. That was reflected in the meetings at the IAU GA, where there was only one short Business Meeting of the Commission as a whole, but several vigorous meetings of the working groups.
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.39
Abstract: With the advent of deep, all-sky radio surveys, the need for ancillary data to make the most of the new, high-quality radio data from surveys like the Evolutionary Map of the Universe (EMU), GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended, Very Large Array Sky Survey, and LOFAR Two-metre Sky Survey is growing rapidly. Radio surveys produce significant numbers of Active Galactic Nuclei (AGNs) and have a significantly higher average redshift when compared with optical and infrared all-sky surveys. Thus, traditional methods of estimating redshift are challenged, with spectroscopic surveys not reaching the redshift depth of radio surveys, and AGNs making it difficult for template fitting methods to accurately model the source. Machine Learning (ML) methods have been used, but efforts have typically been directed towards optically selected s les, or s les at significantly lower redshift than expected from upcoming radio surveys. This work compiles and homogenises a radio-selected dataset from both the northern hemisphere (making use of Sloan Digital Sky Survey optical photometry) and southern hemisphere (making use of Dark Energy Survey optical photometry). We then test commonly used ML algorithms such as k -Nearest Neighbours (kNN), Random Forest, ANNz, and GPz on this monolithic radio-selected s le. We show that kNN has the lowest percentage of catastrophic outliers, providing the best match for the majority of science cases in the EMU survey. We note that the wider redshift range of the combined dataset used allows for estimation of sources up to $z = 3$ before random scatter begins to dominate. When binning the data into redshift bins and treating the problem as a classification problem, we are able to correctly identify $\\approx$ 76% of the highest redshift sources—sources at redshift $z 2.51$ —as being in either the highest bin ( $z 2.51$ ) or second highest ( $z = 2.25$ ).
Publisher: Oxford University Press (OUP)
Date: 26-02-2019
DOI: 10.1093/MNRAS/STZ551
Publisher: Elsevier BV
Date: 2009
Publisher: Oxford University Press (OUP)
Date: 1985
Publisher: Oxford University Press (OUP)
Date: 13-12-2022
Abstract: Using the Lyman Dropout technique, we identify 148 candidate radio sources at z ≳ 4–7 from the 887.5 MHz Australian Square Kilometre Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112 radio sources are currently known beyond redshift z ∼ 4. However, simulations predict that hundreds of thousands of radio sources exist in that redshift range, many of which are probably in existing radio catalogues, but do not have measured redshifts, either because their optical emission is too faint or because of the lack of techniques that can identify candidate high-redshift radio sources (HzRSs). Our study addresses these issues using the Lyman Dropout search technique. This newly built s le probes radio luminosities that are 1–2 orders of magnitude fainter than known radio-active galactic nuclei (AGN) at similar redshifts, thanks to ASKAP’s sensitivity. We investigate the physical origin of radio emission in our s le using a set of diagnostics: (i) radio luminosity at 1.4 GHz, (ii) 1.4 GHz to 3.4 μm flux density ratio, (iii) Far-IR detection, (iv) WISE colour, and (v) SED modelling. The radio/IR analysis has shown that the majority of radio emission in the faint and bright end of our s le’s 887.5 MHz flux density distribution originates from AGN activity. Furthermore, ∼10 per cent of our s le are found to have a 250 μm detection, suggesting a composite system. This suggests that some high-z radio-AGNs are hosted by SB galaxies in contrast to low-z radio-AGNs, which are usually hosted by quiescent elliptical galaxies.
Publisher: Oxford University Press (OUP)
Date: 19-11-2019
Abstract: We present a new image of the 9.0 GHz radio emission from the extended Chandra Deep Field South. A total of 181 h of integration with the Australia Telescope Compact Array has resulted in a 0.276 deg2 image with a median sensitivity of ∼20 µJy beam−1 rms, for a synthesized beam of 4.0 × 1.3 arcsec. We present a catalogue of the 9.0 GHz radio sources, identifying 70 source components and 55 in idual radio galaxies. Source counts derived from this s le are consistent with those reported in the literature. The observed source counts are also generally consistent with the source counts from simulations of the faint radio population. Using the wealth of multiwavelength data available for this region, we classify the faint 9 GHz population and find that 91 per cent are radio-loud active galactic nuclei (AGNs), 7 per cent are radio-quiet AGNs, and 2 per cent are star-forming galaxies. The 9.0 GHz radio sources were matched to 5.5 and 1.4 GHz sources in the literature and we find a significant fraction of flat or inverted spectrum sources, with 36 per cent of the 9 GHz sources having $\\alpha _{5.5\\,\\mathrm{ GHz}}^{9.0\\,\\mathrm{ GHz}}$ & −0.3 (for S ∝ να). This flat or inverted population is not well reproduced by current simulations of radio source populations.
Publisher: Oxford University Press (OUP)
Date: 02-1998
Publisher: EDP Sciences
Date: 08-2018
DOI: 10.1051/0004-6361/201832969
Abstract: We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the s les of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of −75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.
Publisher: Oxford University Press (OUP)
Date: 21-09-2019
Abstract: We present two new radio continuum images from the Australian Square Kilometre Array Pathfinder (ASKAP) survey in the direction of the Small Magellanic Cloud (SMC). These images are part of the Evolutionary Map of the Universe (EMU) Early Science Project (ESP) survey of the Small and Large Magellanic Clouds. The two new source lists produced from these images contain radio continuum sources observed at 960 MHz (4489 sources) and 1320 MHz (5954 sources) with a bandwidth of 192 MHz and beam sizes of 30.0 × 30.0 arcsec2 and 16.3 × 15.1 arcsec2, respectively. The median root mean square (RMS) noise values are 186 $\\mu$Jy beam−1 (960 MHz) and 165 $\\mu$Jy beam−1 (1320 MHz). To create point source catalogues, we use these two source lists, together with the previously published Molonglo Observatory Synthesis Telescope (MOST) and the Australia Telescope Compact Array (ATCA) point source catalogues to estimate spectral indices for the whole population of radio point sources found in the survey region. Combining our ASKAP catalogues with these radio continuum surveys, we found 7736 point-like sources in common over an area of 30 deg2. In addition, we report the detection of two new, low surface brightness supernova remnant candidates in the SMC. The high sensitivity of the new ASKAP ESP survey also enabled us to detect the bright end of the SMC planetary nebula s le, with 22 out of 102 optically known planetary nebulae showing point-like radio continuum emission. Lastly, we present several morphologically interesting background radio galaxies.
