Browsing University of Hertfordshire by Author "Shimwell, T. W."

Now showing items 1-20 of 64

    • 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 beautiful mess in Abell 2255 

      Botteon, A.; Brunetti, G.; Weeren, R. J. van; Shimwell, T. W.; Pizzo, R. F.; Cassano, R.; Iacobelli, M.; Gastaldello, F.; Bîrzan, L.; Bonafede, A.; Brüggen, M.; Cuciti, V.; Dallacasa, D.; Gasperin, F. de; Gennaro, G. Di; Drabent, A.; Hardcastle, M. J.; Hoeft, M.; Mandal, S.; Röttgering, H. J. A.; Simionescu, A. (2020-07-07)
      We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby ($z = 0.0806$) merging galaxy cluster hosting one of the first radio halos ever detected in the intra-cluster ...

    • The best of both worlds : Combining LOFAR and Apertif to derive resolved radio spectral index images 

      Morganti, R.; Oosterloo, T. A.; Brienza, M.; Jurlin, N.; Prandoni, I.; Orru', E.; Shabala, S. S.; Adams, E. A. K.; Adebahr, B.; Best, P. N.; Coolen, A. H. W. M.; Damstra, S.; Blok, W. J. G. de; Gasperin, F. de; Denes, H.; Hardcastle, M.; Hess, K. M.; Hut, B.; Kondapally, R.; Kutkin, A. M.; Loose, G. M.; Lucero, D. M.; Maan, Y.; Maccagni, F. M.; Mingo, B.; Moss, V. A.; Mostert, R. I. J.; Norden, M. J.; Oostrum, L. C.; Rottgering, H. J. A.; Ruiter, M.; Shimwell, T. W.; Schulz, R.; Vermaas, N. J.; Vohl, D.; Hulst, J. M. van der; Diepen, G. M. van; Leeuwen, J. van; Ziemke, J. (2021-04-07)
      Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they ...

    • 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 ...

    • Coherent radio emission from a quiescent red dwarf indicative of star-planet interaction 

      Vedantham, H. K.; Callingham, J. R.; Shimwell, T. W.; Tasse, C.; Pope, B. J. S.; Bedell, M.; Snellen, I.; Best, P.; Hardcastle, M. J.; Haverkorn, M.; Mechev, A.; O'Sullivan, S. P.; Röttgering, H. J. A.; White, G. J. (2020-02-17)
      Low-frequency (ν ≲ 150 MHz) stellar radio emission is expected to originate in the outer corona at heights comparable to and larger than the stellar radius. Such emission from the Sun has been used to study coronal structure, ...

    • The contribution of discrete sources to the sky temperature at 144 MHz 

      Hardcastle, M. J.; Shimwell, T. W.; Tasse, C.; Best, P. N.; Drabent, A.; Jarvis, M. J.; Prandoni, I.; Rottgering, H. J. A.; Sabater, J.; Schwarz, D. J. (2021-04-07)
      In recent years, the level of the extragalactic radio background has become a point of considerable interest, with some lines of argument pointing to an entirely new cosmological synchrotron background. The contribution ...

    • Diffuse Radio Emission from Galaxy Clusters in the LOFAR Two-metre Sky Survey Deep Fields 

      Osinga, E.; Weeren, R. J. van; Boxelaar, J.; Brunetti, G.; Botteon, A.; Brüggen, M.; Shimwell, T. W.; Bonafede, A.; Best, P. N.; Bonato, M.; Cassano, R.; Gastaldello, F.; Gennaro, G. di; Hardcastle, M. J.; Mandal, S.; Rossetti, M.; Röttgering, H. J. A.; Sabater, J. (2021-04-07)
      Low-frequency radio observations are revealing an increasing number of diffuse synchrotron sources from galaxy clusters, dominantly in the form of radio halos or radio relics. The existence of this diffuse synchrotron ...

    • Discovery of 24 radio-bright quasars at $4.9 \leq z \leq6.6$ using low-frequency radio observations 

      Gloudemans, A. J.; Duncan, K. J.; Saxena, A.; Harikane, Y.; Hill, G. J.; Zeimann, G. R.; Rottgering, H. J. A.; Yang, D.; Best, P. N.; Banados, E.; Drabent, A.; Hardcastle, M. J.; Hennawi, J. F.; Lansbury, G.; Magliocchetti, M.; Miley, G. K.; Nanni, R.; Shimwell, T. W.; Smith, D. J. B.; Venemans, B.P.; Wagenveld, J. D. (2022-12-31)
      High redshift quasars ($z>5$) that also shine brightly at radio wavelengths are unique signposts of supermassive black hole activity in the early universe. However, bright radio sources at $z\ge5$ are extremely rare and ...

    • 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◦ < ...

