Radio Catalogues Research Articles

The XXL Survey

The 2.1 GHz radio source catalogue of the 25 deg2ultimate XMM extragalactic survey south (XXL-S) field, observed with the Australia Telescope Compact Array (ATCA), is presented. The final radio mosaic achieved a resolution of ~ 4.8″ and a median rms noise ofσ≈ 41μJy/beam. To date, this is the largest area radio survey to reach this flux density level. A total of 6350 radio components above 5σare included in the component catalogue, 26.4% of which are resolved. Of these components, 111 were merged together to create 48 multiple-component radio sources, resulting in a total of 6287 radio sources in the source catalogue, 25.9% of which were resolved. A survival analysis revealed that the median spectral index of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz sources in the field isα= −0.75, consistent with the values of − 0.7 to − 0.8 commonly used to characterise radio spectral energy distributions of active galactic nuclei. The 2.1 GHz and 1.4 GHz differential radio source counts are presented and compared to other 1.4 GHz radio surveys. The XXL-S source counts show good agreement with the other surveys.

The Atacama Cosmology Telescope: two-season ACTPol extragalactic point sources and their polarization properties

ABSTRACT We report on measurements of the polarization of extragalactic sources at 148 GHz made during the first two seasons of the Atacama Cosmology Telescope Polarization (ACTPol) survey. The survey covered 680 deg2 of the sky on the celestial equator. Polarization measurements of 169 intensity-selected sources brighter than 30 mJy, that are predominantly active galactic nuclei, are presented. Above a total flux of 215 mJy where the noise bias removal in the polarization measurement is reliable, we detect 26 sources, 14 of which have a detection of linear polarization at greater than 3σ significance. The distribution of the fractional polarization as a function of total source intensity is analysed. Our result is consistent with the scenario that the fractional polarization of our measured radio source population is independent of total intensity down to the limits of our measurements and well described by a Gaussian distribution with a mean fractional polarization pm = 0.028 ± 0.005 and standard deviation $\sigma _{\mathrm{p_{m}}}$ = 0.054, truncated at p = 0. Extrapolating this model for the distribution of source polarization below the ACTPol detection threshold, we predict that one could get a clean measure of the E-mode polarization power spectrum of the microwave background out to $\ell \approx 6000$ with 1 $\mu$K-arcminute maps over ${10\!{\ \rm \%}}$ of the sky from a future survey. We also study the spectral energy distribution of the total and polarized source flux densities by cross-matching with low radio frequency catalogues. We do not find any correlation between the spectral indices for total flux and polarized flux.

Radio variable sources at 1400 MHz and their optical variability

Abstract In the present study we have cross-correlated NVSS and FIRST radio catalogues having radio flux measurements at the same 1.4 GHz frequency. This way we benefit from repeated observations from both catalogues, as they give more accurate positions and fluxes and more important, reveal large differences between the two measured fluxes, thus allowing to establish radio variability. As a result 79,382 radio variables have been revealed, including 6301 with flux differences at 1.4 GHz larger than 15 mJy, 1917 with flux differences > 45 mJy and 260 with flux differences > 200 mJy. By using a special technique (Mickaelian & Sinamyan 2010, Mickaelian et al. 2011), 2425 optically variable objects out of 6301 radio sources have been revealed. 2425 radio sources with both high radio and optical variability into four categories have been divided. 1206 (19%) out of 6301 radio sources have activity types from available catalogues and 619 (25.5%) out of 2425 radio sources with at the same time radio and optical variability have activity types from available catalogues. In addition, 279 radio sources out of 2425 have high variability in optical range. We have established their activity types when available. The IR fluxes and colours for the 6301 variable radio sources have been studied. Colour–colour diagrams show that most of the “unknown” sources are galaxies. The activity types for 110 (42%) out of 260 extremely high variable radio sources also have been retrieved.

Probing restarting activity in hard X-ray selected giant radio galaxies

AbstractWith their sizes larger than 0.7 Mpc, Giant Radio Galaxies (GRGs) are the largest individual objects in the Universe. To date, the reason why they reach such enormous extensions is still unclear. One of the proposed scenarios suggests that they are the result of multiple episodes of jet activity. Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues (NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four higher than those selected from radio catalogues). Remarkably, all of the sources in the sample show signs of restarting radio activity. The X-ray properties are consistent with this scenario, the sources being in a high-accretion, high-luminosity state with respect to the previous activity responsible for the radio lobes.

