NIR/Optical Counterparts of Hotspots in Radio Galaxies

Abstract

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.

arXiv commentpaper accepted for publication in MNRAS, 11 figures, 5 tables. The definitive version is available at www.blackwell-synergy.com

References in corpus (17)

• The USNO-B Catalog
• The Nature and Evolution of Classical Double Radio Sources from Complete Samples
• Radio galaxies with a `double-double' morphology: I - Analysis of the radio properties and evidence for interrupted activity in active galactic nuclei
• Decelerating Flows in TeV Blazars: A Resolution to the BL Lac -- FR I Unification Problem
• The origins of X-ray emission from the hotspots of FRII radio sources
• Chandra X-ray Observations of Pictor A: High Energy Cosmic Rays in a Radio Galaxy?
• FR II radio galaxies with z<0.3 -- I. Properties of jets, cores and hot spots
• A Chandra Study of the Multi-Component X-ray Emission from the X-shaped Radio Galaxy 3C 403
• A Chandra study of particle acceleration in the multiple hotspots of nearby radio galaxies
• Chandra discovery of extended non-thermal emission in 3C 207 and the spectrum of the relativistic electrons
• The radio structures of southern 2-Jy radio sources: new ATCA and VLA radio images
• In-Situ Particle Acceleration in Extragalactic Radio Hot Spots: Observations Meet Expectations
• Particle Accelerators in the Hot Spots of the Radio Galaxy 3C445 Imaged With the VLT
• Optical structure and polarization of the western hot spot of Pictor A
• Chandra detection of the radio and optical double hot spot of 3C 351
• Are the hotspots of radio galaxies the sites of in-situ acceleration of relativistic particles?
• Discovery of Optical Emission in the Hotspots of Three 3CR Quasars: High-Energy Particle Acceleration in Powerful Radio Hotspots

Cited by in corpus (20)

• The central parsecs of M87: jet emission and an elusive accretion disc
• Radio properties of Compact Steep Spectrum and GHz-Peaked Spectrum radio sources
• FR-II radio galaxies at low frequencies II: spectral ageing and source dynamics
• Spitzer Observations of Hotspots in Radio Lobes
• An X-ray survey of the 2Jy sample. II: X-ray emission from extended structures
• Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism
• Complex particle acceleration processes in the hotspots of 3C105 and 3C445
• The Vanishing & Appearing Sources during a Century of Observations project: I. USNO objects missing in modern sky surveys and follow-up observations of a "missing star"
• On the maximum energy of non-thermal particles in the primary hotspot of Cygnus A
• Evidence that the maximum electron energy in hotspots of FR II galaxies is not determined by synchrotron cooling
• Two types of shock in the hotspot of the giant quasar 4C74.26: a high-resolution comparison from Chandra, Gemini & MERLIN
• Particle acceleration in low-power hotspots: modelling the broad-band spectral energy distribution
• ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445
• Jansky VLA observations of synchrotron emitting optical hotspots of 3C 227 and 3C 445 radio galaxies
• X-ray Spectral Analysis of the Jet Termination Shock in Pictor A on Sub-Arcsecond Scales with Chandra
• Multi-messenger signatures of delayed choked jets in tidal disruption events
• Scalings of the synchrotron cut-off and turbulent correlation of active galactic nucleus jets
• Evidence that particle acceleration in hotspots of FR II galaxies is not constrained by synchrotron cooling
• Far-infrared probing with PRIMA into particle acceleration associated with relativistic jets from active galactic nuclei
• NuSTAR discovery of the hard X-ray emission and a wide-band X-ray spectrum from the Pictor A western hot spot