Studies of kiloparsec-scale, steep-spectrum radio cores. I VLA maps

Abstract

VLA maps with resolution of 0.15 - 0.4 arcsec are presented of the structures and polarization distributions of several of a sample of 23 powerful sources (mostly quasars) with dominant structure on the kiloparsec scale. The radio properties of these 'steep-spectrum core' (SSC) sources (generally: low percentage polarization, complex morphology, kiloparsec size, and high surface brightness) resemble those of the weaker, nearby SSCs such as found in some Seyferts (i.e., NGC 1068) and in sources lke 3C 293, 3C 305, M87, and 4C 26.42. Previous studies of nearby SSCs have shown that these are embedded in gas-rich environments, as evidenced by their associated optical narrow-line regions (NLRs) and rotating gaseous disks, dustlanes, neutral hydrogen, or cooling galactic coronae. The similarities of the radio properties of nearby and distant SSCs, and recent optical evidence that many quasars may reside in spiral-type, and hence gas-rich galaxies, suggest that quasar SSCs are also embedded in relatively dense interstellar media and have associated NLRs. Many of the radio and optical properties of SSCs may thus be understood as being due to the interaction of jets with their dense environments.