Publisher: Wiley
Date: 1948
Publisher: Oxford University Press (OUP)
Date: 14-09-2010
Publisher: American Astronomical Society
Date: 02-2003
DOI: 10.1086/345414
Publisher: Springer Netherlands
Date: 1986
Publisher: Oxford University Press (OUP)
Date: 10-1988
Publisher: Wiley
Date: 04-08-2010
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.46
Publisher: American Astronomical Society
Date: 30-11-2017
Publisher: Oxford University Press (OUP)
Date: 04-06-2015
DOI: 10.1093/MNRAS/STV994
Publisher: Oxford University Press (OUP)
Date: 03-1984
Publisher: Oxford University Press (OUP)
Date: 12-09-2022
Abstract: We present the discovery of highly collimated radio jets spanning a total of 355 kpc around the nearby elliptical galaxy NGC 2663, and the possible first detection of recollimation on kiloparsec scales. The small distance to the galaxy (∼28.5 Mpc) allows us to resolve portions of the jets to examine their structure. We combine multiwavelength data: radio observations by the Murchison Widefield Array (MWA), the Australian Square Kilometre Array Pathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA), and X-ray data from Chandra, Swift, and SRG/eROSITA. We present intensity, rotation measure, polarization, spectral index, and X-ray environment maps. Regions of the southern jet show simultaneous narrowing and brightening, which can be interpreted as a signature of the recollimation of the jet by external, environmental pressure, though it is also consistent with intermittent active galactic nuclei or complex internal jet structure. X-ray data suggest that the environment is extremely poor if the jet is indeed recollimating, the large recollimation scale (40 kpc) is consistent with a slow jet in a low-density environment.
Publisher: American Astronomical Society
Date: 03-2019
Publisher: Oxford University Press (OUP)
Date: 11-1982
Publisher: Oxford University Press (OUP)
Date: 20-08-2014
Publisher: Oxford University Press (OUP)
Date: 13-05-2011
Publisher: Oxford University Press (OUP)
Date: 15-09-1992
Publisher: Cambridge University Press (CUP)
Date: 09-2011
DOI: 10.1017/S1743921312009684
Abstract: EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope, due to be completed in 2012. The primary goal of EMU is to make a deep (~10μJy/bm rms) radio continuum survey of the entire Southern Sky at 1.4 GHz, extending as far North as +30° declination, with a 10 arcsec resolution. EMU is expected to detect and catalog about 70 million galaxies, including typical star-forming galaxies up to z = 1, powerful starbursts to even greater redshifts, and AGNs to the edge of the Universe. EMU will undoubtedly discover new classes of object. Here I present the science goals and survey parameters.
Publisher: Oxford University Press (OUP)
Date: 03-03-2018
Publisher: American Astronomical Society
Date: 03-2006
DOI: 10.1086/498823
Publisher: American Astronomical Society
Date: 20-09-2011
Publisher: EDP Sciences
Date: 08-2021
DOI: 10.1051/0004-6361/202040232
Abstract: We report a detailed CO(1−0) survey of a galaxy protocluster field at z = 2.16, based on 475 h of observations with the Australia Telescope Compact Array. We constructed a large mosaic of 13 in idual pointings, covering an area of 21 arcmin 2 and ±6500 km s −1 range in velocity. We obtained a robust s le of 46 CO(1−0) detections spanning z = 2.09 − 2.22, constituting the largest s le of molecular gas measurements in protoclusters to date. The CO emitters show an overdensity at z = 2.12 − 2.21, suggesting a galaxy super-protocluster or a protocluster connected to large-scale filaments of ∼120 cMpc in size. We find that 90% of CO emitters have distances .′5−4′ to the center galaxy, indicating that small area surveys would miss the majority of gas reservoirs in similar structures. Half of the CO emitters have velocities larger than escape velocities, which appears gravitationally unbound to the cluster core. These unbound sources are barely found within the R 200 radius around the center, which is consistent with a picture in which the cluster core is collapsed while outer regions are still in formation. Compared to other protoclusters, this structure contains a relatively higher number of CO emitters with relatively narrow line widths and high luminosities, indicating galaxy mergers. We used these CO emitters to place the first constraint on the CO luminosity function and molecular gas density in an overdense environment. The litude of the CO luminosity function is 1.6 ± 0.5 orders of magnitude higher than that observed for field galaxy s les at z ∼ 2, and one order of magnitude higher than predictions for galaxy protoclusters from semi-analytical SHARK models. We derive a high molecular gas density of 0.6 − 1.3 × 10 9 M ⊙ cMpc −3 for this structure, which is consistent with predictions for cold gas density of massive structures from hydro-dynamical DIANOGA simulations.
Publisher: Springer Science and Business Media LLC
Date: 09-1988
DOI: 10.1038/335149A0
Publisher: Oxford University Press (OUP)
Date: 09-1985
Publisher: Cambridge University Press (CUP)
Date: 1993
Publisher: Oxford University Press (OUP)
Date: 03-03-2018
DOI: 10.1093/MNRAS/STY564
Publisher: No publisher found
Date: 2016
Publisher: Elsevier BV
Date: 06-2006
Publisher: American Physical Society (APS)
Date: 26-07-2007
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.16
Abstract: We have observed the G23 field of the Galaxy AndMass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase to validate the performance of the telescope and to characterise the detected galaxy populations. This observation covers ~48 deg 2 with synthesised beam of 32.7 arcsec by 17.8 arcsec at 936MHz, and ~39 deg 2 with synthesised beam of 15.8 arcsec by 12.0 arcsec at 1320MHz. At both frequencies, the root-mean-square (r.m.s.) noise is ~0.1 mJy/beam. We combine these radio observations with the GAMA galaxy data, which includes spectroscopy of galaxies that are i-band selected with a magnitude limit of 19.2. Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry is used to determine which galaxies host an active galactic nucleus (AGN). In properties including source counts, mass distributions, and IR versus radio luminosity relation, the ASKAP-detected radio sources behave as expected. Radio galaxies have higher stellar mass and luminosity in IR, optical, and UV than other galaxies. We apply optical and IR AGN diagnostics and find that they disagree for ~30% of the galaxies in our s le. We suggest possible causes for the disagreement. Some cases can be explained by optical extinction of the AGN, but for more than half of the cases we do not find a clear explanation. Radio sources aremore likely (~6%) to have an AGN than radio quiet galaxies (~1%), but the majority of AGN are not detected in radio at this sensitivity.
