FR II radio galaxies at low frequencies – I. Morphology, magnetic field strength and energetics

Harwood, J. J.; Croston, J. H.; Intema, H. T.; Stewart, A.; Ineson, Judith; Hardcastle, M. J.; Godfrey, L.; Best, P. N.; Brienza, M.; Heesen, V.; Mahony, E. K.; Morganti, Raffaella; Murgia, M.; Orrù, E.; Röttgering, H. J. A.; Shulevski, A.; Wise, Michael

doi:10.1093/mnras/stw638

Cited by 55 publications

(75 citation statements)

References 76 publications

(140 reference statements)

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“…Hence, it is uncertain how accurately we can determine the injection spectral index. In any case, within the stated errors, the injection index is in approximate agreement with studies of active radio galaxies (Harwood et al 2015(Harwood et al , 2016. Furthermore, simulations suggest (Kapinska et al 2015) that the observed integrated spectrum can steepen owing to mixing of electron populations.…”

Section: Discussionsupporting

confidence: 85%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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We have observed the steep spectrum radio source B2 0924+30 using the LOw Frequency ARray (LOFAR) telescope. Hosted by a z=0.026 elliptical galaxy, it has a relatively large angular size of 12 (corresponding to 360 kpc projected linear size) and a morphology reminiscent of a remnant Fanaroff-Riley type II (FRII) radio galaxy. Studying active galactic nuclei (AGN) radio remnants can give us insight into the time-scales involved into the episodic gas accretion by AGNs and their dependence on the AGN host environment. The proximity of the radio galaxy allows us to make detailed studies of its radio structure and map its spectral index and radiative age distribution. We combine LOFAR and archival images to study the spectral properties at a spatial resolution of 1 . We derive low frequency spectral index maps and use synchrotron ageing models to infer ages for different regions of the source. Thus, we are able to extend the spectral ageing studies into a hitherto unexplored frequency band, adding more robustness to our results. Our detailed spectral index mapping, while agreeing with earlier lower resolution studies, shows flattening of the spectral index towards the outer edges of the lobes. The spectral index of the lobes is α 609 140 ∼ −1 and gradually steepens to α 609 140 ∼ −1.8 moving towards the inner edges of the lobes. Using radiative ageing model fitting we show that the AGN activity ceased around 50 Myr ago. We note that the outer regions of the lobes are younger than the inner regions which is interpreted as a sign that those regions are remnant hotspots. We demonstrate the usefulness of maps of AGN radio remnants taken at low frequencies and suggest caution over the interpretation of spectral ages derived from integrated flux density measurements versus age mapping. The spectral index properties as well as the derived ages of B2 0924+30 are consistent with it being an FRII AGN radio remnant. LOFAR data are proving to be instrumental in extending our studies to the lowest radio frequencies and enabling analysis of the oldest source regions.

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Section: Discussionsupporting

confidence: 85%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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“…Therefore, in determining the physical parameters of the two radio lobes in G29.37+0.1 we used an intermediate spectral index ∼0.5, a compromise between the values measured between 610 and 1400 MHz in both features. Firstly, we found that similar values of the equipartition magnetic field and energy density were reported in the literature for other FRII radio galaxies also observed with GMRT (Harwood et al 2016), as well as for a sample of giant radio galaxies . Considering a smaller value for K 0 yields magnetic fields up to three times smaller than those computed assuming dominance of protons (K 0 1).…”

Section: Extragalactic Emission From G2937+01?supporting

confidence: 87%

“…Several previously published works have noted such a discrepancy (corresponding to B (0.3-2.5)B eq , e.g. Wilson et al 2001;Grandi et al 2003;Harwood et al 2016) in the lobes of radio galaxies from which the IC X-rays are detected. It is noteworthy that none of the previously published comparisons show differences as significant as that we have found.…”

