AGN duty cycle estimates for the ultra-steep spectrum radio relic VLSS J1431.8+1331
Journal article, 2015
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 VESS 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.
VLSS J1431.8+1331
galaxies
radio continuum
Author
A. Shulevski
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
R. Morganti
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
P. D. Barthel
University of Groningen
J. J. Harwood
Netherlands Institute for Radio Astronomy (ASTRON)
G. Brunetti
Istituto nazionale di astrofisica (INAF)
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
H. Rottgering
Leiden University
G. J. White
Open University
STFC Rutherford Appleton Laboratory
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
M. Kunert-Bajraszewska
Nicolaus Copernicus University
M. Jamrozy
Jagiellonian University in Kraków
K.T. Chyz̊y
Jagiellonian University in Kraków
E. Mahony
Netherlands Institute for Radio Astronomy (ASTRON)
G. Miley
Leiden University
M. Brienza
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
L. Birzan
University of Hamburg
D. Rafferty
University of Hamburg
M. Brüggen
University of Hamburg
M. W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
Anton Pannekoek Institute for Astronomy
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
F. De Gasperin
University of Hamburg
N. Vilchez
Netherlands Institute for Radio Astronomy (ASTRON)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 583 A89- A89Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201525632