Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Beardsley, Adam P.; Johnston‐Hollitt, M.; Trott, Cathryn M.; Pober, Jonathan C.; Morgan, John S.; Oberoi, D.; Kaplan, David L.; Lynch, C.; Anderson, G.; McCauley, Patrick; Croft, Steve; James, C. W.; Wong, O. I.; Tremblay, Chenoa D.; Norris, R. P.; Cairns, Iver H.; Lonsdale, Colin J.; Hancock, P. J.; Gaensler, B. M.; Bhat, N. D. R.; Li, W.; Hurley‐Walker, N.; Callingham, J. R.; Seymour, N.; Yoshiura, Shintaro; Joseph, R.; Takahashi, Keitaro; Sokołowski, M.; Miller-Jones, J. C. A.; Chauhan, Jaiverdhan; Bojičić, Ivan S.; Filipović, Miroslav; Leahy, D. A.; Su, H.; Wu, Tian; McSweeney, S. J.; Meyers, Bradley W.; Kitaeff, Slava; Vernstrom, Tessa; Gürkan, G.; Heald, G.; Xue, Mengyao; Riseley, C. J.; Duchesne, S. W.; Bowman, Judd D.; Jacobs, Daniel; Crosse, B.; Emrich, D.; Franzen, T. M. O.; Horsley, L.; Kenney, D.; Morales, M. F.; Pallot, D.; Steele, Kim; Tingay, S. J.; Walker, M.; Wayth, R. B.; Williams, A.; Wu, Chao

doi:10.1017/pasa.2019.41

Cited by 51 publications

(36 citation statements)

References 446 publications

(618 reference statements)

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“…After this rescaling 4 per cent of simulated filaments have surface brightnesses in the mJy range with an approximate 3 arcminute resolution. If we take the 1.5 arcmin resolution of the Phase II of the MWA (Beardsley et al 2019), an rms of ∼50 μJy beam −1 would be necessary for 3σ direct detections (an order of magnitude lower than estimates for the next deep MWA surveys). For the high-band antenna of the LOFAR telescope, which has much higher resolution, an rms of ∼10 μJy beam −1 would be necessary for a resolution of 30 arcsec.…”

Section: Cosmological Simulationsmentioning

confidence: 96%

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

Vernstrom

Heald

Vazza

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Diffuse filaments connect galaxy clusters to form the cosmic web. Detecting these filaments could yield information on the magnetic field strength, cosmic ray population and temperature of intercluster gas, yet, the faint and large-scale nature of these bridges makes direct detections very challenging. Using multiple independent all-sky radio and X-ray maps we stack pairs of luminous red galaxies as tracers for cluster pairs. For the first time, we detect an average surface brightness between the clusters from synchrotron (radio) and thermal (X-ray) emission with ≳ 5σ significance, on physical scales larger than observed to date (≥3 Mpc). We obtain a synchrotron spectral index of α ≃ −1.0 and estimates of the average magnetic field strength of 30 ≤ B ≤ 60 nG, derived from both equipartition and Inverse Compton arguments, implying a 5 to 15 per cent degree of field regularity when compared with Faraday rotation measure estimates. While the X-ray detection is inline with predictions, the average radio signal comes out higher than predicted by cosmological simulations and dark matter annihilation and decay models. This discovery demonstrates that there are connective structures between mass concentrations that are significantly magnetised, and the presence of sufficient cosmic rays to produce detectable synchrotron radiation.

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Section: Cosmological Simulationsmentioning

confidence: 96%

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

Vernstrom

Heald

Vazza

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…As both radio galaxies cross the 4-Jy threshold, they are included in the G4Jy Sample (as G4Jy 1704 and G4Jy 1705, respectively). However, we emphasise that their integrated flux densities are estimates (rather than direct measurements), and note that they will be superseded by new measurements using the recently upgraded MWA (Beardsley et al 2019). This will provide higher spatial resolution (at ∼ 1arcmin) than is currently available through GLEAM.…”

Section: Sourcementioning

confidence: 99%

The GLEAM 4-Jy (G4Jy) Sample: I. Definition and the catalogue

White

Franzen

Riseley

et al. 2020

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA) has observed the entire southern sky (Declination, $\delta< 30^{\circ}$ ) at low radio frequencies, over the range 72–231MHz. These observations constitute the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we use the extragalactic catalogue (EGC) (Galactic latitude, $|b| >10^{\circ}$ ) to define the GLEAM 4-Jy (G4Jy) Sample. This is a complete sample of the ‘brightest’ radio sources ( $S_{\textrm{151\,MHz}}>4\,\text{Jy}$ ), the majority of which are active galactic nuclei with powerful radio jets. Crucially, low-frequency observations allow the selection of such sources in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). We then use higher-resolution radio images, and information at other wavelengths, to morphologically classify the brightest components in GLEAM. We also conduct cross-checks against the literature and perform internal matching, in order to improve sample completeness (which is estimated to be $>95.5$ %). This results in a catalogue of 1863 sources, making the G4Jy Sample over 10 times larger than that of the revised Third Cambridge Catalogue of Radio Sources (3CRR; $S_{\textrm{178\,MHz}}>10.9\,\text{Jy}$ ). Of these G4Jy sources, 78 are resolved by the MWA (Phase-I) synthesised beam ( $\sim2$ arcmin at 200MHz), and we label 67% of the sample as ‘single’, 26% as ‘double’, 4% as ‘triple’, and 3% as having ‘complex’ morphology at $\sim1\,\text{GHz}$ (45 arcsec resolution). We characterise the spectral behaviour of these objects in the radio and find that the median spectral index is $\alpha=-0.740 \pm 0.012$ between 151 and 843MHz, and $\alpha=-0.786 \pm 0.006$ between 151MHz and 1400MHz (assuming a power-law description, $S_{\nu} \propto \nu^{\alpha}$ ), compared to $\alpha=-0.829 \pm 0.006$ within the GLEAM band. Alongside this, our value-added catalogue provides mid-infrared source associations (subject to 6” resolution at 3.4 $\mu$ m) for the radio emission, as identified through visual inspection and thorough checks against the literature. As such, the G4Jy Sample can be used as a reliable training set for cross-identification via machine-learning algorithms. We also estimate the angular size of the sources, based on their associated components at $\sim1\,\text{GHz}$ , and perform a flux density comparison for 67 G4Jy sources that overlap with 3CRR. Analysis of multi-wavelength data, and spectral curvature between 72MHz and 20GHz, will be presented in subsequent papers, and details for accessing all G4Jy overlays are provided at https://github.com/svw26/G4Jy.

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“…However, the low frequency and moderate resolution (≈3 ) of POGS results in strong beam depolarisation due to fluctuations, including in the Galactic foreground, on scales below the PSF. Polarimetry with the Phase II MWA [192], which provides a factor ∼2 improvement in resolution [216], will provide a big step forward in our understanding of the low-frequency polarised sky. This will not only come through reduced beam depolarisation and improved sensitivity, leading to an increased number of source detections in this comparatively unexplored sky area, but also through direct comparison of our Phase I and Phase II measurements, which will allow us to probe the scale size of Galactic magnetic field fluctuations.…”

Section: Chimementioning

confidence: 99%

Magnetism Science with the Square Kilometre Array

Heald¹,

Mao

Vacca³

et al. 2020

Galaxies

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The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.

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Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Cited by 51 publications

References 446 publications

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

The GLEAM 4-Jy (G4Jy) Sample: I. Definition and the catalogue

Magnetism Science with the Square Kilometre Array

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