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

Now showing items 41-51 of 51

    • Low frequency radio properties of the $z>5$ quasar population 

      Gloudemans, A. J.; Duncan, K. J.; Röttgering, H. J. A.; Shimwell, T. W.; Venemans, B. P.; Best, P. N.; Brüggen, M.; Rivera, G. Calistro; Drabent, A.; Hardcastle, M. J.; Miley, G. K.; Schwarz, D. J.; Saxena, A.; Smith, D. J. B.; Williams, W. L. (2021-12-31)
      Optically luminous quasars at z > 5 are important probes of super-massive black hole (SMBH) formation. With new and future radio facilities, the discovery of the brightest low-frequency radio sources in this epoch would ...

    • NGC 326: X-shaped no more 

      Hardcastle, M. J.; Croston, J. H.; Shimwell, T. W.; Tasse, C.; Gurkan Uygun, Gulay; Morganti, R.; Murgia, M.; Rottgering, H. J. A.; Weeren, R. J. van; Williams, W. L. (2019-09-01)
      We present new 144-MHz LOFAR observations of the prototypical `X-shaped' radio galaxy NGC 326, which show that the formerly known wings of the radio lobes extend smoothly into a large-scale, complex radio structure. We ...

    • A plethora of diffuse steep spectrum radio sources in Abell 2034 revealed by LOFAR 

      Shimwell, T. W.; Luckin, J.; Brüggen, M.; Brunetti, G.; Intema, H. T.; Owers, M. S.; Röttgering, H. J. A.; Stroe, A.; Weeren, R. J. van; Williams, W. L.; Cassano, R.; Gasperin, F. de; Heald, G. H.; Hoang, D. N.; Hardcastle, M.J.; Sridhar, S. S.; Sabater, J.; Best, P. N.; Bonafede, A.; Chyży, K. T.; Ensslin, T. A.; Ferrari, C.; Haverkorn, M.; Hoeft, M.; Horellou, C.; McKean, J. P.; Morabito, L. K.; Orrù, E.; Pizzo, R.; Retana-Montenegro, E.; White, G.J. (2016-06-11)
      With Low-Frequency Array (LOFAR) observations, we have discovered a diverse assembly of steep spectrum emission that is apparently associated with the intra cluster medium (ICM) of the merging galaxy cluster Abell 2034. ...

    • The population of M dwarfs observed at low radio frequencies 

      Callingham, J. R.; Vedantham, H. K.; Shimwell, T. W.; Pope, B. J. S.; Davis, I. E.; Best, P. N.; Hardcastle, M. J.; Rottgering, H. J. A.; Sabater, J.; Tasse, C.; Weeren, R. J. van; Williams, W. L.; Zarka, P.; Gasperin, F. de; Drabent, A. (2021-10-11)
      Coherent low-frequency (≲200 MHz) radio emission from stars encodes the conditions of the outer corona, mass-ejection events and space weather 1–5. Previous low-frequency searches for radio-emitting stellar systems have ...

    • Radio-AGN Feedback : When the Little Ones were Monsters 

      Williams, W. L.; Röttgering, H. J. A. (2015-06-21)
      We present a study of the evolution of the fraction of radio-loud active galactic nuclei (AGN) as a function of their host stellar mass. We make use of two samples of radio galaxies: one in the local universe, $0.01 10^{24}$ ...

    • Radio-loud AGN in the first LoTSS data release: The lifetimes and environmental impact of jet-driven sources 

      Hardcastle, M. J.; Williams, W. L.; Best, P. N.; Croston, J. H.; Duncan, K. J.; Rottgering, H. J. A.; Sabater, J.; Shimwell, T. W.; Tasse, C.; Callingham, J. R.; Cochrane, R. K.; Gasperin, F. de; Gurkan, G.; Jarvis, M. J.; Mahatma, V.; Miley, G. K.; Mingo, B.; Mooney, S.; Morabito, L. K.; O'Sullivan, S. P.; Prandoni, I.; Shulevski, A.; Smith, D. J. B. (2018-11-19)
      We constructed a sample of 23,344 radio-loud active galactic nuclei (RLAGN) from the catalogue derived from the LOFAR Two-Metre Sky Survey (LoTSS) survey of the HETDEX Spring field. Although separating AGN from star-forming ...

