The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

Heald, G.; Pizzo, R.; Orrù, E.; Breton, R. P.; Carbone, D.; Ferrari, C.; Hardcastle, M. J.; Jurusik, W.; Macario, G.; Mulcahy, D. D.; Rafferty, D. A.; Asgekar, A.; Brentjens, M. A.; Fallows, R. A.; Frieswijk, W.; Toribio, M. C.; Adebahr, B.; Arts, M.; Bell, Michael; Bonafede, A.; Bray, J. D.; Broderick, J. W.; Cantwell, T.; Carroll, P.; Cendes, Yvette; Clarke, A. O.; Croston, J. H.; Daiboo, S.; Gasperin, F. de; Gregson, J.; Harwood, J. J.; Hassall, T. E.; Heesen, V.; Horneffer, A.; Horst, A. J. van der; Iacobelli, M.; Jelić, Vibor; Jones, D. I.; Kant, D.; Kokotanekov, G.; Martin, P.; McKean, J. P.; Morabito, L. K.; Nikiel-Wroczyński, B.; Offringa, A. R.; Pandey, V. N.; Pandey-Pommier, M.; Pietka, M.; Pratley, Luke; Riseley, C. J.; Rowlinson, A.; Sabater, J.; Scaife, A.; Scheers, L.H.A.; Sendlinger, K.; Shulevski, A.; Sipior, M.; Sobey, C.; Stewart, A.; Stroe, Andra; Swinbank, J.; Tasse, C.; Trüstedt, J.; Varenius, Eskil; Velzen, S. van; Vilchez, N.; Weeren, R. J. van; Wijnholds, Stefan J.; Williams, W. L.; Bruyn, A. G. de; Nijboer, R.; Wise, Michael; Alexov, A.; Anderson, J. M.; Avruch, I. M.; Beck, Rainer; Bell, M. E.; Bemmel, Ilse van; Bentum, Marinus Jan; Bernardi, G.; Best, P. N.; Breitling, F.; Brouw, W. N.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Conway, J.; Geus, E. de; Jong, A. de; Vos, M. de; Deller, Adam T.; Dettmar, R.‐J.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fender, R. P.; Garrett, M. A.; Grießmeier, J.-M.; Gunst, A. W.; Hamaker, J. P.; Hessels, J. W. T.; Hoeft, M.; Hörandel, J. R.; Holties, H. A.; Intema, H. T.; Jackson, N.; Jütte, E.; Karastergiou, A.; Klijn, Wouter; Kondratiev, V. I.; Koopmans, L. V. E.; Kuniyoshi, M.; Küper, G.; Law, Casey J.; Leeuwen, J. van; Loose, M.; Maat, P.; Markoff, Sera; McFadden, R.; McKay-Bukowski, D.; Mevius, M.; Miller-Jones, J. C. A.; Morganti, Raffaella; Munk, H.; Nelles, A.; Noordam, J. E.; Norden, M. J.; Paas, H.; Polatidis, A. G.; Reich, W.; Renting, A.; Röttgering, H. J. A.; Schoenmakers, A. P.; Schwarz, Dominik J.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Steinmetz, Matthias; Tagger, M.; Tang, Y.; Veen, S. ter; Thoudam, Satyendra; Vermeulen, R. C.; Vocks, C.; Vogt, C.; Wijers, R. A. M. J.; Wucknitz, O.; Yatawatta, S.; Zarka, Philippe

doi:10.1051/0004-6361/201425210

Cited by 107 publications

(72 citation statements)

References 40 publications

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“…A recent workshop on the Radio Synchrotron Background (Singal et al 2018) highlighted the need for a new all-sky diffuse radio background survey to refine our present maps. Source catalogs are also improving with recent contributions from the LOFAR Two Metre Sky Survey (Heald et al 2015) and the LOFAR Multifrequency Snapshot Sky Survey (Shimwell et al 2017) in the northern latitudes, the GaLactic and Extragalactic All-sky MWA (Murchison Widefield Array) (GLEAM) (Wayth et al 2015) in the lower latitudes, and the Giant Metrewave Radio Telescope (GMRT) ).…”

Section: Introductionmentioning

confidence: 78%

Spectral index of the diffuse radio background between 50 and 100 MHz

Mozdzen

Mahesh

Monsalve

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We report the spectral index of diffuse radio emission between 50 and 100 MHz from data collected with two implementations of the Experiment to Detect the Global EoR Signature (EDGES) low-band system. EDGES employs a wide beam zenith-pointing dipole antenna centred on a declination of −26.7 • . We measure the sky brightness temperature as a function of frequency averaged over the EDGES beam from 244 nights of data acquired between 14 September 2016 to 27 August 2017. We derive the spectral index, β, as a function of local sidereal time (LST) using night-time data and a two-parameter fitting equation. We find −2.59 < β < −2.54 ±0.011 between 0 and 12 h LST, ignoring ionospheric effects. When the Galactic Centre is in the sky, the spectral index flattens, reaching β = −2.46 ±0.011 at 18.2 h. The measurements are stable throughout the observations with night-to-night reproducibility of σ β < 0.004 except for the LST range of 7 to 12 h. We compare our measurements with predictions from various global sky models and find that the closest match is with the spectral index derived from the Guzmán and Haslam sky maps, similar to the results found with the EDGES high-band instrument for 90-190 MHz. Three-parameter fitting was also evaluated with the result that the spectral index becomes more negative by ∼0.02 and has a maximum total uncertainty of 0.016. We also find that the third parameter, the spectral index curvature, γ, is constrained to −0.11 < γ < −0.04. Correcting for expected levels of night-time ionospheric absorption causes β to become more negative by 0.008 to 0.016 depending on LST.

