Browsing University of Hertfordshire by Author "Williams, W. L."

Now showing items 1-20 of 51

    • Accretion mode versus radio morphology in the LOFAR Deep Fields 

      Mingo, B.; Croston, J. H.; Best, P. N.; Duncan, K. J.; Hardcastle, M. J.; Kondapally, R.; Prandoni, I.; Sabater, J.; Shimwell, T. W.; Williams, W. L.; Baldi, R. D.; Bonato, M.; Bondi, M.; Dabhade, P.; Gürkan, G.; Ineson, J.; Magliocchetti, M.; Miley, G.; Pierce, J. C. S.; Röttgering, H. J. A. (2022-02-16)
      Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to ...

    • Alignment in the orientation of LOFAR radio sources 

      Osinga, E.; Miley, G. K.; Weeren, R. J. van; Shimwell, T. W.; Duncan, K. J.; Hardcastle, M. J.; Mechev, A. P.; Röttgering, H. J. A.; Tasse, C.; Williams, W. L. (2020-08-25)
      Various studies have laid claim to finding an alignment of the polarization vectors or radio jets of active galactic nuclei (AGN) over large distances, but these results have proven controversial and so far, there is no ...

    • The Application of Ridgelines in Extended Radio Source Cross-Identification 

      Barkus, B.; Croston, J. H.; Piotrowska, J.; Mingo, B.; Best, P. N.; Hardcastle, M. J.; Mostert, R. I. J.; Röttgering, H. J. A.; Sabater, J.; Webster, B.; Williams, W. L. (2021-10-22)
      Extended radio sources are an important minority population in modern deep radio surveys, because they enable detailed investigation of the physics governing radio-emitting regions such as active galaxies and their ...

    • Blazars in the LOFAR Two-Metre Sky Survey First Data Release 

      Mooney, S.; Quinn, J.; Callingham, J. R.; Morganti, R.; Duncan, K.; Morabito, Leah K.; Best, P. N.; Gürkan, G.; Hardcastle, M. J.; Prandoni, I.; Röttgering, H. J. A.; Sabater, J.; Shimwell, T. W.; Shulevski, A.; Tasse, C.; Williams, W. L. (2018-11-19)
      Historically, the blazar population has been poorly understood at low frequencies because survey sensitivity and angular resolution limitations have made it difficult to identify megahertz counterparts. We used the LOFAR ...

    • The bright end of the infrared luminosity functions and the abundance of hyperluminous infrared galaxies 

      Wang, L.; Gao, F.; Best, P. N.; Duncan, K.; Hardcastle, M. J.; Kondapally, R.; Malek, K.; McCheyne, I.; Sabater, J.; Shimwell, T.; Tasse, C.; Bonato, M.; Bondi, M.; Cochrane, R. K.; Farrah, D.; Gurkan, G.; Haskell, P.; Pearson, W. J.; Prandoni, I.; Rottgering, H. J. A.; Smith, D. J. B.; Vaccari, M.; Williams, W. L. (2021-04-07)
      We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities > 10^13 L_solar, thanks to the ...

    • Cosmic evolution of low-excitation radio galaxies in the LOFAR Two-meter Sky Survey Deep Fields 

      Kondapally, R.; Best, P. N.; Cochrane, R. K.; Sabater, J.; Duncan, K. J.; Hardcastle, M. J.; Haskell, P.; Mingo, B.; Röttgering, H. J. A.; Smith, D. J. B.; Williams, W. L.; Bonato, M.; Rivera, G. Calistro; Gao, F.; Hale, C. L.; Małek, K.; Miley, G. K.; Prandoni, I.; Wang, L. (2022-04-26)
      Feedback from low-excitation radio galaxies (LERGs) plays a key role in the lifecycle of massive galaxies in the local Universe; their evolution, and the impact of these active galactic nuclei on early galaxy evolution, ...