New Galactic Planetary nebulae selected by radio and multiwavelength characteristics

We have used the Cornish radio catalogue combined with the use of multi-wavelength data to identify 62 new Planetary Nebula (PN) candidates close to the Galactic mid-plane. Of this sample 11 have weak optical counterparts in deep narrow band H$\alpha$ imaging that allows their spectroscopic follow-up. We have observed eight of these candidates spectroscopically, leading to the confirmation of 7 out of 8 as PNe. All but one of our sample of newly detected PNe appear to be of Type I chemistry with very large [NII]/H$\alpha$ ratios. This indicates that our selection method heavily favours detection of this kind of PN. Cornish is a low Galactic latitude survey where young objects and Type I PNe (thought to derive from higher mass progenitors) are more plentiful, but where optical extinction is large. The very high success rate in correctly identifying PNe in this zone proves the efficacy of our radio and multiple multi-wavelength diagnostic tools used to successfully predict and then confirm their PN nature, at least in the cases where an optical counterpart is found and has been observed. The study reinforces the effective use of a combination of multi-wavelength and optical data in the identification of new Galactic PNe and especially those of Type I chemistries whose dusty environments often prevents their easy detection in the optical regime alone.

Constraints on the Composition, Magnetization, and Radiative Efficiency in the Jets of Blazars

Abstract The composition and energy dissipation in jets are two of the fundamental questions of jet physics that are not fully understood. In this paper, we attempt to constrain the composition, magnetization, and radiative efficiency for blazars with the recently released low-frequency radio catalog of the TIFR GMRT Sky Survey at 150 MHz. The jet power estimated from the low-frequency radio emission is much lower than that derived from spectral energy distribution fitting assuming one proton per electron. Assuming the jet power estimated from low-frequency radio emission is physical, the fraction of electron/positron pairs can be constrained with n pairs/n p ∼ 10. By comparing the power carried by the magnetic field and radiation with the jet power estimated from the low-frequency radio emission, we find both the relatively high magnetization parameter of σ ∼ 0.5 and the radiative efficiency of η ∼ 0.4 in the dissipation region of blazars. These results suggest that magnetic reconnection processes may play an important role in the energy dissipation of blazars. We also explore the connection between these three parameters (n pairs/n p, σ, and η) and the black hole mass, disk luminosity, and Eddington ratio. No significant correlation is found, except that σ shows a possible correlation with disk luminosity.

Работы по сравнению и комбинации каталогов координат радиоисточников в Пулковской обсерватории

Описан опыт работ по сравнению и комбинации каталогов координат радиоисточников в Пулковской обсерватории (ГАО РАН) в 2006-2017 гг. Принятая процедура построения сводного каталога включает два этапа. Сначала разности между исходными каталогами и улучшаемой небесной системой отсчета ICRF (ICRF2) представляются рядом сферических функций по методу Броше. Затем каждый каталог исправляется за найденные разности (системы исходных каталогов), и исправленные каталоги усредняются. После этого усредняются вычисленные на первом этапе системы исходных каталогов, и полученная средняя система рассматривается как систематические поправки к исходной системе каталога ICRF. Сложение средней системы с каталогом, полученным на первом этапе, дает в результате окончательный сводный каталог. Первый пулковский сводный каталог был составлен в 2006 г. и позволил существенно улучшить точность определения всемирного времени и координат небесного полюса. Второй каталог был составлен в 2013 г. и позволил предварительно оценить систематические ошибки каталога ICRF2. Третий каталог 2016 г., описанный в настоящей работе, позволил уточнить эти ошибки.