Publisher: Oxford University Press (OUP)
Date: 06-07-2011
Publisher: Oxford University Press (OUP)
Date: 04-02-2022
Abstract: We report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the large magellanic cloud (LMC). It was first detected at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ∼196 arcsec. This source has phenomenological similarities to odd radio circles (ORCs). Significant differences to the known ORCs – a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size – suggest that J0624–6948 may be a different type of object. We argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (30Dor) or the remnant of a nearby stellar super-flare.
Publisher: Elsevier BV
Date: 03-2017
Publisher: Oxford University Press (OUP)
Date: 12-1988
Publisher: Cambridge University Press (CUP)
Date: 08-1994
DOI: 10.1017/S1323358000019809
Abstract: Our knowledge of the universe comes from recording the photon and particle fluxes incident on the Earth from space. We thus require sensitive measurement across the entire energy spectrum, using large telescopes with efficient instrumentation located on superb sites. Technological advances and engineering constraints are nearing the point where we are recording as many photons arriving at a site as is possible. Major advances in the future will come from improving the quality of the site. The ultimate site is, of course, beyond the Earth’s atmosphere, such as on the Moon, but economic limitations prevent our exploiting this avenue to the degree that the scientific community desires. Here we describe an alternative, which offers many of the advantages of space for a fraction of the cost: the Antarctic Plateau.
Publisher: American Astronomical Society
Date: 27-11-2017
Publisher: IOP Publishing
Date: 30-08-2019
Publisher: Elsevier BV
Date: 09-2003
Publisher: EDP Sciences
Date: 09-2015
Publisher: EDP Sciences
Date: 20-03-2017
DOI: 10.1051/0004-6361/201730438
Abstract: Context. Red giant branch (RGB) stars are very bright objects in galaxies and are often used as standard candles. Interferometry is the ideal tool to characterize the dynamics and morphology of their atmospheres. Aims. We aim at precisely characterising the surface dynamics of a s le of RGB stars. Methods. We obtained interferometric observations for three RGB stars with the MIRC instrument mounted at the CHARA interferometer. We looked for asymmetries on the stellar surfaces using limb-darkening models. Results. We measured the apparent diameters of HD 197989 ( ϵ Cyg) = 4.61 ± 0.02 mas, HD 189276 (HR 7633) = 2.95 ± 0.01 mas, and HD 161096 ( β Oph) = 4.43 ± 0.01 mas. We detected departures from the centrosymmetric case for all three stars with the tendency of a greater effect for lower log g of the s le. We explored the causes of this signal and conclude that a possible explanation to the interferometric signal is the convection-related and/or the magnetic-related surface activity. However, it is necessary to monitor these stars with new observations, possibly coupled with spectroscopy, in order to firmly establish the cause.
Publisher: Oxford University Press (OUP)
Date: 20-02-2023
Abstract: The Evolutionary Map of the Universe (EMU) large-area radio continuum survey will detect tens of millions of radio galaxies, giving an opportunity for the detection of previously unknown classes of objects. To maximize the scientific value and make new discoveries, the analysis of these data will need to go beyond simple visual inspection. We propose the coarse-grained complexity, a simple scalar quantity relating to the minimum description length of an image that can be used to identify unusual structures. The complexity can be computed without reference to the broader s le or existing catalogue data, making the computation efficient on new surveys at very large scales (such as the full EMU survey). We apply our coarse-grained complexity measure to data from the EMU Pilot Survey to detect and confirm anomalous objects in this data set and produce an anomaly catalogue. Rather than work with existing catalogue data using a specific source detection algorithm, we perform a blind scan of the area, computing the complexity using a sliding square aperture. The effectiveness of the complexity measure for identifying anomalous objects is evaluated using crowd-sourced labels generated via the Zooniverse.org platform. We find that the complexity scan identifies unusual sources, such as odd radio circles, by partitioning on complexity. We achieve partitions where 5 per cent of the data is estimated to be 86 per cent complete, and 0.5 per cent is estimated to be 94 per cent pure, with respect to anomalies and use this to produce an anomaly catalogue.
Publisher: Oxford University Press (OUP)
Date: 14-01-2016
Publisher: Springer Berlin Heidelberg
Date: 15-09-2011
Publisher: Oxford University Press (OUP)
Date: 06-09-2015
Publisher: Oxford University Press (OUP)
Date: 30-11-2018
Publisher: Oxford University Press (OUP)
Date: 07-03-2013
Publisher: EDP Sciences
Date: 26-03-2004
Publisher: Sissa Medialab
Date: 18-04-2016
DOI: 10.22323/1.267.0045
Publisher: Oxford University Press (OUP)
Date: 02-2002
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-12-2016
Abstract: The massive Spiderweb galaxy is surrounded by molecular gas as it goes through its formation process.
Publisher: American Astronomical Society
Date: 02-2021
Abstract: In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM c aign by recovering velocity–delay maps for the prominent broad emission lines (Ly α , C iv , He ii , and H β ) in the spectrum of NGC 5548. These are the most detailed velocity–delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He ii response inside 5–10 lt-day has a broad single-peaked velocity profile. The Ly α , C iv , and H β responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s −1 in the 10–20 lt-day delay range. An incomplete ellipse in the velocity–delay plane is evident in H β . We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay τ = ( R / c ) ( 1 − sin i ) ≈ 5 days gives the inclination i ≈ 45°. The inferred black hole mass is M BH ≈ 7 × 10 7 M ⊙ . In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the “BLR Holiday” identified in previous work. Moreover, a helical “Barber-Pole” pattern, with stripes moving from red to blue across the C iv and Ly α line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.
Publisher: Oxford University Press (OUP)
Date: 15-01-1993
Publisher: American Astronomical Society
Date: 09-1994
DOI: 10.1086/174589
Publisher: Oxford University Press (OUP)
Date: 12-10-2023
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.37
Abstract: We describe the performance of the Boolardy Engineering Test Array, the prototype for the Australian Square Kilometre Array Pathfinder telescope. Boolardy Engineering Test Array is the first aperture synthesis radio telescope to use phased array feed technology, giving it the ability to electronically form up to nine dual-polarisation beams. We report the methods developed for forming and measuring the beams, and the adaptations that have been made to the traditional calibration and imaging procedures in order to allow BETA to function as a multi-beam aperture synthesis telescope. We describe the commissioning of the instrument and present details of Boolardy Engineering Test Array’s performance: sensitivity, beam characteristics, polarimetric properties, and image quality. We summarise the astronomical science that it has produced and draw lessons from operating Boolardy Engineering Test Array that will be relevant to the commissioning and operation of the final Australian Square Kilometre Array Path telescope.