    • The environments of radio-loud AGN from the LOFAR Two-Metre Sky Survey (LoTSS) 

      Croston, J. H.; Hardcastle, M. J.; Mingo, B.; Best, P. N.; Sabater, J.; Shimwell, T. W.; Williams, W. L.; Duncan, K. J.; Röttgering, H. J. A.; Brienza, M.; Gürkan, G.; Ineson, J.; Morabito, L. M.; Miley, G. K.; O'Sullivan, S. P.; Prandoni, I. (2018-10-10)
      An understanding of the relationship between radio-loud active galaxies and their large-scale environments is essential for realistic modelling of radio-galaxy evolution and environmental impact, for understanding AGN ...

    • The eROSITA Final Equatorial-Depth Survey (eFEDS). LOFAR view of brightest cluster galaxies and AGN feedback 

      Pasini, T.; Brüggen, M.; Hoang, D. H.; Ghirardini, V.; Bulbul, E.; Klein, M.; Liu, A.; Shimwell, T. W.; Hardcastle, M. J.; Williams, W. L.; Botteon, A.; Gastaldello, F.; Weeren, R. J. van; Merloni, A.; Gasperin, F. de; Bahar, Y. E.; Pacaud, F.; Ramos-Ceja, M. (2021-07-06)
      Context. During the performance verification phase of the Spectrum-Roentgen-Gamma (SRG) eROSITA telescope, the eROSITA Final Equatorial-Depth Survey (eFEDS) was carried out. It covers a 140 deg2 field located at 126◦ < ...

    • Extragalactic Peaked-Spectrum Radio Sources at Low-Frequencies are Young Radio Galaxies 

      Slob, M. M.; Callingham, J. R.; Röttgering, H. J. A.; Williams, W. L.; Duncan, K. J.; Gasperin, F. de; Hardcastle, M. J.; Miley, G. K. (2022-12-20)
      We present a sample of 373 peaked-spectrum (PS) sources with spectral peaks around 150 MHz, selected using a subset of the two LOw Frequency ARray (LOFAR) all-sky surveys, the LOFAR Two Meter Sky Survey and the LOFAR LBA ...

    • The intergalactic magnetic field probed by a giant radio galaxy 

      O'Sullivan, S. P.; Machalski, J.; Eck, C. L. Van; Heald, G.; Brueggen, M.; Fynbo, J. P. U.; Heintz, K. E.; Lara-Lopez, M. A.; Vacca, V.; Hardcastle, M. J.; Shimwell, T. W.; Tasse, C.; Vazza, F.; Andernach, H.; Birkinshaw, M.; Haverkorn, M.; Horellou, C.; Williams, W. L.; Harwood, J. J.; Brunetti, G.; Anderson, J. M.; Mao, S. A.; Nikiel-Wroczynski, B.; Takahashi, K.; Carretti, E.; Vernstrom, T.; Weeren, R. J. van; Orru, E.; Morabito, L. K.; Callingham, J. R. (2018-10-09)
      Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). ...

    • Investigating the Unification of LOFAR-detected powerful AGN in the Boötes Field 

      Morabito, Leah K.; Williams, W. L.; Duncan, Kenneth J.; Röttgering, H.~J.~A.; Miley, George; Saxena, Aayush; Barthel, Peter; Best, Philip N.; Bruggen, M.; Brunetti, G.; Chyży, K. T.; Engels, D.; Hardcastle, M. J.; Harwood, J. J.; Jarvis, Matt J.; Mahony, E. K.; Prandoni, I.; Shimwell, Timothy W.; Shulevski, Alexander; Tasse, C. (2017-08-01)
      Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. ...

    • Link between radio-loud AGNs and host-galaxy shape 

      Zheng, X. C.; Röttgering, H. J. A.; Best, P. N.; Wel, A. van der; Hardcastle, M. J.; Williams, W. L.; Bonato, M.; Prandoni, I.; Smith, D. J. B.; Leslie, S. K. (2020-10-15)
      The morphology of quiescent galaxies has been found to be correlated with the activity of their central super massive black hole. In this work, we use data from the first data release of the LOFAR Two$-$Metre Sky Survey ...