A novel approach for characterizing broad-band radio spectral energy distributions

We present a new broadband radio frequency catalogue across 0.12 GHz $\le \nu \le$ 20 GHz created by combining data from the Murchison Widefield Array Commissioning Survey, the Australia Telescope 20 Gigahertz survey, and the literature. Our catalogue consists of 1285 sources limited by $S_{20\,\rm{GHz}} >$ 40 mJy at $5\sigma$, and contains flux density measurements (or estimates) and uncertainties at 0.074, 0.080, 0.119, 0.150, 0.180, 0.408, 0.843, 1.4, 4.8, 8.6, and 20 GHz. We fit a second-order polynomial in log-log space to the spectral energy distributions of all these sources in order to characterise their broadband emission. For the 994 sources which are well-described by a linear or quadratic model we present a new diagnostic plot arranging sources by the linear and curvature terms. We demonstrate the advantages of such a plot over the traditional radio colour-colour diagram. We also present astrophysical descriptions of the sources found in each segment of this new parameter space and discuss the utility of these plots in the upcoming era of large area, deep, broadband radio surveys.

The 3CR Chandra Snapshot Survey: Extragalactic Radio Sources with 0.5 < z < 1.0

This paper presents the analysis of Chandra X-ray snapshot observations of a subsample of the extragalactic sources listed in the revised Third Cambridge radio catalog (3CR), previously lacking X-ray observations and thus observed during Chandra Cycle 15. This data set extends the current Chandra coverage of the 3CR extragalactic catalog up to redshift $z$=1.0. Our sample includes 22 sources consisting of one compact steep spectrum (CSS) source, three quasars (QSOs), and 18 FR\,II radio galaxies. As in our previous analyses, here we report the X-ray detections of radio cores and extended structures (i.e., knots, hotspots and lobes) for all sources in the selected sample. We measured their X-ray intensities in three energy ranges: soft (0.5--1 keV), medium (1--2 keV) and hard (2-7 keV) and we also performed standard X-ray spectral analysis for brighter nuclei. All radio nuclei in our sample have an X-ray counterpart. We also discovered X-ray emission associated with the eastern knot of 3CR\,154, with radio hotspots in 3CR\,41, 3CR\,54 and 3CR\,225B and with the southern lobe of 3CR\,107. Extended X-ray radiation around the nuclei 3CR\,293.1 and 3CR\,323 on a scale of few tens kpc was also found. X-ray extended emission, potentially arising from the hot gas in the intergalactic medium and/or due to the high energy counterpart of lobes, is detected for 3CR\,93, 3CR\,154, 3CR\,292 and 3CR\, 323 over a few hundreds kpc-scale. Finally, this work also presents an update on the state-of-the-art of Chandra and XMM-Newton observations for the entire 3CR sample.

A Multi-Frequency Study of the Milky Way-Like Spiral Galaxy NGC 6744

AbstractWe present a multi-frequency study of the intermediate spiral SAB(r)bc type galaxy NGC 6744, using available data from the Chandra X-Ray telescope, radio continuum data from the Australia Telescope Compact Array and Murchison Widefield Array, and Wide-field Infrared Survey Explorer infrared observations. We identify 117 X-ray sources and 280 radio sources. Of these, we find nine sources in common between the X-ray and radio catalogues, one of which is a faint central black hole with a bolometric radio luminosity similar to the Milky Way’s central black hole. We classify 5 objects as supernova remnant (SNR) candidates, 2 objects as likely SNRs, 17 as H ii regions, 1 source as an AGN; the remaining 255 radio sources are categorised as background objects and one X-ray source is classified as a foreground star. We find the star-formation rate (SFR) of NGC 6744 to be in the range 2.8–4.7 M⊙~yr − 1 signifying the galaxy is still actively forming stars. The specific SFR of NGC 6744 is greater than that of late-type spirals such as the Milky Way, but considerably less that that of a typical starburst galaxy.

A radio spectral index map and catalogue at 147–1400 MHz covering 80 per cent of the sky

Abstract The radio spectral index is a powerful probe for classifying cosmic radio sources and understanding the origin of the radio emission. Combining data at 147 MHz and 1.4 GHz from the TIFR GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS), we produced a large-area radio spectral index map of ∼80 per cent of the sky (Dec. > − 40 deg), as well as a radio spectral index catalogue containing 1396 515 sources, of which 503 647 are not upper or lower limits. Almost every TGSS source has a detected counterpart, while this is true only for 36 per cent of NVSS sources. We released both the map and the catalogue to the astronomical community. The catalogue is analysed to discover systematic behaviours in the cosmic radio population. We find a differential spectral behaviour between faint and bright sources as well as between compact and extended sources. These trends are explained in terms of radio galaxy evolution. We also confirm earlier reports of an excess of steep-spectrum sources along the galactic plane. This corresponds to 86 compact and steep-spectrum source in excess compared to expectations. The properties of this excess are consistent with normal non-recycled pulsars, which may have been missed by pulsation searches due to larger than average scattering along the line of sight.

