SIMBAD references

Compact symmetric objects (CSOs) are young radio galaxies whose jet axes lie close to the plane of the sky, and whose appearance is therefore not dominated by relativistic beaming effects. The small linear sizes of CSOs make them valuable for studies of both the evolution of radio galaxies and testing unified schemes for active galactic nuclei (AGNs). A parsec-scale region of gas surrounding the central engine is predicted by both accretion and obscuration scenarios. Working surfaces, or ``hot spots'', and the radio jets of CSOs are close enough to the central engines that this circumnuclear gas can be seen in absorption.

The CSOs observed in the northern sky (COINS) sample is comprised of 52 CSO candidates identified in three VLBI surveys. Of these, 27 have now been confirmed as CSOs. Optical redshifts are available in the literature for 28 of the CSO candidates, and H I absorption has been detected toward four. We present new optical spectroscopic redshifts for three of the candidates and summarize the current status of optical identifications. We further report on the discovery of H I in absorption toward the CSO J1816+3457 and summarize the results of neutral hydrogen absorption studies of the sources in this sample.