    • The Lockman Hole project : LOFAR observations and spectral index properties of low-frequency radio sources 

      Mahony, E. K.; Morganti, R.; Prandoni, I.; Bemmel, I. M. van; Shimwell, T. W.; Brienza, M.; Best, P. N.; Brüggen, M.; Rivera, G. Calistro; Gasperin, F. de; Hardcastle, M. J.; Harwood, J. J.; Heald, G.; Jarvis, M. J.; Mandal, S.; Miley, G. K.; Retana-Montenegro, E.; Röttgering, H. J. A.; Sabater, J.; Tasse, C.; Velzen, S. van; Weeren, R. J. van; Williams, W. L.; White, G. J. (2016-12-11)
      The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source ...

    • LOFAR 150-MHz observations of the Boötes field: Catalogue and Source Counts 

      Williams, W. L.; Van Weeren, R. J.; Röttgering, H. J. A.; Best, P.; Dijkema, T. J.; Gasperin, F. de; Hardcastle, M. J.; Heald, G.; Prandoni, I.; Sabater, J.; Shimwell, T. W.; Tasse, C.; Bemmel, I. M. van; Brüggen, M.; Brunetti, G.; Conway, J. E.; Enßlin, T.; Engels, D.; Falcke, H.; Ferrari, C.; Haverkorn, M.; Jackson, N.; Jarvis, M. J.; Kapinska, A. D.; Mahony, E. K.; Miley, G. K.; Morabito, L. K.; Morganti, R.; Orrú, E.; Retana-Montenegro, E.; Sridhar, S. S.; Toribio, M. C.; White, G. J.; Wise, M. W.; Zwart, J. T. L. (2016-08-11)
      We present the first wide area (19 deg$^2$), deep ($\approx120-150$ {\mu}Jy beam$^{-1}$), high resolution ($5.6 \times 7.4$ arcsec) LOFAR High Band Antenna image of the Bo\"otes field made at 130-169 MHz. This image is at ...

    • LOFAR early-time search for coherent radio emission from GRB 180706A 

      Rowlinson, A.; Gourdji, K.; Meulen, K. van der; Meyers, Z. S.; Shimwell, T. W.; Veen, S. ter; Wijers, R. A. M. J.; Kuiack, M. J.; Shulevski, A.; Broderick, J. W.; Horst, A. J. van der; Tasse, C.; Hardcastle, M. J.; Mechev, A. P.; Williams, W. L. (2019-10-21)
      The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio ...

    • LOFAR facet calibration 

      Van Weeren, R. J.; Williams, W. L.; Hardcastle, M.J.; Shimwell, T. W.; Rafferty, D. A.; Sabater, J.; Heald, G.; Sridhar, S. S.; Dijkema, T. J.; Brunetti, G.; Brüggen, M.; Andrade-Santos, F.; Ogrean, G. A.; Röttgering, H. J. A.; Dawson, W. A.; Forman, W.R.; Gasperin, F. de; Jones, C.; Miley, G.K.; Rudnick, L.; Sarazin, C.L.; Bonafede, A.; Best, P. N.; Bîrzan, L.; Cassano, R.; Chyży, K. T.; Croston, J. H.; Ensslin, T.; Ferrari, C.; Hoeft, M.; Horellou, C.; Jarvis, M.J.; Kraft, R.P.; Mevius, M.; Intema, H. T.; Murray, S. S.; Orrú, E.; Pizzo, R.; Simionescu, A.; Stroe, A.; Tol, S. van der; White, G.J. (2016-03-07)
      LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At the same time LOFAR also provides ...

