Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-10-21
Astronomy and Astrophysics
Astrophysics
paper accepted for publication in MNRAS, 11 figures, 5 tables. The definitive version is available at www.blackwell-synergy.co
Scientific paper
10.1111/j.1365-2966.2008.14081.x
We present new high spatial resolution VLT and VLA observations of a sample of nine low-power (P_{1.4 GHz} < 10^{25} W/Hz) radio hotspots. Infrared/optical emission is definitely detected in four of the nine observed objects, resulting in a detection rate of at least 45%. This emission is interpreted as synchrotron radiation from the electrons accelerated in the hot spots. The integrated spectra of these hotspots reveal typical break frequencies between 10^5 and 10^6 GHz, two orders of magnitude higher than typically found in high-power hotspots. This supports the idea that in low-power hotspots with their relatively low magnetic field strengths electrons emit most of their energy at higher frequencies. A simple spectral ageing analysis would imply that the emitting electrons have been injected into the hotspot volume less than ~10^3 years ago. We discuss possible scenarios to explain the lack of older electrons in the hotspot region. In particular, the extended morphology of the NIR/optical emission would suggest that efficient re-acceleration mechanisms rejuvenate the electron populations.
Almudena Prieto M.
Brunetti Gf.
Mack Karl-Heinz
Orienti Monica
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