Section: X-ray Associated With the Radio-lobes In G2937+01?mentioning

confidence: 92%

Radio and X-ray properties of the source G29.37+0.1 linked to HESS J1844−030

Castelletti

Supán

Petriella

et al. 2017

A&A

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Aims. We report on the first detailed multiwavelength study of the radio source G29.37+0.1, which is an as-yet-unclassified object linked to the very-high-energy γ-emitting source HESS J1844−030. The origin of the multiwavelength emission toward G29.37+0.1 has not been clarified so far, leaving open the question about the physical relationship between these sources. Methods. Using observations carried out with the Giant Metrewave Radio Telescope (GMRT), we performed high-quality fullsynthesis imaging at 610 MHz of the field containing G29.37+0.1. The obtained data, combined with observations at 1400 MHz from The Multi-Array Galactic Plane Imaging Survey (MAGPIS) were used to investigate in detail the properties of its radio emission. Additionally, we reprocessed archival data obtained with the XMM-Newton and Chandra observatories in order to get a multiwavelength view of this unusual source. Results. The radio source G29.37+0.1 mainly consists of a bright twisted structure, named the S-shaped feature. The high sensitivity of the new GMRT observations allowed the identification of potential lobes, jets, and a nuclear central region in the S-shaped morphology of G29.37+0.1. We also highlight the detection of diffuse and low surface brightness emission enveloping the brightest emitting regions. The brightest emission in G29.37+0.1 has a radio synchrotron spectral index α=0.59±0.09. Variations in the spectral behaviour are observed across the whole radio source with the flattest spectral features in the central nuclear and jets components (α∼0.3). These results lead us to conclude that the brightest radio emission from G29.37+0.1 likely represents a newly recognized radio galaxy. The identification of optical and infrared counterparts to the emission arising from the core of G29.37+0.1 strengthens our interpretation of an extragalactic origin of the radio emission. We performed several tests to explain the physical mechanism responsible for the observed X-ray emission, which appears overlapping the northeastern part of the radio emission. Our spectral analysis demonstrated that a non-thermal origin for the X-ray emission compatible with a pulsar wind nebula is quite possible. The analysis of the spatial distribution of the CO gas revealed the presence of a complex of molecular clouds located in projection adjacent to the radio halo emission and probably interacting with it. We propose that the faint halo represents a composite supernova remnant with a pulsar powered component given by the diffuse X-ray emission superimposed along the line of sight to the radio galaxy. Further broadband observations of HESS J1844−030 are needed to disentangle its origin, although its shape and position suggest an extragalactic origin connected to G29.37+0.1.

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“…The LOFAR studies of individual active (e.g. Orrù et al 2015;Harwood et al 2016;Heesen et al 2016) and remnant (Shulevski et al 2015b;Brienza et al 2016) radio galaxies have already expanded our understanding of radio galaxies at low frequencies, but studies of the larger sample of sources that we have imaged will provide the opportunity to determine the applicability of these findings to the population as a whole.…”

Section: Scientific Potentialmentioning

confidence: 99%

“…Although ionospheric and beam effects hinder the image fidelity of these preliminary images, we are able to image data from baselines shorter than 12 kλ to produce 25 resolution images that typically have a noise level of 200-500 µJy/beam away from bright sources. Such sensitive, low-frequency images have not previously been produced over such a wide area and are sufficient to accomplish many of the scientific objectives of the survey (see Brienza et al 2016;Harwood et al 2016;Heesen et al 2016;Mahony et al 2016;Shulevski et al 2015a,b for examples).…”

Section: Introductionmentioning

confidence: 99%

The LOFAR Two-metre Sky Survey

Shimwell

Röttgering

Best

et al. 2017

A&A

483

240

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The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120-168 MHz imaging survey that will eventually cover the entire northern sky. Each of the 3170 pointings will be observed for 8 h, which, at most declinations, is sufficient to produce ∼5 resolution images with a sensitivity of ∼100 µJy/beam and accomplish the main scientific aims of the survey, which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Owing to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44 000 sources are detected in the images that have a resolution of 25 , typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45• 00 00 to 57• 00 00 ).

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FR II radio galaxies at low frequencies – I. Morphology, magnetic field strength and energetics

Cited by 55 publications

References 76 publications

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Radio and X-ray properties of the source G29.37+0.1 linked to HESS J1844−030

The LOFAR Two-metre Sky Survey

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