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: Cambridge University Press (CUP)
Date: 1991
DOI: 10.1017/S1323358000023973
Abstract: During 1990 we surveyed the southern sky using a multi-beam receiver at frequencies of 4850 and 843 MHz. The half-power beamwidths were 4 and 25 arcmin respectively. The finished surveys cover the declination range between +10 and −90 degrees declination, essentially complete in right ascension, an area of 7.30 steradians. Preliminary analysis of the 4850 MHz data indicates that we will achieve a five sigma flux density limit of about 30 mJy. We estimate that we will find between 80 000 and 90 000 new sources above this limit. This is a revised version of the paper presented at the Regional Meeting by the first four authors the surveys now have been completed.
Publisher: Cambridge University Press (CUP)
Date: 2000
Publisher: Wiley
Date: 06-2012
Abstract: Radio observations using the Very Long Baseline Interferometry (VLBI) technique typically have fields of view of only a few arcseconds, due to the computational problems inherent in imaging larger fields. Furthermore, sensitivity limitations restrict observations to very compact and bright objects, which are few and far between on the sky. Thus, while most branches of observational astronomy can carry out sensitive, wide‐field surveys, VLBI observations are limited to targeted observations of carefully selected objects. However, recent advances in technology have made it possible to carry out the computations required to target hundreds of sources simultaneously. Furthermore, sensitivity upgrades have dramatically increased the number of objects accessible to VLBI observations. The combination of these two developments have enhanced the survey capabilities of VLBI observations such that it is now possible to observe (almost) any point in the sky with milli‐arcsecond resolution. In this talk I review the development of wide‐field VLBI, which has made significant progress over the last three years (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Cambridge University Press (CUP)
Date: 1984
Publisher: Sissa Medialab
Date: 29-05-2015
DOI: 10.22323/1.215.0073
Publisher: Oxford University Press (OUP)
Date: 09-09-2022
Abstract: New classes of astronomical objects are often discovered serendipitously. The enormous data volumes produced by recent high-time resolution, radio-telescope surveys imply that efficient algorithms are required for a discovery. Such algorithms are usually tuned to detect specific, known sources. Existing data sets therefore likely contain unknown astronomical sources, which will remain undetected unless algorithms are developed that can detect a more erse range of signals. We present the Single-dish PARKES data sets for finding the uneXpected (SPARKESX), a compilation of real and simulated high-time resolution observations. SPARKESX comprises three mock surveys from the Parkes ‘Murriyang’ radio telescope. A broad selection of simulated and injected expected signals (such as pulsars and fast radio bursts), poorly characterized signals (plausible flare star signatures), and ‘unknown unknowns’ are generated for each survey. The goal of this challenge is to aid in the development of new algorithms that can detect a wide range of source types. We show how successful a typical pipeline based on the standard pulsar search software, presto, is at finding the injected signals. The data set is publicly available at 0.25919/fd4f-0g20 (Yong et al. 2022).
Publisher: Oxford University Press (OUP)
Date: 22-02-2012
Publisher: Oxford University Press (OUP)
Date: 24-10-2019
Abstract: We present a catalogue of a large s le of extended radio sources in the SCORPIO field, observed and resolved by the Australia Telescope Compact Array. SCORPIO, a pathfinder project for addressing the early operations of the Australia SKA Pathfinder, is a survey of ∼5 square degrees between 1.4 and 3.1 GHz, centered at l = 343.5○, b = 0.75○ and with an angular resolution of about 10 arcsec. It is aimed at understanding the scientific and technical challenges to be faced by future Galactic surveys. With a mean sensitivity around $100\\ \\mu \\mathrm{Jy\\ beam}^{-1}$ and the possibility to recover angular scales at least up to 4 arcmin, we extracted 99 extended sources, 35 of them detected for the first time. Among the 64 known sources 55 had at least a tentative classification in literature. Studying the radio morphology and comparing the radio emission with infrared we propose as candidates 6 new H ii regions, 2 new planetary nebulae, 2 new luminous blue variable or Wolf–Rayet stars and 3 new supernova remnants. This study provides an overview of the potentiality of future radio surveys in terms of Galactic source extraction and characterization and a discussion on the difficulty to reduce and analyze interferometric data on the Galactic plane.
Publisher: Oxford University Press (OUP)
Date: 02-1980
Publisher: Cambridge University Press (CUP)
Date: 12-2011
Publisher: Zenodo
Date: 2016
DOI: 10.5281/ZENODO.60407
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.44
Abstract: We present a set of peculiar radio sources detected using an unsupervised machine learning method. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to train a self-organizing map (SOM). The radio maps from three ASKAP surveys, Evolutionary Map of Universe pilot survey (EMU-PS), Deep Investigation of Neutral Gas Origins pilot survey (DINGO), and Survey With ASKAP of GAMA-09 + X-ray (SWAG-X), are used to search for the rarest or unknown radio morphologies. We use an extension of the SOM algorithm that implements rotation and flipping invariance on astronomical sources. The SOM is trained using the images of all ‘complex’ radio sources in the EMU-PS which we define as all sources catalogued as ‘multi-component’. The trained SOM is then used to estimate a similarity score for complex sources in all surveys. We select 0.5% of the sources that are most complex according to the similarity metric and visually examine them to find the rarest radio morphologies. Among these, we find two new odd radio circle (ORC) candidates and five other peculiar morphologies. We discuss multiwavelength properties and the optical/infrared counterparts of selected peculiar sources. In addition, we present ex les of conventional radio morphologies including: diffuse emission from galaxy clusters, and resolved, bent-tailed, and FR-I and FR-II type radio galaxies. We discuss the overdense environment that may be the reason behind the circular shape of ORC candidates.
Publisher: China Science Publishing & Media Ltd.
Date: 07-2014
Publisher: American Astronomical Society
Date: 23-05-2011
Publisher: Springer Netherlands
Date: 1994
Publisher: Springer Science and Business Media LLC
Date: 16-06-2021
Publisher: EDP Sciences
Date: 17-09-2008
Publisher: Cambridge University Press (CUP)
Date: 2001
Publisher: EDP Sciences
Date: 07-2014
Publisher: Oxford University Press (OUP)
Date: 07-01-2015
Publisher: American Astronomical Society
Date: 20-02-2000
DOI: 10.1086/308397
Publisher: Informa UK Limited
Date: 29-06-2015
Publisher: Cambridge University Press (CUP)
Date: 08-2007
DOI: 10.1017/S1743921307012240
Abstract: We present a summary of the major contributions to the Special Session on Astronomical Data Management held at the IAU XXVI General Assembly in Prague in 2006. While recent years have seen enormous improvements in access to astronomical data, and the Virtual Observatory aims to provide astronomers with seamless access to on-line resources, more attention needs to be paid to ensuring the quality and completeness of those resources. For ex le, data produced by telescopes are not always made available to the astronomical community, and new instruments are sometimes designed and built with insufficient planning for data management, while older but valuable legacy data often remain undigitised. Data and results published in journals do not always appear in the data centres, and astronomers in developing countries sometimes have inadequate access to on-line resources. To address these issues, an ‘Astronomers' Data Manifesto’ has been formulated with the aim of initiating a discussion that will lead to the development of a ‘code of best practice’ in astronomical data management.
