THE INFRARED PROPERTIES OF COMPACT GALACTIC RADIO-SOURCES - THE YOUNG AND THE RESTLESS

The IRAS Point Source Catalog has been compared with the 20 cm Galactic plane survey (GPS) of Zoonematkermani et al. We have developed a new technique for distinguishing chance from true coincidences using the bands at which the IRAS sources are detected; for each match, we derive an estimate of the probability that the match represents a true association. Of the 1992 radio sources, 330 have high probability associations, with most having reliabilities above 90%. The GPS/IRAS sources are clearly Galactic: they have a very restricted distribution in both Galactic latitude and longitude. We can identify several classes of objects from their IRAS colors. Most of the sources are ultracompact (UC) H II regions distributed with the amazingly small scale height of only 30 pc. We show that the Wood & Churchwell IRAS-selected sample of UC H II regions is significantly contaminated by objects with a much thicker latitude distribution, which accounts for the larger scale height that they derived. We argue that only the combination of infrared and radio observations can distinguish massive embedded O stars from the more numerous, lower mass embedded B stars. There are 35 known planetary nebulae (PNs) with IRAS detections that lie in our survey area. Only 12 of these nebulae are detected in the GPS; however, practically all of the radio-selected PNs have essentially identical IRAS colors, suggesting that they are in very similar evolutionary states. The other 17 sources with similar colors in our survey are thus likely to be previously unrecognized, highly reddened PNs.