VLBI observations of a sample of Palomar–Green quasars – I. Parsec-scale morphology

ABSTRACT We observed 20 Palomar–Green quasars at low redshift (z < 0.5) with total flux density >1 mJy, including four radio-loud (RLQs) and 16 radio-quiet (RQQs), using the Very Long Baseline Array (VLBA) 5 GHz. 10 RQQs are clearly detected in VLBA images, a compact radio core is identified eight of them, indicating prevalence active galactic nucleus (AGN)-related emission this flux-density-limited RQQ sample. The RLQs our sample have division ?30 mJy. from appears to be result combination star formation AGN-associated activities. All GHz ratio Large (VLA) A-array D-array $f_{\rm c} = S_{\rm A}^{\rm VLA}/S_{\rm D}^{\rm VLA}$ above 0.2. fa (VLBA VLA $S^{\rm VLBA}/S_{\rm VLA}) \gt 0.2$ versus 0.2 show significant differences morphology, compactness, density. systematically lower than that RLQs, probably due extended jets or relic on tens hundreds parsecs resolved out images. Future larger samples, especially addition milliarcsec resolution images densities below 1 can test conclusions paper contribute understanding mechanism RQQs, dichotomy physical connection between RLQs.