Radio structures

Radio structures - picture. [8] Often multiple hotspots are...

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Radio structures In more detail, the FRI/FRII division depends on host-galaxy environment in the sense that the FRI/FRII transition appears at higher luminosities in more massive galaxies. [6] FRI jets are known to be decelerating in the regions in which their radio emission is brightest, [7] and so it seems that the FRI/FRII transition reflects whether a jet/beam can propagate through the host galaxy without being decelerated to sub-relativistic speeds by interaction with the intergalactic medium. From analysis of relativistic beaming effects, the jets of FRII sources are known to remain relativistic (with speeds of at least 0.5c) out to the ends of the lobes. The hotspots that are usually seen in FRII sources are interpreted as being the visible manifestations of shocks formed when the fast, and therefore supersonic , jet (the speed of sound cannot exceed c/√3) abruptly terminates at the end of the source, and their spectral energy distributions are consistent with this
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Unformatted text preview: picture. [8] Often multiple hotspots are seen, reflecting either continued outflow after the shock or movement of the jet termination point: the overall hotspot region is sometimes called the hotspot complex. Names are given to several particular types of radio source based on their radio structure: • Classical double refers to an FRII source with clear hotspots. • Wide-angle tail normally refers to a source intermediate between standard FRI and FRII structure, with efficient jets and sometimes hotspots, but with plumes rather than lobes, found at or near the centres of clusters . • Narrow-angle tail or Head-tail source describes an FRI that appears to be bent by ram pressure as it moves through a cluster. • Fat doubles are sources with diffuse lobes but neither jets nor hotspots. Some such sources may be relics whose energy supply has been permanently or temporarily turned off....
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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