Publisher: Oxford University Press (OUP)
Date: 1988
Publisher: Cambridge University Press (CUP)
Date: 1998
Publisher: Oxford University Press (OUP)
Date: 10-1985
Publisher: Oxford University Press (OUP)
Date: 11-02-2014
Publisher: Oxford University Press (OUP)
Date: 04-1994
Publisher: American Astronomical Society
Date: 10-04-1998
DOI: 10.1086/305438
Publisher: Oxford University Press (OUP)
Date: 14-09-2015
Publisher: Oxford University Press (OUP)
Date: 17-04-2014
DOI: 10.1093/MNRAS/STU500
Publisher: Oxford University Press (OUP)
Date: 29-07-2015
Publisher: Oxford University Press (OUP)
Date: 1998
Publisher: American Astronomical Society
Date: 03-1994
DOI: 10.1086/116911
Publisher: Oxford University Press (OUP)
Date: 11-04-2022
Abstract: We present the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the Galaxy and Mass Assembly (GAMA)-23h field. The survey was carried out at 887.5 MHz and covers an ∼83 square deg field. We imaged the calibrated visibility data, taken as part of the Evolutionary Mapping of Universe Early Science Programme, using the latest version of the ASKAPSoft pipeline. The final mosaic has an angular resolution of 10 arcsec and a central rms noise of around 38 $\\mu$Jy beam−1. The derived radio source catalogue has 39 812 entries above a peak flux density threshold of 5σ. We searched for the radio source host galaxy counterparts using the GAMA spectroscopic (with an i-band magnitude limit of 19.2 mag) and multiwavelength catalogues that are available as part of the collaboration. We identified hosts with GAMA spectroscopic redshifts for 5934 radio sources. We describe the data reduction, imaging, and source identification process, and present the source counts. Thanks to the wide area covered by our survey, we obtain very robust counts down to 0.2 mJy. ASKAP’s exceptional survey speed, providing efficient, sensitive, and high-resolution mapping of large regions of the sky in conjunction with the multiwavelength data available for the GAMA23 field, allowed us to discover 63 giant radio galaxies. The data presented here demonstrate the excellent capabilities of ASKAP in the pre-SKA era.
Publisher: Wiley
Date: 04-08-2011
Publisher: EDP Sciences
Date: 11-2017
Publisher: Springer Netherlands
Date: 1996
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921310005806
Abstract: We have identified a new class of object that we term PRONGS (powerful radio objects nested in galaxies with star formation). These are powerful radio sources whose optical properties are that of spiral/star-forming galaxies, unlike classic powerful radio sources which are typically hosted by elliptical galaxies in the local Universe. Here we present a first look at these enigmatic sources.
Publisher: Oxford University Press (OUP)
Date: 24-08-2015
Publisher: American Astronomical Society
Date: 03-2003
DOI: 10.1086/367914
Publisher: Oxford University Press (OUP)
Date: 11-04-2007
Publisher: Springer New York
Date: 07-07-2014
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.4
Publisher: Oxford University Press (OUP)
Date: 20-02-2017
DOI: 10.1093/MNRAS/STX424
Publisher: Springer Netherlands
Date: 1994
Publisher: Oxford University Press (OUP)
Date: 21-10-2019
Abstract: We report the discovery of a very young high-mass X-ray binary (HMXB) system associated with the supernova remnant (SNR) MCSNR J0513-6724 in the Large Magellanic Cloud (LMC), using XMM–Newton X-ray observations. The HMXB is located at the geometrical centre of extended soft X-ray emission, which we confirm as an SNR. The HMXB spectrum is consistent with an absorbed power law with spectral index ∼1.6 and a luminosity of 7 × 1033 erg s−1 (0.2–12 keV). Tentative X-ray pulsations are observed with a periodicity of 4.4 s and the OGLE I-band light curve of the optical counterpart from more than 17.5 yr reveals a period of 2.2324 ± 0.0003 d, which we interpret as the orbital period of the binary system. The X-ray spectrum of the SNR is consistent with non-equilibrium shock models as expected for young/less evolved SNRs. From the derived ionization time-scale we estimate the age of the SNR to be kyr. The association of the HMXB with the SNR makes it the youngest HMXB, in the earliest evolutionary stage known to date. An HMXB as young as this can switch on as an accreting pulsar only when the spin period has reached a critical value. Under this assumption, we obtain an upper limit to the magnetic field of × 1011 G. This implies several interesting possibilities including magnetic field burial, possibly by an episode of post-supernova hyper-critical accretion. Since these fields are expected to diffuse out on a time-scale of 103–104 yr, the discovery of a very young HMXB can provide us the unique opportunity to observe the evolution of the observable magnetic field for the first time in X-ray binaries.
Publisher: Oxford University Press (OUP)
Date: 08-04-2019
DOI: 10.1093/MNRAS/STZ971
Publisher: Oxford University Press (OUP)
Date: 04-1989
Publisher: American Astronomical Society
Date: 10-1987
DOI: 10.1086/185024
Publisher: Informa UK Limited
Date: 22-10-2021
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.48
Publisher: Oxford University Press (OUP)
Date: 20-11-2012
Publisher: American Astronomical Society
Date: 19-12-2014
Publisher: Oxford University Press (OUP)
Date: 14-10-2017
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2016.63
Abstract: Most major discoveries in astronomy are unplanned, and result from surveying the Universe in a new way, rather than by testing a hypothesis or conducting an investigation with planned outcomes. For ex le, of the ten greatest discoveries made by the Hubble Space Telescope , only one was listed in its key science goals. So a telescope that merely achieves its stated science goals is not achieving its potential scientific productivity. Several next-generation astronomical survey telescopes are currently being designed and constructed that will significantly expand the volume of observational parameter space, and should in principle discover unexpected new phenomena and new types of object. However, the complexity of the telescopes and the large data volumes mean that these discoveries are unlikely to be found by chance. Therefore, it is necessary to plan explicitly for unexpected discoveries in the design and construction. Two types of discovery are recognised: unexpected objects and unexpected phenomena. This paper argues that next-generation astronomical surveys require an explicit process for detecting the unexpected, and proposes an implementation of this process. This implementation addresses both types of discovery, and relies heavily on machine-learning techniques, and also on theory-based simulations that encapsulate our current understanding of the Universe.