    • The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2 

      O'Sullivan, S. P.; Shimwell, T. W.; Hardcastle, M. J.; Tasse, C.; Heald, G.; Carretti, E.; Brüggen, M.; Vacca, V.; Sobey, C.; Eck, C. L. Van; Horellou, C.; Beck, R.; Bilicki, M.; Bourke, S.; Botteon, A.; Croston, J. H.; Drabent, A.; Duncan, K.; Heesen, V.; Ideguchi, S.; Kirwan, M.; Lawlor, L.; Mingo, B.; Nikiel-Wroczyński, B.; Piotrowska, J.; Scaife, A. M. M.; Weeren, R. J. van (2023-01-02)
      A Faraday rotation measure (RM) catalogue, or RM Grid, is a valuable resource for the study of cosmic magnetism. Using the second data release (DR2) from the LOFAR Two-metre Sky Survey (LoTSS), we have produced a catalogue ...

    • Giant radio galaxies in the LOFAR Two-metre Sky Survey-I 

      Dabhade, P.; Rottgering, H. J. A.; Bagchi, J.; Shimwell, T. W.; Hardcastle, M. J.; Sankhyayan, S.; Morganti, R.; Jamrozy, M.; Shulevski, A.; Duncan, K. J. (2020-03-01)
      Giant radio galaxies (GRGs) are a subclass of radio galaxies which have grown to megaparsec scales. GRGs are much rarer than normal sized radio galaxies ( less than 0.7 Mpc) and the reason for their gigantic sizes is still ...

    • 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). ...

    • The life cycle of radio galaxies in the LOFAR Lockman Hole field 

      Jurlin, N.; Morganti, R.; Brienza, M.; Mandal, S.; Maddox, N.; Duncan, K. J.; Shabala, S. S.; Hardcastle, M. J.; Prandoni, I.; Röttgering, H. J. A.; Mahatma, V.; Best, P. N.; Mingo, B.; Sabater, J.; Shimwell, T. W.; Tasse, C. (2020-06-08)
      Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial ...

    • 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 144-MHz follow-up observations of GW170817 

      Broderick, J. W.; Shimwell, T. W.; Gourdji, K.; Rowlinson, A.; Nissanke, S.; Hotokezaka, K.; Jonker, P. G.; Tasse, C.; Hardcastle, M. J.; Oonk, J. B. R.; Fender, R. P.; Wijers, R. A. M. J.; Shulevski, A.; Stewart, A. J.; Veen, S. ter; Moss, V. A.; Wiel, M. H. D. van der; Nichols, D. A.; Piette, A.; Carbone, D.; Corbel, S.; Eislöffel, J.; Grießmeier, J. -M.; Keane, E. F.; Law, C. J.; Muñoz-Darias, T.; Pietka, M.; Serylak, M.; Horst, A. J. van der; Leeuwen, J. van; Wijnands, R.; Zarka, P.; Anderson, J. M.; Bentum, M. J.; Blaauw, R.; Brouw, W. N.; Brüggen, M.; Ciardi, B.; Vos, M. de; Duscha, S.; Fallows, R. A.; Franzen, T. M. O.; Garrett, M. A.; Gunst, A. W.; Hoeft, M.; Hörandel, J. R.; Iacobelli, M.; Jütte, E.; Koopmans, L. V. E.; Krankowski, A.; Maat, P.; Mann, G.; Mulder, H.; Nelles, A.; Paas, H.; Pandey-Pommier, M.; Pekal, R.; Reich, W.; Röttgering, H. J. A.; Schwarz, D. J.; Smirnov, O.; Soida, M.; Toribio, M. C.; Haarlem, M. P. van; Weeren, R. J. van; Vocks, C.; Wucknitz, O.; Zucca, P. (2020-06-01)
      We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO-Virgo. These data, with a ...

    • 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 Deep Fields : Probing a broader population of polarized radio galaxies in ELAIS-N1 

      Ruiz, N. Herrera; O'Sullivan, S. P.; Vacca, V.; Jelić, V.; Nikiel-Wroczyński, B.; Bourke, S.; Sabater, J.; Dettmar, R. -J.; Heald, G.; Horellou, C.; Piras, S.; Sobey, C.; Shimwell, T. W.; Tasse, C.; Hardcastle, M. J.; Kondapally, R.; Chyży, K. T.; Iacobelli, M.; Best, P. N.; Brüggen, M.; Carretti, E.; Prandoni, I. (2021-04-07)
      We present deep polarimetric observations of the European Large Area ISO Survey-North 1 (ELAIS-N1) field using the Low Frequency Array (LOFAR) at 114.9-177.4 MHz. The ELAIS-N1 field is part of the LOFAR Two-metre Sky Survey ...

    • LOFAR discovery of a radio halo in the high-redshift galaxy cluster PSZ2 G099.86+58.45 

      Cassano, R.; Botteon, A.; Gennaro, G. Di; Brunetti, G.; Sereno, M.; Shimwell, T. W.; Weeren, R. J. van; Brüggen, M.; Gastaldello, F.; Izzo, L.; Bîrzan, L.; Bonafede, A.; Cuciti, V.; Gasperin, F. de; Rötttgering, H. J. A.; Hardcastle, M.; Mechev, A. P.; Tasse, C. (2019-08-19)
      In this Letter, we report the discovery of a radio halo in the high-redshift galaxy cluster PSZ2 G099.86+58.45 ($z=0.616$) with the LOw Frequency ARray (LOFAR) at 120-168 MHz. This is one of the most distant radio halos ...