1998/01/29 by I. A. G. Snellen, Snellen, I. A. G., R. T. Schilizzi +5
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astrophysics (astro-ph) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9801304
11 pages, LaTeX, accepted by A&A 26/Jan/1998
arxiv created 1998/01/29 · openalex publication_date 1998/01/29 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
A relativistic radio component, which moves in a direction close to the sky\nplane, will increase in flux density when it decelerates. This effect is the\nbasis for the qualitative model for GPS galaxies we present in this paper,\nwhich can explain their low-variability convex spectrum, their compact double\nor compact symmetric morphology, and the lack of GPS quasars at similar\nredshifts. Components are expelled from the nucleus at relativistic speeds at a\nlarge angle to the line of sight, and are decelerated (eg. by ram-pressure or\nentrainment of the external gas) before contributing to a mini-lobe. The young\ncomponents are Doppler boosted in the direction of motion but appear fainter\nfor the observer. The non-relativistic mini-lobes dominate the structure and\nare responsible for the low variability in flux density and the convex radio\nspectrum as well as the compact double angular morphology. Had the same source\nbeen orientated at a small angle to the line of sight, the young components\nwould be boosted in the observer's direction resulting in a flat and variable\nradio spectrum at high frequencies. Hence the characteristic convex spectrum of\na GPS source would not be seen. These sources at small angles to the line of\nsight are probably identified with quasars, and are not recognized as GPS\nsources, but are embedded in the large population of flat spectrum variable\nquasars and BL Lac objects. This leads to a deficiency in GPS/CSOs identified\nwith quasars.\n