VLBI observations at 2.3 GHz of the compact galaxy 1934-638

Abstract

VLBI observations of the strong radio source 1934 - 638 have been made at 2.3 GHz as part of the Southern Hemisphere VLBI Experiment (SHEVE; see Preston et al. 1989), using five antennas in Australia and one in South Africa. The source was found to be double with a component separation of 42.0 +/- 0.2 mas (84h^-1^ pc for H_0_=100h km s^-1^ Mpc^-1^), a position angle of 90.5^deg^ +/- 1^deg^, and component sizes of about 2.5 mas. Comparison with single-baseline data taken 12 yr earlier (Gubbay et al. 1971) shows no evidence for any significant change in structure within the reported errors, which places a limit of 0.05c +/- 0.2c on the expansion velocity. About 40% of the total flux density is seen only on the shorter baselines and is modeled as an additional elongated component aligned with and between the compact double components. The source's almost equal compact double structure, peaked spectrum, low variability, small polarization, and particle-dominated radio lobes indicate that it belongs to the class of symmetric compact double sources first noted by Phillips and Mutel (1980, 1981, 1982). The relationships between component size, surface brightness, and luminosity as a function of component separation are concordant with other known compact doubles in the evolutionary model of double radio sources presented by Carvalho (1985) and Mutel and Phillips (1988). However, no other known member of this class has a substantial portion of its flux density in an additional extended component.