Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 436, Issue 2, Pages 1286-1301Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stt1662
Keywords
techniques: interferometric; galaxies: active; galaxies: individual: NGC 5128; radio continuum: galaxies
Categories
Funding
- U.S. National Science Foundation [AST-0457585, PHY-0835713, CAREER-0847753, AST-0908884]
- Australian Research Council (LIEF) [LE0775621, LE0882938]
- U.S. Air Force Office of Scientific Research [FA9550-0510247]
- Centre for All-sky Astrophysics (an Australian Research Council Centre of Excellence) [CE110001020]
- Smithsonian Astrophysical Observatory
- MIT School of Science
- Raman Research Institute
- Australian National University
- Victoria University of Wellington (via the New Zealand Ministry of Economic Development) [MED-E1799]
- Victoria University of Wellington (via IBM Shared University Research Grant)
- Australian Federal government via the Commonwealth Scientific and Industrial Research Organisation (CSIRO)
- National Collaborative Research Infrastructure Strategy
- Education Investment Fund
- Australia India Strategic Research Fund
- Astronomy Australia Limited
- NVIDIA at Harvard University
- International Centre for Radio Astronomy Research (ICRAR)
- Western Australian State government
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We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118 MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen A's giant radio lobes. We compare our images to 1.4 GHz maps of Cen A and compute spectral indices using temperature-temperature plots and spectral tomography. We find that the morphologies at 118 MHz and 1.4 GHz match very closely apart from an extra peak in the southern lobe at 118 MHz, which provides tentative evidence for the existence of a southern counterpart to the northern middle lobe of Cen A. Our spatially averaged spectral indices for both the northern and southern lobes are consistent with previous analyses, however we find significant spatial variation of the spectra across the extent of each lobe. Both the spectral-index distribution and the morphology at low radio frequencies support a scenario of multiple outbursts of activity from the central engine. Our results are consistent with inverse-Compton modelling of radio and gamma-ray data that support a value for the lobe age of between 10 and 80 Myr.
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