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Przejdź do strony domowej biblioteki Pedagogiczna Biblioteka Wojewódzka im. Komisji Edukacji Narodowej w Lublinie Link otwiera się w nowym oknie Logo biblioteki Prolib Integro - strona głównaPedagogiczna Biblioteka Wojewódzka im. Komisji Edukacji Narodowej w Lublinie
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Wyświetlanie 1-10 z 29
Tytuł:
LOFAR discovery of a 700-kpc remnant radio galaxy at low redshift
Autorzy:
Harwood, J. J.
Brüggen, M.
Jarvis, M. J.
Maddox, N.
Brienza, M.
Orru, E.
Murgia, M.
Jamrozy, Marek
McKean, J.
Morganti, R.
Röttgering, H. J. A.
Shulevski, A.
Best, P. N.
Vilchez, N.
Mahony, E. K.
Godfrey, L.
Opis:
Context. Remnant radio galaxies represent the final dying phase of radio galaxy evolution in which the jets are no longer active. Remnants are rare in flux-limited samples, comprising at most a few percent. As a result of their rarity and because they are difficult to identify, this dying phase remains poorly understood and the luminosity evolution is largely unconstrained. Aims. Here we present the discovery and detailed analysis of a large (700 kpc) remnant radio galaxy with a low surface brightness that has been identified in LOFAR images at 150 MHz. Methods. By combining LOFAR data with new follow-up Westerbork observations and archival data at higher frequencies, we investigated the source morphology and spectral properties from 116 to 4850 MHz. By modelling the radio spectrum, we probed characteristic timescales of the radio activity. Results. The source has a relatively smooth, diffuse, amorphous appearance together with a very weak central compact core that is associated with the host galaxy located at z = 0.051. From our ageing and morphological analysis it is clear that the nuclear engine is currently switched off or, at most, active at a very low power state. We find that the source has remained visible in the remnant phase for about 60 Myr, significantly longer than its active phase of 15 Myr, despite being located outside a cluster. The host galaxy is currently interacting with another galaxy located at a projected separation of 15 kpc and a radial velocity offset of $\sim$ 300 km s$^{-1}$. This interaction may have played a role in the triggering and/or shut-down of the radio jets. Conclusions. The spectral shape of this remnant radio galaxy differs from most of the previously identified remnant sources, which show steep or curved spectra at low to intermediate frequencies. Our results demonstrate that remnant radio galaxies can show a wide range of evolutionary paths and spectral properties. In light of this finding and in preparation for new-generation deep low-frequency surveys, we discuss the selection criteria to be used to select representative samples of these sources.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
AGN duty cycle estimates for the ultra-steep spectrum radio relic VLSS J1431.8+1331
Autorzy:
Brienza, M.
Shulevski, A.
Barthel, P. D.
Vilchez, N.
Miley, G.
Rafferty, D. A.
White, G. J.
Morganti, R.
Bîrzan, L.
Mahony, E.
Harwood, J. J.
Brüggen, M.
Jamrozy, Marek
Chyży, Krzysztof
Brunetti, G.
Röttgering, H. J. A.
van Weeren, R. J.
Wise, M. W.
Kunert-Bajraszewska, M.
de Gasperin, F.
Horellou, C.
Conway, J.
Opis:
Context. Steep spectrum radio sources associated with active galactic nuclei (AGN) may contain remnants of past AGN activity episodes. Studying these sources gives us insight into the AGN activity history. Novel instruments like the LOw Frequency ARray (LOFAR) are enabling studies of these fascinating structures to be made at tens to hundreds of MHz with sufficient resolution to analyse their complex morphology. Aims: Our goal is to characterize the integrated and resolved spectral properties of VLSS J1431+1331 and estimate source ages based on synchrotron radio emission models, thus putting constraints on the AGN duty cycle. Methods: Using a broad spectral coverage, we have derived spectral and curvature maps, and used synchrotron ageing models to determine the time elapsed from the last time the source plasma was energized. We used LOFAR, Giant Metrewave Radio Telescope (GMRT) and Jansky Very Large Array (VLA) data. Results: We confirm the morphology and the spectral index values found in previous studies of this object. Based on our ageing analysis, we infer that the AGN that created this source currently has very low levels of activity or that it is switched off. The derived ages for the larger source component range from around 60 to 130 Myr, hinting that the AGN activity decreased or stopped around 60 Myr ago. We observe that the area around the faint radio core located in the larger source component is the youngest, while the overall age of the smaller source component shows it to be the oldest part of the source. Conclusions: Our analysis suggests that VLSS J1431.8+1331 is an intriguing, two-component source. The larger component seems to host a faint radio core, suggesting that the source may be an AGN radio relic. The spectral index we observe from the smaller component is distinctly flatter at lower frequencies than the spectral index of the larger component, suggesting the possibility that the smaller component may be a shocked plasma bubble. From the integrated source spectrum, we deduce that its shape and slope can be used as tracers of the activity history of this type of steep spectrum radio source. We discuss the implications this conclusion has for future studies of radio sources having similar characteristics.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Wyświetlanie 1-10 z 29

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