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Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620

E Orrù 1 S van Velzen 1 R. F. Pizzo 1 S Yatawatta 1 R Paladino 2 M Iacobelli 3 M Murgia H Falcke 4 R Morganti 5 A. G. de Bruyn 5 C Ferrari 6 J Anderson 7 A Bonafede 8 D Mulcahy 9 A Asgekar I. M. Avruch 10 R Beck M.E. Bell 9 I van Bemmel 1 M. J. Bentum G Bernardi P Best 1 F Breitling M Brüggen 8 J.W. Broderick 9 B Ciardi 11 A Corstanje 4 J. E. Conway E de Geus H. R. Butcher B. Ciardi 11 A Deller 1 S Duscha J Eislöffel 12 D Engels 13 W Frieswijk 1 Jean-Mathias Grießmeier 14, 15 G Heald 1 M Hoeft 12 H Intema 3 E Juette 16 J Kohler 17 M Kuniyoshi 18 G Kuper 1 M Loose P Maat G Mann 19 S Markoff 20 R Mcfadden D Mckay-Bukowski G Miley 3 J Moldon G Molenaar 20 H Munk A Nelles 4 H Paas M Pandey-Pommier 21 G Pietka 22 W Reich 18 H Röttgering 3 A Rowlinson 23 A Scaife 24 A Schoenmakers 1 D. Schwarz 25 M Serylak 14, 15 A Shulevski 5 O Smirnov M Steinmetz 26 A Stewart 27 J Swinbank 20 Michel Tagger 14 C. Tasse 28 S Thoudam 4 M.C Toribio 1 R Vermeulen 1 C Vocks 19 R.J. van Weeren R.A.M.J Wijers 29 M.W. Wise 29 O Wucknitz 30
Abstract : Context. The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in AGN, as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources, on the other hand, provide statistical information about the evolution of the radio-loud AGN population out to high redshifts. Aims. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view. Methods. We present a high resolution image of the DDRG B1834+620 obtained at 144 MHz using LOFAR commissioning data. Our image covers about 100 square degrees and contains over 1000 sources. Results. The four components of the DDRG B1834+620 have been resolved for the first time at 144 MHz. Inner lobes were found to point towards the direction of the outer lobes, unlike standard FR II sources. Polarized emission was detected at +60 rad m −2 in the northern outer lobe. The high spatial resolution allows the identification of a large number of small double-lobed radio sources; roughly 10% of all sources in the field are doubles with a separation smaller than 1. Conclusions. The spectral fit of the four components is consistent with a scenario in which the outer lobes are still active or the jets recently switched off, while emission of the inner lobes is the result of a mix-up of new and old jet activity. From the presence of the newly extended features in the inner lobes of the DDRG, we can infer that the mechanism responsible for their formation is the bow shock that is driven by the newly launched jet. We find that the density of the small doubles exceeds the density of FR II sources with similar properties at 1.4 GHz, but this difference becomes smaller for low flux densities. Finally, we show that the significant challenges of wide-field imaging (e.g., time and frequency variation of the beam, directional dependent calibration errors) can be solved using LOFAR commissioning data, thus demonstrating the potential of the full LOFAR telescope to discover millions of powerful AGN at redshift z ∼ 1.
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E Orrù, S van Velzen, R. F. Pizzo, S Yatawatta, R Paladino, et al.. Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 584, pp.A112. ⟨10.1051/0004-6361/201526501⟩. ⟨insu-01323421⟩

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