Radio Recombination Lines in Extragalactic Sources
Attempts to detect Hydrogen recombination lines from extragalactic sources using narrow 10MHz observing windows began at least as far back as 19T15 when E. Seaquist and I searched for emission lines in 3C273. Other unreported searches with negative results were almost certainly made, but meaningful observations began only in late 1975 when wider observing windows (30-90 MHz) became available. Although many improvements In instrumentation and observing techniques have been made in the last four years mere detection of the wide, weak recombination lines found in external galaxies Is still a struggle. However detections have now been made in at least two sources with sufficient accuracy to enable us to define the line producing mechanism and, with some improvements in instrumentation many more detections may be made soon, in what is turning out to be an exciting new field of astronomy.
KeywordsRecombination Line Seyfert Galaxy Extragalactic Source Extragalactic Object External Galaxy
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