Publisher: Oxford University Press (OUP)
Date: 16-05-2011
Publisher: Cambridge University Press (CUP)
Date: 03-1980
DOI: 10.1017/S0003598X00042848
Abstract: ‘A cairn supported at its edge by large stones may be removed. … The ring which is left looks like a stone circle.’ (Thom, 1967, 65). Professor A. Thom has surveyed a large number of archaeological sites (Thom, 1967 1971). These surveys provide the basis from which he deduces the existence of the Megalithic Yard (MY), Megalithic Geometry and Megalithic Astronomy. In considering his evidence for these aspects of ‘megalithic science’ it is pertinent to enquire of each site: Does it date from the Late Neolithic or Early Bronze Age? Is it correctly identified? Do the stones occupy their original positions? Is the site plan accurate? Has the site already been discussed, or since discussed, in the archaeological literature? The ex le of Unival, discussed in detail later, shows that here Thom has made a serious error in identifying the site, and very probably made surveying errors. These errors vitiate part of his discussion of an important site. This mis-identification, and similar ones, could have been avoided if the archaeological literature had been consulted.
Publisher: Oxford University Press (OUP)
Date: 03-1984
Publisher: American Physical Society (APS)
Date: 05-11-2008
Publisher: American Astronomical Society
Date: 03-06-2016
Publisher: Oxford University Press (OUP)
Date: 11-04-2023
Abstract: We present a novel natural language processing (NLP) approach to deriving plain English descriptors for science cases otherwise restricted by obfuscating technical terminology. We address the limitations of common radio galaxy morphology classifications by applying this approach. We experimentally derive a set of semantic tags for the Radio Galaxy Zoo EMU (Evolutionary Map of the Universe) project and the wider astronomical community. We collect 8486 plain English annotations of radio galaxy morphology, from which we derive a taxonomy of tags. The tags are plain English. The result is an extensible framework, which is more flexible, more easily communicated, and more sensitive to rare feature combinations, which are indescribable using the current framework of radio astronomy classifications.
Publisher: EDP Sciences
Date: 29-11-2012
Publisher: Oxford University Press (OUP)
Date: 04-1984
Publisher: Oxford University Press (OUP)
Date: 03-06-2015
DOI: 10.1093/MNRAS/STV930
Publisher: American Astronomical Society
Date: 21-01-2010
Publisher: Oxford University Press (OUP)
Date: 25-04-2018
Publisher: Frontiers Media SA
Date: 08-08-2019
Publisher: American Astronomical Society
Date: 05-1988
DOI: 10.1086/191267
Publisher: EDP Sciences
Date: 03-2013
Publisher: EDP Sciences
Date: 11-2012
Publisher: Oxford University Press (OUP)
Date: 30-04-2021
Abstract: 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 ex le, with the companion galaxy, DES J010226.15–245104.9, located in or projected on to the south-eastern part of the ring. We encourage the search for further ORCs in radio surveys to study their properties and origin.
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: American Astronomical Society
Date: 07-1993
DOI: 10.1086/172914
Publisher: Oxford University Press (OUP)
Date: 21-02-1998
Publisher: Oxford University Press (OUP)
Date: 11-1982
Publisher: Oxford University Press (OUP)
Date: 22-02-2022
Abstract: Low- and intermediate-mass stars end their life dispersing their outer layers into the circumstellar medium, during the asymptotic and post-asymptotic giant branch phases. OH masers at 18 cm offer an effective way to probe their circumstellar environment. In this work, we present the discovery of seven OH maser sources likely associated with such evolved stars from the visual inspection of Australian SKA Pathfinder (ASKAP) continuum images. These seven sources do not emit real continuum emission, but the high sensitivity of our images allows us to detect their maser emission, resembling continuum sources. To confirm their nature, we carried out spectral-line observations with ATCA. All the sources showed the double-peaked spectra at 1612 MHz, typical of evolved stars. The detection of maser emission in continuum images can be a complementary and easy-to-use method to discover new maser sources with the large-area deep surveys conducted with the Square Kilometre Array (SKA) precursors. The implication for radio stars studies are remarkable since pure OH maser sources (i.e. with no continuum associated) represent, at a sensitivity of $100\\,\\mu \\mathrm{Jy\\,beam}^{-1}$, about 4 per cent of all Galactic sources and by far the most numerous stellar population.
Publisher: Cambridge University Press (CUP)
Date: 1985
Publisher: Springer Science and Business Media LLC
Date: 02-1989
DOI: 10.1038/337625A0
Publisher: Elsevier BV
Date: 09-2015
Publisher: IOP Publishing
Date: 30-08-2019
Publisher: Oxford University Press (OUP)
Date: 04-1985
Publisher: Oxford University Press (OUP)
Date: 10-1992
Publisher: Oxford University Press (OUP)
Date: 03-1985
Publisher: Oxford University Press (OUP)
Date: 1989
Publisher: SPIE
Date: 09-07-2018
DOI: 10.1117/12.2313504
Publisher: IOP Publishing
Date: 07-2012
DOI: 10.1086/666945
Publisher: Cambridge University Press (CUP)
Date: 1999
DOI: 10.1071/AS99152
Abstract: The Square Kilometre Array Radio Telescope is the next generation radio telescope. An international project is currently under way to design and build an instrument having an effective collecting area two orders of magnitude greater than that of any existing telescope. A number of separate studies are presently investigating how to design the Square Kilometre Array to best carry out the kinds of observations desired by the astronomical community. We present a summary of one of these studies, a workshop called The ‘Sub-microJansky Radio Sky’ held at the ATNF, Sydney, on 17 June 1998. This workshop addressed the nature of the radio sky at the very faint flux densities likely to be attainable by the Square Kilometre Array. In particular, each speaker investigated a separate population of radio sources and how the expected appearance of that population at such faint flux densities would dictate how to refine some of the design constraints for the Square Kilometre Array.