A High Resolution Survey of the Galactic Plane at 408 MHz

Abstract The interstellar medium is a complex “ecosystem” with gas constituents in the atomic, molecular and ionized states, dust, magnetic fields, and relativistic particles. The Canadian Galactic Plane Survey has imaged these constituents at multiple radio and infrared frequencies with angular resolution of the order of arcminutes. This paper presents radio continuum data at 408 MHz over the area of , , with an extension to in the range of , with angular resolution cosecδ. Observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey. The calibration of the survey using existing radio source catalogs is described. The accuracy of 408 MHz flux densities from the data is 6%. Information on large structures has been incorporated into the data using the single-antenna survey of Haslam et al. The paper presents the data, describes how it can be accessed electronically, and gives examples of applications of the data to ISM research.

A Search for FRB 121102-like Persistent Radio-luminous Sources—Candidates and Implications for the FRB Rate and Searches

Abstract The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within Mpc, in a footprint of 10,600 deg2. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of Mpc−3, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source ( ). Assuming a persistent source lifetime of 100 years, this implies a birth rate of yr−1 Mpc−3. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of yr−1. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.

Coma cluster ultradiffuse galaxies are not standard radio galaxies

Matching members in the Coma cluster catalogue of ultra-diffuse galaxies (UDGs, Yagi et al. 2016) from SUBARU imaging with a very deep radio continuum survey source catalogue of the cluster (Miller et al. 2009) using the Karl G. Jansky Very Large Array (VLA) within a rectangular region of ~ 1.19 square degrees centred on the cluster core reveals matches consistent with random. An overlapping set of 470 UDGs and 696 VLA radio sources in this rectangular area finds 33 matches within a separation of 25 arcsec; dividing the sample into bins with separations bounded by 5 arcsec, 10 arcsec, 20 arcsec and 25 arcsec finds 1, 4, 17 and 11 matches. An analytical model estimate, based on the Poisson probability distribution, of the number of randomly expected matches within these same separation bounds is 1.7, 4.9, 19.4 and 14.2, each respectively consistent with the 95 percent Poisson confidence intervals of the observed values. Dividing the data into five clustercentric annuli of 0.1 degree, and into the four separation bins, finds the same result. This random match of UDGs with VLA sources implies that UDGs are not radio galaxies by the standard definition. Those VLA sources having integrated flux > 1 mJy at 1.4 GHz in Miller et al. (2009) without SDSS galaxy matches are consistent with the known surface density of background radio sources. We briefly explore the possibility that some unresolved VLA sources near UDGs could be young, compact, bright, supernova remnants of type Ia events, possibly in the intracluster volume.

Testing the Isotropy of the Log N–log S Slope for the NVSS Radio Catalog

Abstract The cumulative number count N of sources above a threshold is known to approximately follow a power-law behavior N ∝ S − x . We study the variation of spectral index x across the sky to look for possible signals of a violation of isotropy. We develop a rigorous algorithm of likelihood maximization to accurately fit for the spectral index. We divide the sky into upper and lower hemispheres for a particular choice of the z axis and determine the error normalized difference between the best fit values of the spectral indices between the two hemispheres. The maximum value of this difference obtained by varying over the z axis provides us with a measure of departure from isotropy. We find that the data support isotropy of the spectral index. We also perform a dipole fit to the spectral index as a function of the angular coordinates. The result is found to be consistent with isotropy.

Searching for Primordial Black Holes in the Radio and X-Ray Sky.

We model the accretion of gas onto a population of massive primordial black holes in the MilkyWay and compare the predicted radio and x-ray emission with observational data. We show that, under conservative assumptions on the accretion process, the possibility that O(10)M_{⊙} primordial black holes can account for all of the dark matter in the MilkyWay is excluded at 5σ by a comparison with a Very Large Array radio catalog at 1.4GHz and at ≃40σ by a comparison with a Chandra x-ray catalog (0.5-8keV). We argue that this method can be used to identify such a population of primordial black holes with more sensitive future radio and x-ray surveys.

