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 7 C Ferrari 8 J Anderson 9, 10 A Bonafede 11 D Mulcahy 12 A Asgekar 13 I. M. Avruch 14 R Beck M.E. Bell 12 I Van Bemmel 1 M. J. Bentum 13 G Bernardi 15 P Best 16 F Breitling 17 M Brüggen 11 J.W. Broderick 12 B Ciardi 18 A Corstanje 5 J. E. Conway 19 E De Geus 20 H. R. Butcher 21 B. Ciardi 18 A Deller 1 S Duscha 13 J Eislöffel 22 D Engels 23 W Frieswijk 1 Jean-Mathias Grießmeier 24, 25 G Heald 1 M Hoeft 22 H Intema 3 E Juette 26 J Kohler 27 M Kuniyoshi 28 G Kuper 1 M Loose 29 P Maat 13 G Mann 30 S Markoff 31 R Mcfadden 13 D Mckay-Bukowski 32 G Miley 3 J Moldon 13 G Molenaar 31 H Munk 13 A Nelles 5 H Paas 33 M Pandey-Pommier 34 G Pietka 35 W Reich 28 H Röttgering 3 A Rowlinson 36 A Scaife 37 A Schoenmakers 1 D. Schwarz 38 M Serylak 24, 25 A Shulevski 39 O Smirnov 40 M Steinmetz 41 A Stewart 42 J Swinbank 31 Michel Tagger 24 C Tasse 43, 44 S Thoudam 5 R Vermeulen 1 C Vocks 30 O Wucknitz 45
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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Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 584 (A112), 12 p. 〈10.1051/0004-6361/201526501〉
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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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