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Section: Introductionmentioning

confidence: 78%

Spectral index of the diffuse radio background between 50 and 100 MHz

Mozdzen

Mahesh

Monsalve

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…Differences in noise levels may result from fluctuations of the Milky Way foreground emission, distributions of strong sources in mosaics, imperfect calibration and ionospheric weather conditions during observations. The catalogue of automatically detected sources (the MSSS source catalogue; Heald et al 2015) provides us with flux densities from the individual bands. The MSSS images, and thus the catalogued flux densities, were corrected as part of the MSSS analysis to mitigate the well-known LOFAR flux calibration transfer issues using the "bootstrap" method described by Hardcastle et al (2016); the residual flux calibration error should not exceed 10%.…”

Section: Msss Surveymentioning

confidence: 99%

“…A new observational facility, the Low Frequency Array (LO-FAR; van Haarlem et al 2013), opens up the possibility for systematic studies of nearby galaxies at low frequencies and allows us to reinvestigate the problems related to their lowfrequency spectra. The Multifrequency Snapshot Sky Survey (MSSS; Heald et al 2015) covers the entire northern sky, enabling the detection of many catalogued nearby galaxies, which span a large range of star formation rates (SFRs), sizes, and morphological types.…”

Section: Introductionmentioning

confidence: 99%

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Chyży

Jurusik

Piotrowska

et al. 2018

A&A

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Aims. The shape of low-frequency radio continuum spectra of normal galaxies is not well understood, the key question being the role of physical processes such as thermal absorption in shaping them. In this work we take advantage of the LOFAR Multifrequency Snapshot Sky Survey (MSSS) to investigate such spectra for a large sample of nearby star-forming galaxies. Methods. Using the measured 150 MHz flux densities from the LOFAR MSSS survey and literature flux densities at various frequencies we have obtained integrated radio spectra for 106 galaxies characterised by different morphology and star formation rate. The spectra are explained through the use of a three-dimensional model of galaxy radio emission, and radiation transfer dependent on the galaxy viewing angle and absorption processes. Results. Our galaxies' spectra are generally flatter at lower compared to higher frequencies: the median spectral index α low measured between ≈50 MHz and 1.5 GHz is −0.57 ± 0.01 while the high-frequency one α high , calculated between 1.3 GHz and 5 GHz, is −0.77 ± 0.03. As there is no tendency for the highly inclined galaxies to have more flattened low-frequency spectra, we argue that the observed flattening is not due to thermal absorption, contradicting the suggestion of Israel & Mahoney (1990). According to our modelled radio maps for M 51-like galaxies, the free-free absorption effects can be seen only below 30 MHz and in the global spectra just below 20 MHz, while in the spectra of starburst galaxies, like M 82, the flattening due to absorption is instead visible up to higher frequencies of about 150 MHz. Starbursts are however scarce in the local Universe, in accordance with the weak spectral curvature seen in the galaxies of our sample. Locally, within galactic disks, the absorption effects are distinctly visible in M 51-like galaxies as spectral flattening around 100-200 MHz in the face-on objects, and as turnovers in the edge-on ones, while in M 82-like galaxies there are strong turnovers at frequencies above 700 MHz, regardless of viewing angle. Conclusions. Our modelling of galaxy spectra suggests that the weak spectral flattening observed in the nearby galaxies studied here results principally from synchrotron spectral curvature due to cosmic ray energy losses and propagation effects. We predict much stronger effects of thermal absorption in more distant galaxies with high star formation rates. Some influence exerted by the Milky Way's foreground on the spectra of all external galaxies is also expected at very low frequencies.

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“…Radio sky surveys below 300 MHz such as the VLA Lowfrequency Sky Survey (VLSS; Cohen et al 2007;Lane et al 2012;Lane et al 2014), the GaLactic and Extragalactic Allsky Murchison Wide-field Array Survey (GLEAM; Wayth et al 2015, Hurley-Walker et al 2017, and the LOFAR Multi-frequency Snapshot Sky Survey (MSSS; Heald et al 2015) have a great potential for discovery in this area, but the low spatial resolution of these surveys makes it difficult to distinguish between diffuse radio emission and emission from individual, active radio galaxies. The TIFR GMRT Sky Survey (TGSS ADR; Intema et al 2017) is a highresolution sky survey at 150 MHz.…”

Section: Introductionmentioning

confidence: 99%

Revived fossil plasma sources in galaxy clusters

Mandal

Intema

Weeren

et al. 2020

A&A

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It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intra-cluster medium by radio galaxies. These synchrotron-emitting electrons are very difficult to study, as their radiative life time is only tens of Myrs at GHz frequencies, and are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below a GHz. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-GHz frequencies, creating so-called radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper, we demonstrate the discovery potential of low frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TGSS and 1.4 GHz NVSS sky surveys to identify candidate radio phoenices. A subset of three candidates were studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray (Chandra or XMM-Newton) and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and helps to understand the physical origin of these sources.

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The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

Cited by 107 publications

References 40 publications

Spectral index of the diffuse radio background between 50 and 100 MHz

Spectral index of the diffuse radio background between 50 and 100 MHz

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Revived fossil plasma sources in galaxy clusters

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