Publisher: Springer Science and Business Media LLC
Date: 1990
DOI: 10.1038/343240A0
Publisher: IEEE
Date: 12-2010
Publisher: Cambridge University Press (CUP)
Date: 1984
Publisher: Oxford University Press (OUP)
Date: 06-09-2023
Publisher: American Astronomical Society
Date: 22-05-2017
Publisher: Oxford University Press (OUP)
Date: 11-10-2000
Publisher: Springer Science and Business Media LLC
Date: 09-1982
DOI: 10.1038/299131A0
Publisher: EDP Sciences
Date: 13-12-2010
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.37
Abstract: The Evolutionary Map of the Universe (EMU) is a proposed radio continuum survey of the Southern Hemisphere up to declination + 30°, with the Australian Square Kilometre Array Pathfinder (ASKAP). EMU will use an automated source identification and measurement approach that is demonstrably optimal, to maximise the reliability and robustness of the resulting radio source catalogues. As a step toward this goal we conducted a “Data Challenge” to test a variety of source finders on simulated images. The aim is to quantify the accuracy and limitations of existing automated source finding and measurement approaches. The Challenge initiators also tested the current ASKAPsoft source-finding tool to establish how it could benefit from incorporating successful features of the other tools. As expected, most finders show completeness around 100% at ≈ 10σ dropping to about 10% by ≈ 5σ. Reliability is typically close to 100% at ≈ 10σ, with performance to lower sensitivities varying between finders. All finders show the expected trade-off, where a high completeness at low signal-to-noise gives a corresponding reduction in reliability, and vice versa. We conclude with a series of recommendations for improving the performance of the ASKAPsoft source-finding tool.
Publisher: Cambridge University Press (CUP)
Date: 08-2010
DOI: 10.1017/S1743921310005946
Abstract: The Australia Telescope Large Area Survey (ATLAS Norris et al . 2006) is the widest deep radio survey to date, covering approximately 7 square degrees over two fields, with extensive complementary data. We are investigating all possible discriminants between active galactic nuclei (AGN) and star-forming galaxies (SFG) in ATLAS, to determine a robust formula for distinguishing the two.
Publisher: Springer Science and Business Media LLC
Date: 18-09-2017
Publisher: Oxford University Press (OUP)
Date: 27-10-2018
Publisher: Oxford University Press (OUP)
Date: 21-12-2002
Publisher: Oxford University Press (OUP)
Date: 07-05-2018
Publisher: Oxford University Press (OUP)
Date: 24-03-2022
Abstract: 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 μJy/beam). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarization and spectral index maps. Based on these new data, we consider potential mechanisms that may generate the ORCs.
Publisher: SPIE
Date: 18-05-1987
DOI: 10.1117/12.966771
Publisher: American Astronomical Society
Date: 10-02-2000
DOI: 10.1086/312481
Abstract: We report the discovery of circularly polarized radio emission from the radio-jet X-ray binary SS 433 with the Australia Telescope Compact Array. The flux density spectrum of the circular polarization, clearly detected at four frequencies between 1 and 9 GHz, is of the form V~nu-0.9+/-0.1. Multiple components in the source and a lack of very high spatial resolution do not allow a unique determination of the origin of the circular polarization or of the spectrum of fractional polarization. However, we argue that the emission is likely to arise in the inner regions of the binary, possibly via propagation-induced conversion of linear to circular polarization, and the fractional circular polarization of these regions may be as high as 10%. Observations such as these have the potential to help us investigate the composition, whether pairs or baryonic, of the ejecta from X-ray binaries.
Publisher: American Astronomical Society
Date: 08-1990
DOI: 10.1086/169063
Publisher: IOP Publishing
Date: 30-01-2015
Publisher: Springer Science and Business Media LLC
Date: 06-2004
Publisher: Cambridge University Press (CUP)
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 07-02-2015
Publisher: Oxford University Press (OUP)
Date: 21-06-1999
Publisher: American Astronomical Society
Date: 10-1988
DOI: 10.1086/185291
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2020.52
Abstract: We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.
Publisher: Springer Science and Business Media LLC
Date: 1999
Publisher: Cambridge University Press (CUP)
Date: 1984
Publisher: Cambridge University Press (CUP)
Date: 1991
DOI: 10.1017/S1323358000025418
Abstract: We have successfully demonstrated optical aperture synthesis at the 4-m Anglo-Australian Telescope. By using a multi-hole mask over the (re-imaged) primary mirror and recording the resulting fringe patterns with high time resolution, diffraction-limited images of sufficiently bright objects can be reconstructed. The data processing uses closure phases to overcome the effects of atmospheric turbulence. We show an image of the double star η Oph, with component separation 0″.45.
Publisher: Oxford University Press (OUP)
Date: 10-10-2012
Publisher: Oxford University Press (OUP)
Date: 05-05-2016
Publisher: Oxford University Press (OUP)
Date: 16-09-2020
Abstract: In this paper, we present the identification of five previously unknown giant radio galaxies (GRGs) using Data Release 1 of the Radio Galaxy Zoo citizen science project and a selection method appropriate to the training and validation of deep learning algorithms for new radio surveys. We associate one of these new GRGs with the brightest cluster galaxy (BCG) in the galaxy cluster GMBCG J251.67741+36.45295 and use literature data to identify a further 13 previously known GRGs as BCG candidates, increasing the number of known BCG GRGs by $\\gt 60$ per cent. By examining local galaxy number densities for the number of all known BCG GRGs, we suggest that the existence of this growing number implies that GRGs are able to reside in the centres of rich (∼1014 M⊙) galaxy clusters and challenges the hypothesis that GRGs grow to such sizes only in locally underdense environments.
Publisher: Oxford University Press (OUP)
Date: 15-06-2010
Publisher: EDP Sciences
Date: 05-04-2016
Publisher: Oxford University Press (OUP)
Date: 21-12-1998
Publisher: Springer Science and Business Media LLC
Date: 1990
DOI: 10.1038/343045A0
Publisher: Oxford University Press (OUP)
Date: 05-1992
Publisher: Oxford University Press (OUP)
Date: 03-1996
Publisher: Oxford University Press (OUP)
Date: 03-07-2012
Publisher: EDP Sciences
Date: 05-04-2016
Publisher: Oxford University Press (OUP)
Date: 30-06-2014
Publisher: Ubiquity Press, Ltd.
