Low-frequency observations of the Giant Radio Galaxy NGC 6251

Abstract

We present LOFAR observations at 150 MHz of the borderline FRI/FRII giant radio galaxy NGC 6251. This paper presents the most sensitive and highest-resolution images of NGC 6251 at these frequencies to date, revealing for the first time a low-surface-brightness extension to the northern lobe, and a possible backflow associated with the southern lobe. The integrated spectra of components of NGC 6251 are consistent with previous measurements at higher frequencies, similar to results from other LOFAR studies of nearby radio galaxies. We find the outer structures of NGC 6251 to be either at equipartition or slightly electron dominated, similar to those of FRII sources rather than FRIs; but this conclusion remains tentative because of uncertainties associated with the geometry and the extrapolation of X-ray measurements to determine the external pressure distribution on the scale of the outer lobes. We place lower limits on the ages of the extension of the northern lobe and the backflow of the southern lobe of $t\gtrsim 250$ Myr and $t\gtrsim 210$ Myr respectively. We present the first detection of polarisation at 150 MHz in NGC 6251. Taking advantage of the high Faraday resolution of LOFAR, we place an upper limit on the magnetic field in the group of $B<0.2({\Lambda }_B/10\mathrm{kpc}{)}^{-0.5}\mu$G for a coherence scale of ${\Lambda }_B<60\mathrm{kpc}$ and $B<13\mu$G for ${\Lambda }_B=240$ kpc.

19 pages, 17 figures; accepted by MNRAS

References in corpus (20)

• Revisiting the Fanaroff-Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)
• Calibrating High-Precision Faraday Rotation Measurements for LOFAR and the Next Generation of Low-Frequency Radio Telescopes
• LOFAR/H-ATLAS: A deep low-frequency survey of the Herschel-ATLAS North Galactic Pole field
• An XMM-Newton study of the environments, particle content and impact of low-power radio galaxies
• Structures of the magnetoionic media around the FR I radio galaxies 3C 31 and Hydra A
• The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
• A representative survey of the dynamics and energetics of FRII radio galaxies
• Faraday tomography of the local interstellar medium with LOFAR: Galactic foregrounds towards IC342
• Missing Baryons and the Warm-Hot Intergalactic Medium
• A multifrequency study of giant radio sources-II. Spectral ageing analysis of the lobes of selected sources
• Comparison of algorithms for determination of rotation measure and Faraday structure I. 1100 - 1400 MHz
• On the relationship between a giant radio galaxy MSH 05-22 and the ambient large-scale galaxy structure
• Giant radio galaxies - II. Tracers of large-scale structure
• VLSS Redux: Software Improvements applied to the Very Large Array Low-frequency Sky Survey
• MRC B0319-454: Probing the large-scale structure with a giant radio galaxy
• Unveiling the cause of hybrid morphology radio sources (HyMoRS)
• Multifrequency VLA observations of the FR I radio galaxy 3C 31: morphology, spectrum and magnetic field
• LOFAR reveals the giant: a low-frequency radio continuum study of the outflow in the nearby FR I radio galaxy 3C 31
• Radio Lobes of Pictor A: an X-ray spatially resolved Study
• The new sample of giant radio sources III. Statistical trends and correlations

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