OBSERVATIONS OF LOCAL INTERSTELLAR CO TOWARD 4 COMPACT EXTRAGALACTIC RADIO-SOURCES

We have observed the interstellar J = 1 --> 0 emission line of (CO)-C-12 toward the compact extragalactic continuum sources NRAO 140, NRAO 150, 3C 111, and BL Lacertae. We detect emission lines toward all four sources at higher spatial resolution than was the case for observations reported previously. Compact sources toward which CO is detected are excellent candidates for CO emission-absorption observations using a combination of single antennas (emission) and millimeter-wave interferometers (absorption). Such observations would provide important insights into the radiative transfer of the CO lines as well as the physical conditions inside molecular clouds. The observations reported here, combined with published H I observations, yield values for the total column density in atomic and molecular gas along the lines of sight to the observed sources. This is important for the interpretation of x-ray spectra of these objects since the intervening gas causes photoelectric absorption at low x-ray energies.