Date: 2007
DOI: 10.2481/DSJ.6.S116
Publisher: Oxford University Press (OUP)
Date: 23-02-2016
Publisher: Oxford University Press (OUP)
Date: 10-2002
Publisher: American Physiological Society
Date: 08-1997
Publisher: EDP Sciences
Date: 06-2015
Publisher: Oxford University Press (OUP)
Date: 03-2013
DOI: 10.1093/MNRAS/STT147
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.25
Abstract: The traditional cultures of Aboriginal Australians include a significant astronomical component, perpetuated through oral tradition, ceremony, and art. This astronomical knowledge includes a deep understanding of the motion of objects in the sky, which was used for practical purposes such as constructing calendars and for navigation. There is also evidence that traditional Aboriginal Australians made careful records and measurements of cyclical phenomena, recorded unexpected phenomena such as eclipses and meteorite impacts, and could determine the cardinal points to an accuracy of a few degrees. Putative explanations of celestial phenomena appear throughout the oral record, suggesting traditional Aboriginal Australians sought to understand the natural world around them, in the same way as modern scientists, but within their own cultural context. There is also a growing body of evidence for sophisticated navigational skills, including the use of astronomically based songlines. Songlines are effectively oral maps of the landscape, and are an efficient way of transmitting oral navigational skills in cultures that do not have a written language. The study of Aboriginal astronomy has had an impact extending beyond mere academic curiosity, facilitating cross-cultural understanding, demonstrating the intimate links between science and culture, and helping students to engage with science.
Publisher: Springer Science and Business Media LLC
Date: 05-1987
DOI: 10.1038/327038A0
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS11026
Abstract: The process of determining the number and characteristics of sources in astronomical images is so fundamental to a large range of astronomical problems that it is perhaps surprising that no standard procedure has ever been defined that has well-understood properties with a high degree of statistical rigour on completeness and reliability. The Evolutionary Map of the Universe (EMU) survey with the Australian Square Kilometre Array Pathfinder (ASKAP), a continuum survey of the Southern Hemisphere up to declination +30°, aims to utilise an automated source identification and measurement approach that is demonstrably optimal, to maximise the reliability, utility and robustness of the resulting radio source catalogues. A key stage in source extraction methods is the background estimation (background level and noise level) and the choice of a threshold high enough to reject false sources, yet not so high that the catalogues are significantly incomplete. In this analysis, we present results from testing the SExtractor, Selavy (Duch ), and SFIND source extraction tools on simulated data. In particular, the effects of background estimation, threshold and false-discovery rate settings are explored. For parameters that give similar completeness, we find the false-discovery rate method employed by SFIND results in a more reliable catalogue compared to the peak threshold methods of SExtractor and Selavy.
Publisher: Informa UK Limited
Date: 12-2013
Publisher: Springer Science and Business Media LLC
Date: 04-1981
DOI: 10.1038/290382A0
Publisher: Oxford University Press (OUP)
Date: 02-1991
Publisher: Oxford University Press (OUP)
Date: 26-01-2018
DOI: 10.1093/MNRAS/STY163
Publisher: American Astronomical Society
Date: 12-2000
DOI: 10.1086/316854
Publisher: EDP Sciences
Date: 20-07-2015
Publisher: American Astronomical Society
Date: 18-11-2009
Publisher: Oxford University Press (OUP)
Date: 11-1980
Publisher: EDP Sciences
Date: 26-02-2021
DOI: 10.1051/0004-6361/202039533
Abstract: The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is ~50′ or ~3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of 〈 J 〉 1 GHz 1.2 × 10 −44 W Hz −1 m −3 . A non-detection of diffuse radio emission in the X-ray bridge between these two clusters has implications for particle-acceleration mechanisms in cosmological large-scale structure. We also report extended or otherwise noteworthy radio sources in the 30 deg 2 field around Abell 3391-Abell 3395. We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected sizes greater than 1 Mpc. The sky density of field radio galaxies with largest linear sizes of .7 Mpc is ≈1.7 deg −2 , three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-1983
Publisher: Sissa Medialab
Date: 29-05-2015
DOI: 10.22323/1.215.0086
Publisher: Oxford University Press (OUP)
Date: 03-1986
Publisher: Springer Science and Business Media LLC
Date: 12-2011
Publisher: Cambridge University Press
Date: 02-06-1994
Publisher: EDP Sciences
Date: 20-11-2018
DOI: 10.1051/0004-6361/201732336
Abstract: We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30.4 square degrees, with rms μ Jy beam −1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μ Jy beam −1 , while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μ Jy beam −1 . The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 ×rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey’s incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).
Publisher: EDP Sciences
Date: 09-2016
Publisher: American Astronomical Society
Date: 08-1989
DOI: 10.1086/185509
Publisher: American Astronomical Society
Date: 12-08-2010
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.42
Abstract: We present the data and initial results from the first pilot survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers $270 \\,\\mathrm{deg}^2$ of an area covered by the Dark Energy Survey, reaching a depth of 25–30 $\\mu\\mathrm{Jy\\ beam}^{-1}$ rms at a spatial resolution of $\\sim$ 11–18 arcsec, resulting in a catalogue of $\\sim$ 220 000 sources, of which $\\sim$ 180 000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.
Publisher: Oxford University Press (OUP)
Date: 08-1997
Publisher: American Astronomical Society
Date: 11-04-2016
Publisher: American Astronomical Society
Date: 20-08-2019
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2011
End Date: 2017
Funder: Australian Research Council
View Funded ActivityStart Date: 2020
End Date: 2021
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 2016
Funder: Marsden Fund
View Funded ActivityStart Date: 2012
End Date: 2015
Funder: Royal Society of New Zealand
View Funded ActivityStart Date: 2014
End Date: 2016
Funder: Australian Research Council
View Funded ActivityStart Date: 2005
End Date: 2005
Funder: Australian Research Council
View Funded ActivityStart Date: 2011
End Date: 2014
Funder: Australian Research Council
View Funded ActivityStart Date: 2011
End Date: 2014
Funder: Australian Research Council
View Funded ActivityStart Date: 2003
End Date: 2003
Funder: Australian Research Council
View Funded ActivityStart Date: 2003
End Date: 2003
Funder: Australian Research Council
View Funded ActivityStart Date: 2003
End Date: 2003
Funder: Australian Research Council
View Funded ActivityStart Date: 2003
End Date: 2006
Funder: Australian Research Council
View Funded ActivityStart Date: 2005
End Date: 01-2007
Amount: $402,128.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2003
End Date: 12-2006
Amount: $193,035.00
Funder: Australian Research Council
View Funded ActivityStart Date: 09-2011
End Date: 12-2014
Amount: $278,400.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2011
End Date: 10-2014
Amount: $835,200.00
Funder: Australian Research Council
View Funded ActivityStart Date: 01-2004
End Date: 12-2003
Amount: $10,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 08-2020
End Date: 08-2024
Amount: $530,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 03-2004
End Date: 10-2004
Amount: $15,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 12-2020
Amount: $340,160.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2011
End Date: 03-2018
Amount: $20,600,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 08-2016
Amount: $350,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2004
End Date: 12-2004
Amount: $10,000.00
Funder: Australian Research Council
View Funded Activity