PUMA: The Positional Update and Matching Algorithm

AbstractWe present new software to cross-match low-frequency radio catalogues: the Positional Update and Matching Algorithm. The Positional Update and Matching Algorithm combines a positional Bayesian probabilistic approach with spectral matching criteria, allowing for confusing sources in the matching process. We go on to create a radio sky model using Positional Update and Matching Algorithm based on the Murchison Widefield Array Commissioning Survey, and are able to automatically cross-match ~ 98.5% of sources. Using the characteristics of this sky model, we create simple simulated mock catalogues on which to test the Positional Update and Matching Algorithm, and find that Positional Update and Matching Algorithm can reliably find the correct spectral indices of sources, along with being able to recover ionospheric offsets. Finally, we use this sky model to calibrate and remove foreground sources from simulated interferometric data, generated using OSKAR (the Oxford University visibility generator). We demonstrate that there is a substantial improvement in foreground source removal when using higher frequency and higher resolution source positions, even when correcting positions by an average of 0.3 arcmin given a synthesised beam-width of ~ 2.3 arcmin.

A search for long-time-scale, low-frequency radio transients

We present a search for transient and highly variable sources at low radio frequencies (150-200 MHz) that explores long timescales of 1-3 years. We conducted this search by comparing the TIFR GMRT Sky Survey Alternative Data Release 1 (TGSS ADR1) and the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey catalogues. To account for the different completeness thresholds in the individual surveys, we searched for compact GLEAM sources above a flux density limit of 100 mJy that were not present in the TGSS ADR1; and also for compact TGSS ADR1 sources above a flux density limit of 200 mJy that had no counterpart in GLEAM. From a total sample of 234 333 GLEAM sources and 275 612 TGSS ADR1 sources in the overlap region between the two surveys, there were 99658 GLEAM sources and 38 978 TGSS ADR sources that passed our flux density cutoff and compactness criteria. Analysis of these sources resulted in three candidate transient sources. Further analysis ruled out two candidates as imaging artefacts. We analyse the third candidate and show it is likely to be real, with a flux density of 182 +/- 26 mJy at 147.5 MHz. This gives a transient surface density of rho = (6.2 +/- 6) x 10-5 deg-2 . We present initial follow-up observations and discuss possible causes for this candidate. The small number of spurious sources from this search demonstrates the high reliability of these two new low-frequency radio catalogues.

EXPLORING THE TRANSIENT RADIO SKY WITH VLITE: EARLY RESULTS

ABSTRACT We report on a search for radio transients at 340 MHz with the Jansky Very Large Array Low-band Ionosphere and Transient Experiment (VLITE). Between 2015 July 29 and September 27, operating in commensal mode, VLITE imaged approximately 2800 pointings covering 12,000 deg2 on the sky, sampling timescales ranging from tens of seconds to several hours on a daily basis. In addition, between 2015 February 25 and May 9, VLITE observed 55 epochs of roughly 2–4 hr each toward the COSMOS field. Using existing radio source catalogs, we have searched all of the daily VLITE images for transients, while for the COSMOS field we compared individual images and the summed image to search for new sources in repeated observations of the same field. The wide range of timescales makes VLITE sensitive to both coherent and incoherent transient source classes. No new transients are found, allowing us to set stringent upper limits on transients at milli-jansky levels and at low frequencies where comparatively few such surveys have been carried out to date. An all-sky isotropic surface density of bursting radio transients with similar rates, durations, and intensities as the unusual transient GCRT J1745−3009, discovered in wide-field monitoring toward the Galactic center, is ruled out with high confidence. The resulting non-detections allows us to argue that this is a coherent source, whose properties most resemble the growing class of nulling pulsars. We end with a discussion of the future prospects for the detection of transients by VLITE and other experiments.

SKA weak lensing – III. Added value of multiwavelength synergies for the mitigation of systematics

In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinise synergies between cosmic shear measurements in the radio and optical/near-IR bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments; and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multi-wavelength analysis provides a self-calibration method for experimental systematic effects, only implying <50% increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 0.00001, i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarisation information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher-redshift bins of radio catalogues peak at z~0.8-1, whereas their optical/near-IR counterparts are limited to z<0.5-0.7. This translates into having a cosmological signal 2 to 5 times less contaminated by non-linear perturbations.