Radio core dominance measurements, an indicator of jet orientation, sometimes rely on core flux density measurements from large-area surveys like Faint Images of the Radio Sky at Twenty cm (FIRST) that have an angular resolution of only 5". Such low-resolution surveys often fail to resolve cores from the extended emission, resulting in an erroneous measurement. We focus on investigating this resolution effect for a sample of 119 radio-loud quasars. We obtained continuum observations from NSF's Karl G. Jansky Very Large Array (VLA) at 10GHz in A configuration with a 0.2 resolution. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high even after considering the core variability. For a handful of quasars, 10GHz images reveal extended features, whereas the FIRST image shows a point source. We found that the resolution effect is more prominent for quasars with smaller angular sizes. We further computed two radio core dominance parameters R and R5100 for use in statistical orientation investigations with this sample. We also present the spectral energy distributions between 74MHz and 1.4GHz, which we used to measure the spectral index of the extended emission of these quasars. Our results empirically confirm that determination of radio core dominance requires high spatial resolution data. We highlight the practical issues associated with the choice of frequency and resolution in the measurement of core and extended flux densities.

Cone search capability for table J/ApJ/904/179/table1 (SDSS names, redshifts, optical and radio flux densities, and spectral indices of extended emission of 119 radio-loud quasars)

Cone search capability for table J/ApJ/904/179/table4 (Data for 28 additional objects observed with VLA)