    • The LOFAR LBA Sky Survey I. survey description and preliminary data release 

      Gasperin, F. de; Williams, W. L.; Best, P.; Bruggen, M.; Brunetti, G.; Cuciti, V.; Dijkema, T. J.; Hardcastle, M. J.; Norden, M. J.; Offringa, A.; Shimwell, T.; Weeren, R. van; Bomans, D.; Bonafede, A.; Botteon, A.; Callingham, J. R.; Cassano, R.; Chyzy, K. T.; Emig, K. L.; Edler, H.; Haverkorn, M.; Heald, G.; Heesen, V.; Iacobelli, M.; Intema, H. T.; Kadler, M.; Malek, K.; Mevius, M.; Miley, G.; Mingo, B.; Morabito, L. K.; Sabater, J.; Morganti, R.; Orru, E.; Pizzo, R.; Prandoni, I.; Shulevski, A.; Tasse, C.; Vaccari, M.; Zarka, P.; Rottgering, H. (2021-02-17)
      Context. The LOw Frequency ARray (LOFAR)istheonlyradiotelescopethatispresentlycapableofhigh-sensitivity,high-resolution (i.e. < 1mJybeam−1 and < 1500) observations at ultra-low frequencies(< 100MHz). To utilise these ...

    • The LOFAR LBA Sky Survey II. First data release 

      Gasperin, F. de; Edler, H. W.; Williams, W. L.; Callingham, J. R.; Asabere, B.; Bruggen, M.; Brunetti, G.; Dijkema, T. J.; Hardcastle, M. J.; Iacobelli, M.; Offringa, A.; Norden, M. J.; Rottgering, H. J. A.; Shimwell, T.; Weeren, R. J. van; Tasse, C.; Bomans, D. J.; Bonafede, A.; Botteon, A.; Cassano, R.; Chyzy, K. T.; Cuciti, V.; Emig, K. L.; Kadler, M.; Miley, G.; Mingo, B.; Oei, M. S. S. L.; Prandoni, I.; Schwarz, D. J.; Zarka, P. (2023-05-26)
      Context. The Low Frequency Array (LOFAR) is the only existing radio interferometer able to observe at ultra-low frequencies (<100 MHz) with high resolution (<15′′) and high sensitivity (<1 mJy beam−1 ). To exploit these ...

    • The LOFAR LBA Sky Survey: Deep Fields I. The Boötes Field 

      Williams, W. L.; Gasperin, F. de; Hardcastle, M. J. H.; Weeren, R. van; Tasse, C.; Shimwell, T. W.; Best, P. N.; Bonato, M.; Bondi, M.; Brüggen, M.; Röttgering, H. J. A.; Smith, D. J. B. (2021-11-10)
      We present the first sub-mJy ($\approx0.7$ mJy beam$^{-1}$) survey to be completed below 100 MHz, which is over an order of magnitude deeper than previously achieved for widefield imaging of any field at these low frequencies. ...

    • Lofar low-band antenna observations of the 3C 295 and boötes fields : Source counts and ultra-steep spectrum sources 

      Van Weeren, R. J.; Williams, W. L.; Tasse, C.; Röttgering, H. J.A.; Rafferty, D. A.; Van Der Tol, S.; Heald, G.; White, G. J.; Shulevski, A.; Best, P.; Intema, H. T.; Bhatnagar, S.; Reich, W.; Steinmetz, M.; Van Velzen, S.; Enßlin, T. A.; Prandoni, I.; De Gasperin, F.; Jamrozy, M.; Brunetti, G.; Jarvis, M. J.; McKean, J. P.; Wise, M. W.; Ferrari, C.; Harwood, J.; Oonk, J. B.R.; Hoeft, M.; Kunert-Bajraszewska, M.; Horellou, C.; Wucknitz, O.; Bonafede, A.; Mohan, N. R.; Scaife, A. M.M.; Klöckner, H. R.; Van Bemmel, I. M.; Merloni, A.; Chyzy, K. T.; Engels, D.; Falcke, H.; Pandey-Pommier, M.; Alexov, A.; Anderson, J.; Avruch, I. M.; Beck, R.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Breitling, F.; Broderick, J.; De Vos, M. (2014-10-01)
      We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam-1, making them the deepest images ever obtained ...