    • Remnant radio-loud AGN in the Herschel-ATLAS field 

      Mahatma, V. H.; Hardcastle, M. J.; Williams, W. L.; Brienza, M.; Bruggen, M.; Croston, J. H.; Gurkan, G.; Harwood, J. J.; Kunert-Bajraszewska, M.; Morganti, R.; Rottgering, H. J. A.; Shimwell, T. W.; Tasse, C. (2018-04-21)
      Only a small fraction of observed active galactic nuclei (AGN) display large-scale radio emission associated with jets, yet these radio-loud AGN have become increasingly important in models of galaxy evolution. In determining ...

    • Revisiting the Fanaroff-Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS) 

      Mingo, B.; Croston, J. H.; Hardcastle, M. J.; Best, P. N.; Duncan, K. J.; Morganti, R.; Rottgering, H. J. A.; Sabater, J.; Shimwell, T. W.; Williams, W. L.; Brienza, M.; Gurkan, G.; Mahatma, V. H.; Morabito, L. K.; Prandoni, I.; Bondi, M.; Ineson, J.; Mooney, S. (2019-09-01)
      The relative positions of the high and low surface brightness regions of radio-loud active galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their luminosity. We revisit this canonical ...

    • T-RaMiSu : The Two-meter Radio Mini Survey I. The Bootes Field 

      Williams, W. L.; Intema, H. T.; Röttgering, H. J. A. (2013-01-01)
      We present wide area, deep, high-resolution 153 MHz GMRT observations of the NOAO Bootes field, adding to the extensive, multi-wavelength data of this region. The observations, data reduction, and catalogue construction ...

    • The origin of radio emission in broad absorption line quasars: Results from the LOFAR Two-metre Sky Survey 

      Morabito, L. K.; Matthews, J. H.; Best, P. N.; Gürkan, G.; Jarvis, M. J.; Prandoni, I.; Duncan, K. J.; Hardcastle, M. J.; Kunert-Bajraszewska, M.; Mechev, A. P.; Mooney, S.; Sabater, J.; Röttgering, H. J. A.; Shimwell, T. W.; Smith, D. J. B.; Tasse, C.; Williams, W. L. (2018-08-16)
      We present a study of the low-frequency radio properties of broad absorption line quasars (BALQSOs) from the LOFAR Two-metre Sky-Survey Data Release 1 (LDR1). The value-added LDR1 catalogue contains Pan-STARRS counterparts, ...

    • The WEAVE-LOFAR Survey 

      Smith, D. J. B.; Best, P. N.; Duncan, K. J.; Hatch, N. A.; Jarvis, M. J.; Röttgering, H. J. A.; Simpson, C. J.; Stott, J. P.; Cochrane, R. K.; Coppin, K. E.; Dannerbauer, H.; Davis, T. A.; Geach, J. E.; Hale, C. L.; Hardcastle, M. J.; Hatfield, P. W.; Houghton, R. C. W.; Maddox, N.; McGee, S. L.; Morabito, L.; Nisbet, D.; Pandey-Pommier, M.; Prandoni, I.; Saxena, A.; Shimwell, T. W.; Tarr, M.; Bemmel, I. van; Verma, A.; White, G. J.; Williams, W. L. (Societe Francaise d'Astronomie et d'Astrophysique, 2016-10-14)
      In these proceedings we highlight the primary scientific goals and design of the WEAVE-LOFAR survey, which will use the new WEAVE spectrograph on the 4.2m William Herschel Telescope to provide the primary source of ...