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 4 H Falcke 5 R Morganti 6 A. G. de Bruyn 6 C Ferrari 7 J Anderson 8 A Bonafede 9 D Mulcahy 10 A Asgekar 11 I. M. Avruch 12 R Beck M.E. Bell 10 I van Bemmel 1 M. J. Bentum 11 G Bernardi 13 P Best 14 F Breitling 15 M Brüggen 9 J.W. Broderick 10 B Ciardi 16 A Corstanje 5 J. E. Conway 17 E de Geus 18 H. R. Butcher 19 B. Ciardi 16 A Deller 1 S Duscha 11 J Eislöffel 20 D Engels 21 W Frieswijk 1 Jean-Mathias Grießmeier 22, 23 G Heald 1 M Hoeft 20 H Intema 3 E Juette 24 J Kohler 25 M Kuniyoshi 26 G Kuper 1 M Loose 27 P Maat 11 G Mann 28 S Markoff 29 R Mcfadden 11 D Mckay-Bukowski 30 G Miley 3 J Moldon 11 G Molenaar 29 H Munk 11 A Nelles 5 H Paas 31 M Pandey-Pommier 32 G Pietka 33 W Reich 26 H Röttgering 3 A Rowlinson 34 A Scaife 35 A Schoenmakers 1 D. Schwarz 36 M Serylak 22, 23 A Shulevski 6 O Smirnov 37 M Steinmetz 38 A Stewart 39 J Swinbank 29 Michel Tagger 22 C Tasse 40, 41 S Thoudam 5 R Vermeulen 1 C Vocks 28 O Wucknitz 42
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 (A112), 12 p. ⟨10.1051/0004-6361/201526501⟩. ⟨insu-01323421⟩

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